Dissertations / Theses: 'Cyclic tests'

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Fiorin, Laura. "Seismic assessment of suspended ceilings through cyclic quasi-static tests." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3423162.

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The purpose of this work is the evaluation of the seismic behaviour of suspended ceilings by means of a combined experimental and numerical approach. As concerning the experimental aspects, nowadays the most common experimental produre applied to suspended ceilings worldwide regards shake-table tests, with a protocol defined to certify the ceilings for a determined seismic level. This methodology has some shortcomings, including the high cost and the influence of the input chosen on the experimental results. In fact, these tests have the aim to certify the product rather than providing mechanical characteristics of the specimen tested. Moreover, the results obtained with the certification process cannot be extended to similar products or geographic zones with different seismic risk. To overcome these limitations, an innovative experimental setup for monotonic and cyclic testing of suspended ceiling systems was designed, realized and applied. In order to have a complete characterization of suspended ceilings, an initial experimental campaign on inner joints was realized. These components, in fact, performed poorly in past earthquakes. In detail, 'standard' joints were compared to 'seismic' joints, specifically designed to resist to earthquake motion. Real-scale tests were then performed on the most common T-Grid suspended ceilings and other two typologies of metal ceilings with different structure. Moreover, dry-wall suspended ceilings with single and double plasterboard were tested. For each typology one monotonic and one cyclic quasi-static test were performed. Monotonic tests have the aim to identify the yielding parameters and the damage mechanisms and cyclic tests are performed according to the protocol described in FEMA 461 for cyclic quasi-static tests of non-structural components. The results allow to define the performance of suspended ceilings and to elaborate their capacity curves. As concerning the numerical part of the work, a numerical cascading approach was applied to study the uncoupled behaviour of suspended ceilings installed at different levels of buildings. Results from experimental campaign were used as input data for the numerical anlyses. Elastic linear time history analyses were performed on multi-story buildings with different vibration periods and the elastic floor response spectra were defined. Capacity curves defined experimentally and floor spectra were plotted in an ADRS (Acceleration Displacement Response Spectrum) domain in order to assess the seismic demand in terms of acceleration and displacement of suspended ceilings compared to their capacities. Dynamic analyses of suspended ceilings were conduced both in linear and non linear hypothesis and the results compared in order to assess the effectiveness of standard linear, or equivalent linear, static calculations.
Lo scopo della tesi è la valutazione del comportamento sismico di controsoffitti, tramite prove cicliche quasi statiche. La tipologia di prove più comune ad oggi, infatti, riguarda prove su tavole vibrante con un protocollo definito per certificare il prodotto per una certa azione sismica. Queste prove presentano varie limitazioni, tra cui il costo elevato e la stretta correlazione tra risultato e input scelto. Le prove infatti non hanno specifico scopo di ricerca se non l’obiettivo di certificare un prodotto, non forniscono informazioni sulle prestazioni meccaniche dei componenti testati e non permettono di estendere i risultati ottenuti ne su prodotti simili ne in zone geografiche con diverso rischio sismico. È stato quindi progettato un setup di prova innovativo in grado di realizzare prove monotone e cicliche quasi statiche su controsoffitti. Questa tipologia di prove permette di superare le limitazioni dell’attuale procedura sperimentale. Al fine di ottenere una caratterizzazione completa dei controsoffitti, sono stati testati i giunti interni, questi componenti infatti sono risultati danneggiati in seguito a eventi sismici. In particolare, sono stati testati sia giunti ‘standard’ che giunti ‘antisismici’, facenti parte di una particolare linea progettata per resistere all’azione sismica. Sono stati testati a grandezza reale sia controsoffitti con struttura a T (che rappresentano la tipologia più diffusa globalmente), che altri due controsoffitti con diversa sottostruttura metallica, infine le prove hanno riguardato anche controsoffitti con pannelli continui in cartongesso. Per ogni tipologia sono stati eseguite una prova monotona, al fine di individuare i parametri di snervamento e il meccanismo di rottura, e una prova ciclica, seguendo il protocollo indicato nelle FEMA 461 per prove cicliche quasi statiche per componenti non strutturali. I risultati ottenuti hanno permesso di definire la prestazione degli elementi testati e di elaborarne la curva di capacità. Tramite approccio numerico “a cascata”, che permette di eseguire uno studio disaccoppiato dei due elementi, è stato possibile studiare il comportamento dei controsoffitti installati a diversi piani. Sono state realizzate analisi time-history lineari elastiche su edifici multi-piano con diverso periodo di vibrazione e sono stati ricavati gli spettri di risposta al piano. Le curve di capacità dei controsoffitti, definite sperimentalmente, e gli spettri al piano sono stati definiti in un dominio ADRS (Acceleration Displacement Response Domain) al fine di valutare la domanda sismica in termini di spostamento e accellerazione in funzione della capacità dei controsoffitti.

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Sharma, Acharya Shambhu Sagar. "Characterisation of cyclic behaviour of calcite cemented calcareous soils." University of Western Australia. School of Civil and Resource Engineering, 2004. http://theses.library.uwa.edu.au/adt-WU2005.0040.

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[Truncated abstract] Characterising the behaviour of calcareous sediments that possess some degree of bonding between their constituents has attracted worldwide research interest in recent years. Although many recent studies have made significant contributions in delineating the behaviour of these sediments, there is still paucity of information particularly on the cyclic behaviour of cemented calcareous soils. This thesis describes in detail the characteristic features of cemented calcareous soils and proposes methods for characterising their cyclic behaviour. Two different calcareous soils Goodwyn (GW) and Ledge Point (LP) soils representing extreme depositional environments were examined in this study. Artificially cemented sample were created using the CIPS (Calcite Insitu Precipitation Systems) technique, considering its superiority over other most commonly available cementation techniques in replicating the natural pattern of cementation, and the behaviour of natural calcarenite under monotonic loading conditions. The experimental program involved triaxial testing of both uncemented and calcite-cemented calcareous soils under different loading conditions, i.e. isotropic compression tests to high-pressure (16 MPa), monotonic shearing tests, undrained cyclic shearing tests and undrained monotonic post-cyclic shearing tests. Significant emphasis has been placed on the cyclic behaviour of these soils. Internal submersible LDVTs were used for the accurate and continuous measurement of strain down to about 10-5

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Du, Plooy Rudolph. "Characterisation of rigid polyurethane foam reinforced ballast through cyclic loading box tests." Diss., University of Pretoria, 2015. http://hdl.handle.net/2263/57518.

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Train speeds and heavy haul axle loads are constantly increasing the forces and stresses experienced by track structures. This is especially true for track transitions that generate high dynamic forces on both the track and vehicles as a result of differing track stiffness values on either side of the track transition. Reducing differential settlement between the two track structures at a track transition is one method of improving the life of the track and increasing maintenance intervals. Ballast attrition and breakdown at these track transition zones is also of major concern as ballast fouling can lead to reduced drainage performance of the ballast as well as a potential loss of strength as the ballast becomes increasingly fouled. In this study rigid polyurethane foam was used as a means to reinforce ballast. Various tests were conducted using a dynamic load hydraulic load frame in a large ballast box test at heavy haul axle loads. Unreinforced, reinforced and 50 % reinforced ballast layers of 300 mm depth were tested to approximately 5,000,000 load cycles. The results showed that rigid polyurethane foam reinforced ballast exhibited in the order of 60 % less settlement for a fully reinforced layer and 42 % less settlement for a half reinforced layer. The increase in layer stiffness with increasing load cycles was also observed for the reinforced ballast layers which is contrast with the decrease in layer stiffness for conventional unreinforced ballast. The use of rigid polyurethane foam (RPF) to reinforce ballast has a number of benefits which could result in better track geometry and longer maintenance cycles resulting in lower overall costs.
Dissertation (MEng)--University of Pretoria, 2015.
tm2016
Civil Engineering
MEng
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Mucolli, Gent. "Fuzzy modeling of suction anchor behavior based on cyclic model tests data." Digital WPI, 2016. https://digitalcommons.wpi.edu/etd-theses/1313.

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This paper proposes a novel model that can predict the displacement of suction caisson anchors under monotonic and cyclic loading. Failure is assumed to occur when the accumulative monotonic and cyclic displacement along the load attachment point is over 60% of the diameter of the anchor. The anchors will go through lateral failure when the accumulative monotonic and cyclic displacement along the loading direction at the load attachment point is over 30% of the diameter. Hence, it is important to predict this displacement and therefore determine the expected failure of the anchor. However, it is difficult to predict displacement using the modern software without knowing the material properties of the soil and piles. Hence a new model that relies only on the normalized static load (Fa/Ff), normalized cyclic load (Fcy/Ff ), loading angle (Θ), and the number of cycles (N) is proposed. The inputs for training of the proposed model are (Fa/Ff), (Fcy/Ff), (Θ), (α) and (N). The output of the model will be the displacement normalized by the diameter of the anchor. To generalize the trained model, unused sets of data are used to validate the model. Furthermore, a comparative study is performed to evaluate the effectiveness of the proposed model. It is shown from extensive simulation that the model can accurately predict the normalized displacement of suction caisson anchors.

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Honnette, Taylor R. "Measuring Liquefied Residual Strength Using Full-Scale Shake Table Cyclic Simple Shear Tests." DigitalCommons@CalPoly, 2018. https://digitalcommons.calpoly.edu/theses/1998.

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This research consists of full-scale cyclic shake table tests to investigate liquefied residual strength of #2/16 Monterey Sand. A simple shear testing apparatus was mounted to a full-scale one-dimensional shake table to mimic a confined layer of saturated sand subjected to strong ground motions. Testing was performed at the Parson’s Geotechnical and Earthquake Laboratory at California Polytechnic State University, San Luis Obispo. T-bar penetrometer pullout tests were used to measure residual strength of the liquefied soil during cyclic testing. Cone Penetration Testing (CPT) was performed on the soil specimen throughout testing to relate the laboratory specimen to field index test data and to compare CPT results of the #2/16 Monterey sand before and after liquefaction. The generation and dissipation of excess pore pressures during cyclic motion are measured and discussed. The effects of liquefied soil on seismic ground motion are investigated. Measured residual strengths are compared to previous correlations comparing liquefied residual strength ratios and CPT tip resistance.

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Bodzay, Steve J. "Organotin reagents toward the preparation of cyclic disulfides and related compounds." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72827.

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Babadopulos, Lucas. "Phenomena occurring during cyclic loading and fatigue tests on bituminous materials : Identification and quantification." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSET006/document.

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La fatigue est un des principaux mécanismes de dégradation des chaussées. En laboratoire, la fatigue est simulée en utilisant des essais de chargement cyclique, généralement sans période de repos. L’évolution du module complexe (une propriété du matériau utilisée dans la caractérisation de la rigidité des matériaux viscoélastiques) est suivie de manière à caractériser l’endommagement. Son changement est généralement interprété comme étant dû au dommage, alors que d’autres phénomènes (se distinguant du dommage par leur réversibilité) apparaissent. Des effets transitoires, propres aux matériaux viscoélastiques, apparaissent lors des tout premiers cycles (2 ou 3) et produisent une erreur dans la détermination du module complexe. La non-linéarité (dépendance du module complexe avec le niveau de déformation) est caractérisée par une diminution réversible instantanée du module et une augmentation de l’angle de phase qui est observée avec l’augmentation de l’amplitude de déformation. De plus, pendant le chargement, de l’énergie mécanique est dissipée en raison du caractère visqueux du comportement du matériau. Cette énergie se transforme principalement en chaleur ce qui induit une augmentation de température. Cela produit une diminution de module liée à cet auto-échauffement. Quand le matériau revient à la température initiale, le module initial est alors retrouvé. La partie restante du changement de module peut être expliquée, d’une part par un autre phénomène réversible, appelé dans la littérature « thixotropie », et d’autre part par le dommage « réel », qui est irréversible. Cette thèse explore ces phénomènes dans les bitumes, mastics (bitume mélangé avec des particules fines, dont le diamètre est inférieur à 80μm) et enrobés bitumineux. Un chapitre (sur la nonlinearité) présente des essais de « balayage d’amplitude de déformation » avec augmentation ou/et diminution des amplitudes sont présentés. Un autre se concentre sur l’auto-échauffement. Il comprend une proposition de procédures de modélisation dont les résultats sont comparés avec des résultats des cycles initiaux d’essais de fatigue. Finalement, un chapitre est dédié à l’analyse du module complexe mesuré pendant le chargement et les phases de repos. Des essais de chargement et repos ont été réalisés sur bitume (où le phénomène de thixotropie est supposé avoir lieu) et mastic, de manière à déterminer l’effet de chacun des phénomènes identifiés sur l’évolution du module complexe des matériaux testés. Les résultats de l’étude sur la nonlinearité suggèrent que son effet vient principalement du comportement non linéaire du bitume, qui est déformé de manière très non-homogène dans les enrobés bitumineux. Il est démontré qu’un modèle de calcul thermomécanique simplifié de l’échauffement local, ne considérant aucune diffusion de chaleur, peut expliquer le changement initial de module complexe observé au cours des essais cycliques sur enrobés. Néanmoins, la modélisation de la diffusion de chaleur a démontré que cette diffusion est excessivement rapide. Cela indique que la distribution de l’augmentation de température nécessaire pour expliquer complètement le module complexe observé ne peut pas être atteinte. Un autre phénomène réversible, qui a des effets sur le module complexe similaires à ceux d’un changement de température, doit donc avoir lieu. Ce phénomène est considéré être de la thixotropie. Finalement, à partir des essais de chargement et repos, il est démontré qu’une partie majeure du changement de module complexe au cours des essais cycliques vient des processus réversibles. Le dommage se cumule de manière approximativement linéaire par rapport au nombre de cycles. Le phénomène de thixotropie semble partager la même direction sur l’espace complexe que la nonlinéarité. Cela indique que les deux phénomènes sont possiblement liés par la même origine microstructurelle. Des travaux supplémentaires sur le phénomène de thixotropie sont nécessaires
Fatigue is a main pavement distress. In laboratory, fatigue is simulated using cyclic loading tests, usually without rest periods. Complex modulus (a material stiffness property used in viscoelastic materials characterisation) evolution is monitored, in order to characterise damage evolution. Its change is generally interpreted as damage, whereas other phenomena (distinguishable from damage by their reversibility) occur. Transient effects, proper to viscoelastic materials, occur during the very initial cycles (2 or 3) and induce an error in the measurement of complex modulus. Nonlinearity (strain-dependence of the material’s mechanical behaviour) is characterised by an instantaneous reversible modulus decrease and phase angle increase observed when strain amplitude increases. Moreover, during loading, mechanical energy is dissipated due to the viscous aspect of material behaviour. This energy turns mainly into heat and produces a temperature increase. This produces a modulus decrease due to self-heating. When the material is allowed to cool back to its initial temperature, initial modulus is recovered. The remaining stiffness change can be explained partly by another reversible phenomenon, called in the literature “thixotropy”, and, then, by the “real” damage, which is irreversible. This thesis investigates these phenomena in bitumen, mastic (bitumen mixed with fine particles, whose diameter is smaller than 80μm) and bituminous mixtures. One chapter (on nonlinearity) presents increasing and/or decreasing strain amplitude sweep tests. Another one focuses on selfheating. It includes a proposition of modelling procedures whose results are compared with the initial cycles from fatigue tests. Finally, a chapter is dedicated to the analysis of the measured complex modulus during both loading and rest periods. Loading and rest periods tests were performed on bitumen (where the phenomenon of thixotropy is supposed to happen) and mastic in order to determine the effect of each of the identified phenomena on the complex modulus evolution of the tested materials. Results from the nonlinearity investigation suggest that its effect comes primarily from the nonlinear behaviour of the bitumen, which is very non-homogeneously strained in the bituminous mixtures. It was demonstrated that a simplified thermomechanical model for the calculation of local selfheating (non-uniform temperature increase distribution), considering no heat diffusion, could explain the initial complex modulus change observed during cyclic tests on bituminous mixtures. However, heat diffusion modelling demonstrated that this diffusion is excessively fast. This indicates that the temperature increase distribution necessary to completely explain the observed complex modulus decrease cannot be reached. Another reversible phenomenon, which has effects on complex modulus similar to the ones of a temperature change, needs to occur. That phenomenon is hypothesised as thixotropy. Finally, from the loading and rest periods tests, it was demonstrated that a major part of the complex modulus change during cyclic loading comes from the reversible processes. Damage was xivfound to cumulate in an approximately linear rate with respect to the number of cycles. The thixotropy phenomenon seems to share the same direction in complex space as the one of nonlinearity. This indicates that both phenomena are possibly linked by the same microstructural origin. Further research on the thixotropy phenomenon is needed

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Clayton, Russell Adrian. "Investigation of stabilized Berea Red soil with emphasis on tensile and cyclic triaxial tests." Master's thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/8319.

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This dissertation investigates the soil mechanical properties of a sample of Berea Red soil and the most suitable methods of treatment to improve it. Special attention has been paid to lime stabilization and different curing techniques. Gradings, special indicators and California Bearing Ratios were determined on both natural and lime stabilized Berea Red soil. Consolidometer tests were performed on natural and lime or cement stabilized soil at various densities to establish the compressibility and collapse potential. A computer controlled Indirect Tensile Testing with data logging facilities was developed in apparatus order that some of the soil mechanical properties of Berea Red soil may be determined. Natural and stabilized Berea Red soil was tested in a monotonic and cyclic triaxial apparatus to determine the short and long stress strain characteristics.

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Hassan, Zehtab Kaveh. "An Assessment Of The Dynamic Properties Of Adapazari Soils By Cyclic Direct Simple Shear Tests." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612228/index.pdf.

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Among the hard-hit cities during 17 August 1999 Kocaeli Earthquake (Mw 7.4), Adapazari is known for the prominent role of site conditions in damage distribution. Since the strong ground motion during the event was recorded only on a rock site, it is necessary to estimate the response of alluvium basin before any study on the relationship between the damage and the parameters of ground motion. Therefore, a series of site and laboratory tests were done on Adapazari soils in order to decrease the uncertainty in estimation of their dynamic properties. In downtown Adapazari, a 118 m deep borehole was opened in the vicinity of heavily damaged buildings for sample recovery and in-situ testing. The stiffness of the soils in-situ is first investigated by standard penetration tests (SPT) and by velocity measurements with P-S suspension logging technique. Disturbed samples were recovered by core-barrel and split-barrel samplers. 18 Thin-Walled tubes were successively used for recovering undisturbed samples. A series of monotonic and cyclic direct simple shear tests were done on specimens recovered from the Thin-Walled tubes. It is concluded that the secant shear modulus and damping ratio of soils exposed to severe shaking during the 1999 event are significantly smaller than those estimated by using the empirical relationships in literature. It is also observed that the reversed-S shaped hysteresis loops are typical for cyclic response of the samples.

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Azimikor, Nazli. "Out-of-plane stability of reinforced masonry shear walls under seismic loading : cyclic uniaxial tests." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42113.

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In recent years, widespread application of low-rise masonry construction, including post-disaster buildings like fire halls, has become limited in seismic regions of Canada. This is because the Canadian Masonry Design Standard (CSA S304.1-04) [Canadian Standard Association 2004] mandates stringent requirements on the design of ductile reinforced masonry (RM) shear walls, especially with regard to their height-to-thickness (h/t) ratios, which were restricted to ensure against out-of-plane instability. This failure mechanism has been observed in the end zones of reinforced concrete shear walls loaded in-plane in experimental research and in past earthquakes. However, there is a lack of similar evidence for RM shear walls; this is a motivation for the research program described in this thesis. The research consists of several major tasks. First, a review of the literature on previous experimental research studies on RM shear walls was conducted, followed by comprehensive investigation into the parameters affecting out-of-plane instability of RM shear walls,. Based on the results of this literature review, the first phase of the experimental program was designed with a focus on modeling the RM wall end zone and understanding the mechanism of lateral instability. Five full-scale specimens representing the wall end zones were constructed and subjected to reversed cyclic axial tension and compression until failure. The effect of varying h/t ratios of the plastic hinge zone, as well as level of axial tensile strain on the out-of-plane instability was examined. Based on the results of the experimental study, it was concluded that the level of applied tensile strain in the wall end zone is one of the critical factors governing its lateral instability. Therefore, the maximum tensile strain that may be imposed on a moderately ductile RM wall end-zone is determined based on a kinematic relationship between the axial strain and the out-of-plane displacement. A preliminary mechanic model has been proposed to predict the maximum tensile strain before instability takes place. The model can be incorporated into design provisions related to the thickness of shear walls of a given height. A comparison with the experimental results showed that the model offers conservative prediction of the maximum tensile strain.

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Jurko, Jozef. "Liquefaction behavior and cyclic response of non-plastic and low plasticity silt-clay mixtures in ring-shear tests." 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136896.

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OLTMAN, JONATHAN A. "MODELING OF SLIP AND BEARING INTERACTIONS IN BOLTED CONNECTIONS SUBJECTED TO CYCLIC LOADING." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1181516304.

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Laham, Noor. "Episodic DSS tests to measure changing strength for whole-life geotechnical design." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.

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Changes in seabed soil strength due to loading events during the life of a structure, affect the response of the structure to any future event. This change in soil strength due to loading events, in particular cyclic loads, was of great concern in the field of offshore geotechnics during the last decades. Allowing for these changes can have a beneficial outcome on the design. Studying the changes occurring in the soil can be mainly done using large scale centrifuge tests or Laboratory element testing, where the latter proved to be able to successfully illustrate soil strength changes during periods of cyclic loads and reconsolidation. A new approach of life design known as “the whole life design” has been introduced lately to the industry “. Whole life design embraces the time-varying evolution of actions and resistances to create a continuous assessment of conditions of a structure. This dissertation studies the possibility of one of the most famous element tests which is the “Direct simple shear testing” to capture the changing in strength under cyclic (i.e., episodic in this context) loads and the settlement of subsea layers for the whole life geotechnical design. The outcome of the DSS testing in addition to outcomes from other previous methods (eg T-bar penetrations and Triaxial testing) can form the basis for a new framework to be adopted in the future for demonstrating a whole life design for subsea structures. In general, the project introduces the concept of whole-life geotechnical design through practical examples and shed lights on Direct simple shear testing ability to simulate specific cyclic loading scenarios. The topic closes with a discussion of next steps to enable whole-life geotechnical design to be more readily adopted in routine practice where appropriate.

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Bathini, Udaykar. "A Study of Microstructure, Tensile Deformation, Cyclic Fatigue and Final Fracture Behavior of Commercially Pure Titanium and a Titanium Alloy." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1281973687.

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Schiavon, José Antonio. "Behaviour of helical anchors subjected to cyclic loadings." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18132/tde-10072017-090437/.

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Helical anchors, used widely to resist uplift loading for a variety of applications, including in transmission towers, pipelines, offshore structures, etc., are subjected to environmental cyclic loads that influence the anchor performance and may induce fatigue failure. However, the influence of cyclic loading on helical anchor behaviour is unknown. A comprehensive evaluation of the effect of cyclic loading on the load-displacement response of single-helix anchors in sandy soils is presented here, including an interaction diagram to help designers evaluate the impact of different conditions in cyclic loadings. The experimental work of this thesis includes geotechnical centrifuge modelling and field load tests. The centrifuge model tests were carried out with reduced scale models of helical anchors in sand, at IFSTTAR (Nantes, France). The field load tests were performed on helical anchors installed in a tropical residual soil of the Experimental Site of the University of São Paulo (São Carlos, Brazil). In addition, numerical modelling was used to predict the pre- and postcyclic responses of the single-helix anchors tested in a centrifuge. The main findings of this research are: (a) helical anchor behaviour is governed by helix bearing resistance, and no loss of helix bearing capacity was observed in the range of cyclic loadings tested, (b) the degradation of shaft resistance was noticed mainly during the first 100 cycles, when the accumulation of permanent displacements is more significant, (c) an interaction diagram showing the different conditions of cyclic stability is proposed from the results of the experimental data, (d) modified values of the bearing capacity factor in tension (Nq) are suggested for the estimation of post-cyclic uplift capacity of single-helix anchors in sand, (e) the installation effect of the anchor should be taken into account in the numerical model in order to obtain reliable predictions of the helical anchor performance.
As estacas helicoidais são largamente utilizadas para resistir a carregamentos de tração em uma variedade de aplicações como torres de linhas de transmissão de energia, dutos enterrados, estruturas offshore, etc. Estes tipos de estruturas são normalmente submetidos a carregamentos cíclicos que influenciam o desempenho de fundações por estacas helicoidais submetidas a esforços de tração, e podem induzir ruptura por degradação da capacidade de carga. Contudo, a influência do carregamento cíclico no comportamento das estacas helicoidais (ou ancoragens helicoidais, quando submetidas apenas a esforços de tração) é pouco conhecida. Uma avaliação abrangente do efeito de carregamentos cíclicos sobre o comportamento das ancoragens helicoidais é apresentada nesta tese, incluindo um diagrama de interação para auxiliar na avaliação do impacto de diferentes condições de carregamento cíclico. O trabalho experimental desta tese inclui modelagem em centrífuga geotécnica e ensaios de carregamento cíclico em estacas na grandeza real em campo. Os ensaios em centrífuga foram realizados com modelos reduzidos de estacas helicoidais em areia, no IFSTTAR (Nantes, França). Os ensaios de campo foram realizados em ancoragens helicoidais instaladas no solo residual tropical do Campo Experimental de Fundações da Universidade de São Paulo (São Carlos, Brasil). Além disso, modelos numéricos foram utilizados para simular os resultados do comportamento das ancoragens helicoidais ensaiadas em centrífuga nas condições pré- e pós-ciclos. Os principais resultados desta pesquisa são: (a) a capacidade de carga à tração da ancoragem helicoidal é controlada pela capacidade de carga da hélice, (b) a degradação da resistência por atrito lateral foi observada principalmente durante os primeiros 100 ciclos, período em que a acumulação dos deslocamentos permanentes é mais significante, (c) um diagrama de interação mostrando as diferentes condições de estabilidade cíclica é proposto a partir dos resultados experimentais em centrífuga, (d) valores modificados do fator de capacidade de carga em tração (Nq) são sugeridos para estimativa da capacidade pós-ciclos de ancoragens helicoidais com uma hélice em areia, (e) o efeito da instalação da ancoragem deve ser levado em consideração no modelo numérico para que se obtenha previsões confiáveis do desempenho de ancoragens helicoidais.

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Alkhtany, Moshabab Mobarek H. "MODELING STRUCTURAL POLYMERIC FOAMS UNDER COMBINED CYCLIC COMPRESSION-SHEAR LOADING." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1469532064.

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Schiavon, José Antonio. "Behaviour of helical anchors subjected to cyclic loadings." Thesis, Ecole centrale de Nantes, 2016. http://www.theses.fr/2016ECDN0014/document.

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Les ancrages hélicoïdaux, largement utilisés pour résister à des efforts de traction pour une variété d’applications comme les pylônes électriques, les pipelines, les structures offshore, etc., sont soumis à des chargements cycliques qui influent sur la performance d’encrage et peuvent induire une rupture par fatigue. Cependant, l’influence des sollicitations cycliques sur le comportement d’encrage hélicoïdal est mal connue. Une évaluation approfondie de l’effet des charges cycliques sur la réponse effort – déplacement des ancrages avec une seule hélice dans les sols sableux est présentée, incluant un diagramme d’interaction pour aider à évaluer l’impact des différentes conditions de chargement cyclique. La partie expérimentale de cette thèse comprend des essais en centrifugeuse géotechnique et des essais de chargement in situ. Les essais en centrifugeuse ont été effectués sur des modèles réduits d’encrages hélicoïdaux dans du sable à l’IFSTTAR (Nantes, France). Les essais de chargement in situ ont été réalisés sur des ancrages hélicoïdaux installés dans le sol tropical résiduel du site expérimental de l’Université de Sao Paulo (Sao Carlos, Brésil). De plus la modélisation numérique a été utilisée pour prédire les réponses pré et post cycliques des ancrages d’une hélice testée en centrifugeuse. Les principales conclusions de cette recherche sont : (a) le comportement d’un ancrage hélicoïdal est régi par la capacité portante de l’hélice, et aucune perte de capacité portante d’hélice n’a été observée pour la gamme de charges cycliques testée, (b) la dégradation de la résistance par frottement latéral sur le fut a été remarquée principalement pendant les 100 premiers cycles, lorsque l’accumulation des déplacements permanents est plus importante, (c) un diagramme d’interaction montrant les différentes conditions de stabilité cyclique est proposé à partir des résultats des données expérimentales, (d) des valeurs modifiées du facteur de capacité portante (Nq) sont proposées pour l’estimation de la capacité et post-cyclique des ancrages avec une hélice dans du sable, (e) l’effet de l’installation de l’ancrage doit être pris en compte dans le modèle numérique afin d’obtenir des prédictions fiables de la performance de l’ancrage hélicoïdal
Helical anchors, used widely to resist uplift loading for a variety of applications, including in transmission towers, pipelines, offshore structures, etc., are subjected to environmental cyclic loads that influence the anchor performance and may induce fatigue failure. However, the influence of cyclic loading on helical anchor behaviour is unknown. A comprehensive evaluation of the effect of cyclic loading on the load-displacement response of single-helix anchors in sandy soils is presented here, including an interaction diagram to help designers evaluate the impact of different conditions in cyclic loadings. The experimental work of this thesis includes geotechnical centrifuge modelling and field load tests. The centrifuge model tests were carried out with reduced scale models of helical anchors in sand, at IFSTTAR (Nantes, France). The field load tests were performed on hekical anchors installed in a tropical residual soil of the Experimental Site of the University of Sao Paulo (Sao Carlos, Brazil). In addition, numerical modelling was used to predict the pre- and post-cyclic responses of the single-helix anchors tested in a centrifuge. The main findings of this research are : (a) helical anchor behaviour is governed by helix bearing resistance and no loss of helix bearing capacity was observed in the range of cyclic loadings tested, (b) the degardation of shaft resistance was noticed mainly during the first 100 cycles, when the accumulation of permanent displacements is more significant, (c) an interaction diagramshowing the different conditions of cyclic stability is proposed from the results of the experimental data, (d) modified values of the bearing capacity factor in tension (Nq) are suggested for the estimation of post-cyclic uplift capacity of single-helix anchors in sand, (e) the installation effect of the anchor should be taken into account in the numerical model in order to obtain reliable predictions of the helical anchor performance

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18

Carret, Jean-Claude. "Linear viscoelastic characterization of bituminous mixtures from dynamic tests back analysis." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSET012/document.

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La caractérisation du comportement des matériaux bitumineux est primordiale pour pouvoir dimensionner les structures de chaussées, mais aussi pour prédire de manière plus précise leur durée de vie. En effet, ces matériaux sont soumis à des phénomènes complexes, mécaniques, thermiques, physiques et chimiques qui apparaissent souvent de manière couplée. Devant la complexité des problèmes observés et avec l’apparition des nouveaux matériaux et nouvelles techniques de fabrication, des études avancées de laboratoire et des modélisations rhéologiques sont nécessaires. Les méthodes existantes permettent de caractériser les matériaux en laboratoire grâce à l’utilisation de presses hydrauliques très couteuses. De plus, la plupart de ces essais ne sont pas adaptés à une utilisation directe sur chaussées. Dans cette thèse, un essai dynamique qui repose sur le phénomène de propagation d’onde a été développé pour caractériser les enrobés bitumineux dans le domaine viscoélastique linéaire. Il s’agit d’un essai non destructif, bien moins couteux que les essais existants et qui pourrait à terme s’adapter à une utilisation in-situ. Des méthodes complexes d’analyse inverse de propagation d’ondes en milieu viscoélastique ont été mises au point afin d’obtenir les propriétés thermomécaniques des enrobés bitumineux à partir des signaux mesurés expérimentalement. Les propriétés viscoélastiques linéaires de différents enrobés bitumineux déterminées à partir de l’essai dynamique développé ont été comparées aux résultats obtenus avec des essais cycliques plus conventionnels de traction-compression
Characterizing the behaviour of bituminous materials is essential for the design of pavement structures and to predict their service life more accurately. Indeed, these materials are subjected to complex phenomenon, mechanical, thermal, physical and chemical that are often coupled. Due to the complexity of the phenomenon observed and with the emergence of new materials and new production techniques, advances laboratories studies and rheological modelling are necessary. With the existing methods, it is possible to characterize the materials in laboratories using expensive hydraulic presses. Moreover, most of these tests cannot be used directly on pavement structures. In this thesis, a dynamic test based on wave propagation was developed to characterize bituminous mixtures in the linear viscoelastic domain. It is a nondestructive test, far less expensive than the existing tests and that could be adapted for in situ measurements. Complex methods of inverse analysis of wave propagation in a viscoelastic medium were developed to obtain the thermomechanical properties of bituminous mixtures from the signals measured experimentally. The linear viscoelastic properties of different mixtures obtained from the developed dynamic test were compared to the results of more conventional cyclic tension-compression tests

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Pruett, Joshua M. "Performance of a Full-Scale Lateral Foundation with Fine and Coarse Gravel Backfills Subjected to Static, Cyclic, and Dynamic Lateral Loads." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/2317.

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Full-scale lateral load tests were performed on a pile cap with five backfill conditions: no backfill, densely compacted fine gravel, loosely compacted fine gravel, densely compacted coarse gravel, and loosely compacted coarse gravel. Static loads, applied by hydraulic load actuators, were followed by low-frequency, actuator-driven cyclic loads as well as higher frequency dynamic loads from an eccentric mass shaker. Passive resistance from the backfill significantly increased the lateral capacity of the pile cap. Densely compacted backfill materials contributed about 70% of the total system resistance, whereas loosely compacted backfill materials contributed about 40%. The mobilized passive resistance occurred at displacement-to-height ratios of about 0.04 for the densely compacted gravels, whereas passive resistance in the loosely compacted materials does not fully mobilize until greater displacements are reached. Three methods were used to model the passive resistance of the backfill. Comparisons between calculated and measured responses for the densely compacted backfills indicate that in-situ shear strength test parameters provide reasonable agreement when a log-spiral method is used. Reasonable agreement for the loosely compacted backfills was obtained by either significantly reducing the interface friction angle to near zero or reducing the soil's frictional strength by a factor ranging from 0.65 to 0.85. Cracking, elevation changes, and horizontal strains in the backfill indicate that the looser materials fail differently than their densely compacted counterparts. Under both low frequency cyclic loading and higher frequency shaker loading, the backfill significantly increased the stiffness of the system. Loosely compacted soils approximately doubled the stiffness of the pile cap without backfill and densely compacted materials roughly quadrupled the stiffness of the pile cap. The backfill also affected the damping of the system in both the cyclic and the dynamic cases, with a typical damping ratio of at least 15% being observed for the foundation system.

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Kathekeyan, Myuran. "Fatigue performance and design of cold-formed steel roof battens under cyclic wind uplift loads." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/122471/1/Myuran_Kathekeyan_Thesis.pdf.

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This thesis investigates the fatigue pull-through failures of steel roof batten to rafter connections and proposes suitable design equations to enhance the safety of thin steel roof battens in cyclones. Suitable design equations were developed based on both linear and nonlinear damage theories by carefully investigating the factors affecting the failure via small and full-scale experimental studies and associated numerical studies. The proposed design equations have the potential to replace the current Australian design method based on complex and time-consuming prototype cyclic tests, and also those used in many other countries.

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Pehlivan, Menzer. "Assessment Of Liquefaction Susceptibility Of Fine Grained Soils." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610744/index.pdf.

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Recent ground failure case histories after 1994 Northridge, 1999 Kocaeli and 1999 Chi-Chi earthquakes revealed that low-plasticity silt-clay mixtures generate significant cyclic pore pressures and can exhibit a strain-softening response, which may cause significant damage to overlying structural systems. These observations accelerated research studies on liquefaction susceptibility of fine-grained soils. Alternative approaches to Chinese Criteria were proposed by several researchers (Seed et al. 2003, Bray and Sancio 2006, Boulanger and Idriss 2006) most of which assess liquefaction triggering potential based on cyclic test results compared on the basis of index properties of soils (such as LL, PI, LI, wc/LL). Although these new methodologies are judged to be major improvements over Chinese Criteria, still there exist unclear issues regarding if and how reliably these methods can be used for the assessment of liquefaction triggering potential of fine grained soils. In this study, results of cyclic tests performed on undisturbed specimens (ML, CL, MH and CH) were used to study cyclic shear strain and excess pore water pressure generation response of fine-grained soils. Based on comparisons with the cyclic response of saturated clean sands, a shift in pore pressure ratio (ru) vs. shear strain response is observed, which is identified to be a function of PI, LL and (wc/LL). Within the confines of this study, i) probabilistically based boundary curves identifying liquefaction triggering potential in the ru vs. shear strain domain were proposed as a function of PI, LL and (wc/LL), ii) these boundaries were then mapped on to the normalized net tip resistance (qt,1,net) vs. friction ratio (FR) domain, consistent with the work of Cetin and Ozan (2009). The proposed framework enabled both Atterberg limits and CPT based assessment of liquefaction triggering potential of fine grained low plasticity soils, differentiating clearly both cyclic mobility and liquefaction responses.

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RADAMPOLA, Senanie Sujeewa, and senanie s. radampola@mainroads qld gov au. "EVALUATION AND MODELLING PERFORMANCE OF CAPPING LAYER IN RAIL TRACK SUBSTRUCTURE." Central Queensland University. Centre for Railway Engineering, 2006. http://library-resources.cqu.edu.au./thesis/adt-QCQU/public/adt-QCQU20060817.115415.

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In the design of rail track structures where the subgrade cannot achieve the desired capacity, enabling the required standard of track geometry to be maintained for the speed, axle load and tonnage to be hauled, a capping layer of granular material is placed between the natural ground or the embankment fill material and the ballast to protect the underlying weaker layers. In spite of the important role played by the capping layer, very little research has been carried out on its performance. The current practice of design of the capping layer, therefore, is based on working stress philosophy where reduced levels of stresses are assumed not to degrade the subgrade. Even on tracks containing a thick ballast layer that ensures allowable levels of working stress the subgrade has been found to have permanently deformed. Design of capping layers based on plastic deformation, therefore, appears appropriate. This thesis aims at determining the load levels that cause detrimental plastic deformation in the capping layer. The suite of material properties that characterise plastic deformations of capping layer is neither readily available nor easily determined. This thesis proposes a cheaper method of evaluating a range of capping layer material properties using penetration tests on specimens contained in California Bearing Ratio (CBR) test moulds coupled with a finite element modelling based back calculation technique. The suite of material properties thus determined are used for the simulation of the behaviour of capping layers under the boundary and loading conditions similar to those in practice. The predicted results are validated using laboratory experiments on large size capping layer specimens.

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Gudmarsson, Anders. "Resonance Testing of Asphalt Concrete." Doctoral thesis, KTH, Väg- och banteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-155906.

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This thesis present novel non-destructive laboratory test methods to characterize asphalt concrete. The testing is based on frequency response measurements of specimens where resonance frequencies play a key role to derive material properties such as the complex modulus and complex Poisson’s ratio. These material properties are directly related to pavement quality and used in thickness design of pavements. Since conventional cyclic loading is expensive, time consuming and complicated to perform, there has been a growing interest to apply resonance and ultrasonic testing to estimate the material properties of asphalt concrete. Most of these applications have been based on analytical approximations which are limited to characterizing the complex modulus at one frequency per temperature. This is a significant limitation due to the strong frequency dependency of asphalt concrete. In this thesis, numerical methods are applied to develop a methodology based on modal testing of laboratory samples to characterize material properties over a wide frequency and temperature range (i.e. a master curve). The resonance frequency measurements are performed by exciting the specimens using an impact hammer and through a non-contact approach using a speaker. An accelerometer is used to measure the resulting vibration of the specimen. The material properties can be derived from these measurements since resonance frequencies of a solid are a function of the stiffness, mass, dimensions and boundary conditions. The methodology based on modal testing to characterize the material properties has been developed through the work presented in paper I and II, compared to conventional cyclic loading in paper III and IV and used to observe deviations from isotropic linear viscoelastic behavior in paper V. In paper VI, detailed measurements of resonance frequencies have been performed to study the possibility to detect damage and potential healing of asphalt concrete. The resonance testing are performed at low strain levels (~10^-7) which gives a direct link to surface wave testing of pavements in the field. This enables non-destructive quality control of pavements, since the field measurements are performed at approximately the same frequency range and strain level.

QC 20141117

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Paritala, Phani Kumari. "Atherosclerotic plaque tissue characterization by combining imaging, pathological and mechanical analysis." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/134005/1/Phani%20Kumari_Paritala_Thesis.pdf.

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This thesis was a step forward in understanding the behaviour and variations of structural and mechanical characteristics of the atherosclerotic plaque tissue, to better assess the plaque vulnerability. A framework is developed for the comprehensive characterization of the plaque tissue and enhance our knowledge of the plaque heterogeneity and its response to the complex interactions between systemic, hemodynamic and biological factors. The outcomes of this research and the framework developed when applied on long-term longitudinal studies will be useful for developing a risk stratification plan for improving treatment strategies before an acute event happens.

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Bernardi, Martina. "Industrial steel storage racks subjected to static and seismic actions: an experimental and numerical study." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/322402.

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Industrial steel storage racks are pre-engineered lightweight structures commonly used to store goods from supermarkets to big warehouses. These systems are framed structures, usually made of cold-formed steel profiles and characterised by non-standard details. Their performance is quite complex and the prediction of their global response is more difficult than for the traditional steel frames. This difficulty is due to the racks’ main features: the use of cold-formed thin-walled steel sections which are sensitive to different buckling modes, the presence of regular perforation patterns on the uprights, the highly non-linear behaviour of joints, the influence of the structural imperfections and the significant frame sensitivity to second order effects. The behaviour of racks becomes even more complex when seismic or accidental events induce significant horizontal forces acting on the structures. The complexity and variability that characterise racks make it difficult to identify general design solutions. Hence, racks design is traditionally carried out by using the “design by testing” approach, which requires the experimental characterisation of the main structural components, of the joints and the sub-assemblies. The complexity of the racks also affects their numerical modelling, which results in complex analyses that must take into account all the aforementioned features. The work presented in this thesis focuses on the study of a typical steel pallet rack, identified as case study. The research aims to contribute to building up a comprehensive knowledge of the response of both the main rack components and of the whole structure. The main rack components were first individually studied. The behaviour of the uprights, of the base-plate joints and of the beam-to-column joints was experimentally investigated. The experimental data were then taken as reference for the calibration of FE models that enabled exploring each component’s performance. These models were then incorporated into the whole rack model. The response of the uprights was first investigated through stub column tests. The non-negligible interaction between axial force and bending moment of the upright response was then experimentally and numerically analysed to define the M-N domains. In addition, the rules provided by different European standards for the design of isolated members subjected to combined axial load and bending moment were considered and critically compared, identifying the main critical issues of the different design approaches. Although the contribution of joints on the rack global response is of paramount importance, to date, the knowledge is quite limited. In particular, the experimental studies of the behaviour of base-plate joints are still rather modest, especially for the cyclic range. Therefore, an experimental campaign on the rack base-plate joints was carried out: three levels of axial load were considered and the response in both the down-aisle and the cross-aisle direction was investigated under monotonic and cyclic loadings. Similarly, the beam-to-column joint was tested both monotonically and cyclically, taking into account its non-symmetric behaviour. Numerical models for both joint types were developed and validated enabling the characterisation of joints in the monotonic and cyclic range. This in-depth knowledge of the response of individual components facilitated the evaluation of the global rack behaviour. As a final stage of the research, full-scale tests of four-level two-bay racks were performed taking advantage of an innovative full-scale testing set-up and, on the basis of the experimental outcomes, the racks’ global behaviour was numerically investigated. Critical standards issues and needs for future research were further identified.

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Larignon, Céline. "Mécanismes d'endommagement par corrosion et vieillissement microstructural d'éléments de structure d'aéronef en alliage d'aluminium 2024-T351." Phd thesis, Toulouse, INPT, 2011. http://oatao.univ-toulouse.fr/6994/1/larignon_partie_1_sur_2.pdf.

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Cette thèse s'inscrit dans le cadre d'une collaboration avec EADS Innovation Works et AIRBUS. L'objectif des travaux est d'identifier les modes d'endommagements possibles d'éléments de structure métalliques d'aéronefs développés en service et d'en comprendre les mécanismes et les effets sur les propriétés des matériaux afin de contribuer au développement d'une méthode de contrôle non destructif innovante. Le matériau sélectionné est un alliage d'aluminium 2024-T351, l'un des matériaux constitutifs de la voilure et du fuselage d'avions civils. Les modes d'endommagement étudiés sont la corrosion et le vieillissement microstructural. La première partie de ces travaux est consacrée à l'analyse de l'influence des conditions d'exposition au milieu corrosif sur le développement de la corrosion intergranulaire et à l'identification des mécanismes de dégradation associés et de leurs cinétiques. Des conditions d'exposition originales alternant des phases d'immersion et d'émersion à différentes températures ont été explorées dans la mesure où elles semblent particulièrement représentatives des conditions d'exposition réelles. Les mécanismes proposés pour comprendre l'endommagement observé dans certaines de ces conditions d'exposition au milieu corrosif, impliquent un phénomène apparenté à de la fragilisation par l'hydrogène, phénomène qui n'est, à l'heure actuelle, pas encore reconnu pour les alliages d'aluminium de la série 2xxx. L'influence de l'hydrogène sur les propriétés physico-chimiques et mécaniques du matériau est donc étudiée dans la seconde partie de ces travaux. Enfin, l'influence d'un vieillissement microstructural sur les propriétés de l'alliage ainsi que les couplages possibles entre vieillissement microstructural et phénomènes de corrosion sont abordés dans une dernière partie. L'ensemble des résultats obtenus permet de révéler des pistes pour développer une méthode CND innovante permettant la caractérisation physique in-situ du niveau d'endommagement à l'échelle locale d'éléments de structures en alliages d'aluminium.

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D'hondt, Clément. "Analyse de la plasticité cyclique d'un acier TWIP et du rôle du maclage/démaclage à l'aide d'imagerie et de mesures de champs sub-micrométriques." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX064.

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L’objectif de la thèse est d’approfondir la compréhension de la plasticité cyclique des aciers TWIP et du rôle joué par le maclage / démaclage lors du durcissement cyclique en suivant l’activité de maclage à l’aide d’imagerie et de mesures de champs de déformation plastique submicrométriques, échelle permettant de discerner les nano-macles. La contrainte seuil de maclage en traction a été estimée entre 400 et 475 MPa. Le démaclage (pouvant être accompagné d’un maclage secondaire sur les systèmes coplanaires aux macles primaires), lors de l’inversion du chargement, et le remaclage, lors de la rampe de traction suivante, ont été mis en évidence en traction - compression lors d’essais in situ sous AFM et sous MEB avec corrélation d’images. Un niveau de contrainte en valeur absolue proche de la contrainte seuil de maclage semble nécessaire pour activer le démaclage et le remaclage. La contrainte en retour exercée par les grains voisins freine la croissance des macles primaires et favorise le démaclage et le maclage secondaire. A amplitude de contrainte imposée, la fraction maclée stagne après le premier cycle alors qu’à amplitude de déformation plastique imposée elle augmente lors du durcissement cyclique. Dans les deux cas, le maclage / démaclage accommode une fraction décroissante de l’amplitude de déformation plastique. A l’échelle macroscopique, le durcissement cyclique est suivi d’un adoucissement plus modeste. L’intensité de ces deux stades varie avec l’amplitude imposée. A amplitude de déformation plastique imposée, le durcissement est majoritairement du à l’augmentation de la composante cinématique (X) de la contrainte d’écoulement, qui a été associée au maclage, aux cellules de dislocations et aux fautes d’empilement, alors que l’adoucissement est majoritairement du à la diminution de la composante isotrope (R), qui a été attribuée à la destruction de l’ordre à courte distance. A amplitude de contrainte imposée, R suit une évolution similaire et X démarre à une valeur élevée, due au maclage intense lors de la première traction, et évolue ensuite assez peu. Une loi de comportement simulant convenablement les essais a été identifiée à partir des données recueillies à amplitude de déformation plastique imposée
This work aims at clarifying the cyclic plasticity of TWIP steels and the role of twinning / detwinning during cyclic hardening by monitoring the twinning activity using sub-micrometric imaging and plastic strain field measurements to distinguish nanotwins. The stress for the onset of twinning in tension was estimated between 400 and 475 MPa. Detwinning (as well as secondary twinning on systems coplanar to primary twins), during load reversal, and retwinning, during subsequent forward loading were observed during push - pull in situ tests under an AFM and a SEM with HR-DIC. Detwinning and retwinning seems to be activated at a stress level close (in absolute value) to the threshold stress for twinning. The backstress induced by the neighbouring grains hinders the growth of primary twins and favors detwinning or secondary coplanar twinning. Under fixed stress amplitude, the twin fraction saturates after the first cycle while under fixed plastic strain amplitude it increases continuously during the cyclic hardening stage. In both cases, twinning / detwinning accommodates a decreasing fraction of the plastic strain amplitude. At the macroscopic scale, cyclic hardening stage is followed by a more modest softening stage. The importance of both hardening and softening rises with the loading amplitude. Under fixed plastic strain amplitude, the hardening is mostly due to an increase of the kinematic component (X) of the flow stress, which is associated to twinning, dislocation cells and stacking faults, while the softening is mostly due to the decrease of the isotropic component (R), which has been attributed to the destruction of the short range order. Under fixed stress amplitude, R follows a similar evolution and X starts at a high value, due to the intense twinning during the first tension, and then it hardly evolves. A constitutive law that adequately simulates the cyclic tests was identified from the data collected under fixed plastic strain amplitude

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Takeda, Marcelo de Castro. "A influência da variação da umidade pós-compactação no comportamento mecânico de solos de rodovias do interior paulista." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/18/18143/tde-25112006-225630/.

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Na construção de rodovias, as condições de umidade e densidade observadas na compactação são, geralmente, próximas daquelas correspondentes ao pico da curva de compactação obtida no ensaio Proctor. É sabido que variações ambientais no decorrer da vida do pavimento podem alterar, de maneira significativa, a umidade do subleito e dos seus componentes e assim, as suas propriedades resilientes. O objetivo principal desta pesquisa é avaliar a influência da variação da umidade pós-compactação no módulo de resiliência de solos de rodovias do interior paulista a partir de resultados de ensaios de laboratório. Foram coletados e caracterizados setenta e três solos, e, dentre estes, selecionados trinta para a etapa de estudo da variação da umidade pós-compactação, após a realização de ensaios MCT, difração de raios-x, microscopia eletrônica de varredura e azul de metileno para determinação da gênese. Os solos selecionados apresentam características distintas quanto à gênese, sendo metade laterítico e metade não-laterítico. Os corpos-de-prova foram compactados na umidade ótima e submetidos a processos de secagem e umedecimento e, posteriormente, realizados ensaios triaxiais cíclicos. Os resultados permitiram a modelagem do 'M IND.R' em função do estado de tensão para diferentes umidades e a avaliação da competência de alguns modelos matemáticos nesta representação. Estudou-se a influência da gênese e da granulometria sobre o valor do 'M IND.R' e avaliou-se a conseqüência da variação da umidade sobre este para solos lateríticos e não-lateríticos. Determinou-se uma expressão para estimar a variação do 'M IND.R' com a variação da umidade a partir do parâmetro k1, independentemente do estado de tensão. Pesquisou-se a existência de relações entre os parâmetros de regressão do modelo composto e os resultados dos ensaios de compressão simples e as propriedades físicas dos solos, de forma a permitir a estimativa do módulo de resiliência a partir do resultado de ensaios mais simples. Investigou-se a possibilidade de se utilizar as relações entre a variação do módulo tangente inicial com a variação da umidade para estimar os efeitos sobre o 'M IND.R'.
On road construction, the field compaction conditions are usually close to those determined from Proctor tests. Environmental variations may lead to changes in the pavement moisture and also changing its resilient properties. The main objective of this research is to study the influence of post-compaction moisture content variation on the resilient modulus of soils from São Paulo state pavements, using laboratory tests. To accomplish this objective, seventy three soils samples were collected and characterized. Among them, thirty samples were selected, after four different tests were carried out to determine the soils genesis, to study the post-compaction moisture content variation. Half of these selected soils are lateritic ones, and the other half are non-lateritic soils. The specimens were compacted at optimum moisture content and submitted to drying and moistening processes prior cyclic triaxial test to be carried out. The results allowed the resilient modulus modeling as a function at the stress state and the performance evaluation of five different models. The genesis and grain size distribution influence on the resilient modulus values were studied. The effects of moisture content variations on lateritic and non-lateritic soils were investigated. An expression to estimate the resilient modulus variations with the moisture variations was determined, independently of the stress state. The existence of relations of the compound model regression parameters with the results of unconfined compressive strength and soil properties were studied. The possibility of using the initial tangent modulus variations with the moisture variations to estimate the effects on the resilient modulus were also investigated.

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Maggi, Patrícia Lizi de Oliveira. "Comportamento de pavimentos de concreto estruturalmente armados sob carregamentos estáticos e repetidos." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-31052006-162340/.

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Apresenta-se um trabalho numérico e experimental, com o objetivo de estudar o comportamento dos pavimentos de concreto estruturalmente armados, quando submetidos a forças verticais estáticas e repetidas. Avalia-se a contribuição da armadura de flexão, na resistência de placas de concreto apoiadas sobre meio elástico. Verifica-se experimentalmente o modo de ruína de placas submetidas a carregamento monotônico e a carregamento repetido, com e sem armadura, e acompanha-se o desenvolvimento das fissuras no concreto e das deformações no aço. Comparam-se os resultados obtidos, com as recomendações da NBR 6118:2003, para o dimensionamento de estruturas submetidas à fadiga. É desenvolvido modelo numérico capaz de representar a interface do solo com a placa do pavimento, a fissuração do concreto, a contribuição da armadura e o comportamento pós-fissuração. Com auxílio do modelo numérico, validado a partir dos resultados experimentais, estuda-se a influência de alguns parâmetros importantes para o dimensionamento dos pavimentos, tais como: capacidade de suporte da fundação, espessura das placas, área de aço, dimensões das placas em planta, posição de aplicação da força e presença de juntas de transferência de deslocamento. Os resultados experimentais mostram uma significativa contribuição da armadura positiva na resistência de placas isoladas sob forças verticais centradas. Verificou-se que as forças repetidas provocam fadiga do aço e que o número de ciclos depende da deformação provocada na armadura. A partir dos resultados são traçadas diretrizes para o dimensionamento, no qual devem ser considerados os momentos positivos e os negativos, e deve ser feita a verificação da fadiga do concreto e da armadura
A numerical and experimental study on the behavior of structurally reinforced concrete pavement under vertical static and repeated load is presented. The contribution of bending reinforcement to the strength of concrete slab is assessed. It is experimentally verified the fracture of reinforced and plain concrete slabs under monotonic loads and under cyclic loads. The concrete cracking and the strain on steel are monitored. The results are compared to the brazilian code recommendations to the design of structures under fatigue. A numerical model that represents the soil-slab interface, the concrete cracking, the reinforcement contribution and the tension stiffening behavior is developed. Some important parameters to the pavement design are analyzed using this finite element model, whose reliability was verified to experimental results. These parameters are: the soil capacity; the slab thickness; reinforcement ratio; slab dimensions; load positions; and joints conditions. The tests data show an important contribution of the positive reinforcement on the strength of an isolated slab with centered load. It has been verified the fatigue of the steel. The number of cycles depends on the reinforcement strain. The results are used to propose some directions to the design. The positive and negative bending moments have to be considered and the fatigue on the concrete and on the reinforcement has to be verified

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Elshesheny, Ahmed. "Dynamic soil-structure interaction of reinforced concrete buried structures under the effect of dynamic loads using soil reinforcement new technologies. Soil-structure interaction of buried rigid and flexible pipes under geogrid-reinforced soil subjected to cyclic loads." Thesis, University of Bradford, 2019. http://hdl.handle.net/10454/18312.

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Recent developments in constructions have heightened the need for protecting existing buried infrastructure. New roads and buildings may be constructed over already existing buried infrastructures e.g. buried utility pipes, leading to excessive loads threatening their stability and longevity. Additionally applied loads over water mains led to catastrophic damage, which result in severe damage to the infrastructure surrounding these mains. Therefore, providing protection to these existing buried infrastructure against increased loads due to new constructions is important and necessary. In this research, a solution was proposed and assessed, where the protection concept would be achieved through the inclusion process of geogrid-reinforcing layers in the soil cover above the buried infrastructure. The controlling parameters for the inclusion of geogrid-reinforcing layers was assessed experimentally and numerically. Twenty-three laboratory tests were conducted on buried flexible and rigid pipes under unreinforced and geogrid-reinforced sand beds. All the investigated systems were subjected to incrementally increasing cyclic loading, where the contribution of varying the burial depth of the pipe and the number of the geogrid-reinforcing layers on the overall behaviour of the systems was investigated. To further investigate the contribution of the controlling parameters in the pipe-soil systems performance, thirty-five numerical models were performed using Abaqus software. The contribution of increasing the amplitude of the applied cyclic loading, the number of the geogrid-reinforcing layers, the burial depth of the pipe and the unit-weight of the backfill soil was investigated numerically. The inclusion of the geogrid-reinforcing layers in the investigated pipe-soil systems had a significant influence on decreasing the transferred pressure to the crown of the pipe, generated strains along its crown, invert and spring-line, and its deformation, where reinforcing-layers sustained tensile strains. Concerning rigid pipes, the inclusion of the reinforcing-layers controlled the rebound that occurred in their invert deformation. With respect to the numerical investigation, increasing the number of the reinforcing-layers, the burial depth of the pipe and the unit-weight of the backfill soil had positive effect in decreasing the generated deformations, stresses and strains in the system, until reaching an optimum value for each parameter. Increasing the amplitude of the applied loading profile resulted in remarkable increase in the deformations, stresses and strains generated in the system. Moreover, the location of the maximum tensile strain generated in the soil was varied, as well as the reinforcing-layer, which suffered the maximum tensile strain.
Government of Egypt

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Pra-ai, Suriyavut. "Essais et modélisation du cisaillement cyclique sol-struture à grand nombre de cycles. Application aux pieux." Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00809729.

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On présente tout d'abord une série d'essais de cisaillement direct 2D monotones et cycliques sur l'interface sable de Fontainebleau-plaque rugueuse et lisse, 'a contrainte normale constante (CNL) et à rigidité normale imposée (CNS). Le but de ces essais est de simuler la situation mécanique le long de pieux soumis à un grand nombre de cycles d'origine environnementale ou anthropique. Ces cycles (typiquement 10000) de faible amplitude (10'a 40 kPa en terme de contrainte de cisaillement) ne sont pas cens'es produire de rupture prématurée. Ces tests incluent une série de cycles d'amplitudes (successives) variées. Le problème de la perte de sable entre la boite et la plaque est trait'e avec attention. Nous avons interprété l'effet de la position du "centre des cycles" dans le plan de contraintes (variables cycliques moyennes) et de la densité initiale. Plusieurs facteurs tels que l'indice initial de densité (ID0), la contrainte normale cyclique moyenne (_n cm0), le niveau initial moyen de contrainte de cisaillement (_cm0), l'amplitude cyclique réduite (__) et la rigidité normale imposée (k qui dans cette thèse, va de 1000 'a 5000 kPa/mm), influencent les déplacements relatifs cycliques moyens normal ([u]cm) et tangentiel [w]cm) et sont pris en considération.On observe soit de la dilatance, soit de la contractance en accord avec l'état caractéristique développé par Luong. L'influence du chemin de contrainte (CNL ou CNS) est également analysée. Un modèle phénoménologique et analytique de comportement d'interface sur chemins cycliques CNL est propos'e. C'est également le cas pour le comportement monotone sur chemins oedométrique et CNL, la variable de mémoire unique étant la densité d'interface (sous contrainte) ou le déplacement relatif normal. Cette formulation permet de traiter, par incréments analytiques finis, les chemins comportant une variation d'amplitude cyclique, et les chemins CNS, ce qui introduit la notion de nombre de cycles équivalent. On notera que les chemins CNS sont toujours contractants. Ces essais sont utilisés pour aborder la simulation par éléments finis, avec le logiciel Plaxis, selon une approche de pseudo-viscoplasticité, le nombre de cycles tenant lieu de temps fictif. L'essai de cisaillement monotone'a la boite est modélisé en densités faible et forte, ainsi que deux essais de pieux modèles centrifugés, l'un en traction, l'autre en compression. Des recommandations sont proposées pour le calcul courant des pieux sous sollicitations cycliques. Cette thèse a été soutenue par l'ANR SOLCYP et le programme national " recherches sur le comportement des pieux soumis à des sollicitations cycliques".

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Evin, Harold. "Low Cr alloys with an improved high temperature corrosion resistance." Thesis, Dijon, 2010. http://www.theses.fr/2010DIJOS082/document.

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Les aciers ferritiques à faible teneur en chrome tel que le T/P91 sont largement utilisés dans les centrales de productions d’électricité pour leurs bonnes propriétés mécaniques et leur faible coefficient d’expansion thermique. Cependant, la demande croissante en énergie alliée à la nécessité de réduire les émissions de gaz à effet de serre, conduisent à envisager l’augmentation des conditions d’utilisation (température et pression) de ces matériaux. Des études ont montré qu’en modifiant la température de fonctionnement et la pression de vapeur d’eau de 538°C/18.5 MPa à 650°C/30 MPa, le rendement des centrales thermiques progressait d’environ 8%. Se pose alors la question de la tenue à la corrosion à haute température des aciers à 9% de chrome. Au cours de ces travaux, le comportement d’un acier ferritique/ martensitique à 9% de chrome a été étudié à 650°C sous air sec et sous vapeur d’eau de matière isotherme et en conditions de cyclage thermique. La prise de masse des échantillons renseigne sur la cinétique de la réaction d’oxydation et l’adhérence des couches d’oxydes formées. Les produits de corrosion ont été caractérisés par plusieurs techniques d’analyses dans l’optique de clairement identifiés les oxydes en présences et leurs mécanismes de formation. Des oxydes mixtes de fer et de chrome (Cr,Fe)2O3 sont dans un premier temps formés et assurent s’avèrent être temporairement protecteur. Pour des longs temps d’oxydation ou des températures supérieures à 650°C, la magnétite Fe3O4 et l’hématite Fe2O3 sont les principaux oxydes formés, montrant ainsi l’inadéquation des nuances à faible teneur en chrome pour une utilisation dans des conditions aussi drastiques. Dans l’optique d’augmenter la résistance à la corrosion à haute température de cet alliage, diverses solutions ont été envisagées tel que l’aluminisation par cémentation en caisse, les revêtements d’oxydes de terre rare par MOCVD, ou encore l’ajout d’éléments d’addition. Ces solutions ont été également testées à 650°C sous air sec et sous vapeur d’eau
The improvement of high temperature oxidation resistance of low chromium content steels, such as T/P91, is of great interest in regards with their application in thermal power generating plants. Indeed, they possess good creep properties, and low thermal expansion coefficient. Important needs in energy together with environmental issues place power generation plants under constraints which lead to develop high efficiency systems. A usual way to increase the efficiency consists in increasing temperature and pressure parameters of the power generating plant. Studies has shown that the total efficiency of a plant increases by nearly 8 % when changing the steam parameters from 538°C/18.5 MPa to 650°C/30 MPa. Then, the problem of corrosion resistance of 9% chromium steel in those conditions is asked. In this work, the behavior of a ferritic / martensitic 9% chromium steel has been studied at 650°C in dry air and in water vapor containing environment in both isothermal and thermal cyclic conditions. The weight gain of samples provides information on the kinetics of the oxidation reaction and the adhesion of formed oxide scale. Corrosion products were characterized by several analytical techniques in order to identify oxides with accuracy and to understand their formation mechanisms. Mixed iron and chromium oxides (Cr, Fe) 2O3 are initially formed and provide temporary protection to the substrate. For long time exposure or temperatures above 650°C, magnetite, Fe3O4 and hematite Fe2O3 are the main oxides formed, highlighting the fact that low chromium steel are inappropriate for applications in such drastic conditions. In order to increase the high temperature corrosion resistance of this alloy, various solutions have been proposed as aluminizing by pack cementation, reactive element oxides coatings of by MOCVD, or addition of alloying elements in the steel composition. These solutions were then tested at 650 ° C in dry air and in water vapor environments

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Lamberts, Robert Patrick. "The development of an evidenced-based submaximal cycle test designed to monitor and predict cycling performance : the Lamberts and Lambert submaximal cycle test (LSCT)." Doctoral thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/2757.

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Includes abstract.
Includes bibliographical references.
The HIMS test, which consists of controlled exercise at increasing workloads, has been developed to monitor changes in training status and accumulative fatigue in athletes. As the workload can influence the day-to-day variation in heart rate, the exercise intensity which is associated with the highest sensitivity needs to be established with the goal of refining the interpretability of these heart rate measurements. The aim of the study was to determine the within subject day-to-day variation of submaximal and recovery heart rate in subjects who reached different exercise intensities.

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Sweeney, Claire. "Cell cycle regulators in the murine testis." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364276.

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Chen, Linling. "Developing Constitutive Equations for Polymer Foams Under Cyclic Loading." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1354739399.

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Farrell, Jeanne. "The molecular identity of soluble adenylyl cyclase /." Access full-text from WCMC, 2008. http://proquest.umi.com/pqdweb?did=1528353801&sid=2&Fmt=2&clientId=8424&RQT=309&VName=PQD.

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Koziris, L. Perry (Lymperis Perry). "Blood lactates following intermittent and continuous cycling tests of anaerobic capacity." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60051.

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The purpose of this study was to compare the concentration of and the time to peak blood lactate following three 90-s cycle ergometer tests--intermittent all-out (Int-A), continuous all-out (Cont-A), and continuous constant (Cont-C), and to compare group peak lactate to blood lactate at individual peak time. Eight fingertip blood samples were drawn between 1 and 12min post-exercise. Subjects were university hockey players (n = 19) and physical education students (n = 19). The two all-out tests had a higher peak concentration than the Cont-C test (P $<$ 0.05). The Int-A test had an earlier peak than the two continuous tests (P $<$ 0.05) but this difference vanished if peak time was measured from the onset of the tests. A number of sampling times had lactate concentrations similar to the individual peak concentration (P $<$ 0.05): (1) 1, 2, 3, and 4min for Int-A; (2) 2, 3, 4, 5, and 6min for Cont-A; (3) 2 and 4min for Cont-C.

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Skoglund, Mattias. "Evaluation of test cycles for freight locomotives." Licentiate thesis, KTH, Elektriska maskiner och effektelektronik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-48066.

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Diesel locomotives provide versatility to the railway system as they do not depend on electric feeding. Worldwide they constitute important parts of locomotive fleets used for various tasks such as mainline services, shunting and terminal operations. The main drawbacks are emissions of CO2, NOx and other pollutants. The emissions to air are in general controlled by legislation. The European testing and approval procedure for locomotive engines is performed with the ISO 8178-F test cycle. It is alone meant to resemble all European locomotives. Good correlation was found between mainline operations and the ISO 8178-F test cycle. A good correlation was furthermore found between shunting operations and North American shunting test cycles. However, this thesis has shown that this results in inadequate description of for instance shunting operations. Typical characteristics for shunting are relatively high ratio of transient loading, low mean power output and high amount of idling. Therefore important aspects of diesel locomotive usage are thereby disregarded in certifications. Deficient correlation between test cycle and intended operations may lead to locomotives that are not properly optimised for the type of operation they are intended for. Improperly dimensioned and optimised locomotives cause impaired fuel economy and more emissions emitted. Many Swedish diesel locomotives are to a large extent used in shunting-like conditions in yards and industries for instance. Therefore, it is recommended to supplement the present ISO test cycle with a test cycle that includes the characteristic of shunting. Knowledge about duty cycles for specific operations can be of importance in locomotive acquisition, dimensioning of new locomotives or when estimating emissions and/or fuel consumption. It is essential to make proper dimensioning of propulsion systems as it can imply lower life cycle costs as well as fewer emissions. Appropriate dimensioning of the propulsion system is particularly important for non-conventional propulsion systems. If the application range of a test cycle is narrow, its emulating capability ought to be better at describing and representing the indented application. Today's test cycles state fractional power or torque as a function of engine speed. This may result in misleading duty cycles when the same kind of operation is undertaken with different locomotives that have widespread power ratings. A more powerful locomotive used for the very same load as a less powerful locomotive will result in a different duty cycle. Non-conventional propulsion systems are gaining popularity also in the railway industry where implementation of new technology usually is slow. Dual mode and hybrid systems are two examples. Related to test and duty cycles the build-up of these new propulsion systems change the prerequisites of the propulsion systems. From a duty cycle perspective it is reasonable to implement an additional test cycle for non-conventional propulsion systems if the popularity rises.
QC 20111115

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Meless, Dejen. "Test Cycle Optimization using Regression Analysis." Thesis, Linköping University, Automatic Control, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-54809.

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Industrial robots make up an important part in today’s industry and are assigned to a range of different tasks. Needless to say, businesses need to rely on their machine park to function as planned, avoiding stops in production due to machine failures. This is where fault detection methods play a very important part. In this thesis a specific fault detection method based on signal analysis will be considered. When testing a robot for fault(s), a specific test cycle (trajectory) is executed in order to be able to compare test data from different test occasions. Furthermore, different test cycles yield different measurements to analyse, which may affect the performance of the analysis. The question posed is: Can we find an optimal test cycle so that the fault is best revealed in the test data? The goal of this thesis is to, using regression analysis, investigate how the presently executed test cycle in a specific diagnosis method relates to the faults that are monitored (in this case a so called friction fault) and decide if a different one should be recommended. The data also includes representations of two disturbances.

The results from the regression show that the variation in the test quantities utilised in the diagnosis method are not explained by neither the friction fault or the test cycle. It showed that the disturbances had too large effect on the test quantities. This made it impossible to recommend a different (optimal) test cycle based on the analysis.

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Holley, Timothy Michael. "Development of a test protocol for cyclic pullout of geosynthetics in roadway base reinforcement." Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/holley/HolleyT0509.pdf.

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Geosynthetics, or manmade materials used in soils engineering, have successfully been used as base reinforcement of pavements for over 40 years. Use of geosynthetics can result in cost savings by allowing the aggregate base layer to be reduced in thickness and/or the service life of the pavement to be extended. Design methods for this type of reinforcement have typically been developed by individual manufacturers for specific products. These methods are not widely used by state transportation agencies because 1) they are proprietary, 2) they are empirically based, and 3) they lack compatibility with the current national trend towards mechanistic-empirical pavement design procedures. This project was initiated to develop testing methods to determine one of the critical material properties needed for mechanistic-empirical base-reinforced pavement design, namely, the resilient interface shear stiffness. This property describes the interaction, in particular the shear stiffness, between the geosynthetic and the surrounding aggregate. This new test protocol closely mimics vehicular load patterns, resulting in design parameters pertinent to the use of the geosynthetics to reinforce the base course. A study was conducted to evaluate the repeatability of these tests and to develop a standardized test method. Specific parameters under investigation include load pulse and rest period duration, embedment length of the geosynthetic, and differences in results using different soils and types of geosynthetics. Some parameters seemed to have little effect on values of resilient interface shear stiffness, while others vastly impacted the results. Load pulse and rest period durations did not affect output results significantly. Maintaining a constant confinement or shear stress during the test duration produced higher repeatability and correlated well to the adapted resilient modulus equation. Three-aperture length tests on polyester geogrid also correlated well with this equation, however repeatability was moderately low. Polypropylene geogrid and a woven geotextile confined in Ottawa sand displayed low correlation to this equation. During testing, very small displacements occur, and therefore, every effort should be made to ensure that these measurements are accurate and not skewed by electrical noise and interference.

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Marinheiro, Carlos Alberto. "Desenvolvimento de máquina de movimentos cíclicos para testes biomecânicos." Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/82/82131/tde-22042004-100959/.

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O ser humano locomove-se utilizando-se do complexo sistema neuro-músculo-esquelético, o que lhe confere qualidade de vida. Partes do sistema esquelético são passíveis de tratamento ou mesmo de substituição pelo emprego de materiais estranhos ao corpo humano mas que provocam pequena reação biológica e necessitam ser dimensionados de modo a suportar toda tensão resultante do movimento humano. O objetivo deste trabalho foi desenvolver uma máquina de ensaio cíclico para testes biomecânicos, de implantes utilizados nas cirurgias de reconstrução ósteo-articular, utilizando tecnologia nacional. A máquina possui um sistema de acionamento por meio de um motor trifásico de 2 HP, 1800 rpm; um sistema de transmissão de cargas cíclicas utilizando um eixo excêntrico, que aciona um pistão, que promove o movimento de duas alavancas que transmitem a carga para os componentes a serem ensaiados. Há um inversor de freqüência para controle do número de ciclos do motor, um reservatório de soro fisiológico com um sistema que mantém o soro aquecido entre 36 e 38 ºC, e uma bomba hidráulica submersa que mantém o soro em constante movimentação. Foi feito um teste cíclico de fadiga de componente femoral de artroplastia de quadril, com torção, seguindo determinações das normas ISO 7206/89, parte 4 e ASTM F 1612/95, e utilizada para o teste a Prótese Femoral Cimentada Modelo Alpha ® da empresa Baumer ®, haste polida de 150 mm e off-set de 37,5 mm. Também foi feito um ensaio para verificação de trincas seguindo determinações da Norma ABNT NBR ISO 9583/1997. Durante as 139 horas previstas para o teste de fadiga do componente femoral, a máquina de ensaio não apresentou problemas mecânicos, demonstrando eficiência e o êxito na confecção de uma máquina de ensaios cíclicos para testes biomecânicos
The human being locomotes using the complex neuro-muscle-skeletal system, what confers him life quality. Parts of the skeletal system can submit to treatment or even to the substitution for the employment of strange materials to the human body but that provoke small biological reaction and they need to be projected in way to support every resulting tension of the human movement. The objective of this work was to develop a machine of cyclic trial for biomechanical tests using national technology. The machine has an activation system by means of a triphasic motor of 2 HP, 1800 rpm; a system of transmission of cyclic loads using an eccentric axis, that activates a piston, that promotes the movement of two levers that transmit the load for the components at be tested. There is a frequency inverter for control of the number of cycles of the motor, a reservoir of physiologic serum with a system that maintains the serum heated up to 36-38 ºC, and a submerged hydraulic bomb that maintains the serum in constant movement. It was made a cyclic test of fatigue of femoral component of hip arthroplasty, with torsion, following determinations of the norms ISO 7206/89, part 4 and ASTM F 1612/95, and used for the test the Prosthesis Femoral Cemented Model Alpha ® of the company Baumer ®, polished stem of 150 mm and off-set of 37,5 mm. It was also made a trial for verification of cracks following determinations of the norm ABNT NBR ISO 9583/1997. During the 139 hours foreseen for the test of fatigue of the femoral component, the trial machine didnt present mechanical problems, demonstrating efficiency and the success in the production of a machine of cyclic trials for biomechanical tests

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Mun, Byoung-Jae. "Unsaturated soil behavior under monotonic and cyclic stress states." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1361.

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The objectives of this dissertation are to measure and calculate surface free energies of soil particles, to understand the mechanical behavior of unsaturated silty sand through first studying the stress-strain relationship, the effects of matric suction and pore water chemistry and second to interpret the behavior by the critical state frame work, to develop a method to predict cone tip resistance in unsaturated soils, and to present the concept of pseudo strain and dissipated pseudo strain energy. Universal Sorption Device (USD) is developed to measure surface free energies of soil particles. The test results on a soil sample shows that specific surface area increased with decreasing particle size. The components of surface free energies and the work of adhesion increased with decreasing particle size. A servo controlled triaxial testing device is developed to test 15.24 cm in height and 7.62 cm in diameter, recompacted specimens of unsaturated soil under varying matric suction and different pore chemistry. During the test, the matric suction is maintained constant. Results from the triaxial drained tests are used for validation of the constitutive models proposed by Alonso et al. (1990). Predictions from the model are in good agreement with experimental results. The critical state model for unsaturated soil is used to calculate cone tip resistance in unsaturated silty sand. The calculated cone tip resistance is used to evaluate the liquefaction potential of unsaturated soils. The results from the stress based liquefaction potential analysis reveal that even in an unsaturated condition soil is susceptible to liquefaction. By applying the pseudo strain concept, it is possible to account for the viscous resistance of water during cyclic loading. The results of undrained cyclic triaxial tests are used to calculate pseudo-strain and dissipated pseudo strain energy. The results of calculated dissipated pseudo strain energy suggest that the effect of initial matric suction is evident. On the other hand, the effect of surface tension increase or decrease due to existence of chemical on the pore water is negligible.

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CHIEN, YU-HO, and 錢有和. "A calibration test on new cyclic triaxial apparatus and some liquefaction tests." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/3867nt.

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碩士
國立高雄應用科技大學
土木工程與防災科技研究所
106
In this study, six mixtures of Kaohsiung sand and soil were added with different proportions of fine aggregate and different relative densities to conduct some dynamic triaxial tests in order to investigate the effect of the content of fines on soil liquefaction resistance. Some research issues were studied such as amplitude's influence on relative density and soil liquefaction resistance, and effect of amplitude on soil liquefaction resistance and critical state parameters. The results of dynamic triaxial test showed that under the condition of 0% of the fine material and 30% of the relative density, the results four of different amplitude were obtained, which shows that the cyclic number required for the liquefaction of the sample gradually decreased with increasing amplitude. If amplitude equaling to 0.2 kN and 0.4 kN, it is found that the axial stress of amplitude = 0.4 kN is larger than that of amplitude = 0.2 kN and the corresponding axial strain is ranged from 1% to -6%. By plotting the relationship between the cyclic number and the relative density under the two amplitude amplitudes, we can find that when the amplitude is increased, both the initial liquefaction response (cyclic number) and the strain 2.5% response (cyclic number) are apparently reduced, indicating that the soil reduced resistance to liquefaction. With the plot of the cyclic number versus the criticality parameter, as the amplitude increases from 0.3 to 0.4, the cyclic number drastically decreases, with the trend line falling from a high slope to a gentler straight line. When the relative density of the test reaches to 70%, and 0% and 15% of fines (CSRs are set to 0.45 and 0.4, respectively), the difference of axial difference stress of fine material 15% is smaller than that of pure sand and conversely the axial strain ratio pure sand has a greater stress than 15% fines. As far as the pore water pressure is concerned, the number of reflections required for the fine material 15% is more difficult to liquefy than pure sand.

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Chen, Kuan-Yu, and 陳冠羽. "Cyclic Lateral Loading Tests on Model Pile in Sand." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/16862001241356927414.

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碩士
國立中央大學
土木工程學系
104
Offshore wind turbines have been one significant piece of development of renewable energy. The pile foundation of offshore wind turbines in Taiwan must resist the influences of waves, earthquakes, typhoons, and other natural forces.The research simulates fatigue effect caused by long-term lateral loads, which is developed from wind and wave, and this also investigates the loading behavior of pile foundation that carries long-term cyclic lateral loads.The research uses model pile made of polypropylene to simulate the response of flexible pile subject to lateral loading. The study applies regression analysis model to examine the nonlinear response of pile foundation. In this research, it demonstrates designs of instruments and plans series of experiments to discuss the behavior of piles subject to lateral loading. This study will use Chunan sand to prepare the model ground by a mobile pluviator. Two sets of static ultimate lateral pile load tests will be carried out first in the model grounds with two kinds of relative densities. According to static ultimate lateral pile load tests to determine the loading amplitude of one-way cyclic lateral pile load tests. Eight sets of one-way cyclic lateral pile load tests will be performed by considering different densities and stress levels of long-term cyclic loads, to obtain permanent displacement and pile stiffness of pile foundation under long-term cyclic lateral loading.This research derives subgrade reaction coefficient of pile-soil system from static p-y curve, and comprehend the influence of subgrade reaction coefficient under cyclic lateral loading from dynamic p-y curve. Lastly, research offers the comparison of p-y curves between the test result and API and Reese.

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ChristianRegis, Humphrey, and 雷格斯. "Cyclic Tests on the Performance of Reinforced Unpaved Roads." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/75701735815799540579.

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碩士
國立成功大學
土木工程學系碩博士班
100
The purpose of a geosynthetic layer or separator beneath the base course of a road pavement is to provide extra resistance and support capacity, as well as prevent the aggregate and the subgrade from intermixing or contamination, which in turn causes the weakening of the pavement structure. However, it is hypothesized that the absence of a geosynthetic layer, in this case a geotextile or a geogrid, will allow the generally tough aggregate of the base course and the generally soft subgrade to intermix. Some cyclic loading tests on unpaved road structures were performed to investigate and understand the performance of the design parameters currently in use. With these tests, a better and more comprehensive approach could be sought to improve the life span and economic impact of the road network, so as to aid in the overall highway design criteria. The test results demonstrated that a geogrid-reinforced ground outperformed the woven-geotextile-reinforced one. In general, the use of two layers of geosynthetics, one layer as a reinforcement and the other as a separator greatly enhances the roadway’s life span; in the sense that a smaller rutting, a smaller degree of intermixing can be achieved through correct placement of reinforcement and separation layers

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46

Chen, Ssu-Kai, and 陳思凱. "Cyclic Axial Loading Tests on Model Pile in Sand." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/jvnbnd.

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碩士
國立中央大學
土木工程學系
105
Because the offshore wind turbine pile foundations such as that jacket and tripod are subjected to the WTG loading and long-term wind and wave loading transmitted from upper structure to lower substructure, the generated cyclic axial compression and tension, result in pile groups of difference settlement, affecting the stability of operation of the wind turbine. Therefore to investigate different pile behavior under cyclic axial load, is the destination of this study. 　　In this study, air pluviation method of sample was adopted to prepare a dense homogeneous dry sand specimen with a relative density of 60%, and 1-g model pile load test was conducted. When conducting axial cyclic load test, the loading which approach 1/3 of ultimate static in the axial load capacity was applied to simulate the normal conditions under safety factor of 3.In the static load tests it was, found that near bottom of the pile the sand relative density significantly affects the pile bearing capacity, the ultimate static load test total was totally 10 groups, with recording the relative density of sand layers in order to observe the variation of pile bearing capacity, and to ensure the consistent in preparation of sand samples in the future. Six unidirectional cyclic axial load test were conducted, in which three tests were under cyclic axial compression, and three tests under cyclic axial tension. The magnitude of loading were 1/3Pu, 1/6Pu and 1/12Pu, and the number of cycles were 10000, 10000 and 20000 respectively. 　　The results represent that the larger number of axial load cycles apply, the smaller equivalent stiffness of pile head was obtained as well as pile head displacement increases with an increasing number of cycles. Under the same condition of axial load cycles, the accumulated residual displacement of pile foundation under cyclic axial compression was larger than cyclic axial tension case. When increasing number of cycles, the pile shaft friction decreases. But the bearing capacity of pile tip increases.

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47

Yang, Chun-Hsiang, and 楊鈞翔. "Cyclic Lateral Loading Tests on Model Pile in Saturated Sand." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/38034259598927163548.

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Abstract:

碩士
國立中央大學
土木工程學系
105
In recent years, Taiwan has tried to develop green renewable energy. Because Taiwan is an island and has good wind energy potential, offshore wind turbine has become the focus of renewable energy development. At present offshore wind turbine foundation commonly used form of monopile, in the life cycle need to resist wind, waves, earthquakes and other cyclic lateral force. Therefore, this study uses in situ Zhunan sand to remold the dry sand and saturated sand specimen, and use the model pile to carry out the lateral loading tests. The test results will use regression analysis to obtain the pile response, and compare the difference between the piles in the dry sand and the saturated sand specimen. In this research, each type of specimen were carried out two sets of ultimate lateral pile load test. According to test results to determine the loading amplitude of one-way cyclic lateral pile load tests. Four sets of one-way cyclic lateral pile load tests will be performed with different stress level of cyclic load, the number of cycle of cyclic loading up to 10,000 times, to obtain permanent displacement and equivalent stiffness of pile under long-term cyclic lateral loading. The p-y curve of the pile-soil system is obtained by regression analysis, and the behavior of pile-soil interaction is discussed. From the test results, it is found that the saturated sand specimen is relatively weak, so that it can not provide a large soil resistance to constraint the pile displacement, and the coefficient of subgrade reaction also has a greater attenuation.

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48

SHENG, HSU CHING, and 許敬昇. "Cyclic Axial Loading Tests on Model Pile in Saturated Sand." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/sn2scg.

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Abstract:

碩士
國立中央大學
土木工程學系
107
In this study, a model pile is used to perform the long-term cyclic axial load tests in saturated sands, and the behavior of the pile-soil interaction is observed. In order to simulate jacket foundation of offshore wind turbine is long-term subjected to the upper structure weight and periodic wave force. The long-term cyclic axial pressure and tension forces are behaved on the pile, causing differential settlement for pile foundation and slowly tilting of the bottom of wind turbine, affecting the stability of the fan system long-term operation. Before the cyclic load test is performed, static ultimate compressive load test is carried out, and then gets static ultimate load P_u. Loading static load 1/3 Pu initially owing to considering the static loads safety factor of the offshore wind turbine equal to 3, before the one-way cyclic axial load test carried out. A total of 6 sets cyclic axial load are carried out, 3 sets are performed cyclic compression type, and other 3 sets performed cyclic tension type. Three sets cyclic axial load amplitudes are1/3Pu, 1/6Pu and 1/12Pu respectively, and the number of cyclic cycles are 10000, 10000 and 20,000, respectively. When comparing with previous studies done by dry sands, these are performed cyclic axial load tests show some of same results. Long-term cyclic axial load tests show that the stiffness of pile head decreases obviously owing to large of axial amplitude. And the incremental rate of pile head displacement velocity faster when axial amplitude large. Under the tension and compression load tests of the same amplitude, the residual displacement caused by the long-term cyclic axial load tests. When cyclic axial load tests in dry sands, the residual displacement are larger in condition that first pression then tension. In contrast, where tests in saturated sands, the residual displacement are larger under the first tension then pression conditions.

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49

Ko, Jen-wen, and 柯人文. "Cyclic Tests of Reinforced Concrete Corner Beam-Column Joint with Eccentricity." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/83350701072382767334.

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碩士
國立雲林科技大學
營建工程系碩士班
93
Cyclic loading response of five 3/4-scale reinforced concrete corner beam-column connections with a concentric beam framing into a rectangular column in strong or weak direction is reported. Each T-shaped subassembly had a concentric or eccentric beam framing into an identical rectangular column in strong or weak direction. Member proportions, design, and details were compatible with the ACI provisions for the special moment-resisting frames to ensure anticipated beam plastic mechanisms. The specimen variables are loading directions and the eccentricity between the beam and column centerlines. Experimental results show that two joints connecting a beam in strong direction were capable of supporting adjacent beam plastic mechanisms. The other three connecting a beam in weak direction, exhibited significant damage and loss of strength after flexural hinging in the beams. Eccentricity between beam and column centerlines had detrimental effects on the strength degradation, energy dissipation capacity, and displacement ductility of the specimens. It was concluded that ACI design procedures for estimating nominal joint shear strength were unconservative for the tested corner connections under loading on the weak direction. Rational predictions on the connection strengths, ductility, and failure modes were obtained using the plastic hinge length method and a diagonal strut-and-tie model.

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50

Chou, Ting-Wei, and 周廷韋. "Bearing behavior of pile under axial cyclic loading in centrifuge tests." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/ewkkhb.

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Abstract:

碩士
國立中央大學
土木工程研究所
97
A series of centrifuge modeling tests was conducted in the study to investigate the behavior of piles subjected to two types of cyclic axial loadings, including the compressive-tensile and tensile-compressive modes. Three kinds of piles were selected with different slender ratios but with the same embedded length. The model pile was slowly penetrated into the dry sand at 1g condition. Then, the tested model was set on the platform of centrifuge and subjected to an artificial gravity of 80g to simulate a full-scale prototype pile. Subsequently, five cycles of axial cyclic loadings were applied on pile head by a double active air cylinder. From the test results, it can be found that the stiffness of pile increases with increasing number of cyclic loading. The damping ratio increases with decreasing slender ratio. Besides, a tensile force occurs near the bottom of the pile resulting from the release of the tensile force at the pile head.

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