Littérature scientifique sur le sujet « Localized strains »
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Articles de revues sur le sujet "Localized strains"
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Marri, Laura, Emanuela Barboni, Tiziana Irdani, Brunella Perito et Giorgio Mastromei. « Restriction enzyme and DNA hybridization analysis of cellulolytic Streptomyces isolates of different origin ». Canadian Journal of Microbiology 43, no 4 (1 avril 1997) : 395–99. http://dx.doi.org/10.1139/m97-055.
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Streptomyces rochei A2 endoglucanase (eglS) and β-glucosidase (bgs1) genes were used as probes to survey their distribution among 16 Streptomyces strains isolated from different sources and characterized for their cellulolytic activities. The eglS probe hybridized to the genomic DNA of 12 strains with a restriction pattern different from that of S. rochei A2. The DNA from all strains, except one, hybridized with the bgsl probe and one strain showed the same restriction pattern as seen in S. rochei A2. The sequence localized by the eglS probe in S. thermoviolaceus and the one localized by the bgs1 probe in strain EC1 were cloned and expressed in E. coli in plasmids pTAE and pCSF203, respectively. The restriction maps showed that the cloned genes were identical to eglS and bgs1. The restriction enzyme analysis of genomic DNA from all the strains identified nine different groups, each characterized by a distinctive pattern and in agreement with the results of the hybridization experiments.Key words: Streptomyces, cellulase genes, hybridization, restriction enzyme analysis.
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Lavagnino, Michael, Steven P. Arnoczky, Niell Elvin et Julie Dodds. « Patellar Tendon Strain is Increased at the Site of the Jumper's Knee Lesion during Knee Flexion and Tendon Loading ». American Journal of Sports Medicine 36, no 11 (3 septembre 2008) : 2110–18. http://dx.doi.org/10.1177/0363546508322496.
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Background Patellar tendinopathy (jumper's knee) is characterized by localized tenderness of the patellar tendon at its origin on the inferior pole of the patella and a characteristic increase in signal intensity on magnetic resonance imaging at this location. However, it is unclear why the lesion typically occurs in this area of the patellar tendon as surface strain gauge studies of the patellar tendon through the range of motion have produced conflicting results. Hypothesis The predicted patellar tendon strains that occur as a result of the tendon loads and patella-patellar tendon angles (PPTAs) experienced during a jump landing will be significantly increased in the area of the patellar tendon associated with patellar tendinopathy. Study Design Descriptive laboratory study. Methods A 2-dimensional, computational, finite element model of the patella-patellar tendon complex was developed using anatomic measurements taken from lateral radiographs of a normal knee. The patella was modeled with plane strain rigid elements, and the patellar tendon was modeled with 8-node plane strain elements with neo-Hookean material properties. A tie constraint was used to join the patellar tendon and patella. Patella-patellar tendon angles corresponding to knee flexion angles between 0° and 60° and patellar tendon strains ranging from 5% to 15% were used as input variables into the computational model. To determine if the location of increased strain predicted by the computational model could produce isolated tendon fascicle damage in that same area, 5 human cadaveric patella-patellar tendon-tibia specimens were loaded under conditions predicted by the model to significantly increase localized tendon strain. Pre- and posttesting ultrasound images of the patella–patellar tendon specimens were obtained to document the location of any injured fascicles. Results Localized tendon strain at the classic location of the jumper's knee lesion was found to increase in association with an increase in the magnitude of applied patellar tendon strain and a decrease in the PPTA. The principal stresses and strains predicted by the model for this localized area were tensile and not compressive in nature. Applying the tendon strain conditions and PPTA predicted by the model to significantly increase localized strain resulted in disruption of tendon fascicles in 3 of the 5 cadaveric specimens at the classic location of the patellar tendinopathy lesion. Conclusion The localized increase in patellar tendon strain that occurs in response to the application of tendon loads and decreased PPTA could induce microdamage at the classic location of the jumper's knee lesion. Clinical Relevance The association of decreasing PPTA with increasing localized tendon strain would implicate the role of knee-joint angle as well as tendon force in the etiopathogenesis of jumper's knee.
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Fichtelova, V., et K. Kovarcik. « Characterization of two BHV-4 strains isolated in the Czech Republic ». Veterinární Medicína 55, No. 3 (15 avril 2010) : 106–12. http://dx.doi.org/10.17221/18/2010-vetmed.
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This study describes the isolation of bovine herpesvirus 4 (BHV-4) from the respiratory tract of animals suffering from respiratory disease. DNA of new isolates, CH and Ni, was cleaved with <I>Bam</I>HI, <I>Eco</I>RI and <I>Hind</I>III in restriction enzyme analysis and the fragments were identified by co-migration with the restriction profile of the reference strain Movar 33/63 cleaved with the appropriate endonuclease. Typical profiles with polyrepetitive DNA (prDNA) fragments were detected. In order to localize the size variation within the obtained digestion fragments, Southern blot hybridization was performed. Differences between the isolates CH, Ni were localized in both the prDNAs and the unique central part of the genome and were restricted to fragment size variation.
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Jie, M., C. L. Chow et X. Wu. « Damage-coupled FLD of Sheet Metals for Warm Forming and Nonproportional Loading ». International Journal of Damage Mechanics 20, no 8 (21 janvier 2011) : 1243–62. http://dx.doi.org/10.1177/1056789510396331.
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A method of forming limit prediction for sheet metals at high temperatures and under nonproportional loading is presented. The method takes into account the strain-softening behaviors of the material at elevated temperatures. A localized necking criterion based on an isotropic damage-coupled acoustic tensor is developed and employed to determine the forming limits of strain-softening materials. The damage evolution equation is developed within the thermo-mechanical framework. A closed-form expression of the forming limit strains is derived by coupling the damage evolution equation into the localized necking criterion. A computer program, incorporating the incremental theory of plasticity, the damage evolution equation and the localized necking criterion, is developed to compute the forming limit strains under several nonproportional loading paths. A series of the uniaxial tensile tests is performed to measure the relevant mechanical properties of AA6061 at the elevated temperature of 450°C. The material damage variables are determined from the measured elastic modulii from a series of loading and unloading paths. The damage evolution equation of AA6061 at 450°C is formulated based on the test data. The computed limit strains are compared with the test results under various loading paths and a good agreement is observed. It is found that the critical damage value is independent on the stress states and loading paths. It may be concluded that the application of the material damage as a reliable criterion of localized necking including the nonproportional loading cases.
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Dorn, C. R., S. M. Scotland, H. R. Smith, G. A. Willshaw et B. Rowe. « Properties of Vero cytotoxin-producingEscherichia coliof human and animal origin belonging to serotypes other than O157 : H7 ». Epidemiology and Infection 103, no 1 (août 1989) : 83–95. http://dx.doi.org/10.1017/s0950268800030387.
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SUMMARYEight non-O157: H7 Vero cytotoxin (VT)-produeingEscherichia coli(VTEC) strains isolated from ill persons and nine bovine and lamb strains of serogroups matching the human strains, were characterized for various properties known to be associated withE. colivirulence. Five different serogroups were represented: O5. O55, O103, O111 and O153. The bovine and lamb strains produced VT1, while 3 human strains produced VT1, 3 produced VT2 and 2 were positive for both VT1 and VT2. The strains were non-haemolytic on horse blood agar, did not produce either heat stable toxin A (STA) or heat labile toxin (LT), and were non-invasive. The CVD419 probe which has been proposed to identify enterohaemorrhagicE. coli(EHEC) hybridized with all of the 05 and 0103 strains, none of the 055 and 0153 strains, and 3 of the 4 0111 strains. The strains carried several different sized plasmids and hybridization of Southern blots with the CVD419 probe identified plasmids ranging in size from 42 × 10 to 90 × 10. The strains did not hybridize with the enteroadherence factor (EAF) probe derived from an enteropathogenic strain and associated with the ability to give localized adherence to HEp-2 cells. Nevertheless five of the strains adhered in a localized pattern to HEp-2 cells and Intestine 407 cells. Adhesion to either HEp-2 or Intestine 407 cells did not correlate with hybridization with the CVD419 probe or haemagglutinating properties.
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Kabrane-Lazizi, Yamina, Mingdong Zhang, Robert H. Purcell, Kirk D. Miller, Richard T. Davey et Suzanne U. Emerson. « Acute hepatitis caused by a novel strain of hepatitis E virus most closely related to United States strains ». Journal of General Virology 82, no 7 (1 juillet 2001) : 1687–93. http://dx.doi.org/10.1099/0022-1317-82-7-1687.
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A unique hepatitis E virus (HEV) strain was identified as the aetiological agent of acute hepatitis in a United States (US) patient who had recently returned from vacation in Thailand, a country in which HEV is endemic. Sequence comparison showed that this HEV strain was most similar, but not identical, to the swine and human HEV strains recovered in the US. Phylogenetic analysis revealed that this new HEV isolate was closer to genotype 3 strains than to the genotype 1 strains common in Asia. The fact that this HEV was closely related to strains recovered in countries where HEV is not endemic and was highly divergent from Asian HEV strains raises the questions of where the patient’s infection was acquired and of whether strains are geographically as localized as once thought.
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Verma, Anita, et Drusilla L. Burns. « Requirements for Assembly of PtlH with the Pertussis Toxin Transporter Apparatus of Bordetella pertussis ». Infection and Immunity 75, no 5 (5 mars 2007) : 2297–306. http://dx.doi.org/10.1128/iai.00008-07.
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ABSTRACT PtlH is an essential component of the Ptl system, the type IV transporter responsible for secretion of pertussis toxin (PT) across the outer membrane of Bordetella pertussis. The nine Ptl proteins are believed to interact to form a membrane-spanning apparatus through which the toxin is secreted. In this study, we monitored the subcellular localization of PtlH in strains of B. pertussis lacking PT, lacking other Ptl proteins, or from which ATP has been depleted in order to gain insight into the requirements for assembly of PtlH with the remainder of the Ptl transporter complex that is thought to be tightly embedded in the membrane. We found that PtlH is exclusively localized to the inner membrane fraction of the cell in a wild-type strain of B. pertussis. In contrast, PtlH localized to both the cytoplasmic and inner membrane fractions of a mutant strain of B. pertussis that does not produce PT. In comparison to how it localized in wild-type strains of B. pertussis, PtlH exhibited aberrant localization in strains lacking PtlD, PtlE, PtlF, and PtlG. We also found that localization of PtlH was perturbed in B. pertussis strains that were treated with carbonyl cyanide m-chlorophenylhydrazone and sodium arsenate, which are capable of depleting cellular ATP levels, and in strains of B. pertussis that produce an altered form of PtlH that lacks ATPase activity. When taken together, these results indicate that tight association of PtlH with the membrane, likely through interactions with components of the transporter-PT complex, requires the toxin substrate, a specific subset of the Ptl proteins, and ATP. Based on these data, a model for the assembly of the Ptl transporter-PT complex is presented.
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Rakitin, Andrey L., Yulia K. Yushina, Elena V. Zaiko, Dagmara S. Bataeva, Oksana A. Kuznetsova, Anastasia A. Semenova, Svetlana A. Ermolaeva et al. « Evaluation of Antibiotic Resistance of Salmonella Serotypes and Whole-Genome Sequencing of Multiresistant Strains Isolated from Food Products in Russia ». Antibiotics 11, no 1 (21 décembre 2021) : 1. http://dx.doi.org/10.3390/antibiotics11010001.
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Food products may be a source of Salmonella, one of the main causal agents of food poisoning, especially after the emergence of strains resistant to antimicrobial preparations. The present work dealt with investigation of the occurrence of resistance to antimicrobial preparations among S. enterica strains isolated from food. The isolates belonged to 11 serovars, among which Infantis (28%), Enteritidis (19%), and Typhimurium (13.4%) predominated. The isolates were most commonly resistant to trimethoprim/sulfamethoxazole (n = 19, 59.38%), cefazolin (n = 15, 46.86%), tetracycline (n = 13, 40.63%), and amikacin (n = 9, 28.13%). Most of the strains (68.75%) exhibited multiple resistance to commonly used antibiotics. High-throughput sequencing was used to analyse three multidrug-resistant strains (resistant to six or more antibiotics). Two of them (SZL 30 and SZL 31) belonged to S. Infantis, while one strain belonged to S. Typhimurium (SZL 38). Analysis of the genomes of the sequenced strains revealed the genes responsible for antibiotic resistance. In the genomes of strains SZL 30 and SZL 31 the genes of antibiotic resistance were shown to be localized mostly in integrons within plasmids, while most of the antibiotic resistance genes of strain SZL 38 were localized in a chromosomal island (17,949 nt). Genomes of the Salmonella strains SZL 30, SZL 31, and SZL 38 were shown to contain full-size pathogenicity islands: SPI-1, SPI-2, SPI-4, SPI-5, SPI-9, SPI-11, SPI-13, SPI-14, and CS54. Moreover, the genome of strain SZL 38 was also found to contain the full-size pathogenicity islands SPI-3, SPI-6, SPI-12, and SPI-16. The emergence of multidrug-resistant strains of various Salmonella serovars indicates that further research on the transmission pathways for these genetic determinants and monitoring of the distribution of these microorganisms are necessary.
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Abishkenov, Maxat, Zhassulan Ashkeyev, Kayrosh Nogaev, Yerbol Bestembek, Kuathan Azimbayev et Ilgar Tavshanov. « On the possibility of implementing a simple shear in the cross-section of metal materials during caliber rolling ». Engineering Solid Mechanics 11, no 3 (2023) : 253–62. http://dx.doi.org/10.5267/j.esm.2023.3.004.
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The article analyzes the stress-strain state in the zone of plastic deformation during special caliber rolling. The principle of caliber rolling technology is described, which makes it possible to combine shear and compression deformations in the cross-section of metals, alloys, and metal-matrix composites. The analysis results of stresses and strains during shear rolling in a diamond pass, which included compressive strains that had not been considered in previous studies, revealed that localization or point inversion of stresses and strains is observed in the plastic deformation zone. Stress and strain are localized along the minor and major diagonals of the diamond pass.
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Soares, Guilherme Corrêa, et Mikko Hokka. « Synchronized Full-Field Strain and Temperature Measurements of Commercially Pure Titanium under Tension at Elevated Temperatures and High Strain Rates ». Metals 12, no 1 (23 décembre 2021) : 25. http://dx.doi.org/10.3390/met12010025.
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Understanding the mechanical behavior of materials at extreme conditions, such as high temperatures, high strain rates, and very large strains, is fundamental for applications where these conditions are possible. Although tensile testing has been used to investigate material behavior under high strain rates and elevated temperatures, it disregards the occurrence of localized strains and increasing temperatures during deformation. The objective of this work is to combine synchronized full-field techniques and an electrical resistive heating system to investigate the thermomechanical behavior of commercially pure titanium under tensile loading at high temperatures and high strain rates. An electrical resistive heating system was used to heat dog-bone samples up to 1120 °C, which were then tested with a tensile Split Hopkinson Pressure Bar at strain rates up to 1600 s−1. These tests were monitored by two high-speed optical cameras and an infrared camera to acquire synchronized full-field strain and temperature data. The displacement and strain noise floor, and the stereo reconstruction error increased with temperature, while the temperature noise floor decreased at elevated temperatures. A substantial decrease in mechanical strength and an increase in ductility were observed with an increase in testing temperature. The localized strains during necking were much higher at elevated temperatures, while adiabatic heating was much lower or non-existent at elevated temperatures.
Thèses sur le sujet "Localized strains"
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Whang, Kyunghyun. « Some problems of localized crack closure due to nearby concentrated loads / ». The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487326511712949.
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ABATI, ANDREA. « Models and finite element methods for porous media subjected to localized strains ». Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2008. http://hdl.handle.net/2108/523.
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In questa tesi si presenta una teoria termodinamica per continui porosi multi-fase
basata sul lavoro di Biot e la relativa formulazione numerica mediante elementi finiti non convenzionali che consentono di modellare fenomeni di localizzazione delle deformazioni. In una prima fase si ricava una forma generale per le relazioni iperelastiche incrementali. Si ottengono quindi espressioni particolari per gli operatori iperelastici tangenti utilizzando argomenti tipici della teoria delle miscele. Si verifica la compatibilità di tali operatori con la suddetta teoria termodinamica utilizzando le condizioni di simmetria e di Maxwell. Fra i principali risultati della trattazione considerata vi è una semplice espressione della dissipazione, che sarà utilizzata in un approccio multi-scala alla localizzazione delle deformazioni.
Si considera quindi una formulazione agli elementi finiti del modello costitutivo ot
tenuto, concentrando l'attenzione sulla linearizzazione del sistema risolvente. Tra le possibili fonti di non-linearità, si considerano anche quelle dovute a condizioni al contorno unilatere sul flusso fluido, introdotte per modellare e±cacemente l'interfaccia tra mezzo poroso e atmosfera. Si analizzano semplici esempi numerici monodimensionali, allo scopo di valutare le prestazioni numeriche delle tecniche di regolarizzazione di tipo penalty e Lagrangiano aumentato utilizzate. In tali esempi si evidenzia anche l'analogia formale e numerica tra problemi di filtrazione con vincoli unilateri e problemi di contatto in assenza di attrito. Si prendono inoltre in considerazione altre situazioni di interesse pratico, come la propagazione di un fronte di saturazione in uno strato di terreno e la parziale saturzione in una diga di calcestruzzo a gravità.
Per modellare meccanismi dissipativi localizzati, si analizza la presenza di discontinuità negli spostamenti e nei flussi fluidi nel caso di mezzi porosi multi-fase. Nel corrispondente metodo agli elementi finiti, l'insorgere di tali discontinuità è simulato mediante "enhancement" locale delle funzioni interpolanti. Infine, si presentano i risultati della simulazione numerica di una prova di compressione piana su un mezzo poroso parzialmente saturo. Tale simulazione consente di evidenziare tutte le caratteristiche delle formulazioni teoriche e numeriche presentate in questa tesi.In this thesis we present a thermodynamic theory for multiphase porous continua based on Biot work and the corresponding numerical formulation by non-standard finite element methods modelling strain localization phenomena. Firstly, a general form of hyperelastic rate equations is provided. Particular expressions for hyperelastic tangent operators are then obtained by using arguments typically employed in the mixture theory. The compatibility of such operators with the aforementioned thermodynamic theory is then investigated by means of symmetry and Maxwell conditions. Among the main results of the presented formulation there is a simple expression for dissipation, that will be used in a multi-scale approach to the localization of deformations in multiphase solids. A finite element formulation of this constitutive model is then presented, focusing the attention on the linearization of the resulting solving system. Among the different sources of non-linearity, also the ones due to unilateral boundary conditions on the fluid flow are considered. Such boundary conditions are introduced to effectively model the interface between the porous solid and the atmosphere. In order to investigate numerical performance of penalty and augmented Lagrangian regularization techniques employed herein, simple one-dimensional numerical examples are considered. In these examples, both the numerical and formal analogies between seepage problems with unilateral constraints and frictionless contact problems are pointed out. Further situations of practical interest are considered, as the propagation of a saturation front in a soil sample and the partial saturation of a concrete gravity dam. To model localized dissipative mechanisms, we analyze the presence of discontinuities in displacements and fluid flows. In the corresponding finite element method, the appearance of these discontinuities is simulated by local enhancement of interpolating functions. Finally, results of the numerical simulation of a plain strain compression test on a partially saturated porous solid are presented. This simulation allows us to point out all the features of theoretical and numerical formulations presented in this thesis.
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Tsai, Ming-Yi. « Application of localized hybrid methods of stress analysis to some problems in the mechanics of composites ». Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/39697.
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Saloustros, Savvas. « Tracking localized cracks in the computational analysis of masonry structures ». Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/461714.
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Numerical methods aid significantly the engineering efforts towards the conservation of existing masonry structures and the design of new ones. Among them, macro-mechanical finite element methods based on the smeared crack approach are commonly preferred as an affordable choice for the analysis of large masonry structures. Nevertheless, they usu-ally result in a non-realistic representation of damage as smeared over large areas of the structure, which hampers the correct interpretation of the damage pattern. Additionally, a more critical pathology of this approach is the mesh-dependency, which influences nota-bly the safety and stability predictions.
To overcome these limitations, this thesis proposes a novel computational tool based on the {enrichment} of the classical smeared crack approach with a local tracking algorithm. The objective of this localized damage model is the realistic and efficient non-linear anal-ysis of masonry structures with an enhanced representation of cracking.
The non-linear behaviour of masonry is simulated through the adoption of a continuum damage mechanics model with two damage indices, allowing the differentiation between the tensile and compressive mechanical responses of masonry. In this context, a novel explicit formulation for the evolution of irreversible strains is proposed and implemented. Two new expressions are derived for the regularization of the tensile and compressive softening responses according to the crack-band approach, ensuring the mesh-size objec-tivity of the damage model.
The simulation of the structural behaviour of masonry structures under versatile loading and boundary conditions necessitates some developments in the context of local tracking algorithms. To this end, this thesis presents the enhancement of local tracking algorithms with novel procedures that make possible the simulation of multiple, arbitrary and inter-secting cracking under monotonic and cyclic loading. Additionally, the effect of different crack propagation criteria is investigated and the selection among more than one potential failure planes is tackled.
The proposed localized damage model is validated through the simulation of a series of structural examples. These vary from small-scale tests on concrete specimens with few dominant cracks, to medium and large-scale masonry structures with multiple tensile, shear and flexural cracking. The analyses are compared with analytical, experimental and numerical results obtained with alternative methods available in the literature. Overall, the localized damage model developed in this thesis largely improves the mesh-independency of the classical smeared crack approach and reproduces crack patterns and collapse mech-anisms in an efficient and realistic way.Los métodos numéricos son decisivos en la ingeniería para la conservación de estructuras de mampostería existentes y el diseño de estructuras nuevas. Entre ellos, los métodos macro-mecánicos de elementos finitos, basados en el concepto de fisuras distribuidas, son habitualmente los preferidos como opción asequible para el análisis de grandes estructuras de mampostería. Sin embargo, suelen resultar en a una representación poco realista del daño, distribuido en grandes áreas de la estructura, lo que impide la correcta interpretación del patrón de daño. Además, esta metodología presenta una patología más crítica, la dependencia de la malla, que influye notablemente en las predicciones de seguridad y estabilidad. Para superar estas limitaciones, esta tesis propone una nueva herramienta numérica basada en el enriquecimiento del clásico enfoque de fisuras distribuidas con un algoritmo de trazado local. El objetivo de este modelo de daño localizado es el análisis no-lineal de las estructuras de mampostería de manera realista y eficiente con una representación mejora-da de fisuras. El comportamiento no lineal de la mampostería se simula a través de la adopción de un modelo de mecánica de daño continuo con dos índices de daño, permitiendo la diferenciación entre las respuestas mecánicas de tensión y compresión de la mampostería. En este contexto, se propone e implementa una nueva formulación explícita para la evolución de deformaciones irreversibles. Se derivan dos nuevas expresiones para la regularización del ablandamiento de tracción y compresión según el ancho de banda de la fisura, garantizan-do la objetividad del modelo de daño al respecto del tamaño de la malla. La simulación del comportamiento estructural de las estructuras de mampostería en condiciones de carga y contorno generales precisa de algunos desarrollos en el contexto de los algoritmos locales de trazado. Con este objetivo, se presenta la mejora de los algoritmos locales de trazado con nuevos procedimientos que posibilitan la simulación de fisuración múltiple, arbitraria e secante bajo cargas monótonas y cíclicas. Además, se investiga el efecto de diferentes criterios de propagación de fisuras y se aborda la selección entre más de un plano de falla posible. El modelo de daño localizado propuesto se valida mediante la simulación de una serie de ejemplos estructurales. Éstos van desde pruebas a pequeña escala en probetas de hormigón, con pocas fisuras dominantes, hasta estructuras de mampostería de mediana y gran escala con fisuración múltiple de tracción, de cortante y de flexión. Los análisis se comparan con los resultados analíticos, experimentales y numéricos obtenidos con métodos alternativos disponibles en la literatura. El modelo de daño localizado mejora en gran medida la independencia de la malla del clásico método de fisuras distribuidas y reproduce patrones de daño y mecanismos de colapso de una manera eficiente y realista
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Motamedi, MohammadHosein. « Numerical Simulation of Mechanical Response of Geomaterials from Strain Hardening to Localized Failure ». Thesis, University of Illinois at Chicago, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10295585.
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The Sandia GeoModel is a continuum elastoplastic constitutive model which captures many features of the mechanical response for geological materials over a wide range of porosities and strain rates. Among the specific features incorporated into the formulation are a smooth compression cap, isotropic/kinematic hardening, nonlinear pressure dependence, strength differential effect, and rate sensitivity. This study attempts to provide enhancements regarding computational tractability, domain of applicability, and robustness of the model. A new functional form is presented for the yield and plastic potential functions. The model is also furnished with a smooth, elliptical tension cap to account for the tensile failure. This reformulation renders a more accurate, robust and efficient model as it eliminates spurious solutions attributed to the original form. In addition, this constitutive model is adopted in bifurcation analysis to track the inception of new localization and crack path propagation. For the post-localization regime, a cohesive-law fracture model, able to address mixed-model failure condition, is implemented to characterize the constitutive softening behavior on the surface of discontinuity. To capture propagating fracture, the Assumed Enhanced Strain (AES) method is invoked. Particular mathematical treatments are incorporated into the simulation concerning numerical efficiency and robustness issues. Finally, the aforementioned modified cap plasticity model is employed to investigate the nonlinear dynamic response of the earthen substructure of the rail. Studying the effects of high-speed trains on the track substructure.
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Al, Nemer Rana. « Effect of two-phase fluid percolation on remodeling of geo-materials ». Electronic Thesis or Diss., Ecole centrale de Nantes, 2023. http://www.theses.fr/2023ECDN0012.
Texte intégralRésumé :
L'objectif de neutralité carbone reposant massivement sur les sources d'énergie renouvelables peut être accéléré en envisageant la séquestration souterraine du CO2 et le stockage souterrain (i) de l'hydrogène produit par l'électrolyse de l'eau à partir d'électricité renouvelable et (ii) du méthane synthétisé produit par la méthanisation. Cependant, l'injection de ces fluides dans des aquifères salins profonds peut déclencher des instabilités locales sous la forme de digitations, qui sont les précurseurs d'instabilités macroscopiques telles que la microsismicité, l'affaissement ou le gonflement du sol. L'interaction entre le fluide injecté, le fluide résidentiel et le milieu poreux hôte est un problème complexe. Pour étudier la réponse d'un squelette solide percolé par un écoulement diphasique instable, une machine originale bi-axiale adaptée aux géo-matériaux partiellement saturés et fournissant un contrôle hydro- mécanique, a été mise en place. Des expériences de drainage ont été menées sur des échantillons de sable saturés en eau et chargés mécaniquement, par injection d'air via une pression capillaire imposée. Un protocol d’essai détaillant les étapes nécessaires à la réussite du test de drainage, allant de la préparation de l'échantillon à l'injection d'air, a été établi. Grâce à un système optique haute résolution, l'infiltration de l’air à travers un ou plusieurs chemins préférentiels dans le milieu granulaire, a été acquise. Le suivi du ou des doigts a nécessité le développement d'un algorithme robuste permettant la détection automatique de l'interface pour l'ensemble des images disponibles. De plus, le réarrangement de la squelette granulaire induit par la percolation du fluide a été quantifié via la corrélation d'images numériques par éléments finis. Le couplage entre la propagation de l'interface et les déformations localisées a été mesuré quantitativement en fonction du chargement mécanique, contrôlé par la contrainte effective. Les résultats ont montré une corrélation entre le chargement mécanique et la percolation hétérogène sous la forme de digitation et de déformations localiséesThe goal of carbon neutrality relying massively on the renewable energy sources can be accelerated by considering underground CO2 sequestration and underground storage of (i) hydrogen produced by the water electrolysis from renewable electricity, and (ii) synthesized methane produced by the methanation. However, the injection of these fluids into deep saline aquifers, can trigger local instabilities in the form of fluid fingering, which are precursors of macroscopic instabilities such as micro-seismicity, subsidence or ground swelling. The interaction between the injected fluid, the residential one and the host porous medium is a complex problem. To investigate the response of a solid skeleton percolated by an unsteady bi-phasic flow, an original bi-axial machine adapted to partially saturated geo-materials and providing a hydro-mechanical control, has been set-up. Drainage experiments have been conducted on mechanically loaded water-saturated sand samples by injecting air via an imposed capillary pressure. A testing protocol detailing the steps required to achieve successful drainage test, starting from sample preparation to air injection, has been established. Thanks to a high resolution optical system, the air infiltration through preferential pathway(s) within the granular medium, has been acquired. The monitoring of the propagating finger(s) has required the development of robust algorithm allowing the automatic interface detection for the set of available images. In addition, the skeleton remodeling driven by the fluid percolation has been quantified via finite- element based digital image correlation. The coupling between interface propagation and localized strains has been quantitatively measured as function of the mechanical loading, controlled by the effective stress. The results have shown a correlation between mechanical loading and the heterogeneous percolation in the form of fingering and localized strains
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Smith, Michael Philip. « Microstructural analysis of plates with large strains as a result of central localised blast loading ». Master's thesis, University of Cape Town, 1999. http://hdl.handle.net/11427/9600.
Texte intégralRésumé :
Includes bibliographical references.The defonnation response and subsequent tearing of built in plates subjected to central impulsive loading has been investigated experimentally in the past. Theoretical predictions of the structural response have also been made and compared to these experiments. In this thesis, a new method is developed whereby the strains within the defonned plates were measured using micrographs of the grain structure of the plate. The aim of the thesis was to gain a fuller understanding of the internal defonnation of blast loaded plate so as to enable more accurate theoretical predictions of plate defonnation and tearing. The dimensions of the grains of the plate material both in the virgin state and after defonnation were measured by image analysis of scanning electron micrographs. These measurements were processed and averaged at various points within the structure. This enabled the strain distribution throughout the defonned plate to be analysed. Tensile tests were undertaken in order to calibrate this method of strain measurement. The tests were arrested during the loading, after the specimen had undergone a known amount of strain. The strain measured from the microstructure was then compared to the strain measured during the tensile tests. The method was found to give a satisfactory measurement of the strain in the tensile tests.
8
Miletić, Marta. « Modeling of localized deformation in high and ultra-high performance fiber reinforced cementitious composites ». Diss., Kansas State University, 2016. http://hdl.handle.net/2097/34538.
Texte intégralRésumé :
Doctor of PhilosophyDepartment of Civil Engineering
Dunja Peric
A low ratio between the compressive strength of concrete and its cost makes concrete one of the most widely used construction materials in civil engineering. Despite of a very good response to compressive stress, concrete exhibits a low tensile strength and limited tensile strain capacity. Adding short discrete fibers to a cementitious matrix can significantly improve its performance under tensile stress, thus ultimately exhibiting a ductile behavior. Nevertheless, in spite of their beneficial properties fiber reinforced cementitious composites remain underutilized in engineering practice. One of the main reasons for this is a lack of an adequate characterization of the tensile behavior as well as a lack of analysis methods that would allow engineers to incorporate fiber reinforced structural concrete elements into their design. Therefore, this dissertation has four key objectives: 1) to computationally model a stress-strain response of high performance fiber reinforced cementitious composites in uniaxial tension and uniaxial compression prior to macro-crack localization, 2) to develop and perform a diagnostic strain localization analysis for high performance fiber reinforced cementitious composites, the results of which can characterize effects of fibers on failure precursors, 3) to devise and perform an experimental program for characterization of ultra-high performance fiber reinforced cementitious composites, and 4) to characterize a full-fledged behavior including stress-strain and stress-crack opening displacement responses of ultra-high performance fiber reinforced cementitious composites in uniaxial tension. To quantify effects of fibers on onset of strain localization in fiber reinforced cementitious composites a combined computational/analytical models have been developed. To this end, linear-elastic multi-directional fibers were embedded into a cementitious matrix. The resulting composite was described by different types of two-invariant non-associated Drucker-Prager plasticity models. In order to investigate effects of a shape of a yield surface and hardening type linear and nonlinear yield surfaces, and linear and nonlinear hardening rules were considered. Diagnostic strain localization analyses were conducted for several plane stress uniaxial tension and uniaxial compression tests on non-reinforced cementitious composites as well as on high performance fiber-reinforced cementitious composites. It was found that presence of fibers delayed the inception of strain localization in all tests on fiber-reinforced composites. Furthermore, presence of fibers exerted a more significant effect on the strain localization direction and mode in uniaxial compression than in uniaxial tension. The main objective of experimental program was to facilitate characterization of the post-cracking tensile behavior of ultra-high performance fiber reinforced cementitious composites. To this end, five different mixes of fiber-reinforced cementitious composites were cast, whereby volumetric fiber content, fiber shape and water to binder ratio were the experimental variables. Two testing methods were adopted, a direct uniaxial tension test and four-point prism bending test. Two different post-cracking behaviors were observed in direct tension tests, softening and strain hardening accompanied with multiple cracking. On the other hand, the response from prism bending tests was less scattered. Several different inverse analyses were carried out to predict stress-strain and stress-crack opening displacement responses in uniaxial tension based on the prism bending tests. The analyses resulted in worthy correlations with the experimental data, thus suggesting that the prism bending test is a viable alternative to a much more challenging to perform direct tension test for ultra-high performance fiber reinforced composites.
9
Lazari, Maria. « Finite Element Regularization for Post Localized Bifurcation in Variably Saturated Media ». Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424491.
Texte intégralRésumé :
Computational investigation of the stability of natural slopes within a coupled hydro-mechanical approach becomes more and more attractive due to an increasing number of slope movements caused by heavy rainfall events. Seasonal cycles of summer drying and winter-spring wetting affect the stability and serviceability of natural and man-made slopes, threatening lives and property worldwide. Heavy rainfall will increase the soil moisture content and lead to a reduction in suction and a consequent weakening of the soil. As a result, the slope may fail either in a diffused or in a localized pattern.
The localization process is a classical mode of mechanical instability and is described as the concentration of shear strains in narrow bands within the soil strata. As it is well-known, the width of those bands cannot be properly computed using the standard continuum mechanical approach with unstable materials (in the sense of Drucker). In the framework of the standard finite element method the computation of shear band phenomena reveals a strong mesh dependency of the numerical solution and the objectivity of the computational results is blown. Each mesh refinement results in an overall different outcome and the width of the localization band has the size of the element of the adopted mesh. In the literature two main categories of methodologies can be found for regularizing this problem. One is to simulate the formation and propagation of such discontinuities via suitable enrichment functions and is the concept of the so-called extended finite elements. The other solution is to exploit enhanced continuum theories. These theories contain an internal length scale which is an additional material parameter related to the shear band width and removes the spurious mesh sensitivity of the numerical simulation results.
The present work is focused on the second category. In this context, viscoplasticity and non-local theories are adopted to effectively study strain localization mechanism, assuming the soil as a multiphase porous medium. This means that the localization analysis is considered as a fully coupled hydro-mechanical problem with the material consisting of an elasto-viscoplastic skeleton and open pores filled with incompressible liquid water and compressible gas. Both regularization techniques are physically sound. Rate dependency is experimentally motivated as the mechanical response of granular materials seems to be rapid, but not instantaneous and a viscoplastic constitutive model is able to reproduce creep and relaxation processes. The physical interpretation of the non-local theory stems from the fact that no real material is an ideal continuous medium and the evolution of the microstructure at one point influences the surrounding points when irreversible strains take place.
Two types of viscoplastic models are applied; the Perzyna and the Duvaut-Lions. The former is extended with respect to the non-local integral approach. In the first part of this work, the generalized effective stress is limited by the Drucker-Prager yield criterion. The models are implemented and numerically validated in the finite element code Comes-geo and further verified by simulating an experimental plane-strain biaxial test and a benchmark slope failure problem. This work is in essence aimed at answering key questions, such as: what are the most significant influential factors in the development of strain localization for each regularization technique and what is the role of suction and drainage conditions; is the viscosity of the soil affected by the presence of water and how does this fact influence the regularizing capabilities of the method; how do the internal lengths introduced by viscosity and non-locality interact with each other and under which circumstances is the one method preferable to the other?
The second half of this work comprises the extension to viscoplasticity of the existing advanced elastoplastic constitutive model for unsaturated sands developed by Buscarnera and Nova. This model allows for hydraulic bonding and debonding effects and therefore the main mechanisms of unsaturated materials are captured. The elastoplastic version of the model is first implemented in the finite element code Comes-geo and validated with results from the literature. The model is then extended to viscoplasticity and is also implemented and validated in the code. The proposed viscoplastic formulation, as further novelty, is enhanced with the dependence of the constitutive parameters on the relative density. To validate the elastoplastic model in the finite element code Comes-geo a series of tests are simulated: triaxial shear tests at different suction and net confining pressure, oedometric tests with drying and wetting paths and triaxial and plane-strain compression tests in drained and undrained conditions. The viscoplastic model is also validated through oedometric tests, creep tests and triaxial compression tests on different sand densities. The onset of shear strain localization is then studied and the finite element results are compared with the results of a theoretical stability analysis. The verification of the viscoplastic model is finalized with the simulation of a triaxial compression test.
The main motivation for the present work stems from these premises and this thesis presents an efficient tool to simulate strain localization with regularization techniques, which do not need to increase the number of the state variables of the numerical model, taking into account fully coupled hydro-mechanical analysis and using advanced constitutive model for unsaturated sands.
This dissertation has been performed for the first two years in the University of Padova (Italy) and for the last year at Baugrund Dresden (Germany), geotechnical design and construction company within the Marie Curie Initial Training Network project MuMoLaDe (Multiscale Modelling of Landslide and Debris flow, 7th Framework Programme of the European Union, project n. 289911, http://www.mumolade.com/). This practice is in the scope of linking academia and industry and the transfer of knowledge. In this framework, the advanced elastoplastic and elasto-viscoplastic models for unsaturated soils are implemented and validated in PLAXIS commercial finite element analysis software. The validation included single element tests of drained and undrained triaxial loading and triaxial tests at different suction levels. The implementation is verified and the effectiveness of the model is displayed by numerical simulations of a partially saturated slope failure of the laboratory scale.Lo studio numerico della stabilità dei pendii con un approccio idro-meccanico accoppiato è sempre più importante e necessario nella pratica ingegneristica a causa del continuo aumento dei fenomeni franosi, che determinano perdite di vite umane e danni all’ambiente naturale e costruito. In genere, tali fenomeni sono provocati da eventi metereologici violenti, che determinano la riduzione delle forze capillari intergranulari e della resistenza del materiale costituente i pendii. Inoltre, anche cicli stagionali di essicazione estiva e imbibizione invernale e primaverile favoriscono l’instabilità di pendii naturali e artificiali. Il collasso dei pendii avviene con un meccanismo diffuso oppure localizzato; in quest’ultimo caso avviene mediante la formazione di zone di ampiezza limitata dette bande di taglio in cui si concentrano le deformazioni del materiale. Quando si simula numericamente il collasso causato dalla formazione di bande di taglio e si utilizza la meccanica classica del continuo di Cauchy con un modello costitutivo per materiale instabile nel senso di Drucker, è noto che la larghezza delle bande di taglio non può essere calcolata né definita nel modello. In particolare, lo studio numerico di fenomeni di localizzazione delle deformazioni con il metodo degli elementi finiti evidenzia una forte dipendenza della soluzione numerica e della larghezza delle bande di taglio dalla mesh utilizzata, con perdita della soluzione all’infittimento della mesh. Infatti, accade che la larghezza delle bande di taglio risulta fissata dalla dimensione dell’elemento finito utilizzato, tendendo a zero al tendere a zero della dimensione dell’elemento finito. Di conseguenza, per poter simulare in modo obiettivo fenomeni di localizzazione delle deformazioni, è necessario modificare (o regolarizzare) il continuo di Cauchy. In letteratura si trovano due classi principali di regolarizzazione a cui ricorrere per risolvere questo problema. Il primo propone di simulare la formazione e la propagazione delle bande di taglio utilizzando campi discontinui di spostamento, dando origine al metodo degli elementi finiti estesi (extended finite element method). Il secondo propone di arricchire il modello continuo a livello cinematico oppure a livello costitutivo (enhanced continuum theories), in modo da fornire al modello una lunghezza di scala interna da cui dipende la larghezza della banda di taglio, eliminando in questo modo il problema della mesh dipendenza citata in precedenza. Questa tesi di dottorato è svolta scegliendo di arricchire il continuo di Cauchy a livello costitutivo e individua nella viscoplasticità locale e non-locale l’approccio utile allo studio della localizzazione delle deformazioni nei suoli. Inoltre, per tenere conto delle interazioni fra la parte solida e quella fluida, i suoli sono analizzati come mezzi porosi multifase. Di conseguenza, l’analisi della localizzazione delle deformazioni nei suoli è compiuta considerando il materiale dei pendii come un mezzo poroso costituito da uno scheletro solido elasto-viscoplastico e pori contenenti acqua liquida e aria umida. La scelta delle due tecniche di regolarizzazione sopra citate è stata dettata dal loro significato fisico, in quanto la risposta meccanica dei materiali granulari non è istantanea a causa dei processi viscosi o di rilassamento. Inoltre, l’introduzione della teoria non-locale deriva dalla considerazione che nessun materiale reale è un continuo nel senso matematico, a causa dell’evoluzione della microstruttura in un punto materiale che influenza i punti del suo intorno quando si sviluppano deformazioni irreversibili. In questa tesi sono utilizzati due approcci viscoplastici: quello di Perzyna e quello di Duvaut-Lions. Il primo è stato esteso con l’approccio non-locale. Nella prima parte di questo lavoro di tesi i modelli viscoplastici sono sviluppati utilizzando il criterio di snervamento di Drucker-Prager, implementati nel codice agli elementi finiti Comes-geo, validati e verificati numericamente simulando test sperimentali di compressione biassiale in stato piano di deformazione e un test numerico di collasso di un pendio. Questa parte del lavoro ha lo scopo di rispondere alle seguenti domande-chiave sulla localizzazione delle deformazioni nei mezzi porosi viscoplastici: quali sono i fattori più importanti che influenzano lo sviluppo della bande di taglio e qual è il ruolo delle pressioni capillari e delle condizioni di drenaggio; se la viscosità dei suoli è influenzata dalla presenza dell’acqua e se influenza le proprietà di regolarizzazione del metodo locale o non-locale; come interagiscono la lunghezza di scala interna indotta dalla viscosità e quella introdotta dalla non-località; quando un metodo è preferibile ad un altro. La seconda parte di questo lavoro di tesi ha per oggetto lo sviluppo di un nuovo e avanzato modello viscoplastico a partire dal modello costitutivo elasto-plastico per le sabbie parzialmente sature proposto da Buscarnera e Nova. Questo modello permette di simulare i principali meccanismi del comportamento micromeccanico di materiali parzialmente saturi, ovvero la coesione idraulica (hydraulic bounding) e gli effetti di decoesione (debonding) nelle sabbie. Questa parte del lavoro è stata svolta in due fasi; nella prima fase si è discretizzato e implementato il modello elasto-plastico nel codice agli elementi finiti Comes-Geo, successivamente validato utilizzando risultati di letteratura. In particolare sono state simulate: test di taglio a vari valori di pressione capillare (suzione) e pressione di confinamento, test di compressione edometrica con percorsi di desaturazione e saturazione e test di compressione drenata e non drenata in condizione di stato piano di deformazione. Nella seconda fase, questo modello è stato esteso alla viscoplasticità, in modo da tener conto del comportamento viscoso delle sabbie, implementato nel codice Comes-Geo e validato simulando prove di laboratorio di letteratura. La formulazione viscoplastica proposta è stata poi arricchita formulando la dipendenza dei parametri costitutivi dalla densità relativa. Il modello viscoplastico di base e quello arricchito sono stati validati simulando prove di compressione edometrica, prove di viscosità e prove di compressione triassiale a vari valori di densità. Inoltre, con il modello arricchito, è stata simulata una prova di localizzazione su sabbie dense e sciolte e i risultati numerici ottenuti sono stati confrontati con i risultati dell’analisi di stabilità. Con questa tesi si è sviluppato uno strumento numerico efficiente per la simulazione della localizzazione delle deformazioni con metodi regolarizzati che non necessitano di aumentare il numero di variabili di stato e che utilizza modelli costitutivi avanzati considerando il comportamento idro-meccanico accoppiato delle sabbie parzialmente sature. Questo lavoro è stato svolto presso l’Università degli Studi di Padova (Italia) durante i primi due anni di dottorato e presso l’unità di ricerca e sviluppo della società di progettazione e costruzione Baugrund Dresden (Germania) durante il terzo anno di dottorato; l’attività è stata svolta all’interno del progetto Marie Curie Initial Training Network MuMoLaDe (Multiscale Modelling of Landslide and Debris flow), 7th Framework Programme of the European Union, progetto n. 289911, http://www.mumolade.com/. I modelli costitutivi avanzati elasto-plastico e viscoplastici sono stati inoltre implementati e validati anche nel codice commerciale agli elementi finiti Plaxis durante la collaborazione con Baugrund Dresden.
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Dias, Denise de Almeida Marques. « Persistência de cepas de Listeria monocytogenes em linha de abate industrial de frango em um matadouro localizado no Estado de São Paulo ». Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/9/9131/tde-07042010-155128/.
Texte intégralRésumé :
Listeria monocytogenes é um microrganismo conhecido como causador de enfermidades transmitidas por alimentos desde a década de 80 quando foram descritos surtos de listeriose ocorridos na América do Norte e Europa. Dentre os alimentos de origem animal que veiculam esse patógeno, as aves e seus produtos têm merecido atenção especial por parte de alguns pesquisadores devido à associação feita entre aves e uma possível contaminação durante o processamento, acarretando a contaminação dos produtos finais. Os objetivos desta pesquisa foram avaliar a ocorrência de L. monocytogenes em diferentes etapas da produção de carcaça de frango em um matadouro frigorífico situado no Estado de São Paulo; avaliar a diversidade genética e sorológica das cepas de L. monocytogenes isoladas; correlacionar a diversidade genética das cepas isoladas com a distribuição nas diferentes etapas da linha de processamento, avaliar a persistência das cepas isoladas nesse matadouro e comparar os perfis genéticos de cepas de L. monocytogenes obtidos em nosso país com aqueles obtidos em um matadouro de aves com capacidade similar na Espanha. Foram realizadas 4 amostragens nos meses de julho e novembro de 2005, e março e maio de 2006 em um matadouro situado no Estado de São Paulo. Foi examinado um total de 178 amostras de carcaças de frango, pele de pescoço e de superfícies de contato e superfícies sem contato com o alimento. Os isolados foram submetidos à caracterização de sorogrupos por Reação de Polimerização em Cadeia (multiplex PCR) e à subtipagem por Eletroforese em Gel de Campo Pulsado (PFGE). Das 178 amostras analisadas, 28 (15,7%) foram positivas para L. Monocytogenes. Dentre as amostras positivas, 12 (42,9%) foram oriundas de superfícies sem contato com o produto, 9 (32,1%) de superfícies de contato com o produto e 7 (25%) da carcaça inteira de frango, não sendo detectada L. monocytogenes em pele de pescoço de frango. Dos 41 isolados de L. monocytogenes avaliados, 11 (26,8%) pertencem ao grupo 1 (1/2a ou 3a), 5 (12,2%) ao grupo 3 (1/2b, 3b ou 7) e vinte e cinco (61%) ao grupo 4 (4b, 4d ou 4e). A análise por PFGE forneceu 9 pulsotipos AscI, 6 ApaI e 14 perfis combinados, caracterizando quatro grupos clonais. Estes grupos clonais estavam amplamente disseminados ao longo das etapas de processamento. Quando comparado com dados de estudo prévio realizado no mesmo matadouro, verifica-se a existência de cepas persistentes de L. monocytogenes no ambiente. A comparação entre os pulsotipos de L. monocytogenes isolados no Brasil e aqueles da Espanha mostrou que não há correlação genética entre as cepas, sendo gerado dos grupos distintos. Isto é uma indicação de que o comércio de carcaças de frango entre os dois países não está ocasionando a disseminação de L. monocytogenes no país importador.Listeria monocytogenes is a well-known microorganism as cause of foodborne illness since the occurrence of the first outbreak in 1980. Among foods of animal origin that serve as vehicle of this pathogen, poultry and their products are receiving special attention due to their association with outbreaks. The aims of this research were to evaluate the occurrence of L. monocytogenes in different steps of production of chicken carcasses in an abattoir in São Paulo state; to evaluate the genetic and serological diversity of L. monocytogenes isolates; to correlate the isolates with their distribution along processing line and to evaluate the persistence of strains of L. monocytogenes in the environment and evaluate the occurrence of L. monocytogenes in different steps of production of chicken carcasses in an abattoir in Brazil and at genetically correlate our data with the ones obtained in an equivalent abattoir in Spain. Samples were collected in July and November 2005, and March and May 2006. A total of 178 samples comprising chicken carcasses, neck skin, surfaces that enter in contact with the product and surfaces that not enter in contact with product were analysed. The isolates were submitted to characterization of serogroup through multiplex PCR and subtyping using PFGE. Among 178 samples, 28 (15.7%) were positive for L. monocytogenes: 12 (42.9%) were from the surfaces that do not enter in contact with the product, 9 (32.1%) from the surfaces that enter in contact with the product and 7 (25%) from the carcasses samples. No L. monocytogenes was detected among the neck skin samples. The 41 isolates were classified as group 1 [11 (26.8%)]; group 3 [5 (12.2%)] and group 4 [25 (61%)]. The molecular typing by PFGE resulted in 9 AscI and 6 ApaI profiles, and 14 composite profiles, resulting in four clonal groups. These clonal groups were spread throughout the processing line. When these results were compared with the results obtained in a previous study, persistent strains could be observed. The comparison between pulsotypes of L. monocytogenes isolated in Brazil and those isolated in Spain showed that there is no genetic correlation between strains. Two distinct clonal groups were obtained. This results indicates that chicken carcasses trade between Brazil and Spain is not disseminating L. monocytogenes in the importer country.
Livres sur le sujet "Localized strains"
1
Valis, Tomas. Localized and distributed fiber-optic strain sensors embedded in composite materials. [Downsview, Ont.] : University of Toronto, 1991.
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2
Valis, Tomas. Localized and distributed fiber-optic strain sensors embedded in composite materials. [Downsview, Ont.] : Institute for Aerospace Studies, University of Toronto, 1992.
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3
Hogg, William Daylesford. Strain and temperature measurements using a localised polarimetric fibre optic sensor. [Downsview, Ont.] : University of Toronto, 1989.
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4
Hogg, William Daylesford. Strain and temperature measurements using a localised polarimetric fibre optic sensor. Ottawa : National Library of Canada, 1990.
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5
Tapanes, Edward E. Static and dynamic strain measurements within composite materials using a localized Michelson fiber optic sensor. [Downsview, Ont.] : University of Toronto, 1990.
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6
Tapanes, Edward E. Static and dynamic strain measurements within composite materials using a localized Michelson fiber optic sensor. Ottawa : National Library of Canada = Bibliothèque nationale du Canada, 1991.
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7
Valis, Tomas *. Localized and distributed fiber-optic strain sensors embedded in composite materials. 1991.
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8
Erll, Astrid. Media and the Dynamics of Memory. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190230814.003.0014.
Texte intégralRésumé :
This chapter brings together two new strands of memory studies: media memory studies and transcultural memory studies. It highlights the fundamental mediatedness of memory and explores the role of media as a motor of transcultural memory. The chapter argues that cultural memory is dynamic rather than fixed, and based on “remediation”, an ongoing process of transcription from one medium to the next. The chapter explores in particular the role that media assume in a globalizing age for individual and localized forms of remembering. Using the example of World War I, it shows how literature, film, and digital media have shaped and continue to shape historical memories across cultural boundaries. Finally, the chapter introduces the concept of “premediation” in order to describe how media-derived schemata preform new experiences, memories and their mediation.
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Gross, Wolfgang L., et Julia U. Holle. Clinical features of ANCA-associated vasculitis. Oxford University Press, 2013. http://dx.doi.org/10.1093/med/9780199642489.003.0131.
Texte intégralRésumé :
The primary ANCA-associated vasculitides are granulomatosis with polyangiitis (Wegener's, GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA, Churg-Strauss syndrome, CSS). They predominantly affect small (and medium-sized) vessels and share a variable association with ANCA (anti-neutrophil cytoplasm antibody) directed against neutrophil proteinase 3 (PR3, mainly in GPA) and myeloperoxidase (MPO, mainly in MPA and CSS). Crescentic necrotizing glomerulonephritis and alveolar haemorrhage due to pulmonary capillaritis represent classical (vasculitic) organ manifestations of the ANCA-associated vasculitides (AAV). MPA occurs as a 'pure' small (to medium-size) vessel vasculitis, whereas GPA and CSS are characterized by additional distinct clinical and pathological features. In GPA, granulomatous lesions of the upper and/or lower respiratory tract are a hallmark of the disease. Granulomatous lesions may be large in appearance and occur as space-consuming, infiltrating, and destructive inflammatory masses. GPA is believed to follow a stagewise course with an initial localized form, restricted granulomatous lesions of the upper and/or lower respiratory tract without clinical signs of vasculitis, and a consecutive generalization to systemic vasculitis which may be either non-organ-threatening (early systemic) or organ- and life- threatening (generalized GPA). Rarely, patients arrest in the localized stage and do not progress to systemic disease. In EGPA asthma, hypereosinophilia and eosinophilic organ infiltration (e.g. eosinophilic myocarditis) are typical features of the disease apart from vasculitis. Similarly to GPA, EGPA follows a stagewise course: asthma and eosinophilia may precede full-blown disease for several months or years. Recent cohort studies suggest different phenotypes in EGPA (predominantly vasculitic and MPO-ANCA-positive and predominantly with eosinophilic organ infiltration, usually ANCA-negative). This chapter focuses on the clinical features of the primary AAV and their outcome.
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Reid, Hugh W., et Mark P. Dagleish. Poxviruses. Oxford University Press, 2011. http://dx.doi.org/10.1093/med/9780198570028.003.0040.
Texte intégralRésumé :
The poxviruses are a large family of complex viruses infecting many species of vertebrates as well as arthropods, and members of the three genera Orthopoxvirus, Yatapoxvirus and Parapoxvirus are the cause of sporadic zoonotic infections originating from both wildlife and domestic livestock. Infections of humans are generally associated with localized lesions, regarded as inconvenient rather than life-threatening, although severe illnesses have occurred, particularly in immunologically compromised individuals.The most celebrated of the orthopoxvirus infections is cowpox — a zoonotic infection which has been exploited to the enormous benefit of mankind as it had a pivotal role in the initiation of vaccination strategies that eventually led to the eradication of smallpox. Cowpox occurs only in Eurasia and in recent years it has become evident that infection of cattle is fortuitous and the reservoir of infection is in wild rodents. Monkeypox is another orthopoxvirus causing zoonotic infections in central and west Africa resembling smallpox and is the most serious disease in this category. While monkeypox does not readily spread between people, the potential of the virus to adapt to man is of concern and necessitates sustained surveillance in enzootic areas.The third orthopoxvirus zoonoses of importance is buffalopox in the Indian subcontinent, which is probably a strain of vaccinia that has been maintained in buffalo for at least 30 years following the cessation of vaccination of the human population. Likewise in Brazil, in recent years widespread outbreaks of vaccinia have occurred in milkers and their cattle.Orf virus, the most common of the parapoxviruses to cause zoonotic infection, is largely restricted to those in direct contact with domestic sheep and goats. Generally, infection is associated with a single localized macule affecting the hand which resolves without complications. Infection would appear to be prevalent in all sheep and goat populations and human orf is a relatively common occupational hazard. Sporadic parapoxvirus infections of man also occur following contact with cattle infected with pseudocowpoxvirus, and wildlife, in particular seals.A final serious consideration with the poxvirus zoonoses is the clinical similarity of such infections with smallpox. In view of the potential for smallpox virus to be employed by bio-terrorists there can be an urgency for laboratory confirmation of unexplained zoonotic poxvirus infections. Thus there is a requirement to maintain the capacity for rapid confirmation of poxvirus infections by molecular technique. As representatives of the known poxviruses have all been sequenced, generic and virus specific Polymerase Chain Reactions (PCR) can readily be performed to ensure rapid confirmation of any suspect infection.
Chapitres de livres sur le sujet "Localized strains"
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Needleman, A. « Localized Plastic Flow in Single Crystals : A Nonlocal Analysis ». Dans IUTAM Symposium on Computational Mechanics of Solid Materials at Large Strains, 131–40. Dordrecht : Springer Netherlands, 2003. http://dx.doi.org/10.1007/978-94-017-0297-3_11.
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Malvick, E. J., R. Kulasingam, B. L. Kutter et R. W. Boulanger. « Void redistribution and localized shear strains in slopes during liquefaction ». Dans Physical Modelling in Geotechnics, 495–500. London : Routledge, 2022. http://dx.doi.org/10.1201/9780203743362-90.
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Okada, Hiroshi, et Satya N. Atluri. « Embedded Localized Strain Zone Constitutive Model in Finite Strain and Finite Rotation ». Dans Computational Mechanics ’95, 2154–59. Berlin, Heidelberg : Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-642-79654-8_358.
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Okada, Hiroshi, et Satya N. Atluri. « Embedded Localized Strain Zone Constitutive Model in Finite Strain and Finite Rotation ». Dans Computational Mechanics ’95, 2480–85. Berlin, Heidelberg : Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-642-79654-8_412.
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Ogata, Shigenobu. « Free-energy-based Atomistic Study of Nucleation Kinetics and Thermodynamics of Defects in Metals ; Plastic Strain Carrier “Plaston” ». Dans The Plaston Concept, 37–56. Singapore : Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-7715-1_2.
Texte intégralRésumé :
AbstractPlastic deformation proceeds through the nucleation and migration of localized atomistic defects, i.e., plastons (e.g., dislocations, disconnections, disclinations, and shear transformation zones), as plastic strain carriers. Revealing the atomistic details, as well as the kinetics and thermodynamics, of nucleation and migration of localized atomistic defects is crucial for achieving a fundamental understanding and control of plasticity. Free-energy-based atomistic modeling is a promising approach for achieving this task. In this paper, recent free-energy-based atomistic studies on the nucleation kinetics of defects—particularly, (1) shuffling-dominant deformation twinning in magnesium, (2) dislocation nucleation from grain boundaries, and (3) homogeneous dislocation nucleation in nanoindentation—are introduced to demonstrate the advantages of free-energy-based atomistic modeling.
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Porubov, A. V., et B. R. Andrievsky. « Localized Nonlinear Strain Waves in Media with Internal Structure ». Dans Springer Proceedings in Physics, 687–92. Dordrecht : Springer Netherlands, 2011. http://dx.doi.org/10.1007/978-94-007-2069-5_92.
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Erofeev, Vladimir I., Vladimir V. Kazhaev et Igor S. Pavlov. « Nonlinear Localized Strain Waves in a 2D Medium with Microstructure ». Dans Advanced Structured Materials, 91–110. Berlin, Heidelberg : Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-36394-8_6.
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Erofeev, Vladimir I., Anna V. Leontyeva, Alexey O. Malkhanov et Igor S. Pavlov. « Structural Modeling of Nonlinear Localized Strain Waves in Generalized Continua ». Dans Higher Gradient Materials and Related Generalized Continua, 55–68. Cham : Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-30406-5_4.
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Armigliato, A., R. Balboni, A. Benedetti et S. Frabboni. « Analysis of Localised Strains in Crystals by Convergent Beam Electron Diffraction ». Dans High-Pressure Crystallography, 277–94. Dordrecht : Springer Netherlands, 2004. http://dx.doi.org/10.1007/978-1-4020-2102-2_17.
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Zou, Chunjiang, Jianchun Li, Kai Liu et Xiaobao Zhao. « Principles of localized strain rate, strength field and transition strain rate in cracking processes under dynamic loadings ». Dans Rock Dynamics : Progress and Prospect, Volume 1, 91–95. London : CRC Press, 2022. http://dx.doi.org/10.1201/9781003359142-11.
Texte intégralActes de conférences sur le sujet "Localized strains"
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Leewis, Keith, et Shawn Laughlin. « Understanding Strain Performance Considerations in Composite Repair of Dents and SCC ». Dans 2010 8th International Pipeline Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ipc2010-31586.
Texte intégralRésumé :
This paper reviews the key strain principles behind the technical design regarding the effect of a repair and reinforcement of steel pipelines with composite sleeves and composite wraps. Data is presented for the repair of large strains–dents, and the repair of small localized strains–SCC cracks.
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Nun˜ez, J. E., et G. Glinka. « Approximate Analysis of Creep Strains and Stresses at Notches ». Dans ASME 2003 Pressure Vessels and Piping Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/pvp2003-1888.
Texte intégralRésumé :
A method for the estimation of creep induced strains and stresses at notches has been developed. The purpose of the method is to generate a solution for the time-dependent strain and stress at the notch root based on the linear-elastic stress state, the constitutive law, and the material creep model. The proposed solution is an extension of Neuber’s rule used for the case of time-independent plasticity. The method was derived for both localized and non-localized creep in a notched body. Predictions were compared with finite element data and good agreement was obtained for various geometrical and material configurations in plane stress conditions.
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Chow, C. L., et X. J. Yang. « A Generalized Mixed Kinematic-Isotropic Hardening Plastic Model Coupled With Anisotropic Damage for Sheet Metal Forming ». Dans ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-33019.
Texte intégralRésumé :
The paper presents a generalized mixed isotropic-kinematic hardening plastic model coupled with anisotropic damage for sheet metal forming. A nonlinear anisotropic kinematic hardening is developed. For the predication of limit strains at localized necking in stamping under complex strain history, the model and its associated damage criterion for localized necking are established and implemented into LS-DYNA3D by compiling it as a user subroutine. The finite element simulation of LS-DYNA3D based on the present model is carried out. The location of localized necking for sheet metal forming has been successfully identified.
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Rehorn, Michael R., et Silvia S. Blemker. « 3D Finite Element Modeling of the Biceps Femoris Muscle ». Dans ASME 2009 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2009. http://dx.doi.org/10.1115/sbc2009-206695.
Texte intégralRésumé :
Hamstring strain injury is a significant problem for many athletes [1]. Muscle-tendon (MT) length changes and activation patterns during the sprinting cycle likely contribute to the high risk of injury. It has been suggested that injury may occur during the late swing phase of the sprinting cycle when the hamstring fibers experience activated muscle lengthening [2]. Of the hamstrings muscles, the biceps femoris longhead (BFLH) is the most commonly injured, with the injury most frequently localized along the proximal muscle-tendon junction [3]. We hypothesize that the injuries are localized in this region because it is also the area of highest localized strains.
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Blikharskyy, Yaroslav, Jacek Selejdak, Roman Khmil et Zinoviy Blikharskyy. « Research on concrete properties by DIC method ». Dans 22nd International Scientific Conference Engineering for Rural Development. Latvia University of Life Sciences and Technologies, Faculty of Engineering, 2023. http://dx.doi.org/10.22616/erdev.2023.22.tf191.
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Reliable measurement of strains in the material is essential in studying the building structure stress-strain state. The practice of operating concrete and reinforced concrete elements used in the construction industry shows that achieving the ultimate equilibrium state in these elements takes place in localized places. After the long-term operation of reinforced concrete structures, the concentration of stresses and strains is localized within such places, which can lead to the development of irreversible processes. Determining the stress-strain state based on classical criteria does not always give an exact answer. In such cases, the load-bearing capacity of structural elements must be assessed based on standards and invariant mechanical characteristics of materials, by which real strength and durability can be established. When the body is deformed, both on the surface and in the middle of the material, the process is accompanied by various breaks and changes in the phase field of the speckle image in the zones of singularities and various surface inhomogeneities. It is practically impossible to quantitatively assess the stressed zones of the material surface using speckle interferometry methods since the phase component is not considered in the case of a correlation fragment in speckle patterns. At the same time, the digital image correlation (DIC) methods can be used to estimate displacement and strain fields without restrictions. Therefore, such approaches can be effective technologies for determining the stress-strain state on smooth surfaces and parts with a stress concentrator. This article presents the results of testing concrete using DIC. A method of testing concrete samples using the process of determining strains by the method of digital image correlation and monitoring strains using sub-micron indicators has been developed. Transverse strains of concrete up to and including the moment of destruction of concrete samples were determined.
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Mohaghegh Motlagh, Amin, Harold A. Cook, Sunghwan Kim, Laurel Kuxhaus, Mandy Brogdon, Patrick J. DeMeo et Mark Carl Miller. « The Strain in the Medial Ulnar Collateral Ligament is Localized in Both the Anterior and Posterior Bands of the Anterior Bundle ». Dans ASME 2010 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2010. http://dx.doi.org/10.1115/sbc2010-19343.
Texte intégralRésumé :
The multi-bundle structure of the medial ulnar collateral ligament (mUCL) has been documented [1]. Mechanically, the anterior bundle of the mUCL is the primary restraint to valgus stress of the elbow [2] and research has indicated that the anterior band of this bundle becomes taut in extension while the posterior band becomes taut in flexion [3]. Injury of the mUCL in throwing athletes due to overuse or extreme valgus load can require surgical repair. In order to achieve a successful surgical reconstruction of the UCL, one can expect the appropriate tension during graft placement to be an important variable. The strain in the ligament is known to vary with flexion angle. Therefore, the in situ strains of the mUCL are potentially vital information and determination of a flexion angle at which the native ligament has no strain may guide the repair. To determine the slack length, i.e., the reference length with no strain, previous work examined the particular regions of the anterior and posterior bands [3]. The slack length was readily determined, but all regions did not behave in the same way. The purpose of the current work was to determine whether a consistent behavior was apparent in each of the bands, that is, to determine if bands could be identified by consistent strains along their lengths.
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Li, Bing, et Tim J. Nye. « Prediction of Forming Limit Diagrams for Aluminum Alloy Sheet Using Finite Element Analysis ». Dans ASME 2006 Pressure Vessels and Piping/ICPVT-11 Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/pvp2006-icpvt-11-93402.
Texte intégralRésumé :
Prediction of forming limit diagram (FLD) for aluminum alloy sheet using finite element analysis without implementing pre-defined geometrical imperfections or material imperfections was studied. The limit strains of the FLD were determined by applying a new proposed localization criterion in the dome stretching test. The elements just outside the necking area, where their major and minor principal strains have no simultaneous change after localized necking happens, were chosen as the reference elements for measurement of limit strains. Simulations were carried out for various strain paths ranging from balanced biaxial stretching to uniaxial stretching. The effects of material properties, sheet thickness, anisotropic parameter and friction coefficient at the sheet punch interface on the locus of FLD were investigated. It was found that the material yield stress and average anisotropic parameter value has almost no effect on forming limits; larger strain-hardening exponent and higher sheet thickness result in higher level of forming limit strains; the friction coefficient has little influence on the locus of FLD but does affect the strain path taken during the deformation. The predicted FLD of AA 5182-O was compared with an experimentally determined FLD and very good agreement has been achieved. It was demonstrated that forming limit diagrams can be predicted by the finite element method without requiring any assumed geometric or material imperfections in the numerical model.
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Messer, Barry, Keith Beaulieu, Andrew Wright et Kevin Hatch. « In-Service Refinery and Pipeline Cracking Initiated by Hydrostatically Induced Strain ». Dans ASME 2009 Pressure Vessels and Piping Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/pvp2009-77038.
Texte intégralRésumé :
A new phenomenon of in-service cracking has been observed in carbon steel pipelines, refinery piping and refinery equipment that is initiated by sources such as hydrostatic testing and is identified as Strain Accrual Hydrogen Cracking. Although hydrostatic testing is beneficial to blunting crack tips and reducing crack propagation, high hydrostatic test pressures approaching yield cause localized threshold strains in weldments and base materials that consequently increases the susceptibility to nascent hydrogen embrittlement at strain boundaries. This paper discusses strain accrual hydrogen cracking mechanisms, beneficial and detrimental effects of high hydrostatic test pressures, increased Code allowable stresses, micro alloying additions and strain based design, case histories, and suggests mitigation practices.
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Dewar, Douglas, Greg Van Boven, Mohamed ElSeify, Paul Bjorn et Nick Bruce. « Operational Experiences With Axial Strain Inline Inspection Tools ». Dans 2018 12th International Pipeline Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/ipc2018-78466.
Texte intégralRésumé :
Axial Strain Inline Inspection has transitioned from an experimental to commercial technology that will develop significantly as the industry requires. Axial strain tool measures total elastic longitudinal strain on a pipeline including: imposed strains due to manufacturing; construction/cold bending; backfilling; and loading associated with abnormal forces such as ground movement and settlement. The technology is based on magnetostriction, which measures the permeability and magnetic induction of ferromagnetic materials. Magnetostriction is well understood, but the application of the technology to active pipelines is relatively recent. Currently, Inertial Measurement Unit (IMU) inline inspections (ILI) effectively identify areas of localized bending strains and can be used for monitoring of pipeline movements run to run, but they do not detect axial strain associated with either tensile or compressive loading. Currently, axial strain modules are mounted behind Magnetic Flux Leakage (MFL) platforms and have either 4 or 8 probes that provide circumferential readings typically at 0.5 to 1 m intervals. Data is either considered “trend” or “calibrated” depending on whether representative test samples are available. Interpretations are provided by the vendor in the form of Axial Strain Variation which is the averaged value of a set of readings with the hoop strain component removed. Additionally, data from each probe is analyzed to establish the maximum and minimal longitudinal strains (εmax/εmin) with locations around the circumference of the pipeline. Given the potential complexity of locked-in strains, simple calculations using sinusoidal bending relationships do not apply. Therefore, curve fitting analysis is required to determine the circumferential strains. This paper includes operational learnings from the analyses of data from eight (8) Axial Strain ILI runs within variable terrain on some natural gas transmission and gathering pipelines in British Columbia by verifying strains due to known abnormal loading as well as identifying previously unknown features (landslides, in particular). In addition, sources of error, data anomalies, current limitations and potential improvements of the technology are discussed.
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Das, Sreekanta, J. J. Roger Cheng, David W. Murray, S. A. Wilkie et Z. Joe Zhou. « Laboratory Study of Local Buckling, Wrinkle Development, and Strains for NPS12 Linepipe ». Dans 2000 3rd International Pipeline Conference. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/ipc2000-210.
Texte intégralRésumé :
Buried pipelines are subjected to fluid pressure (oil/gas/water), axial loads, moments, and complex load combination histories. As a result, they may develop large compressive strains and curvatures leading to formation of localized buckles or wrinkles in the pipe shell. Recently, full-scale tests on 12.75″ diameter (NPS12) energy pipes have been carried out at the University of Alberta to study the behavior of wrinkle development and the ultimate limiting strains at the wrinkle locations. Different internal pressures, and axial loads were applied to produce a wrinkle, followed by load variations intended to produce fracture that could develop in buried pipelines in the field. Three different axially loaded tests are reported. Two different internal pressures were applied, namely, (i) 0.8py and (ii) 0.4py, where py is the required internal pressure to cause the yield stress of the pipe material to be developed in the circumferential direction. Also, two different specimen lengths were adopted. They are: (i) 406 mm (16 inch) and (ii) 736 mm (29 inch). All specimens were loaded axially until the wrinkle formed. It was observed that the pipes are highly ductile and very large compressive strains can be developed without fracture or leakage in the pipe wall. Because the pipe specimens of the first two tests did not fail (i.e. fracture) under monotonically increasing displacements and strains, the third wrinkled specimen was subjected to load histories involving strain reversals. This load history resulted in a low cycle failure after a very few cycles. The paper addresses test procedures, buckling and post-buckling behavior of NPS12 energy pipelines and relates them to three different types of strain measures, namely, material strain, wrinkle strain and overall strain as observed from these tests.
Rapports d'organisations sur le sujet "Localized strains"
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Dinovitzer, Aaron. PR-214-154503-R01 Pipeline Strains Induced by Slope Movement. Chantilly, Virginia : Pipeline Research Council International, Inc. (PRCI), août 2019. http://dx.doi.org/10.55274/r0011609.
Texte intégralRésumé :
Pipeline integrity may be affected by the action of the external soil loads that can be generated by ground movements or slope failures and the structural integrity threat of these geotechnical failures is not well understood. The threat presented to a pipeline by a localized slope failure is not directly related to magnitude of the soil movement involved, but related to the stress and strains induced in the pipeline by the moving soil block. This project demonstrated and applied advanced pipe-soil interaction numerical modeling tools in the assessment of slope movements directed long the pipeline axis. The geotechnical hazard assessments completed in this project provide a conservative means of estimating the pipeline axial strain accumulation resulting from slope movements. These modeling results are presented such that an understanding of the influence of pipeline, slope and operational parameters on strain accumulation is demonstrated and the relative importance of each parameter is demonstrated. The relationship between surface expression of a geotechnical event and the subsurface parameters to facilitate conservative characterization of the event is defined. The data describing axial strain as a function of ground movement magnitude presented in this project may be compared to the axial strain capacity (resistance) engineering tools to evaluate the significance of slope movements on pipeline integrity.
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Kiefner, J. F., J. M. Tuten et T. A. Wall. L51516 Preventing Pipeline Failure in Areas of Soil Movement - Part 1. Chantilly, Virginia : Pipeline Research Council International, Inc. (PRCI), janvier 1987. http://dx.doi.org/10.55274/r0010303.
Texte intégralRésumé :
Ordinarily, buried pipelines undergo little or no movement in service. In a stable soil environment the longitudinal stress in a pipeline seldom approaches the limiting design value set by applicable codes and regulations. Pipeline serviceability under such conditions is seldom, if ever, threatened by the degree of longitudinal stress. In contrast, localized areas may exist along a pipeline where soils and/or slopes are unstable or where subsidence or differential settlement can occur. In these areas, longitudinal stresses may become severe enough to cause a failure. Over the years various techniques have been developed to monitor the status of pipelines in unstable areas, and various remedial techniques have been attempted. In more recent times, with the advent of Arctic and offshore pipelining, such potential movements of pipelines are being taken into account in the initial designs. In any case, there is a continuing need to develop better monitoring and remedial techniques to prevent pipeline failures in unstable soil areas. The objectives of this project are to develop a versatile and reliable prototype strain monitoring system, to demonstrate its applicability on an actual pipeline, and to establish allowable limits on strains due to soil movement or subsidence. The scope of the project includes:(1) Review of previous or on-going monitoring efforts by others.(2) Analysis of strains and development of models to predict strain behavior(3) Calculations to establish limits on strains(4) The design and construction of a microprocessor-controlled automatic monitoring system(5) The implementation of the system on an actual pipeline(6) The collection, analysis and interpretation of strain data from the system.
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Leis, Brian, Xian-Kui Zhu et Tom McGaughy. PR-185-133739-R01 Quantifying Re-Rounding in Pipeline Damage Severity Models. Chantilly, Virginia : Pipeline Research Council International, Inc. (PRCI), avril 2018. http://dx.doi.org/10.55274/r0011479.
Texte intégralRésumé :
The objective of this work was to quantify re-rounding effects on mechanically damaged pipelines. This was done to determine if curvature suffices to identify where the effects of re-rounding are localized. It also was done to establish a framework that could be calibrated through subsequent analysis as an input to guidelines for damage severity assessment. Recognizing the expanding role of ILI and related in-the-ditch evaluation tools to help size and characterize damage, brief consideration was also given to ongoing work within the PRCI Nondestructive Evaluation (NDE) Program. This was done regarding the use of such technologies to assess metallurgical changes in the damaged zone and their integration into model development and sensitivity analysis. Key conclusions for the analysis completed for this project and its validation by comparison to full-scale data include: - Re-rounding can cause significant nonlinear effects in otherwise simple pressure cycling, due in part to localized strain hardening and localized kink formation when it occurs within dents and/or gouges; - Metal-loss due to gouging can be simply idealized without jeopardizing the utility of analysis of the effects of re-rounding, as shown by three validation cases benchmarked against full-scale test-ing; - Re-rounding showed a first-order dependence on pipe geometry and pressure; and - Curvature change appears adequate to quantify re-rounding, but is inadequate to quantify local damage severity in a Level 1 damage screening tool: this also requires consideration of membrane strain (stress) and wall thinning where it is evident. The dependence of re-rounding on pipe geometry and pressure should be broadly quantified, with analyses to trend the role of membrane stress included to build the basis for an ILI-based model to screen damage severity.
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Christman. L51577 Prediction of SCC Susceptibility Based on Mechanical Properties of Line Pipe Steels. Chantilly, Virginia : Pipeline Research Council International, Inc. (PRCI), août 1988. http://dx.doi.org/10.55274/r0010278.
Texte intégralRésumé :
If a relationship between the deformation properties of a line pipe steel and its stress-corrosion cracking resistance can be established, then steels may be selected or designed for improved stress-corrosion resistance, based on their mechanical properties. Benefit: In this research program three line pipe steels, removed from long-term service, were examined to determine if there is a correlation between their mechanical properties and stress-corrosion cracking resistance. The hypothesis was that the steel with the greatest tendency for strain hardening, under cyclic and monotonic stress conditions would also have the highest threshold stress for stress-corrosion crack initiation. This hypothesis was verified by the laboratory experiments, which showed the steel with the greatest tendency for strain hardening to have the highest resistance to stress-corrosion. Two other steels, with distinctly lower resistance to plastic deformation, had lower threshold stresses for stress-corrosion. This observation is consistent with the present concept of stress-corrosion crack growth, which holds that crack tip dissolution, and hence crack propagation, occurs because localized plastic deformation ruptures passive films or prevents film formation resulting in crack growth. Result: The cyclic strain behavior of these three steels is consistent with their monotonic stress-strain curves. Both Steels A and B showed a point of extreme strain as the cyclic stress was increased. Their monotonic stress-strain curves both showed well pronounced yield points above which a considerable strain accompanied a small stress increment (low strain hardening). For both steels the rapid increase in cyclic strain occurred at approximately the elevated temperature yield point (\45 ksi for Steel A
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Foxall, W. Preliminary Report on the Feasibility of Using Synthetic Aperture Radar Interferometry to Image Localized Strain as a Discriminator of Geothermal Resources. Office of Scientific and Technical Information (OSTI), juin 2005. http://dx.doi.org/10.2172/877907.
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Haggag, Fahmy M. Nondestructive and Localized Measurements of Stress-Strain Curves and Fracture Toughness of Ferritic Steels at Various Temperatures Using Innovative Stress-Strain Microprobe Technology. Final Report for Period 8/13/1996--06/16/1999. Office of Scientific and Technical Information (OSTI), octobre 1999. http://dx.doi.org/10.2172/769202.
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Haggag. L52280 In-Situ Measurement of Pipeline Mechanical Properties Using Stress-Strain Microprobe - Validation. Chantilly, Virginia : Pipeline Research Council International, Inc. (PRCI), avril 2007. http://dx.doi.org/10.55274/r0010668.
Texte intégralRésumé :
Most pipeline companies operate infrastructure that spans a wide range of vintages including pipelines that were built in 1950s to the 2000s. Some of the pipelines have changed hands, and in many cases, more than once, resulting in a loss of the operating history and of pertinent pipeline data relating to the grade or mechanical properties. In the case of pipelines of unknown grades, PHMSA (OPS/DOT) stipulates the assumption of a 24 ksi yield strength, regardless of its construction. OPS also allows the establishment of the Specified Minimum Yield Strength (SMYS) of the pipeline by verifying its yield strength by carrying out statistically valid sampling. Conventional tensile testing requires the removal of samples from the pipeline for testing which results in temporary line shut down and loss of transmission service. The constructability issues around this are complex, and it requires line repair after sample extraction. In addition, this can result in a loss of throughput and consequent disruption of supply. An appropriate and relevant amount of data from the nondestructive Automated Ball Indentation (ABI) tests and the destructive tensile and fracture toughness tests provides reasonable statistical data sets to establish the validity and accuracy of the ABI technique which produces both tensile and fracture toughness properties from each single test. The ABI test (accomplished in less than two minutes) is now proven to replace both the tensile and fracture toughness tests without specimen machining or service interruption, and it requires only localized surface polishing of in-service pipelines.
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Dafoe, L. T., G. L. Williams, K. Dickie, U. Gregersen, P. C. Knutz, G. Dam, G. K. Pedersen, H. Nøhr-Hansen, J. W. Haggart et K. J. DesRoches. Overview of the stratigraphy, paleoclimate, and paleoceanography of the Labrador-Baffin Seaway. Natural Resources Canada/CMSS/Information Management, 2022. http://dx.doi.org/10.4095/321853.
Texte intégralRésumé :
The tectonic evolution of the Labrador-Baffin Seaway began with Early Cretaceous extension between Greenland and North America, resulting in the development of basins infilled with nonmarine and shallow-marine clastic strata. The Late Cretaceous was a time of continued rifting and local subsidence, with deposition of widespread deeper water marine mud and localized sand deposits. Seafloor spreading began in the south in the Latest Cretaceous and propagated throughout the seaway by the Early Paleocene. Regional seafloor spreading coincided with the onset of significant volcanism in the Davis Strait to central West Greenland region, as well as a regional regression. A change in the spreading direction around the Paleocene- Eocene boundary, was accompanied by strike-slip motion in the Davis Strait and Baffin Bay, deformation and basin inversion, and development of regional unconformities. After seafloor spreading ceased in the late Eocene, the seaway was filled by upper Paleogene to Recent sediments, with clinoform progradation building the modern-day shelves.
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Clapham, Lynann, et Vijay Babbar. PR-320-113706-R01 Neutron Diffraction Measurements of Residual Strain from Dents and Gouges in Pipelines. Chantilly, Virginia : Pipeline Research Council International, Inc. (PRCI), janvier 2020. http://dx.doi.org/10.55274/r0011643.
Texte intégralRésumé :
Mechanical damage is one of the most prevalent causes of pipeline failure in North America and Europe. Gouged dents are much more likely to produce a failure than "plain" dents (i.e., a dent with no coincident metal loss or crack features), however the residual stresses around gouged dents are more difficult to model and predict. The Pipeline Aggression Rig (PAR) located in the St. Denis facility of GdF Suez was used to introduce backhoe-type gouging into pipe samples, which were nine pressurized pipe sections of varying grades. Five (5) samples were created using high-impact dynamic aggression (termed High Dynamic) and the other four (4) samples were created using lower impact energy and an axial-dragging mechanism (termed Low Dynamic). This project involved using neutron diffraction to measure the residual stresses in and around these gouged dents. Key findings are as follows: - In the undamaged regions of all samples, residual stresses were low (typically medium gouges were localized and residual stresses were largely bending-related: mild tensile at the outer wall/gouge base and compressive at the inner wall. - Residual stresses in and around one (1) High Dynamic severe gouge were tensile and critically high. - Residual stresses in and around Low Dynamic gouges had inconsistent and unpredictable residual stress magnitudes and distributions. PRCI members will find value in this information for understanding the severity of gouges in pipelines, for use in stress modelling verification, and, finally, for understanding characterizing MFL signals from ILI tools.
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Wozniakowska, P., D. W. Eaton, C. Deblonde, A. Mort et O. H. Ardakani. Identification of regional structural corridors in the Montney play using trend surface analysis combined with geophysical imaging. Natural Resources Canada/CMSS/Information Management, 2022. http://dx.doi.org/10.4095/329795.
Texte intégralRésumé :
Induced (anthropogenic) earthquakes are caused by reactivation of pre-existing faults due to human activities, including hydraulic fracturing and saltwater disposal. The Montney play, the pre-eminent shale gas play in Canada, contains localized regions with relatively high geological susceptibility to induced seismicity. Identification of potential seismogenic structures is hindered because published fault maps in the Montney play are often focused on small areas, leading to inconsistencies when these are compiled across the region. We have developed a regional framework based on structural corridors: complex, multi-strand faults systems. A three-step structural interpretation workflow was used, including seismic and structural interpretation along with trend surface analysis (TSA). This approach was used to identify 34 structural corridors in NE BC and NW Alberta.