Dissertations / Theses on the topic 'Tolerance to fatigue'
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Ristori, Vjola <1982>. "Fatigue and Damage Tolerance in Primary Composite Aeronautical Structures." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amsdottorato.unibo.it/8045/1/Ristori_Vjola_Tesi.pdf.
Full textGoksel, Lorens Sarim. "Fatigue and damage tolerance assessment of aircraft structure under uncertainty." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49124.
Full textBailey, Stephen John. "O2 uptake kinetics as a determinant of exercise tolerance." Thesis, University of Exeter, 2011. http://hdl.handle.net/10036/3078.
Full textAlexander, Andrew M. "Exercise tolerance through the severe and extreme intensity domains." Thesis, Kansas State University, 2017. http://hdl.handle.net/2097/38249.
Full textDepartment of Kinesiology
Thomas J. Barstow
Background and Aim: The power-duration relationship accurately predicts exercise tolerance for constant power exercise performed in the severe intensity domain. At intensities above critical power (CP), the power-duration relationship establishes a hyperbolic curve. However, the prediction of exercise tolerance is currently unclear for work rates within the extreme intensity domain (durations <2min). We hypothesized that the power-duration relationship deviates from a linear 1/time relationship for WRs within the extreme intensity domain. Methods: Six men completed nine bilateral knee-extension tests on non-consecutive days and then performed 3 exercise tests in the severe intensity domain (S1-S3; T[subscript lim]>2–15min) and 4 in the extreme domain at 60%, 70%, 80%, and 90%1RM (T[subscript lim]<2min), in random order. Twitch force (Q[subscript tw]), maximal voluntary contraction (MVC), and voluntary activation (VA) were measured on the right vastus lateralis before and after <80s) each test; EMG was measured on the right vastus lateralis throughout each test. T[subscript lim] were plotted as a function of 1/Time. T[subscript lim] for the extreme intensities were compared to the predicted T[subscript lim] of the slope of the S1-S3 regression. Results: The r² for the severe domain 1/time model was 0.99 ± 0.007. T[subscript lim] for exercise at 60%1RM was not different than the predicted T¬lim, however, T¬lim for exercise at 70–90%1RM was shorter than the predicted T[subscript lim] (p<0.05). Post hoc analysis of the extreme domain (70–90%1RM) revealed a significant linear relationship, suggesting a W’ within the extreme domain (W’ext). T[subscript lim] of exercise at 60% 1RM was not different from the predicted value of the 1/Time relationship of the extreme domain. Q[subscript tw] and MVC were significantly decreased following exercise at S1-S3 and 60% 1RM, while no changes existed in Q[subscript tw] or MVC following exercise at 80 and 90%1RM. Further, no changes were found in VA following any exercise intensity. Conclusion: These data suggest that exercise tolerance in the extreme domain is limited by different factors than in the severe domain. However, there is a separate but measurable W’ext. Further, the factors limiting exercise in the extreme domain must be those from can be recovered by the time post-exercise measurements were made.
Dawes, Helen. "Perception of fatigue and exertion during a cycling exercise test in brain injured subjects." Thesis, University of East London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365905.
Full textChang, Po-Yu. "Modeling of fatigue behavior and damage tolerance/durability in fiber metal laminates." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1608577901&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
Full textKinawy, Moustafa. "Static and fatigue propagation of buckle-driven delaminations under bending and compressive loads." Thesis, University of Bath, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545324.
Full textCasas-Rodriguez, Juan P. "Damage in adhesively bonded joints : sinusoidal and impact fatigue." Thesis, Loughborough University, 2008. https://dspace.lboro.ac.uk/2134/11814.
Full textLiu, Bangyan. "Fatigue and damage tolerance analysis of composite laminates - stiffness loss, damage modellig, and life prediction." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60701.
Full textRhead, Andrew T. "Analysis and optimisation of postbuckled damage tolerant composite laminates." Thesis, University of Bath, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520992.
Full textVaněk, David. "Analýzy damage tolerance s uvážením interakce zatěžovacích kmitů." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-254285.
Full textPokorný, Pavel. "Zbytková únavová životnost železničních náprav." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-256578.
Full textBroxterman, Ryan M. "The influence of oxygen delivery and oxygen utilization on the determinants of exercise tolerance." Diss., Kansas State University, 2015. http://hdl.handle.net/2097/19083.
Full textDepartment of Anatomy and Physiology
Thomas J. Barstow
The physiological mechanisms determining the tolerable duration of exercise dictate human physical accomplishments across all spectrums of life. Despite extensive study, these specific mechanisms, and their dependence on oxygen delivery and oxygen utilization, remain, a certain extent, undefined. The purpose of this dissertation was to test the overarching hypothesis that muscle contraction characteristics (i.e., intensity of contraction, muscle contraction-relaxation duty cycle, etc.) alter oxygen delivery and oxygen utilization, which directly influence the power-duration relationship and fatigue development, and therefore, exercise tolerance. To accomplish this, specific interventions of altered muscle contraction-relaxation duty cycle and blood flow occlusion were utilized. In the first investigation (Chapter 2), we utilized low and high muscle contraction-relaxation duty cycles to alter blood flow to the active skeletal muscle, demonstrating that critical power (CP) was reduced with the high muscle contraction-relaxation duty cycle due to a reduction in blood flow, while the curvature constant (W’) was not altered. The second investigation (Chapter 3) utilized blood flow occlusion to show that CP was reduced and W’ increased for blood flow occlusion exercise conditions compared to control blood flow exercise conditions. The final investigation (Chapter 4) utilized periods of blood flow occlusion during and post-exercise to reveal greater magnitudes of peripheral and central fatigue development during blood flow occlusion exercise compared to control blood flow exercise. Moreover, this investigation demonstrated that W’ was significantly related to the magnitude of fatigue development. Collectively, alterations in oxygen delivery and oxygen utilization via muscle contraction characteristics and blood flow occlusion directly influence CP and the magnitude of fatigue development. However, W’ does not appear to be influenced by manipulations in oxygen delivery and oxygen utilization, per se. Rather, W’ may be determined by the magnitude of fatigue accrued during exercise, which is dependent upon oxygen delivery and oxygen utilization. The novel findings of the investigations presented in this dissertation highlight important physiological mechanisms that determine exercise tolerance and demonstrate the need for interventions that improve oxygen delivery and oxygen utilization in specific populations, such as those with chronic heart failure or chronic obstructive pulmonary disease, to improve exercise tolerance.
Tarragó, Cifre Jose María. "Damage tolerance of cemented carbides under service-like conditions." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/403888.
Full textPor un lado, la industria del metal duro está sumergida en una búsqueda constante de materiales de altas prestaciones a un coste reducido. Por el otro lado, las materias primas tienen precios altos y volátiles, que comprometen la estabilidad del mercado. En esta coyuntura, los productores y los usuarios finales están muy interesados, tanto en aumentar el rendimiento, incrementar la vida útil y mejorar la fiabilidad de estos productos, como en su sustitución por materiales alternativos y considerados menos críticos. En este contexto, el desgaste y la ruptura prematura son los dos principales mecanismos que limitan la vida útil de las aplicaciones de metal duro. En la gran mayoría de los casos las rupturas prematuras derivan de la combinación de altas tensiones, tanto monótonas como cíclicas, con el daño inducido durante la vida en servicio, como la corrosión, y el choque térmico. Por lo tanto, con el fin de aumentar fiabilidad en estas aplicaciones, es necesario entender los mecanismos de daño y fallo en estos materiales. Así, el propósito de esta tesis es mejorar el rendimiento y aumentar la fiabilidad de los carburos cementados a partir del desarrollo de materiales con una mayor tolerancia al daño y una menor sensibilidad a fatiga, a través de un óptimo diseño microestructural. La presente investigación se compone de tres partes que abarcan diferentes aspectos relacionados con el desempeño de los metales duros en condiciones de servicio. Las dos primeras secciones están dedicadas a realizar un estudio general sobre la influencia de la microestructura en el comportamiento a fractura y fatiga del metal duro. El objetivo de la tercera sección es evaluar los efectos microestructurales en la tolerancia al daño de los carburos cementados, ya sea inducido por corrosión o por choque térmico. El principal mecanismo de tenacidad en los carburos cementados reside en el estiramiento plástico de ligamentos metálicos de puenteo que se forman detrás de la punta de la grieta, llamada la zona de multiligamentos. El desarrollo del mecanismo de puenteo implica un incremento de la resistencia a fractura a medida que aumenta la longitud de la grieta. Este mecanismo es conocido como curva-R y su eficacia está íntimamente relacionada con las características microestructurales del material. Así, la primera parte de esta tesis doctoral está dedicada a llevar a cabo una investigación detallada de los mecanismos de fractura en los carburos cementados, y a proponer una relación que permita captar los efectos microestructurales en las características de curva-R de estos materiales. Por otro lado, la segunda parte de la tesis está dedicada a estudiar la influencia de la microestructura, incluyendo tanto el tamaño de grano de la fase carburo como el contenido de la fase ligante y su naturaleza química, en la sensibilidad a fatiga de los carburos cementados. Así, se ha prestado una atención particular en estudiar el comportamiento a fatiga de los carburos cementados con base níquel y en su comparación con los de base cobalto. Por otro lado, también se ha estudiado la influencia del tamaño de grano en la deflexión de grieta como un mecanismo adicional de aumento de tenacidad, inmune a las solicitaciones cíclicas. Por último, la tercera sección de esta tesis consiste en un estudio sistemático de la influencia de la microestructura de los carburos cementados en su tolerancia al daño, inducido tanto por corrosión como por choque térmico, con el fin de establecer las directrices para un diseño microestructural óptimo. De este modo, la integridad estructural de carburos cementados se evalúa sobre la base de su resistencia residual a flexión después de la inducción de daño
Renault, Michel. "Tolerance a l'endommagement de composites carbone-resine et stratifies t300-914." Paris, ENMP, 1988. http://www.theses.fr/1988ENMP0109.
Full textCase, Scott Wayne. "Mechanics of Fiber-Controlled Behavior in Polymeric Composite Materials." Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/30568.
Full textPh. D.
FILIPAS, LUCA. "THE EFFECT OF MENTAL FATIGUE ON SPORT-SPECIFIC PHYSICAL AND TECHNICAL PERFORMANCE." Doctoral thesis, Università degli Studi di Milano, 2020. http://hdl.handle.net/2434/697519.
Full textDuchoň, Peter. "Analýza spoje křídlo-trup letounu L 410 NG z hlediska filozofie konstrukce s přípustným poškozením." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231189.
Full textHalbert, Keith. "Estimation of probability of failure for damage-tolerant aerospace structures." Thesis, Temple University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3623167.
Full textThe majority of aircraft structures are designed to be damage-tolerant such that safe operation can continue in the presence of minor damage. It is necessary to schedule inspections so that minor damage can be found and repaired. It is generally not possible to perform structural inspections prior to every flight. The scheduling is traditionally accomplished through a deterministic set of methods referred to as Damage Tolerance Analysis (DTA). DTA has proven to produce safe aircraft but does not provide estimates of the probability of failure of future flights or the probability of repair of future inspections. Without these estimates maintenance costs cannot be accurately predicted. Also, estimation of failure probabilities is now a regulatory requirement for some aircraft.
The set of methods concerned with the probabilistic formulation of this problem are collectively referred to as Probabilistic Damage Tolerance Analysis (PDTA). The goal of PDTA is to control the failure probability while holding maintenance costs to a reasonable level. This work focuses specifically on PDTA for fatigue cracking of metallic aircraft structures. The growth of a crack (or cracks) must be modeled using all available data and engineering knowledge. The length of a crack can be assessed only indirectly through evidence such as non-destructive inspection results, failures or lack of failures, and the observed severity of usage of the structure.
The current set of industry PDTA tools are lacking in several ways: they may in some cases yield poor estimates of failure probabilities, they cannot realistically represent the variety of possible failure and maintenance scenarios, and they do not allow for model updates which incorporate observed evidence. A PDTA modeling methodology must be flexible enough to estimate accurately the failure and repair probabilities under a variety of maintenance scenarios, and be capable of incorporating observed evidence as it becomes available.
This dissertation describes and develops new PDTA methodologies that directly address the deficiencies of the currently used tools. The new methods are implemented as a free, publicly licensed and open source R software package that can be downloaded from the Comprehensive R Archive Network. The tools consist of two main components. First, an explicit (and expensive) Monte Carlo approach is presented which simulates the life of an aircraft structural component flight-by-flight. This straightforward MC routine can be used to provide defensible estimates of the failure probabilities for future flights and repair probabilities for future inspections under a variety of failure and maintenance scenarios. This routine is intended to provide baseline estimates against which to compare the results of other, more efficient approaches.
Second, an original approach is described which models the fatigue process and future scheduled inspections as a hidden Markov model. This model is solved using a particle-based approximation and the sequential importance sampling algorithm, which provides an efficient solution to the PDTA problem. Sequential importance sampling is an extension of importance sampling to a Markov process, allowing for efficient Bayesian updating of model parameters. This model updating capability, the benefit of which is demonstrated, is lacking in other PDTA approaches. The results of this approach are shown to agree with the results of the explicit Monte Carlo routine for a number of PDTA problems.
Extensions to the typical PDTA problem, which cannot be solved using currently available tools, are presented and solved in this work. These extensions include incorporating observed evidence (such as non-destructive inspection results), more realistic treatment of possible future repairs, and the modeling of failure involving more than one crack (the so-called continuing damage problem).
The described hidden Markov model / sequential importance sampling approach to PDTA has the potential to improve aerospace structural safety and reduce maintenance costs by providing a more accurate assessment of the risk of failure and the likelihood of repairs throughout the life of an aircraft.
Eriksen, Claire Anne. "Sleepiness - night work, time zones and activity /." Stockholm, 2006. http://diss.kib.ki.se/2006/91-7140-790-1/.
Full textGarnier, Christian. "Etude du comportement dynamique des structures composites réalisées par LRI : application à l’impact et à la fatigue." Phd thesis, Toulouse, INPT, 2011. http://oatao.univ-toulouse.fr/6920/1/garnier.pdf.
Full textShipsha, Andrey. "Failure of Sandwich Structures with Sub-Interface Damage." Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3184.
Full textDaniel, Giovani Sacchetto. "Dano em materiais compósitos: SAFECom (Sistema de Análise de Fadiga de Estruturas em Compósito)." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-25032012-103251/.
Full textThis work firstly presents an overview about various methods of analysis of fatigue and damage tolerance of composite materials and, in particular, the concept of critical element and the method of residual strength are studied and applied to the analysis of polymer composites reinforced by continuous fibers under cyclic loading. Cases of laminates with stress concentrators are also addressed, mainly due to increasing use of composite materials. In this context, this work aimed to develop a computational tool that was able to consistently predict both the fatigue life of structures in composite material and the residual strength of these structures under the action of cyclic loads. Thus, a model based on residual strength, which involves numerical integration, is implemented in a computer program called SAFECom (System of Analysis of Fatigue for Composites), which is applied to some case studies. The SAFECom is evaluated by comparing results obtained from literature data. There is a good convergence between the results of this assessment. Finally, possibilities for improvement are listed on the program that can make it applicable to other case studies, which were not covered in this study, in addition to its evaluation by experimental tests.
Petaishiski, Jayme Nichole. "The buffering effects of perceived fitness on stress reactivity." CSUSB ScholarWorks, 2002. https://scholarworks.lib.csusb.edu/etd-project/2212.
Full textBergner, Frank. "Skaleninvarianz und deren Bedeutung für die Modellierung der Ermüdungsrißausbreitung in Aluminiumlegierungen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1098957032500-77796.
Full textThe work is based upon two essentials: the first one is the preparation and application of techniques of scale invariance analysis, the second one consists in a database of experimental results for heat-treatable thin-sheet wrought aluminium alloys obtained under uniform conditions. Progress with respect to methodology was achieved regarding, first, the algebraic correlation between sets of coefficients and exponents of any power law, second, the transfer of the concept of finite scale invariance to the phenomenon of fatigue crack growth (FCG), and third, the combination of the ideas of a rate-controlling step and dimensional analysis of environmental-assisted FCG including the mapping of rate-controlling steps. In the experimental part, a database containing both measured scatterbands of FCG and strengthening characteristics for several orientations and aging conditions of aluminium alloys amounting to a total of 39 different material conditions was established. This database was supplemented with results of selected measurements of near-threshold FCG rates, residual strength, crack closure, roughness of fatigue cracks, and frequency-dependent environmental-assisted FCG as well as investigations of three plain-carbon steels and a magnesium alloy. Based on these prerequisites, the influence of the material on the FCG behaviour of thin-sheet wrought aluminium alloys under constant-amplitude loading was investigated within the limits of validity of linear-elastic fracture mechanics. The following influence factors were identified to be essential: The assignment of alloys to one out of two groups is mainly determined by the degrees of coherency and order of the strength-controlling precipitates and the resulting type of slip distribution. The normalized-Paris-law coefficient for the first group is mainly dependent on the modulus of elasticity and the stress ratio. The Paris-law exponents for the first group are dominated by a dimensionless power monomial of the 0.2% proof stress, the athermal strengthening coefficient, sheet thickeness and the critical stress intensity factor. The retardation of the FCG rates of alloys of the second group relative to the first group is mainly determined by the amount of crack deflection and by a residual mode-II component of crack opening displacement. Finally, the environment-assisted FCG for aluminium alloy 6013 T6 reveals a coupled dependence on loading frequency and cyclic stress intensity factor. The discussion covers the evaluation of the results in relation to observations and models from the literature, the explanation of the modes of operation of the major influence factors and a model based on a mixing rule for the alloys of the first group. It turned out that there is not any model that reflects all of the observations simultaneously. Some of the ideas presented require to be worked out in more detail
Seneviratne, Waruna Prasanna. "Fatigue life determination of a damage-tolerant composite airframe." Diss., Wichita State University, 2008. http://hdl.handle.net/10057/2078.
Full textWichita State University, College of Engineering, Dept. of Aerospace Engineering
Seneviratne, Waruna Prasanna Tomblin John S. "Fatigue life determination of a damage-tolerant composite airframe /." A link to full text of this dissertation in SOAR, 2008. http://hdl.handle.net/10057/2078.
Full textBergner, Frank. "Skaleninvarianz und deren Bedeutung für die Modellierung der Ermüdungsrißausbreitung in Aluminiumlegierungen." Doctoral thesis, Technische Universität Dresden, 2002. https://tud.qucosa.de/id/qucosa%3A24390.
Full textThe work is based upon two essentials: the first one is the preparation and application of techniques of scale invariance analysis, the second one consists in a database of experimental results for heat-treatable thin-sheet wrought aluminium alloys obtained under uniform conditions. Progress with respect to methodology was achieved regarding, first, the algebraic correlation between sets of coefficients and exponents of any power law, second, the transfer of the concept of finite scale invariance to the phenomenon of fatigue crack growth (FCG), and third, the combination of the ideas of a rate-controlling step and dimensional analysis of environmental-assisted FCG including the mapping of rate-controlling steps. In the experimental part, a database containing both measured scatterbands of FCG and strengthening characteristics for several orientations and aging conditions of aluminium alloys amounting to a total of 39 different material conditions was established. This database was supplemented with results of selected measurements of near-threshold FCG rates, residual strength, crack closure, roughness of fatigue cracks, and frequency-dependent environmental-assisted FCG as well as investigations of three plain-carbon steels and a magnesium alloy. Based on these prerequisites, the influence of the material on the FCG behaviour of thin-sheet wrought aluminium alloys under constant-amplitude loading was investigated within the limits of validity of linear-elastic fracture mechanics. The following influence factors were identified to be essential: The assignment of alloys to one out of two groups is mainly determined by the degrees of coherency and order of the strength-controlling precipitates and the resulting type of slip distribution. The normalized-Paris-law coefficient for the first group is mainly dependent on the modulus of elasticity and the stress ratio. The Paris-law exponents for the first group are dominated by a dimensionless power monomial of the 0.2% proof stress, the athermal strengthening coefficient, sheet thickeness and the critical stress intensity factor. The retardation of the FCG rates of alloys of the second group relative to the first group is mainly determined by the amount of crack deflection and by a residual mode-II component of crack opening displacement. Finally, the environment-assisted FCG for aluminium alloy 6013 T6 reveals a coupled dependence on loading frequency and cyclic stress intensity factor. The discussion covers the evaluation of the results in relation to observations and models from the literature, the explanation of the modes of operation of the major influence factors and a model based on a mixing rule for the alloys of the first group. It turned out that there is not any model that reflects all of the observations simultaneously. Some of the ideas presented require to be worked out in more detail.
Shirani, Mehdi. "Probabilistic and defect tolerant fatigue assessment of wind turbine castings." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for produktutvikling og materialer, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15558.
Full textXu, Yigeng. "Closure assessment and overload transient behaviour in damage tolerant airframe materials." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390752.
Full textTakara, Glaucia Nency. "O teste do degrau de seis minutos avalia a capacidade funcional aeróbia de pacientes com doença pulmonar obstrutiva crônica?" Universidade Federal de São Carlos, 2011. https://repositorio.ufscar.br/handle/ufscar/5274.
Full textFinanciadora de Estudos e Projetos
Objective: To assess the six-minute step test (6MST) in terms of its ability to evaluate the aerobic functional capacity of COPD patients. In addition to compare, correlate and verify if there is an agreement between the metabolic (oxygen uptake-VO2), ventilatory (minute ventilation-VE) and cardiovascular variables (heart rate-HR), and perceived exertion of the 6MST and the incremental cardiopulmonary exercise test (ICPET). Methods: Metabolic and ventilatory variables, heart rate, dyspnea and lower limb (LL) fatigue were recorded from 18 COPD patients (five had mild COPD, five moderate, six severe and two very severe) performing the 6MST and the submaximal ICPET on cycle ergometer (work rate was increased by 5-10 watts) on different and not consecutive days. Results: There were no significant differences between VO2, HR, VE, dyspnea and LL fatigue mean values at the peak of both tests. Moderate correlations were found between the 6MST performance and ICPET s VO2 (r=0.49;p=0.05) and performance (r=0.63;p=0.005), high correlations were found between both VO2 (L/min and mL/kg/min) (r=0.76 and r=0.77;p=0.001), and moderate correlations were found between HR (r=0.68;p=0.002) and LL fatigue (r=0.59;p=0.011) between the tests. There was no agreement between VO2, HR and LL fatigue values between the tests. Conclusion: The 6MST has the ability to assess aerobic functional capacity and presents cardiorespiratory responses and perceived exertion similar to the ICPET in magnitude, however it cannot replace the ICPET, since the 6MST assesses and demands greater and more localized work from peripheral muscles, thus not reflecting the same ICPET cardiorespiratory capacity.
Objetivo: Verificar se o teste do degrau de seis minutos (TD6) permite avaliar a capacidade funcional aeróbia de pacientes com doença pulmonar obstrutiva crônica (DPOC) além de comparar, correlacionar e verificar se há concordância entre as variáveis metabólica (consumo de oxigênio-VO2), ventilatória (ventilação minuto-VE), cardiovascular (frequência cardíaca- FC) e de percepção de esforço entre o TD6 e o teste de exercício cardiopulmonar incremental (TECPI). Métodos: 18 pacientes com DPOC (cinco com obstrução leve, cinco moderada, seis grave e dois muito grave) executaram o TD6 e o TECPI submáximo em cicloergômetro (incrementos de 5 a 10W) em dias não coincidentes e não consecutivos. O TD6 foi realizado em um degrau cuja altura media 20cm e durante seis minutos os pacientes foram orientados a subir o mais rápido possível em cadência livre. Durante os testes foram avaliados o VO2, a VE, a FC, a sensação de dispneia (SD) e a sensação de fadiga de membros inferiores (SFMMII), por meio da escala de Borg. Resultados: Não houve diferenças significativas entre as médias dos valores de VO2, FC, VE, SD e SFMMII no pico de ambos os testes. Observaram-se correlações moderadas entre o desempenho no TD6 (número total de subidas no degrau) e o VO2 no TECPI (r=0,49;p=0,05) e entre o desempenho no TD6 com o desempenho no TECPI (r=0,63;p=0,005); correlações fortes entre os VO2 (L/min e mL/kg/min) (r=0,76 e r=0,77;p=0,001) e correlações moderadas das FC (r=0,68;p=0,002) e das SFMMII (r=0,59;p=0,011) entre os testes. Não se observou concordância entre os valores de VO2, FC e SFMMII entre os testes. Conclusão: O TD6 pode avaliar a capacidade funcional aeróbia e apresenta respostas cardiorrespiratórias e de percepção de esforço semelhantes ao TECPI em magnitude, porém não substitui o TECPI, uma vez que o TD6 não reflete a mesma capacidade cardiorrespiratória do TECPI por ser um teste que avalia e exige um trabalho maior e mais localizado da musculatura periférica.
Abramovici, Eugen. "Quantitative fractographic examination of aircraft components subjected to fatigue and damage tolerance testing." Thesis, 1985. http://spectrum.library.concordia.ca/4052/1/ML30656.pdf.
Full text(5930921), Michael C. Waddell. "INVESTIGATION OF SHORT FATIGUE CRACK GROWTH AND DAMAGE TOLERANCE IN ADDITIVE MANUFACTURED Ti-6Al-4V." Thesis, 2019.
Find full textAeronautical products additively manufactured by Selective Laser Melting (SLM), are known to have fatigue properties which are negatively impacted by porosity defects, microstructural features and residual stresses. Little research is available studying these phenomena with respect to the short fatigue crack growth (FCG) inconsistency problem, the large focus being on the long FCG. This thesis seeks to add useful knowledge to the understanding of the mechanisms for short crack growth variability in SLM manufactured Ti-6Al-4V, with the two variables for the process conditions and build directions investigated. An in-situ FCG investigation using x-ray synchrotron computed micro-tomography (μXSCT) was used to visually observe and quantify the short crack path evolution. Crack growth, deflections and porosity interactions were noted and discussed in relation to microstructure, build layer thickness and build layer orientation. A novel use of in-situ energy dispersive x-ray diffraction (EDD) was able to show the lattice strains evolving as a propagating crack moved through a small region of interest. The results presented show the ability to reliably obtain all six elastic strain tensor components, and interpret useful knowledge from a small region of interest.
There are conflicting views in literature with respect to the damage tolerance behavior of as built SLM manufactured Ti-6Al-4V. In the 2018 review by Agius et al., the more prominent studies were considered with Leuders et al. showing the highest long FCG rates for cracks parallel to the build layer and Cain et al. showing cracks propagating through successive build layers as highest [1]–[3]. Cain et al. and Vilaro et al. report significant anisotropy in long FCG for different build orientations whereas Edwards and Ramulu present similar FCG behavior for three different build directions [2]–[5]. Kruth et al. concluded that for optimized build parameters without any (detectable) pores, the building direction does not play a significant role in the fracture toughness results [6]. All of the mentioned literature reported martensitic microstructures and the presence of prior grain structures for as built SLM Ti-6Al-4V.
No studies to the authors knowledge have considered the short FCG of SLM manufactured Ti‑6Al‑4V and its implications to the conflicting damage tolerance behaviors reported in literature [1]. In this work small cross-sectional area (1.5 x 1.5 ) samples in two different build conditions of as built SLM Ti-6Al‑4V are studied. The short FCG rate of three different build directions was considered with cracks parallel to the build layers shown to be the most damaging. The microstructure and build layer are shown to be the likely dominant factors in the short FCG rate of as built Ti-6Al-4V. In terms of porosity, little impact to the propagating short crack was seen although there is local elastoplastic behavior around these defects which could cause toughening in the non-optimized build parameter samples tested. The fracture surfaces were examined using a Scanning Electron Microscope (SEM) with the results showing significant differences in the behavior of the two build conditions. From the microindentation hardness testing undertaken, the smooth fracture surface of the optimized sample correlated with a higher Vickers Hardness (VH) result and therefore higher strength. The non-optimized samples had a ‘rough’ fracture surface, a lower VH result and therefore strength. Furthering the knowledge of short FCG in SLM manufactured Ti-6Al-4V will have positive implications to accurately life and therefore certify additive manufactured aeronautical products.
(8081285), Samuel John Noone. "ANALYSIS OF LASER CLAD REPAIRED TI-6AL-4V FATIGUE LIFE." Thesis, 2021.
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