O presente estudo avalia a associação entre estresse no trabalho e auto-relato de diagnóstico médico de lesão por esforço repetitivo (LER). Trata-se de um estudo seccional, inserido no Estudo Pró-Saúde, que consiste no acompanhamento de uma coorte de funcionários técnico-administrativos de uma universidade no Estado do Rio de Janeiro. Os dados foram obtidos, no ano de 2001, a partir da aplicação de um questionário auto-preenchível. A população de estudo constou de 3.314 funcionários, dentre os quais, 485 apresentaram auto-relato de diagnóstico médico de LER, após sua admissão como funcionários da universidade. A prevalência de LER foi maior entre as mulheres (19,4%) do que entre os homens (8,8%). O estresse no trabalho foi avaliado através da versão reduzida do Job Content Questionnaire, desenvolvido por Karasek e Theorell, cujas questões se destinam a avaliar a demanda psicológica, o controle sobre o próprio trabalho e, o apoio social no trabalho. A análise do estresse no trabalho foi realizada de acordo com os quadrantes propostos por Karasek (1979): baixa exigência (baixa demanda e alto controle); trabalho passivo (baixa demanda e baixo controle); alta exigência (alta demanda e baixo controle) e; trabalho ativo (alta demanda e alto controle). Nesta análise, utilizou-se como categoria de referência, a baixa exigência, por compor um cenário ideal de trabalho. Após ajuste por variáveis socioeconômicas e demográficas (idade, escolaridade e renda familiar per capita) e, ocupacionais (anos de trabalho na universidade e ocupação), homens e mulheres com alta exigência no trabalho, apresentaram uma chance maior de serem acometidos por LER (homens: OR= 1,88; IC95% 1,07-3,29 e mulheres: OR= 1,90; IC95% 1,32-2,02). No ajuste adicional pelo apoio social no trabalho, houve redução da força da associação, para ambos os sexos. Para as mulheres com alta exigência no trabalho, esta associação manteve-se significativa (OR= 1,63; IC95%= 1,12-2,37); enquanto que para os homens, esta associação ficou marginalmente significante (OR= 1,62; IC95%= 0,91-2,87). Este estudo reforça que o desequilíbrio entre a demanda psicológica no trabalho e o controle sobre o próprio trabalho é importante na ocorrência de LER e, portanto, pode ser útil na elaboração de medidas preventivas desse crescente problema de sáude pública. Espera-se que as hipóteses geradas neste estudo possam ser testadas em novas investigações que incorporem o desenho longitudinal, como o Estudo Pró-Saúde, no qual este se insere. / The study evaluates the association between job strain and self-reported medical diagnosis of repetitive strain injury (RSI). This is a cross-sectional study, included in the Pro-Saude Study, which consists of tracking a cohort of technical and administrative employees of a university in the State of Rio de Janeiro. The data were obtained in 2001 from the application of a self-administered questionnaire. The study population consisted of 3314 employees, among which 485 were self-reported medical diagnosis of RSI, after this admission to university. The prevalence of RSI was higther among women (19.4%) than amog men (8.8%). Job strain was assessed by the shortened version of Job Content Questionnaire, developed by Karasek and Theorell, whose questions are intended to assess the psychological demands, control over work, and social support. The analysis of job strain was performed according to the quadrants proposed by Karasek (1979): low strain (low demand and high control), passive job (low demand and low control), high strain (high demand and low control) and, active job (high demand and high control). In this analysis, was used as the reference category, the low strain, an ideal setting for composing work. After adjusting for socioeconomic and demographic variables (age, education and family income per capita) and occupational (years work and occupation), men and women with high demands at work were more likely to be affected by RSI (men : OR = 1.88, 95% CI 1.07; 3.29 and women: OR = 1.90, 95% CI 1.32; 2.02). In additional adjustment for social support at work, a reduction in strength of association for both sexes was founded. For women at high strain at work, this association remained significant (OR = 1.63, 95% CI 1.12 to 2.37), while for men, this association was marginally significant (OR = 1, 62, 95% CI 0.91 to 2.87). This study reinforces that the imbalance between job psycological demands and job control is important in the occurrence of RSI and therefore may be useful in developing preventive measures of this growing problem of public health. It is expected that the hypoteses generated in this study can be tested in further investigations that include the longitudinal design, as the Pro-Saude Study, in which it falls.

O presente estudo avalia a associação entre estresse no trabalho e auto-relato de diagnóstico médico de lesão por esforço repetitivo (LER). Trata-se de um estudo seccional, inserido no Estudo Pró-Saúde, que consiste no acompanhamento de uma coorte de funcionários técnico-administrativos de uma universidade no Estado do Rio de Janeiro. Os dados foram obtidos, no ano de 2001, a partir da aplicação de um questionário auto-preenchível. A população de estudo constou de 3.314 funcionários, dentre os quais, 485 apresentaram auto-relato de diagnóstico médico de LER, após sua admissão como funcionários da universidade. A prevalência de LER foi maior entre as mulheres (19,4%) do que entre os homens (8,8%). O estresse no trabalho foi avaliado através da versão reduzida do Job Content Questionnaire, desenvolvido por Karasek e Theorell, cujas questões se destinam a avaliar a demanda psicológica, o controle sobre o próprio trabalho e, o apoio social no trabalho. A análise do estresse no trabalho foi realizada de acordo com os quadrantes propostos por Karasek (1979): baixa exigência (baixa demanda e alto controle); trabalho passivo (baixa demanda e baixo controle); alta exigência (alta demanda e baixo controle) e; trabalho ativo (alta demanda e alto controle). Nesta análise, utilizou-se como categoria de referência, a baixa exigência, por compor um cenário ideal de trabalho. Após ajuste por variáveis socioeconômicas e demográficas (idade, escolaridade e renda familiar per capita) e, ocupacionais (anos de trabalho na universidade e ocupação), homens e mulheres com alta exigência no trabalho, apresentaram uma chance maior de serem acometidos por LER (homens: OR= 1,88; IC95% 1,07-3,29 e mulheres: OR= 1,90; IC95% 1,32-2,02). No ajuste adicional pelo apoio social no trabalho, houve redução da força da associação, para ambos os sexos. Para as mulheres com alta exigência no trabalho, esta associação manteve-se significativa (OR= 1,63; IC95%= 1,12-2,37); enquanto que para os homens, esta associação ficou marginalmente significante (OR= 1,62; IC95%= 0,91-2,87). Este estudo reforça que o desequilíbrio entre a demanda psicológica no trabalho e o controle sobre o próprio trabalho é importante na ocorrência de LER e, portanto, pode ser útil na elaboração de medidas preventivas desse crescente problema de sáude pública. Espera-se que as hipóteses geradas neste estudo possam ser testadas em novas investigações que incorporem o desenho longitudinal, como o Estudo Pró-Saúde, no qual este se insere. / The study evaluates the association between job strain and self-reported medical diagnosis of repetitive strain injury (RSI). This is a cross-sectional study, included in the Pro-Saude Study, which consists of tracking a cohort of technical and administrative employees of a university in the State of Rio de Janeiro. The data were obtained in 2001 from the application of a self-administered questionnaire. The study population consisted of 3314 employees, among which 485 were self-reported medical diagnosis of RSI, after this admission to university. The prevalence of RSI was higther among women (19.4%) than amog men (8.8%). Job strain was assessed by the shortened version of Job Content Questionnaire, developed by Karasek and Theorell, whose questions are intended to assess the psychological demands, control over work, and social support. The analysis of job strain was performed according to the quadrants proposed by Karasek (1979): low strain (low demand and high control), passive job (low demand and low control), high strain (high demand and low control) and, active job (high demand and high control). In this analysis, was used as the reference category, the low strain, an ideal setting for composing work. After adjusting for socioeconomic and demographic variables (age, education and family income per capita) and occupational (years work and occupation), men and women with high demands at work were more likely to be affected by RSI (men : OR = 1.88, 95% CI 1.07; 3.29 and women: OR = 1.90, 95% CI 1.32; 2.02). In additional adjustment for social support at work, a reduction in strength of association for both sexes was founded. For women at high strain at work, this association remained significant (OR = 1.63, 95% CI 1.12 to 2.37), while for men, this association was marginally significant (OR = 1, 62, 95% CI 0.91 to 2.87). This study reinforces that the imbalance between job psycological demands and job control is important in the occurrence of RSI and therefore may be useful in developing preventive measures of this growing problem of public health. It is expected that the hypoteses generated in this study can be tested in further investigations that include the longitudinal design, as the Pro-Saude Study, in which it falls.

Deliberate and accidental explosions along with the heightened risk of loss of life and property damage during such events have highlighted the need for research in the behaviour of materials under high strain rates. Where an extensive body of research is available on steel and concrete structures, little to no details on how to address the design or retrofitting of wood structures subjected to a blast threat are available. Studies reported in the literature that focused on full scale light-frame wood structures did not quantify the increase in capacity due to the dynamic loading while the studies that did quantify the increase mostly stems from small clear specimens that are not representative of the behaviour of structural size members with defects. Tests on larger-scale specimens have mostly focused on the material properties and not the structural behaviour of subsystems. Advancements in design and construction techniques have greatly contributed to the emergence of taller and safer wood structures which increase potential for blast threat. This thesis presents results on the flexural behaviour of light-frame wood stud walls subjected to shock wave loading using the University of Ottawa shock tube. The emphasis is on the overall behaviour of the wall subsystem, especially the interaction between the sheathing and the studs through the nailed connection. The approach employed in this experimental program was holistic, where the specimens were investigated at the component and the subsystem levels. Twenty walls consisting of 38 mm x 140 mm machine stress-rated (MSR) studs spaced 406 mm on center and sheathed with two different types and sheathing thicknesses were tested to failure under static and dynamic loads. The experimental results were used to determine dynamic increase factors (DIFs) and a material predictive model was validated using experimental data. The implications of the code are also discussed and compared to the experimental data. Once validated, an equivalent single-degree-of-freedom (SDOF) model incorporating partial composite action was used to evaluate current analysis and design assumptions. The results showed that a shock tube can effectively be used to generate high strain-rate flexural response in wood members and that the material predictive model was found suitable to effectively predict the displacement resulting from shock wave loading. Furthermore, it was found that current analysis and design approaches overestimated the wall displacements.

Plasticity in crystalline solids is controlled by the microscopic line defects known as “dislocations”. Decisive role of dislocations in crystal plasticity in addition to fundamentals of plastic deformation are presented in the current thesis work. Moreover, major features of numerical modeling method “Discrete Dislocation Dynamics (DDD)” technique are described to elucidate a powerful computational method used in simulation of crystal plasticity. First part of the work is focused on the investigation of strain rate effect on the dynamic deformation of crystalline solids. Single crystal copper is chosen as a model crystal and discrete dislocation dynamics method is used to perform numerical uniaxial tensile test on the single crystal at various high strain rates. Twenty four straight dislocations of mixed character are randomly distributed inside a model crystal with an edge length of 1 µm subjected to periodic boundary conditions. Loading of the model crystal with the considered initial dislocation microstructure at constant strain rates ranging from 103 to 105s1 leads to a significant strain rate sensitivity of the plastic flow. In addition to the flow stress, microstructure evolution of the sample crystal demonstrates a considerable strain rate dependency. Furthermore, strain rate affects the strain induce microstructure heterogeneity such that more heterogeneous microstructure emerges as strain rate increases. Anisotropic characteristic of plasticity in single crystals is investigated in the second part of the study. Copper single crystal is selected to perform numerical tensile tests on the model crystal along two different loading directions of [001] and [111] at two high strain rates. Effect of loading orientation on the macroscopic behavior along with microstructure evolution of the model crystal is examined using DDD method. Investigation of dynamic response of single crystal to the mechanical loading demonstrates a substantial effect of loading orientation on the flow stress. Furthermore, plastic anisotropy is observed in dislocation density evolution such that more dislocations are generated as straining direction of single crystal is changed from [001] to [111] axis. Likewise, strain induced microstructure heterogeneity displays the effect of loading direction such that more heterogeneous microstructure evolve as single crystal is loaded along [111] direction. Formation of slip bands and consequently localization of plastic deformation are detected as model crystal is loaded along both directions. / <p>QC 20151015</p>

No description available.

An investigation of the microstructure-mechanical property relationships for gray cast iron and a vintage ASTM A7 steel are presented herein. Gray cast iron was shown to have a moderate sensitivity to strain rate and a large disparity in behavior between compression, tension, and torsion. ASTM A7 steel was shown to behave in a more complex manor with the strain rate sensitivity having a negative relationship in tension and positive relationship in compression and torsion, the tensile stress-state producing the highest stress response, and the material producing a higher stress response when exposed to elevated temperatures. The counterintuitive behavior observed in A7 steel was attributed to dynamic strain aging. The Mississippi State University Internal State Variable Plasticity-Damage model was updated to accurately capture negative strain rate sensitivity and DSA embrittlement by developing kinematic, thermodynamic, and kinetic constitutive relationships for dynamic strain aging. A parametric study was performed to elucidate the behavior of the new internal state variable for dynamic strain aging. Gray cast iron was successfully calibrated to a pre-DSA version of the plasticity-damage model and A7 steel was successfully calibrated to the updated plasticity-damage model.

No description available.

No description available.

Dynamic testing provides valuable insight into the behavior of materials undergoing fast deformation. During Split-Hopkinson Pressure Bar testing, stress waves are measured using strain gauges as voltage variations that are usually very small. Therefore, an amplifier is required to amplify the data and analyze it. One of the few available amplifiers designed for this purpose is provided by Vishay Micro-Measurements which limits the user’s options when it comes to research or industry. Among the challenges of implementing the Hopkinson technology in the industry are the size and cost of the amplifier. In this work, we propose a novel design of a signal conditioning amplifier that provides the following functionalities: voltage excitation for strain gauges, wide gain range (1-1000), signal balancing, shunting, and filtering. The main objective is to make a smaller and cheaper amplifier that provides equivalent or better performance allowing larger application of the Hopkinson technology in the industry.

This work focuses on understanding the impact-initiated combustion of aluminum powder compacts. Aluminum is typically one of the components of intermetallic-forming structural energetic materials (SEMs), which have the desirable combination of rapid release of thermal energy and high yield strength. Aluminum powders of various sizes and different levels of mechanical pre-activation are investigated to determine their reactivity under uniaxial stress rod-on-anvil impact conditions, using a 7.62 mm gas gun. The compacts reveal light emission due to combustion upon impact at velocities greater than 170 m/s. Particle size and mechanical pre-activation influence the initiation of aluminum combustion reaction through particle-level processes such as localized friction, strain, and heating, as well as continuum-scale effects controlling the amount of energy required for compaction and deformation of the powder compact during uniaxial stress loading. Compacts composed of larger diameter aluminum particles (~70µm) are more sensitive to impact initiated combustion than those composed of smaller diameter particles. Additionally, mechanical pre-activation by high energy ball milling (HEBM) increases the propensity for reaction initiation. Direct imaging using high-speed framing and IR cameras reveals light emission and temperature rise during the compaction and deformation processes. Correlations of these images to meso-scale CTH simulations reveal that initiation of combustion reactions in aluminum powder compacts is closely tied to mesoscale processes, such as particle-particle interactions, pore collapse, and particle-level deformation. These particle level processes cannot be measured directly because traditional pressure and velocity sensors provide spatially averaged responses. In order to address this issue, quantum dots (QDs) are investigated as possible meso-scale pressure sensors for probing the shock response of heterogeneous materials directly. Impact experiments were conducted on a QD-polymer film using a laser driven flyer setup at the University of Illinois Urbana-Champaign (UIUC). Time-resolved spectroscopy was used to monitor the energy shift and intensity loss as a function of pressure over nanosecond time scales. Shock compression of a QD-PVA film results in an upward shift in energy (or a blueshift in the emission spectra) and a decrease in emission intensity. The magnitude of the shift in energy and the drop in intensity are a function of the shock pressure and can be used to track the particle scale differences in the shock pressure. The encouraging results illustrate the possible use of quantum dots as mesoscale diagnostics to probe the mechanisms involved in the impact initiation of combustion or intermetallic reactions.