Up to 85% of cyclists experience repetitive strain injuries (RSI's). During long bouts of repetitive tasks, muscle fatigue may cause mal-alignments in kinematics, having cumulative effects, leading to an RSI. Purpose: The study's purpose was to examine how changes in localized muscle fatigue relate to changes in movement kinematics in highly trained cyclists throughout a full fatigue protocol. Methods: Seven highly trained cyclists participated in a 2 session experiment. Session 1 included a VO2 max test and familiarization trial and Session 2 was the fatigue protocol. Kinematic angles measured were trunk lean, hip, knee, ankle, and knee splay angle. Mean angle (MA) and range of motion (ROM) was calculated for each revolution thought the trial. Muscles monitored were the quadriceps, hamstring, gastrocnemius, and tibialis anterior. EMG median frequency (MDF) for each muscle was calculated for each revolution by averaging MDF for the two halves of each revolution. Cross-correlation analysis was done on MDF and MA data and MDF and ROM data. Results: All subjects exhibited increases in trunk lean and decreases in ankle angle. Non-monotonic changes were observed in trunk lean, ankle, knee splay angle, and among ROM results for all 5 angles. A 1-tailed T-tests for all subjects, revealed that HAM (p = 0.020) and GAS (p = 0.018) exhibited significant muscle fatigue. One-tailed T-tests yielded significantly negative cross-correlation time lags [Greek small letter tau] for trunk lean MA, ROM, and hip MA. Conclusions: Non-monotonic changes are present in kinematics and MDF. Therefore pre vs. post experimental designs cannot quantify fatigue processes. Shifts in trunk lean MA, ROM and hip MA are significantly correlated with preceding decreasing shifts of MDF (indicative of onset of fatigue). / text

In an effort to improve the fuel efficiency of automobiles, car designers are investigating new materials to reduce the overall vehicle weight. Magnesium alloys are good candidates to achieve that weight reduction due in part to their low density and high specific strength. To support their introduction into vehicle body structures, the dynamic behavior of magnesium alloys must be determined to assess their performance during a crash event. In this work, the tensile high strain rate behavior of AZ31B magnesium alloy sheets was characterized. Two different temper conditions were considered: AZ31B-O (fully annealed) and AZ31B-H24 (partially hardened). Three different sheet thicknesses were considered for the O temper condition, 1.0, 1.6 and 2.5 mm, while the H24 temper was 1.6 mm in thickness. The sheet condition of the magnesium alloys implies an in-plane anisotropy induced by the rolling process. Therefore, both the rolling and transverse directions were investigated in the current research. In order to characterize the constitutive behaviour of AZ31B-O and AZ31B-H24 magnesium alloy sheets, tensile tests were performed over a large range of strain rates. Quasi-static experiments were performed at nominal strain rates of 0.003s-1, 0.1s-1 and 1s-1 using a servohydraulic tensile machine. Intermediate strain rate experiments were performed at 30s-1 and 100s-1 using an instrumented falling weight impact (IFWI) apparatus, and high strain rate experimental data at 500s-1, 1000s-1 and 1500s-1 was collected using a tensile split Hopkinson bar (TSHB) apparatus. Elevated temperature experiments (up to 300°C) were also performed at high strain rates using a radiative furnace mounted on the TSHB apparatus. The tensile experiments show a significant strain rate sensitivity of the constitutive behavior of both the O and H24 temper conditions. The two tempers exhibit an average increase of stress level of 60-65 MPa over the range of strain rates considered. As the strain rate increases, the strain rate sensitivity of both tempers also increases. The strain rate has a different effect on the ductility of the two material conditions. The ductility of AZ31B-O is significantly improved under high strain rate deformations, whereas the AZ31B-H24 exhibits similar ductility at low and high strain rates. Both material conditions presented a strong in-plane anisotropy, with an average stress level in the transverse direction higher than in the rolling direction by 15 MPa and 35 MPa for the O and H24 tempers, respectively. The thermal sensitivity for both tempers at high strain rates was obtained. The two material conditions exhibit a clear thermal softening. From room temperature to 250°C, the loss in strength at 5% plastic strain was found to be 55 MPa and 125 MPa for the AZ31B-O and AZ31B-H24 materials, respectively. The thickness of the AZ31B-O sheets has a mild effect on the measured constitutive behavior. The flow stress increases with increasing thickness. An average difference of 10-15 MPa was seen between the flow stress of the 1.0mm and 2.5mm sheets. However, similar strain rate sensitivity was seen for the three thicknesses. The experimental data was fit to three constitutive models: the Johnson-Cook model, its modified version with a Cowper-Symonds strain rate sensitivity formulation, and the Zerilli-Armstrong model. The three models were evaluated by numerical simulation of the TSHB experiment under various testing conditions. It was found that the Zerilli-Armstrong model was the most accurate in predicting the flow stress of the different material conditions. However, finite element models incorporating the three constitutive fits failed to predict necking in the specimen.

The traditional bridge evaluation process contains uncertainty that affects management decisions. Numerical models require assumptions regarding structural response, and code load models are inherently conservative to ensure uniform applicability. This research investigated how structural monitoring could reduce uncertainty in the evaluation and management process. Targeted instrumentation was implemented on the MacKay Bridge. Controlled load testing was conducted to refine an existing numerical model. Long-term monitoring was completed to compare extreme in-situ traffic effects with the Canadian Highway Bridge Design Code. Throughout the project, accuracy of information collected was a priority; deviation from code recommendations requires absolute confidence in the data. Outputs from controlled testing indicated that the existing numerical model for load distribution and structural response required minimal tuning. Long-term testing indicated that actual load effects are less than code requirements. Results from this thesis show that structural monitoring can reduce uncertainty in structural evaluation and management decisions for infrastructure.

In the past few decades, several researchers have studied the effects of ASR induced expansion in concrete. Several models have been proposed to model the effects of ASR in concrete. While most of these models focus on plain concrete, there is limited amount of research to model the influence of ASR expansion in reinforced concrete. Additionally, the existing models are complex and difficult to implement for practicing engineers. In this study the shortcomings with the existing models are addressed. A minimalist semi-empirical model is developed to represent the degradation of reinforced concrete due to ASR expansion. The model is validated using historical experimental data. Only two key parameters are needed to represent the expansive behavior, specifically, the maximum unreinforced concrete strain due to ASR expansion and the rise time. Mechanical properties of the reinforced concrete are also needed. From the predicted expansions, it is then shown that it is possible to model the number and spacing of cracks of a partly restrained reinforced concrete beam affected by ASR gels. The model is validated with recent experimental results on large scale reinforced concrete specimens. Predictions agree well with the observed number of cracks.

An aging workforce and stressful work environments are major issues potentially impacting the health, and in particular the cardiovascular health of Canadian hospital nurses. No study, to date, has examined the independent and combined effects between the work environment and indicators of cardiovascular risk among female Canadian nurses. The primary goal of this study was to determine if selected work characteristics influences cardiovascular risk profiles. One hundred and forty four nurses from two hospitals participated in a cross-sectional study. Participants completed a questionnaire containing validated measures of job characteristics as measured by the Job Content Questionnaire and the professional practice work environment as measured by the Nursing Work Index (Revised). Indicators of cardiovascular risk were obtained by anthropometric measures, clinical exam and serum sampling. The prevalence of metabolic syndrome, as classified by the NCEP ATP III Panel, was 7.7 % (n = 11) with 31.9 % having waist circumferences > 88 cm; 22% having a systolic blood pressure ≥ 130 mmHG and 15.2% having a diastolic blood pressure ≥ 80 mmHG. There was no statistically significant association between traditional measures of job strain and cardiovascular risk. In stepwise backward regression analyses, higher age, lower perception of autonomy and higher family income accounted for 22% of the variance in waist circumference (p < .001). Higher age and higher physical job demands accounted for 17% of the variance in systolic blood pressure, and 16% of the variance in diastolic blood pressure. Similar to other female studies, there was no significant relationship between psychosocial job strain characteristics, as measured with traditional job strain measurements, and cardiovascular risk. The findings from this study suggest that female nurses are at risk for cardiovascular disease, and that both physical and organizational characteristics of the work environment influence these associations. One may argue that traditional job strain is not unexpected in nursing practice is perhaps less stressful than dealing with high patient acuity, moral distress and hierarchical healthcare organizations. / Thesis (Master, Nursing) -- Queen's University, 2008-07-14 14:09:00.389

This thesis is an exploration of strain, its sources, its manifestation, and how individuals cope with it. The particular scenario under investigation is that of Christian university students in a secular academic environment. Using Agnew’s general strain theory, Goffman’s theory of discreditable stigma, subcultural theory, and recent advances in the study of social capital, the strain experienced by Christian students in a secular university atmosphere was explored. Ethnographic content analysis of on-campus Christian groups, participant observation and semi-structured interviews of 43 Christian university students were used to investigate four postulates: 1. Christian students experience strain as a result of their religiosity on a secular campus; 2. This strain manifests as a discreditable stigma; 3. This strain results in Christian students becoming members of on-campus Christian groups (seeking a subculture); and 4. Memberships in Christian groups provide access to support through social capital. There was evidence to support postulates 1, 2, and 4, while postulate 3 was not supported by the data collected. Strain theory proved to be a useful concept for understanding how Christian students interacted with their secular environment. The data suggest that the university atmosphere was challenging to their beliefs both inside and outside the classroom. Christian students also indicated that they often censored themselves in front of their colleagues and peers and did not feel comfortable disclosing their Christian beliefs to new friends. The reason given for this was more time was needed in order to quell certain negative assumptions and stereotypes that non-Christians may have about Christians. This description is suggestive of Goffman’s concept of discreditable stigma, in that stigmatized persons attempt to “pass” so that their stigma (Christianity in this case) will not prejudice current and future encounters. Students did not join Christian groups as a way to cope with the strain they felt within academia, as many students joined these groups upon entry into university (rather than joining after encountering strain). It was found that students experienced benefits from membership within Christian groups, demonstrating the utility of social capital (i.e., network of support) as a conceptual framework. / Thesis (Master, Sociology) -- Queen's University, 2008-09-19 14:43:51.989

No description available.

Large strain tensile tests were carried out on OFHC Cu and 99.99% Al with the aim of determining the first and second order work hardening and rate sensitivity coefficients. The tests were performed at room temperature and 473 K and at constant true strain rates in the range 5 x 10('-4) to 10('-1) s('-1). With the aid of a diameter transducer, which was set up to measure and control the rate of reduction of the diameter of the tensile specimen, the strain rate at the minimum cross-section was held constant well beyond the point of maximum load. A second diametral sensor was constructed for use at elevated temperatures. In order to extend the range of conditions covered, constant strain rate compression tests were also performed on Cu at 698 K. In a further series of experiments, tensile tests were carried out on Cu and Al samples at 293 and on Al specimens at 473 K in which the flow localization process was followed by photographic means. / It was observed that the values of the rate sensitivity of the work hardening rate B(,(sigma)) beyond the maximum load are not negligible, but that they are less than 1, in opposition to the theoretical predictions of Kocks et al('(47)). Furthermore, it is shown that, contrary to the suggestion of these workers, the rate sensitivity at constant work hardening rate N is not the material coefficient that controls the growth of strain rate gradients at large strains. / The material coefficients determined using the diametral transducer were employed for the numerical integration of the second order differential equation describing flow localization proposed by Kocks et al('(47)). This equation was integrated at the minimum cross-section of the sample, and the solution is compared with the one calculated by integrating the first order differential equation proposed earlier by Jonas et al('(10)). As expected, the strain measurements obtained from the flow localization experiments are reproduced more closely by the second order solution than by the first order one largely because of the non-negligible values of B(,(sigma)). However, at large deformations, there is a discrepancy between the experimental observations and the predictions of the second order theory. This is attributed to the development of triaxial stresses at these strains. A possible modification of the second order treatment is suggested, based on the gradient in the Bridgman correction term.

This thesis focuses on the high strain rate behavior of Maraging steel 300, High Hardness Armor (HHA) and Aluminum 5083 – H131 Alloy. These materials are used by the Department of National Defense (DND) of Canada as armor plate materials in military applications. The aim of the research is to investigate the dynamic shear-strain response of these armor materials at high strain rate loading to study the occurrence of Adiabatic Shear Bands and the subsequent failure. The effects of impact momentum and strain rates on the dynamic stress-strain curve and on the adiabatic shear failure of these armor materials under impact and torsion loading need to be investigated to evaluate their capability to withstand military conditions.

This dissertation examines the response of piezoelectric material strain to electron flux influence. A plate of PZT5h is prepared as the specimen. The positive electrode is removed, and the negative electrode is connected to a power amplifier. Sixteen strain gages are attached as the strain sensor. The specimen is placed in a vacuum chamber, then the positive side is illuminated by electron beam. The characteristic of the static strain response is predicted by deriving the equation strain/deflection of the plate. Two methods are used, the Electro-Mechanical Equations and numerical analysis using Finite Element Method. The settings of the electron gun system (energy and emission current), along with the electric potential of the negative electrode (back-pressure), are varied to examine piezoelectric material responses under various conditions. Several material characteristics are examined: current flow to and from the material, time response of material strain, charge and strain distribution, and blooming. Results from these experiments suggest several conditions control the strain development in piezoelectric material. The current flow and strain on the material is stable if the backpressure voltage is positive. As a comparison, the current flow is small and the strain drifts down if the backpressure voltage is significantly negative. The material needs only 1 second to follow a positive step in backpressure voltage, but needs almost 1 minute to respond to a negative step backpressure change. This phenomenon is a result of secondary electron emission change and the energy transfer from the primary electrons to the local electrons on the material. The time needed to achieve steady state condition is also a dependent of emission current. After a period of time the primary electron incidence induces strain throughout the 7.5-cm-by-5-cm plate despite the fact that the beam diameter is only 1 cm2. One possibility is blooming due to electron movement under intense electric fields in the dielectric material.