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Modern weapon-mounted technologies, such as novel sighting devices, detachable grenade launchers, and telescopic butt stocks, add considerable weight to weapons and alter the center of mass (COM). Currently, few objective studies have investigated the effects of these alterations on soldiers’ rifle handling. The purpose of this study was to examine the effect of weight and weight distribution on upper extremity muscular fatigue during static rifle aiming. Custom testing rigs were designed to allow the weight and COM of the in-service C7A2 assault rifle to be altered using supplementary weights and an adjustable rail system. Seven rifle configurations, each of which represented the weight and COM of a potential future design, were assessed. Soldiers performed static rifle holds with each of the rifle configurations. Upper extremity muscle activity was monitored using surface electromyography (EMG) and a subjective scale of perceived exertion. Dependent measures included muscular activity level (integrated EMG), rate of muscular fatigue (slope of the median power frequency), and subjective ratings of perceived exertion (Borg CR10 scale). The body areas exhibiting the most muscular strain throughout testing were also subjectively assessed using a body map. The results revealed that the muscle activation levels of the supporting arm were substantially greater (>30% increase) when the COM was shifted forward 7cm. This objective finding was supported by the soldiers’ subjective perceptions of muscle effort. Conversely, muscle activity levels did not make evident the effects of added weight; although this may have been largely due to the fact that muscle activity from the lower back was not captured. Rates of muscle fatigue were found to be greater in the anterior deltoid than other extremity muscles and fatigue levels were greater in the supporting arm than the trigger arm. However, using rates of fatigue it was not possible to differentiate between weight conditions and COM positions. Despite the limitations of this study, it has provided a starting point toward developing a standardized protocol for assessing muscular demands during rifle aiming. / Thesis (Master, Kinesiology & Health Studies) -- Queen's University, 2009-09-18 10:24:26.909

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Composite materials have high in-plane mechanical properties, but are susceptible to out-of-plane impact damage. The use of non-destructive evaluation techniques, combined with mechanical testing, was investigated to characterize the progression of post-impact static and fatigue damage of composite laminates. Quasi-isotropic carbon/epoxy specimens were impacted at energy levels of 35 J and 50 J. The initial damage was characterized using ultrasonic C-scan and thermography. Residual strength testing revealed that the compressive static strength of the test specimens was reduced by over 50%. Digital image correlation was used to characterize the growth of damage and the local strain during compression-compression fatigue tests. Initially, no significant statistical trend could be measured when the fatigue data was plotted as a stress-life curve. When stress concentration factors were used to calculate and plot the local stress amplitude, a correlation with fatigue life was observed. The undamaged fatigue data was altered using damage factors which allowed for post-impact fatigue life predictions.

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