To complement the present research results in the field of fatigue and fracture in elastomers, an analysis of the influence of curing time and mold temperature on the fatigue properties of a carbon black-filled industrial NBR compound was carried out. There was a significant difference in the crack growth rate with respect to the different manufacturing conditions.
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Recycling of plastic packaging waste is a promising approach towards a circular economy due to the high amount used and the short application time. This paper uses the concept of environmental stress cracking resistance (ESCR) to investigate the fatigue behavior of recycled yogurt cup materials. As test environments air and oil where chosen, where the latter imitates the fatty structure of yogurt. Therefore, four fractions of manually sorted post-consumer polypropylene yogurt cup waste was shredded to flakes and washed with different temperatures and media. Additionally, one of these fractions was blended with varying amounts of virgin pipe material. Furthermore, the reference material, which is currently used for yogurt cups was tested for comparison. Various influences of the fatigue tests were detected, which are a more pronounced influence of oil than of air, especially for recyclates but also for virgin materials and a significant improvement of the recyclates which were blended with a pipe grade material.
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The impact response of a composite material is dependent on its microstructure. This study examines the effect of particle size and impact velocity on the temperature rise and strain rate in a composite material containing Ammonium Perchlorate (AP) crystals and Hydroxyl-terminated polybutadiene (HTPB) binder by combining computational and experimental work. Samples of AP-HTPB composite, with AP crystal sizes of 200 and 400 μm, respectively, are impacted at velocities ranging between 5-10 m/s. A volume fraction of 70-80% AP is maintained in each sample.
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The operability of a composite solid propellant is compromised by the presence of cracks, with origin in natural or mechanical ageings. These cracks may cause uneven burning of the propellant leading to a malfunction of the motor or in the worst scenario an overpressure burst. The propellants are characterised by an heterogeneous microstructure, due to many distinct components with very complex and different mechanical performance. Nevertheless, the mechanical behaviour of these propellants is mainly controlled by the elastomeric matrix, the properties of which exhibit a strong time dependence. Therefore, this paper uses Viscoelastic Fracture Mechanics analysis to establish the influence of the mechanical and oxidative ageings on the structural integrity of a booster composite solid propellant, based on a carboxyl-terminated polybutadiene binder reinforced with ammonium perchlorate oxidizer particles.
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The fatigue crack growth mechanisms in polymer electrolyte membranes of fuel cell are investigated under single overload conditions. In-situ SEM testing and in-situ optical microscopy testing combined with digital image correlation technique are conducted. The results show that the residual stress dominates the fatigue crack growth after the application of small overload cycle leading to subsequent fatigue crack growth retardation while larger overload cycle causes crack tip sharpening, resulting in fatigue crack growth retardation reduction or even acceleration.
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