Repetitive impact exposure and characterization of stress-whitening of an American football helmet outer shell material

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• 作者：D.E. Krzeminski^a ; ^b ; ^{david.krzeminski@eagles.usm.edu" class="auth_mail" title="E-mail the corresponding author} ; B.M.D. Fernando^a ; G. Curtzwiler^a ; T.E. Gould^b ; S.G. Piland^b ; J.W. Rawlins^a
• 关键词：Stress-whitening ; Rubber-toughening ; American football helmet ; Outer shell degradation ; Impact performance
• 刊名：Polymer Testing
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：55
• 期：Complete
• 页码：190-203
• 全文大小：2454 K

文摘

Mechanical stress exerted upon impact-modified polycarbonate (PC) and poly(ethylene terephthalate) (PET) blends has been reported to generate microscopic voids via rubber-toughener (RT) particle cavitation which can macroscopically manifest to visibly whiten the material. Previous work has revealed a whitening phenomenon in collegiate American football helmet outer shells after a single season and in helmet-grade plaques following linear impact testing. The purpose of this research was to quantify the effects of repetitive linear drop exposures on the (i) impact performance; (ii) physical and thermal properties; and (iii) surface and tensile mechanical properties of a stress-whitened American football helmet outer shell material. Statistically significant changes in plaque impact performance corresponded to substantial stress-whitening that penetrated up to 40–45% into the plaque thickness and elicited shifts in surface and tensile mechanical properties. Nanoscale microscopy revealed elongation of the PC/PET matrix and delamination at the RT-matrix interface. Thermal property analysis suggested the concomitant occurrence of RT cavitation and strain-induced PET crystallization. Overall, the research identified a battery of diagnostic tools to characterize material property changes of stress-whitening in rubber-toughened helmet outer shell materials.