A Comparison of the Behaviors of Steel and GFRP Hat-Section Components under Axial Quasi-Static and Impact Loading

摘要

Hat-sections, single and double, made of steel are frequently encountered in automotive body structural components. These components play a significant role in terms of impact energy absorption during vehicle crashes thereby protecting occupants of vehicles from severe injury. However, with the need for higher fuel economy and for compliance to stringent emission norms, auto manufacturers are looking for means to continually reduce vehicle body weight either by employing lighter materials like aluminum and fiber-reinforced plastics, or by using higher strength steel with reduced gages, or by combinations of these approaches. Unlike steel hat-sections which have been extensively reported in published literature, the axial crushing behavior of hat-sections made of fiber-reinforced composites may not have been adequately probed. In the current study, the performance of double hat-sections made of a glass fiber-reinforced plastic (GFRP) is compared with steel hat-sections of similar size under axial quasi-static and impact loading conditions. It has been found that during quasi-static testing, despite the occurrence of multiple brittle failure modes in GFRP-based hat-section components, the overall response displays an extremely healthy trend with progressive crush and a comparable mean load vis-a-vis its mild steel counterpart which undergoes well-known progressive dynamic buckling. The overall load-displacement response of GFRP components under quasi-static loading appears to suggest both failures associated with fiber-reinforced composites as well as geometry-driven instability of local buckling resulting in alternate crests and troughs in load-displacement curve following the initial peak load. When subjected to axial impact loading, the GFRP components gave rise to relatively flat but lower mean loads when compared with corresponding quasi-static response. However, the impact response of a given GFRP component has been found to be stable with respect to the entire range of displacement/shortening and although the load oscillates more rapidly as compared to the load response of a steel hat-section under similar impact condition, the deformed GFRP components appear to exhibit progressive fold formation due to local buckling which is the primary failure mode in steel components. Catastrophic failure modes were not encountered in the tested GFRP specimens which is reassuring in terms of seriously considering such lightweight fiber-reinforced composites for vehicle crash safety design.