On crashworthiness design of hybrid metal-composite structures

Abstract

As a class of promising cost-effective lightweight structures, metal-composite hybrid structures has rapidly emerged in automotive industry largely attributable to their outstanding multifunctional and crashworthy characteristics. Recently, continuous efforts have been devoted to the studies on the crashworthiness of various hybrid tubes, which commonly present two typical configurational schemes, namely metal-composite (i.e. a metal outer tube internally filled with an inner carbon fiber reinforced plastic (CFRP) tube) and composite-metal (i.e. an outer composite tube internally filled with an inner metal tube). Nevertheless, rather limited studies have focused on revealing energy absorption mechanisms of hybrid structures; and how to optimize the performance to cost characteristics of hybrid structures still remains an open question in literature to date. This study aimed to maximize the energy absorption of different configurational aluminum/CFRP hybrid tubes. First, the finite element (FE) models were developed and validated by comparing the damage modes and crashworthiness indictors with the dedicated experimental study. Second, the interactive effects of the hybrid tubes were investigated by analyzing the discrepancies in the deformation pattern and internal energy absorption of each material through the validated FE models. For the AL-CF configuration (i.e. CFRP inner tube with aluminum outer tube), changes of deformation mode increased the internal energies of aluminum and CFRP tubes by 43.6% and 17.8% compared to the net aluminum tube and net CFRP tube, respectively; and increased the frictional dissipation energy by 45.6% compared to the sum of that of net aluminum and net CFRP tubes, largely enhancing energy absorption of AL-CF. For the CF-AL configuration (i.e. aluminum inner tube with CFRP outer tube), the internal energy increased by 27.6% for the aluminum tube but decreased 31.9% for the CFRP tube compared to the net aluminum tube and net CFRP tube, respectively; whereas the frictional dissipation energy decreased by 47.6% compared to the sum of that of net aluminum and CFRP tubes, indicating the vital importance of hybrid configuration to energy absorption. Third, the effects of wall thickness, sectional dimension and sectional shape on the energy absorption capacity as well as the performance-cost characteristics of the hybrid tubes were further studied. It was found that from a performance perspective, the hybrid tube with a thicker CFRP tube had higher capacity of energy absorption; whilst from a performance to cost perspective, the hybrid tube with a thinner aluminum tube offered better cost-effective energy absorption characteristics. Moreover, with the same weight, the hybrid tube with a circular sectional shape and a smaller sectional size exhibit a better performance. Finally, a multiobjective discrete optimization was conducted to optimize the AL-CF hybrid tube with various sectional shapes, sizes and wall thicknesses. As a result, the weight, peak crush force (PCF) and cost were finally reduced by 41.3%, 18.0% and 11.2% respectively, while the energy absorption (EA) was enhanced by 48.0% in comparison with the baseline design.