Multi-objective optimization for designing a composite sandwich structure under normal and 45° impact loadings

With their lightweight character and high energy absorption capacity, composite sandwich structures have attracted increasing attention in the transportation industry. The aim of this work is to present a new approach to investigate and optimize a composite sandwich structure by taking into account both normal and 45 degrees low-speed impact loadings. First, a finite element model considering elastic-plastic, damage, and failure behaviours of the composites by using continuum damage mechanics is developed and validated by a normal low-speed impact test. Second, dynamic effects of normal and 45 degrees impacts on energy absorption and failure behaviours of the composite sandwich structures are investigated. Then, a parametric study is performed to systematically understand the influences of core depth and cell thickness on the impact resistance of the sandwich composite structures subjected to both normal and 45 degrees impacts. In contrast to their metal counterparts, it is interestingly found that absorbed energy generally increases with cell thickness, with a small extent of fluctuation, whereas core depth jumps, and the energy absorption capacity remains almost steady under normal impact but varies irregularly under the 45 degrees impact. Afterwards, a multi-objective optimization is performed to enhance the energy absorption under both normal and 45 degrees loadings. The energy absorption capability of the optimal composite sandwich structure can remarkably be improved by 12.447% for normal impact, and 7.9% for 45 degrees impact. This method provides a new manner and systematic guidance for designing a lightweight composite sandwich structure more practical for engineering application.