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° 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° 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° 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° impact. Afterwards, a multi-objective optimization is performed to enhance the energy absorption under both normal and 45° 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° impact. This method provides a new manner and systematic guidance for designing a lightweight composite sandwich structure more practical for engineering application.