Experimental and numerical study of sandwich beams with layered-gradient foam cores under low-velocity impact

The low-velocity impact response of sandwich beams with aluminum alloy face-sheets and three core configurations (i.e., the positive layered-gradient core, negative layered-gradient core and non-gradient monolithic core) was first investigated by using a drop-weight machine. The impact bending tests were performed on specimens at five impact energy levels - 9.80 J, 22.05 J, 39.19 J, 61.24 J and 88.18 J - by varying the drop height of the weight. Based on experimental results, the corresponding numerical simulations and a multiobjective design optimization were performed. The experimental results show that all sandwich beams fail via the global bending deformation without local crack/fracture under lower initial impact energy, while they fail via larger bending deformation accompanied by obvious core tensile crack at mid-span and core shear at clamped ends with the increased initial impact energy. The resistance of both gradient core sandwich beams to impact flexure loading is weaker than that of non-gradient monolithic core sandwich beams. Simulation results indicate that the ratio of energy absorbed by core decreases with the increased impact energy, while the ratio of energy absorbed by face-sheets increases with the increased impact energy. The boundary condition is demonstrated to have great influence on the force-displacement response for all sandwich beams. Finally, the corresponding Pareto fronts representing a group of best trade-off designs were obtained.