Investigation on impact behavior of FMLs under multiple impacts with the same total energy: Experimental characterization and numerical simulation

This paper aims to investigate the low-velocity impact behavior of fiber metal laminates (FMLs) consisting of carbon fiber-reinforced layers and aluminum sheets under multiple impacts with the same total energy. Experimental and numerical methods are implemented to explore the influence of impact energy division, load sequence and metal layer distribution on multiple impact behavior and damage morphologies of FMLs. A series of repeated drop impact tests with different impact energy combinations are implemented on FMLs. Subsequently, an integrated numerical model based on multiple consecutive steps is established to characterize the damage accumulation and failure mechanisms of FMLs, in which a user defined subroutine VUMAT, is developed to consider the stiffness degradation and damage evolution of composite material. The numerical predictions show a good correlation with the corresponding experimental results. The results reveal that multiple impacts with lower energy division and smaller initial impact energy can cause minor damage in FMLs. Generally, the impact load, energy absorption, damage morphologies and the interfacial delamination are closely related to the magnitude, sequence and division of impact energy. In addition, the strain hardening of aluminum sheets after first impact can improve the stiffness of FMLs, and further strengthen the impact resistance significantly.