Impact-induced large elastoplastic damage in fiber-metal laminated panels.

摘要

In this study large elastoplastic damage induced by impact onto fiber-metal laminates (FMLs) were investigated through drop-weight testing and finite element simulations. Two forms of FMLs (GLARE and ARALL) were studied. The main goal of this investigation is to study impact-damage resistance of these novel composites so that they can be designed optimally for engineering applications.; Both destructive cross-sectional microphotography and nondestructive ultrasonic techniques were used to evaluate the damage inflicted by impact. The results indicate that the destructive cross-sectional micrographs give more detailed damage information whereas the nondestructive ultrasonic C-scans can only show the contour of the delamination. For thinner FMLs under lower energy impact, delamination occurs first between the nonimpact-side aluminum-alloy sheet and its adjacent fiber-reinforced epoxy layer; it is followed by visible cracks in the nonimpact-side aluminum layer and, finally, further delamination between the inner aluminum sheets and fiber-reinforced epoxy layers. More severe damages, such as through-thickness fractures, matrix cracking and fiber breakage, occur under higher energy impact. For thicker FMLs, delaminations appeared near the impact-side at relatively lower impact energy. Further damages, including cracks in the outer aluminum sheet and fiber breakage, were induced on the nonimpact-side when higher impact energy was introduced. Many parameters, such as the type of fibers and aluminum, fiber orientations, specimen thickness, impact energy, the size and shape of the impactor and the temperature, had significant effects on the damage patterns.; The finite element code, LS-DYNA3D, was used to perform numerical simulations of low-velocity impact on aluminum/acrylic sandwich panels and GLARE. With the incorporation of proper failure criteria, crack propagation characteristics, nonlinear constitutive laws, and boundary conditions, the computed impact force histories, the post-impact deformed shapes, and damage patterns were found to be fairly close to experimental results.; In this research, the complicated impact damage phenomenon in FMLs and the associated damage tolerance and strength reduction were understood in details. The conclusions obtained by this study should pave way for devising better methodology for optimal design and further development of FMLs.