An experimental and numerical investigation into the low velocity impact response of GLARE subjected to bi-axial preloading

This study investigates the effect of bi-axial preloading (tension and compression) on the low velocity impact behaviour of GLARE (GLAss REinforced laminate) through both experimental testing and numerical simulations. In this study, a bi-axial preloading apparatus has been integrated into a conventional drop-weight impact system, coupled with high-speed three-dimensional digital image correlation, to quantify the full-field deformation profile of the plate. The experimental results demonstrate that tensile preloading enhances the stiffness of the laminate as well as the maximum impact load, but reduces the out-of-plane displacement, the impact duration and the overall level of energy absorption. In contrast, compressive preloading results in effects that run counter to those mentioned above. A finite element model involving a user-defined subroutine VUMAT has been developed, which successfully reproduced the failure modes in the preloaded panels. Discrepancies between the experimental and numerical predictions were within 13 %. The numerical analysis revealed that preloading modifies the damage modes within the laminates, wherein tensile pre-loading reduces delamination, but increases the level of fibre and matrix damage. In contrast, under 7.5 J impact energy, compressive preloading induces a more complex response, i.e. Al-GF debonding is reduced, whereas GF-GF delamination is enhanced. The net effect is dominated by the debonding reduction, resulting in an overall decrease in total delamination. Further, preloading leads to a redistribution of the in-plane stresses, thereby influencing the ability of the FMLs to absorb and dissipate impact energy, it also changes the impact response and damage characteristics of the GLARE laminates. It is believed that the current study provides an insight into the impact response of pre-stressed hybrid materials.