New Insights into the Impact Erosion Response of Glass Fiber-Reinforced Polymer Composites

The leading edges of helicopter rotor and wind turbine blades, largely made of fiber-reinforced polymer composites, are susceptible to impact from small particles of a variety of materials at velocities up to the speed of sound. To ensure structural integrity of these blades over their life spans, it is essential to fundamentally understand how these impacts damage, and subsequently erode, the blade material and structure. However, experimental investigations of single particles at impact velocities simulating realistic impact conditions are scarce. This study is designed to observe the local crater formation process from a single particle impact at the upper limit of rotor tip velocities to identify the key erodent parameters behind the damage mechanisms in a polymer composite. It is also aimed to further examine damage mechanisms in a plate sample to determine the extent of material loss and global deformation of the impact surface. In experiments presented, a glass fiber-reinforced epoxy composite was subjected to single impacts from spherical particles at velocities up to Mach 1. A specifically designed light gas gun was used to launch particles at relevant velocities. Target configurations were selected to examine the highly localized crater formation process and to measure the global deformation of a target plate subjected to high-velocity impact by spherical particles 1.59 mm in diameter. The crater formation processes from impacts by particles of five different materials were evaluated by high-speed in-situ imaging as well as post-mortem inspection with a scanning electron microscope. The global deformation of a target plate was examined in-situ using stereo DIC and post-mortem using optical profilometry. The composite in this study was found to exhibit brittle fracture behavior during the crater formation process at the local level, with ductile behavior observed at the global scale in a plate sample. The formation of the crater in the target material was found to follow a two-stage process from a single impact event. The first stage creates a debris cloud at the perimeter of the impact site, with a very consistent outer diameter across all five projectile materials. In the second stage, material at the center of the crater is removed from the target as the loading wave reflects off the free boundary after the projectile has separated from the target. The second stage behavior depended on two distinct projectile groups: those that experienced plastic deformation on impact with the target material and those that did not undergo any apparent plastic deformation. A GFRP composite with a small yarn, plain weave reinforcement structure was found to exhibit anisotropic flexural wave propagation near the impact site. This degree of anisotropy is reduced as the wave propagates further from the impact site. These results add new insights into a comprehensive fundamental understanding of impact damage and erosion mechanisms in fiber-reinforced polymer composite materials and structures.