Comparing the Impact Response of 3D Fiber Reinforced Foam Core with Monolithic Foam Core in Composite Sandwich Structures

摘要

Foam core composite sandwich structures are sensitive to impact damage. Barely visible impact damage (BVID) is especially alarming because it may lead to a significant decrease in strength without visible indication. This research is to determine the impact energy that will cause BVID in 3D fiber reinforced foam core (3DFRFC) panels and to compare the impact damage relative to panels with monolithic foam core. This is accomplished by performing impact experiments with 100 J, 70 J, and 50 J impact energy levels, then using nondestructive evaluation (NDE) techniques to identify the damage. A drop weight impact testing machine measures the reaction force, energy, and velocity of a steel impactor. The damage is characterized by post-impact inspections, using a profilometer to characterize the surface deformations, and using micro-CT scans to detect internal damage form and reinforcing fibers. Post-impact inspections consisted of visual, tactile, and tap tests, and generated inspection criteria to be used in the field to quickly diagnose impact damage and to determine whether further inspection is warranted. Micro-CT scans identified fiber compressive failure, slight foam crushing, and pin feet disbonding in 3DFRFC panels; and foam crushing, conical shear cracking, and radial cracking in the foam core.