Experimental Assessment of Low Velocity Impact Damage in 3D Angle-Interlock Woven Kevlar/Epoxy Composite Using DIC Analysis

This study investigates the damage and energy absorption of 3D woven Kevlar/epoxy composites under dynamic impact conditions to clarify their impact resistance. Low velocity impact tests were conducted using a drop weight tester at various velocities. Load-displacement curves and energy absorption results, combined with damage morphology analysis, were used to identify different damage modes and the critical energy for complete penetration. High-speed imaging combined with digital image correlation (DIC) technique was employed to examine the full-field strain distribution and damage evolution during the impact process. An enhanced damage-tracking algorithm was implemented, specifically designed for large out-of-plane deformations and discontinuities and could be broadly applicable to other material systems that undergo large out-of-plane deformations. Results showed that maximum load increased with impact velocity, while bending stiffness remained constant. At lower velocities (1 m/s), elastic behavior with significant rebound was observed, with no delamination or penetration. At 2 m/s, the penetration energy threshold was determined to be 44.3 J, while at 3 m/s, the composite was fully penetrated, showing increased maximum load, displacement, and plastic energy absorption. Higher impact velocities led to longer cracks, with weft cracks consistently exceeding warp cracks in length due to the straight arrangement of weft yarns, which facilitates damage propagation. Microstructural analysis identified fiber fracture, interfacial debonding, and matrix cracking as the main failure modes of the 3D woven Kevlar/epoxy composite. These findings provide valuable insights into the damage mechanisms, strain evolution, and mechanical behavior of 3D woven composites.