Evaluation of Low-Cycle Impact Fatigue Damage in CFRPs Using the Virtual Fields Method

Fiber-reinforced composites subject to low-energy repeated impacts can result in subsurface damage that affects their structural integrity. This paper presents a non-destructive damage evaluation technique for carbon-fiber reinforced polymers (CFRP) using the virtual fields method (VFM). Repeated impacts with an energy of 2 J were performed on 8-ply quasi-isotropic unidirectional (UD) CFRP plates, with a maximum of 2000 impact cycles. Stereo-digital image correlation (DIC) was used to extract surface strains of impacted plates under a static bending load. VFM was then used to reveal gaps in local mechanical equilibrium through a technique known as the equilibrium gap (EG) indicator. VFM successfully captured internal relative damage severity which was corroborated with X-ray computed tomography (XCT). Results showed that specimens with measurable EG signals exhibited considerable interlaminar matrix delaminations and flexural failure, thus effectively using VFM as an indicator for subsurface damage from low-cycle impact fatigue.