Evaluation of Impact Damage to Carbon Fiber Composites by Using an Epoxy Indicative Coating

ABSTRACT For composite materials, it is difficult to observe the internal damage after low‐energy impact, which requires a simple and efficient method to identify hazards. Compared with the traditional expensive and complicated non‐destructive testing techniques, this paper proposed a new method for internal damage detection by using an epoxy indicative coating (EIC). Specifically, an epoxy resin coating was bonded to the surface of carbon fiber reinforced epoxy composites to indicate the impact sites and to evaluate the internal flaws. Composite laminates with indicative coatings were subjected to impact tests with different impact energies, which were simultaneously simulated by ABAQUS finite element analysis. The simulation and experimental results were in good agreement and showed that the increase in the degree of internal damage to the laminate was accompanied by the expansion of cracks on the EIC, which included an increase in the number of cracks, the maximum damage radius, and the damage area. The established correlation between the relative residual strength and ultrasonic C‐scan results of the impacted laminate structure with the coating damage metrics confirmed that it was possible and convenient to quantitatively evaluate the mechanical properties of the composites by using the indicative coating.