Failure analysis of single-lap composite joints considering drilling-induced defects

To address the influence of drilling-induced defects on the mechanical properties of the joints, a finite element model of composite bolt joints considering drilling-induced defects is proposed. Ultrasonic testing and finite element methods were employed to characterize the damage around the holes in the laminates, and a damage area around holes with mechanical properties degradation was established. Based on the characteristics of biaxial fabric materials, a VUMAT failure subroutine for orthogonal fabrics using the 3D Hashin failure criterion was developed. The failure behavior of a single-lap carbon fiber reinforced vinyl ester composite joints considering drilling damages was calculated by simulation, and verified by experimental test. The result shows that, for the single-lap composite joints, compared to the undamaged FE model, the FE model considering drilling damage showed closer alignment with test data in joint failure, and the load-displacement curve fitting demonstrated significantly superior performance. With only 4.4% error in failure load, the failure displacement error was reduced by 64.1%, the root mean square error was only 1.08 kN, and the coefficient of determination was 92.0%, which is very close to 1, effectively enhancing simulation accuracy.