Progressive damage and failure analysis of asymmetrical single-lap composite joints with single-bolt and double-bolt

The present study proposes a combined experimental and numerical approach, aiming at identifying the failure behavior and damage evolution mechanisms of single- and double-bolt asymmetrical composite joints. Three-dimensional finite element (FE) models are developed to simulate the joints, which are validated through quasi-static tensile testing, X-ray micro-computed tomography (micro-CT), and ultrasonic C-Scan examinations. The results indicate that the single-bolt joints fail in a bearing mode, whereas the double-bolt joints exhibit a mixed bearing-tension failure. Comparative results demonstrate that the double-bolt joints present significantly higher stiffness and peak load compared with the single-bolt counterpart. The mechanical response is characterized by three stages, i.e., the elastic one, the damage accumulation one, and the loading drop one. Intralaminar damage progression is analyzed using the validated model, revealing that matrix damage initiation correlates with a nonlinear response and that fiber tensile damage onset potentially serves as a peak load prediction indicator. Interlaminar damage patterns are predicted numerically and verified against experimental observations. The most severe delamination is observed at −45°/0° and 45°/0° interfaces in the single-bolt configuration, and at 45°/0° and −45°/90° interfaces in the double-bolt case. Moreover, the hole deformation of both joint configurations is compared to further elucidate their distinct failure mechanisms.