Integrating laminate-level bolted joint failure envelope data into connector-based finite element models for composite joint stiffness and failure prediction

A numerical methodology is proposed to determine the 3D failure criteria of directional composite joints, accounting for both in-plane (in-/off-axis) and out-of-plane behavior. The approach involves simulating standard composite joint characterization tests using a high-fidelity, three-dimensional finite element damage modeling strategy. A simplified modeling strategy to simulate multi-bolt joints is then proposed: the joints are simulated using a combination of linear-elastic multilayer composite shell elements and connector elements, which fail once their internal forces intercept the previously determined 3D failure envelope. The methodology is applied to five multi-bolt single lap shear geometries and the results are compared with those obtained using high-fidelity simulations. Results indicate that the methodology developed to numerically determine the bolt failure envelope, combined with the use of connector elements as fastener representatives, is appropriate to accurately simulate the joint stiffness and load ratios in the first failed bolt, and predict first-drop laminate-level failure in composite bolted connections while providing a substantial reduction in computation expenses, establishing their potential for future use in large-scale models.