Numerical simulation of bolt-bearing behavior of hybrid CFRP–steel laminates at low temperature

Local metal hybridization with steel plies offers an effective route to improve the bolt-bearing performance of CFRP structures. This study develops and validates a finite element framework for hybrid CFRP–steel bolted joints, with emphasis on the role of thermal residual stresses and delamination. The modeling approach is validated against a comprehensive set of bolt-bearing tests at 23 °C and -55 °C, demonstrating accurate reproduction of load-displacement curves up to 4% elongation in monolithic CFRP and up to 10% in hybrid laminates. Analysis of reinforcement mechanisms shows that steel plies relieve stress in the composite, delay damage initiation, and confine damage within composite stacks, thereby increasing the load bearing capacity of the joint. Geometry studies further reveal the correct prediction of failure mode transitions with decreasing specimen width, indicating a critical width-to-diameter ratio of 4-5 for QI-FML joints. The validated framework thus provides predictive capability and mechanistic insight for design and virtual testing of aerospace joints.