Prediction Model for Fatigue Crack Growth Rate of Al-Li Alloy Laminates Under Constant-amplitude Load

As a novel aeronautical material, aluminum-lithium alloy laminates combine the excellent impact resistance of metallic materials with the superior fracture toughness and fatigue resistance of fiber-reinforced composites, and have thus been widely applied in aircraft manufacturing. However, their laminated structure leads to complex fiber bridging effects, making it difficult to accurately characterize and predict the crack growth mechanism. To address this problem, this paper proposed a phenomenological model for predicting the fatigue performance of laminates based on metallic fracture performance, and established a prediction model for the fatigue crack growth rate of laminates using the finite element method. First, fatigue crack growth tests under constant-amplitude load with different reference stresses were conducted on aluminum-lithium alloy laminates and comparative analysis was carried out. Second, a bridging coefficient γ correction factor to describe the influence mechanism of bridging effects on crack growth of aluminum-lithium alloy laminates was introduced to improve the Paris formula, and the relationship equation between bridging coefficient and crack length under various constant-amplitude loads was derived. In addition, the Franc3D-Abaqus co-simulation model was employed to calculate the stress intensity factor of the aluminum-lithium alloy monolayer. On this basis, by combining the finite element simulation with the Paris formula, the precise prediction of crack propagation rate of aluminum-lithium alloy laminates under constant-amplitude load was achieved. Finally, the model prediction results were compared with the experimental data, verifying the effectiveness of the proposed prediction model.