Study on Fatigue Crack Propagation Behavior of Fiber/Al-Li Laminates Under Typical Overload.

Fiber metal laminates are applied in aerospace equipment due to their excellent crack propagation performance. However, during the service process of fiber metal laminates, the coupling between overload effect and fiber bridging effect makes the crack propagation behavior complex, which makes it difficult to predict. Addressing this issue, the fatigue crack propagation behavior of Fiber/Al-Li laminates under typical overload conditions was analyzed and predicted in this paper. Firstly, based on flight loading characteristics, fatigue crack propagation tests under constant amplitude and single-peak tensile/compressive overload were designed and conducted for Fiber/Al-Li laminates. The crack propagation behavior characteristics under typical overload conditions were analyzed and investigated. Secondly, the influence mechanism of thickness dimensions was revealed based on fatigue crack propagation characteristics under constant amplitude loading. A thickness size effect factor was introduced to improve the equivalent crack length model, where the crack propagation behavior of non-overload stages was simulated. Thirdly, improved Wheeler theory was adopted to characterize the overload hysteresis effect in the hysteresis zone under tensile overload; improved incremental plasticity theory was used to describe crack propagation behavior in the overload zone under compression overload. Finally, based on crack behavior characteristics under single-peak tensile and compressive overloads, the improved equivalent crack length model was combined to establish, respectively, the prediction models on crack propagation behavior under single-peak tensile and compressive overloads for Fiber/Al-Li laminates. Through experimental verification, the overall prediction error rate of the crack propagation model under tensile overload is up to 9.7%, and the overall prediction error rate of the crack growth model under compressive overload is up to 8.1%. Compared with similar models (not found) for thicker fiber metal laminates, the effectiveness and advancement of the proposed model are verified.