Abstract

The current study aims to evaluate the application of the CZM technique in low-cycle impact fatigue (LC-IF) life analysis of bonded structures by considering the cohesive properties changes with impact loads. Accordingly, a progressive damage model based on the CZM technique was proposed to predict the LC-IF life of bonded joints subjected to pure shear and mixed mode impact loading conditions. The model is also able to simulate the residual strength of the joints subjected to impact load cycles. In this regard, the developed customized bilinear CZM was implemented in Abaqus using a user material subroutine (UMAT). Experimental data obtained out of LC-IF tests carried out on end-notched flexure (ENF) specimens and single-lap joints (SLJs) were employed to validate the proposed progressive traction separation law. A MATLAB code was also developed to simulate the repetitive LC-IF cycles and take into account changes in the mode II fracture energy GIIC and in the maximum traction Tmax, both as a function of impact cycles. The proposed approach was then evaluated and validated using experimental results obtained by testing ENF joints. According to the observations, adhesive's fracture energy and shear traction decrease by impact cycles. The results show that the developed numerical approach is capable of evaluating the adhesive joints' LC-IF life under pure mode II impact loading cycles and at different impact energy levels. Following the same FE approach in ENF specimens for mixed-mode loadings, the LC-IF life of SLJs were investigated by developing a modified degradable mixed-mode CZM. The model was successfully compared to the empirical results.