An Experimental-Cohesive Zone Model Approach to Predict Fatigue Life of Adhesive Joints with Varying Modes of Loading and Joint Configurations for Automotive Applications

Abstract

Predictive fatigue life models of adhesive joints are necessary to enable the assessment of automotive bonded structures while reducing costly experimental testing. However, contemporary models have typically been calibrated for specific joint configurations and modes of loading, limiting their applicability to large-scale structures. Additionally, available models are based on simulation of cumulative fatigue cycling, making them computationally prohibitive. In the current study, fatigue experimental tests were undertaken on adhesive joints in cross-tension (CT) (load angles of 0°, 45°, and 90°) and single-lap shear joint (SLJ) configurations. A total of nine joint configurations, having symmetrical (same material and thickness) and asymmetrical (dissimilar material or unequal thickness) joints, were tested. Fatigue tests at load levels between 25-75% of the static peak load were performed until joint failure or to runout (two million load cycles). The static tests of the joints were simulated to failure using finite element (FE) models with the cohesive zone method (CZM). The maximum fracture energy release rates (Gmax) were calculated within the adhesive bond line at static loads corresponding to the peak loads of the fatigue tests. The Gmax values, computed from single cycle, specimen-specific FE simulations, were correlated with the measured fatigue life (Nf) of the adhesive joints with varying modes of loading and joint configurations. The fatigue life prediction model, based on Gmax − Nf correlation, predicted the cycles to failure for 85% of the fatigue tests, and 81% of the independent validation tests. The proposed fatigue life prediction approach provides computational efficiency and large-scale compatibility.