Multiaxial Fatigue Life Assessment of Adhesive Joints Based on the Concepts of Critical Planes: Stress-Based Approaches

Experimental observations show that nucleation and initial fatigue crack growth occur in a critical plane, a material plane with the most severe fatigue damage caused by stresses and strains acting on it. Accordingly, models based on critical fatigue damage plans are appropriate for life estimation of materials specially for metals where their ability to estimate life is mainly between the factor of ±2 and ±3 compared to the experimental results. Despite the successful and extensive application of critical planes technique for life assessment of metals, these methods have been rarely considered for fatigue life prediction of bonded joints. The current study presents an evaluation of the fatigue life estimation capacity of different multiaxial fatigue models based on the critical planes technique and using stress components. Subroutines were developed and used to analyze all material planes and all stress components to find a crack initiation plane where the fatigue parameter is maximum. Different fatigue damage models, including Findley, McDiarmid, Sines, and Crossland, were evaluated and compared using experimental fatigue data obtained at different mode mixities using Arcan joints. Using the calibrated models, fatigue lives of joints subjected to mixed-mode and pure mode loading conditions were estimated. Good agreement between the predictions and the experimental observations were found for McDiarmid, Sines, and Crossland criteria. Despite the lower accuracy in life prediction of the Findley model, it is still a safe method to estimate the fatigue life of bonded joints for mode II and mixed mode.