A study on the effect of different Paris constants in mixed mode (I/II) fatigue life prediction in Al 7075-T6 alloy

Abstract

Mixed-mode (I/II) fatigue crack growth experiments in Al 7075-T6 alloy have been performed using a newly proposed single edge cracked circular (SECC) specimen. An equivalent stress intensify factor (ΔKeq) model based on the generalized MTS criterion (GMTS) has been tested for the first time for mixed-mode fatigue crack growth rate correlation and prediction of the fatigue life. Along with this proposed model, other widely used ΔKeq models have also been considered to study the effect of Paris constants on the fatigue life prediction. Three different mode mixity configurations (30°, 45°, and 60°) have been considered for experiments with multiple specimens to study the reproducibility aspect. With the help of detailed fatigue crack growth finite element simulations and experimental results, the performance of the various ΔKeq models has been tested in terms of correlation with the fatigue crack growth rate and prediction of the fatigue life. The results of the present investigation show that using the mixed-mode Paris constants along with Tanaka’s and Richard’s ΔKeq models accurately and consistently predicts the fatigue life compared to other Paris constants. The GMTS criterion has been shown to exhibit excellent performance in the prediction of crack growth path and thus signifies the importance of T- stress under mixed-mode fatigue loading. Additionally, the results of the present investigation establish the potential application of the SECC specimen for mixed-mode fatigue crack growth studies of metallic materials. Furthermore, fractographic studies also confirm the experimental observations in Al 7075-T6 alloy.