Estimating the orientation of crack initiation planes under constant and variable amplitude multiaxial fatigue loading

This paper investigates the accuracy of the shear strain Maximum Variance Method (γ–MVM) and Maximum Damage Method (MDM) in predicting the orientation of crack initiation planes under both constant and variable amplitude multiaxial fatigue loading. The γ–MVM defines the critical plane as the plane on which the variance of the resolved shear strain reaches its maximum value. In contrast, a specific multiaxial fatigue criterion is needed to be used along with the MDM to predict the orientation of the critical plane under multiaxial fatigue loading. As far as variable amplitude multiaxial loading is concerned, the MDM have to be used by applying with a certain fatigue criterion, a cycle counting method and a cumulative damage rule. In this paper, the MDM is applied with Fatemi & Socie’s criterion, Bannantine & Socie’s cycle counting method and Palmgren-Miner’s linear rule. The MDM assumes that the critical plane is the plane experiencing the maximum accumulated damage. Experimental data for several metals tested under constant and variable amplitude multiaxial fatigue loading taken from literature are used to assess the accuracy of these two methodologies. The results show that the predictions made by both the γ–MVM and MDM have good accuracy for the investigated materials and investigated load histories: 90% of the predictions made by the γ–MVM and 80% of the predictions made by the MDM fall within a scatter band of 20%.