Fatigue Life Prediction of Structural Metals under Mixed Mode Loading Condition

In this paper, fatigue life prediction of two types of structural metals, (2024-T4) Al-alloy and (304L) steel alloy under mixed mode loading (prior torsion and cyclic bending) were investigated. The rotating bending fatigue machine (HSM 19) was utilized to implement all the tests which were carried out at laboratory temperature and zero mean stress. Two types of fatigue tests were conducted namely, constant amplitude loading tests leading to constructing the S-N curves with and without prior torsion for the two alloys and variable amplitude loading tests to study the effect of mixed mode loading on cumulative fatigue damage. The second type of tests was conducted according to the (Low-High) test program and block test program. Based on the experimental results, (4) S-N curves were constructed which clearly show the effect of mixed mode on the predicted fatigue life for the two alloys. In addition, the experimental results of mixed mode loading (with prior torsion 20) show that for 2024-T4 Al alloy fatigue lives increase while for 304L Steel fatigue lives decrease. Moreover, the experimental results for cumulative fatigue damage were safe and agree with Miner rule.