Overload effects on fatigue behaviour and life prediction of low-carbon steels

Abstract

Experimental results of overload effects on the fatigue life and the fatigue crack initiation life of low- carbon steels are summarized and a life prediction model under variable-amplitude loading is put forward in the present paper. Test results show that overload has no marked effect on the fatigue crack initiation (FCI) life of notched elements and butt welds in low-carbon steels with non-continuous strain-hardening characteristics, but decreases the fatigue life of smooth specimens of low-carbon steels. This means that the overloading effect factor z = 0 for notched elements and butt welds in low-carbon steels and z < 0 for smooth specimens. Consequently, the interaction between loads in the load spectrum or/and the load sequence effect should be taken into account in the life prediction of smooth specimens under variable-amplitude loading. For notched elements and welded elements, the original expression of the FCI life and Miner's rule can be used directly to predict the FCI life under variable-amplitude loading without the need to take into account the interaction between loads in the load spectrum, because z = 0. When the FCI life occupies the major part of the fatigue life of the notched elements, the original fatigue life expression and Miner's rule can be approximately used to predict the fatigue life of notched elements under variable-amplitude loading. The above-mentioned life prediction model has been checked by the test results.