In order to evaluate accurately fatigue life of weldments under variable amplitude loading, load interaction effect due to load sequence has to be clarified. A simple case is the fatigue crack growth retardation effect resulting from single or periodic overloads. In the present study, fatigue crack growth rates were measured under single and periodic overload conditions on center-cracked tension specimens of structural steel SS400, SM520B and HT780. Effects of several parameters including overload ratio, stress ratio, yield strength of material and interval between overloads on fatigue crack growth retardation were investigated.
Influence of load interaction on fatigue behavior of highway bridge components under service loading condition is to be clarified for better understanding of variable amplitude fatigue. Fatigue crack growth analyses considering crack closure effect are carried out on non-load-carrying cruciform joints under periodic overload (POL), variable amplitude block loading (BL) and variable amplitude (VA) loading. The analytical results are compared with those of the tests carried out in the past. Crack closure effect exists in most cases, and load interaction effect is significant under POL and BL. However, load interaction effect is insignificant under VA loading.
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