PREDICTION OF FATIGUE-CRACK PROPAGATION LIFE IN NOTCHED MEMBERS UNDERVARIABLE AMPLITUDE LOADING

One of the interesting phenomenon in the study of fatigue crack propag ation under variable amplitude load cycling is the crack growth retard ation that normally occurs due to the application of a periodic overlo ad. Fatigue crack growth rate under simple variable amplitude loading sequence incorporating period overloads is studied using single edge n otched specimens of AISI 304 stainless steel. Load interaction effects due to single and multiple overload have been addressed. Substantial retardation of fatigue crack growth rate is observed due to the introd uction of periodic tensile overloads. Estimates of fatigue life have b een obtained employing Wheeler model(using Paris and modified Paris eq uations) and Elber's model. Analytical predictions are compared with e xperimental results. Results of these analytical fatigue life predicti ons show good agreement with the experimental fatigue life data. Fatig ue crack propagation rates also have been evaluated from the fractogra phic study of fatigue striations seen on the fracture surface. Good ag reement was found between the experimentally observed crack growth rat es and the fatigue crack growth rates determined by the fractographic studies.