Fatigue Behavior and Life Prediction for Argon-Arc Weld Joints Based on Small Crack Methodology

Abstract

Experimental and analytical studies were made on the fatigue behavior and life prediction for argon-arc welded titanium alloy joints, TA15. High cycle fatigue tests at two stress ratios, R=0.5 and 0.06, were carried out on smooth specimens with the argon-arc weld joint located at the specimen center section. Through macroscopic observation and SEM fractographic analysis, it was found that most of the cracks were initiated at weld defects such as voids and inclusions at the edge of weld and in the heat affected zone (HAZ). A small crack methodology based on the plasticity-induced crack-closure concept and the effective stress intensity factor range, ΔKeff , was used to predict the total fatigue life of the weld joints. Large crack growth curve for cracks in the HAZ area was employed as the da/dN-ΔKeff base-line of the TA15 alloy. From fractographic measurements, an average defect size of 100 microns was assumed as the initial small crack size in the life predictions. Predicted total fatigue life by solely considering small crack growth stage agreed well with the experimental data.