Reanalysis of Fatigue Life Assessments of Butt Welds

Abstract

A whole-life fatigue model has been developed and successfully applied to notched specimens, welded components, and threaded pin/box connectors. The predicted fatigue-life results agree very well with the experimental data. The model nonarbitrarity defines the crack initiation size, a1, thereby, nonarbitrarily joins the fatigue-crack initiation life, N1, and the fatigue-crack propagation life, N(subscript P), estimates to give the total fatigue life, N(subscript T). A previous work has shown that the fatigue-life predictions for the double-V, butt-welded specimens of A36, A514 Grade B, A537 Class 1, and A572 Grade 52 steels agree very well with the testing results. The monotonic, cyclic, low-cycle fatigue (LCF), and fatigue- crack propagation rate (da/dN) data of base metal (BM), heat-affected zone (HAZ) and weld metal (WM) were measured and input to computation to account for the actual weldment microstructure. However, it is very often infeasible or impractical to destructively measure these monotonic, cyclic, LCF and da/dN data from the welded structural members. In many cases, the unwelded BM plate is the only material from which we can measure these data. In addition, these measurements are very time-consuming and costly. If the life predictions using only the BM data could give reasonably good results, this whole-life fatigue model would be very useful in fracture control of the welded structures. In this study, the life predictions are made again for the same double-V, butt-welded specimen assuming that the BM, HAZ and WM have equivalent properties.