Improvement of Weld Fatigue Resistance
by
S. T. Chang
Department of Metallurgy and Mining Engineering
and
F. V. Lawrence, Jr.
Professor of Civil Engineering and Metallurgy
Abstract
An analytical model was developed to predict the effect of post-weld treatment on weld fatigue resistance: shot-peening, high powered laser dressing and TIG dressing of the weld toe were studied.
Macro- and microstructural examinations were conducted to characterize microstructures, microhardness, toe geometries and fatigue crack initiation sites resulting from each of the post-weld treatment.
Residual stresses at shot-peened weld toe were estimated from empirical relationships and confirmed by X-ray measurements. A model was developed to estimate the stress concentration factor (Kt) for TIG and laser-dressed toe geometries with undercut. Most fatigue properties were estimated from hardness measured at the region of interest. Bending stresses were considered in the prediction of both the crack initiation and crack propagation life.
Fatigue tests of as-welded and post-treated ASTM A514/E110 and A36/E60S butt weldments were conducted to verify the analytically predicted total fatigue lives. The agreement between analytical predictions and experimental results were quite good. Utilizing the current fatigue crack initiation-progagation model, a general equation was established to calculate fatigue strength (Sa) from base metal tensile strength (S u (BM)) for several post-treated weldments. To do this, several empirical relationships were found between Su (BM) and the necessary material properties. Predicted S0 size=”2″>a was compared with empirical data from open literature and good agreement was obtained.
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