The Effect of Residual Stresses on Weld Fatigue Life
by
J. D. Burk
F. V. Lawrence, Jr.
Department of Metallurgical Engineering
Abstract
In this investigation a model was developed which predicts the influence of residual stress and stress ratio on the total fatigue life of a weld. The total fatigue life of a weld was considered to be composed of both crack initiation and crack propagation. Residual stresses were considered to influence the crack initiation life but not the crack propagation life.
The crack initiation life was estimated by a damage integral method developed from cummulative damage concepts. Actual weld material properties (weld metal and heat affected zone) were considered in the initiation life estimation. Neuber’s rule was used to determine the local cyclic stress-strain behavior at the weld toe, and the fatigue notch factor was evaluated using Peterson’s equation. Residual stresses were introduced into the analysis as a simulated prestressing of the weld. Cyclic relaxation of the mean stress established during the set-up cycle was modeled by a power function and allowed relaxation to be considered in life estimates.
Fatigue tests of ASTM A514 grade F/E110 and ASTM A36/E60S-3 steel weldments and ASTM 5083-0/5183 aluminum butt welds having tensile and compressive residual stresses were conducted to verify the analytically predicted total fatigue life predictions. Agreement between analytical predictions and experimental results were quite good in most cases. The total fatigue life model was extended to investigate the influence of stress relief and stress ratio on fatigue life for the three different welded material considered.
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