Mean stress effects in fatigue of welded steel joints

Abstract

Mean stress effects in steel weldments were examined under both constant and random narrowband amplitude fatigue loadings. The purpose of these tests was to provide experimental data with which to substantiate the use of analytical expressions to account for mean stress effects. Fatigue tests were performed under both tensile and compressive mean stress levels. Test results indicate agreement with the modified Goodman equation to be favorable in accounting for the effect of tensile mean stresses on fatigue life. However, test results from high fatigue loadings (maximum stresses nominally above half ultimate) were found to possess better agreement with the Gerber formulation than with the modified Goodman one. Behavior under compressive mean stresses indicated a linear correction relationship was required, which was less conservative than any of the relationships considered. Test results obtained under random amplitude fatigue loadings exhibited trends similar to those observed under constant amplitude loadings. This finding, along with supporting analysis, indicates that the same correction relationship can be used in the same manner for both constant amplitude and random (narrowband) amplitude loadings.