Fatigue of Welded Cruciforms Subjected to Narrow‐Band Loadings

High‐strength welded steel cruciforms are tested under variable‐amplitude loadings to determine the effect of the root‐mean‐square (rms) of the loading process on the rate of fatigue‐damage accumulation. All variable‐amplitude loadings are narrow‐band and have Rayleigh distributed extrema. The only loading parameter that is varied from one set of experiments to the next is the rms value. Constant‐amplitude tests also are performed to determine the S‐N curve for these cruciforms. Using the constant‐amplitude test results and the Rayleigh approximation method, variable‐amplitude fatigue‐life predictions also are obtained. Comparison of experimental results with analytical predictions indicate that for loadings with relatively high rms values (compared with the specimen's yield strength), the analytical predictions are about twice as long as the experimental fatigue lives. For loadings with intermediate rms values, the analytical predictions generally are in good agreement with experimental results. For loadings with low rms values, the analytical predictions can be twice as long as the experimental results, depending on the interpretation of constant‐amplitude test results in the high‐cycle region.