Volume 5, Issue 5 (May 2008)
The Influence of Residual Stresses on the Fatigue Strength of Cold-Formed Structural Tubes
Rectangular hollow sections (RHS) are widely used in load-carrying structures due to their good load transfer behavior and aesthetic form. During fabrication of a cold-formed rectangular hollow section (CFRHS), the concave inside corner surfaces experience significant compressive plastic strains. The resulting tensile residual stresses in the corner region significantly reduce the fatigue strength in some design applications. Sections cut from CFRHSs with two different wall thicknesses were studied using distortion fatigue loading and using X-ray diffraction residual stress measurements. Residual stresses and fatigue strengths were virtually identical for the two thicknesses even though the corner radius to thickness ratio was different. Residual stresses were found to significantly influence those corners subjected to compression-compression loading. Fatigue strength of these corners was improved by a stress relief heat treatment, but the treatment had no significant effect on corners subjected to tension-tension loading.