Residual stresses in cold-formed square hollow section of high strength steel

In this study, the residual stresses were experimentally studied for cold-formed square hollow section (CFSHS) with dimensions of 150x150x10mm. The residual stresses were measured in both longitudinal and transverse directions for S355J2H/S420MH and S700MLH tubular sections. The results showed that measuring the longitudinal residual stresses on the outer and inner surfaces at a distance of 60−70 mm from the end of the tubular specimen is an accurate and convenient method. For both steel grades studied, the highest residual stresses on inner and outer surfaces were on the flat regions close to corners. On the face opposite to the weld seam, the residual stresses scattered clearly among different repetition tests and differed from values reported in the literature. The influence of the steel grade on the residual stresses was more observable on the faces with the weld and opposite to the weld. As on the face with the weld, the combined effect of cold forming and temperature affect residual stresses, it is recommended to quantify residual stresses separately for the face with the weld and other faces. In the flat regions, the longitudinal residual stresses were so dominating that the transverse residual stresses can be neglected. The scatter of the longitudinal residual stresses on the face opposite to the weld and the irregular values of the transverse residual stresses in the corners indicate that additional tests are needed to quantify the randomness characteristic of local residual stresses.