Experimental investigation on material properties and residual stresses in cold-formed high strength steel irregular octagonal hollow sections

Abstract

A systematic investigation into the variation of the material properties and residual stress distribution across cold-formed high strength steel (HSS) irregular octagonal hollow sections (IOctHS) is presented in this paper. The specimens were fabricated through welding the two cold-formed half-sections by gas metal arc welding (GMAW). Non-destructive inspection was executed to detect any cracks in the welding internally and externally. Tensile tests on coupon specimens taken from the critical locations within the cross sections were carried out to measure the material properties variation within the HSS IOctHS. The material strength variations within different cross sections exhibit an anticipated similar pattern that strength enhancement at corner regions was more obvious than flat coupons counterpart. The largest strength enhancement is 8.4% at corner region compared with the average yield strength of parent plates, whereas the yield strength and ultimate strength of flat coupon specimens generally fluctuate at a certain level. Based on the obtained material properties, the existing material models for predicting the stress-strain curves were assessed and new material models are proposed to generate the stress-strain relationship for materials within the HSS IOctHS. Moreover, the residual stress measurement for cold-formed HSS IOctHS was performed using the sectioning method. A total of 55 strip specimens were extracted from the cross sections of HSS IOctHS with more than 660 strain readings. Based on the residual stress measurement results, the magnitude and distribution pattern of the residual stresses are presented and discussed. A predictive model for residual stress distribution of the cold-formed HSS IOctHS was developed.