Investigations on material properties and residual stresses in cold-formed high strength steel irregular hexagonal hollow sections

This paper presents an experimental investigation on the material properties variation and residual stress distribution within the cold-formed high strength steel (HSS) irregular hexagonal hollow sections (IHexHS) with two different fabrication methods. The test specimens were manufactured through press-braking and gas metal arc welding (GMAW). Tensile coupons tests were conducted on specimens fabricated from the critical locations within cold-formed HSS irregular hexagonal hollow sections, namely the flat portions, corner portions of either half or quarter sections. New material models to predict the material properties for the tensile coupons with both rounded responses and yield plateau followed by significant strain hardening were proposed. In conjunction with conventional tensile coupon testing, non-contact digital image correlation (DIC) measurement through which strain fields along the gauge length before and after the occurrence of diffuse necking was carried out to obtain the accurate strain field after necking. Moreover, the residual stresses measurements for HSS IHexHS were also performed, membrane and bending residual stresses distributions on the investigated sections were measured in longitudinal directions with 59 strips cut by wire-cutting method and more than 708 strain readings obtained. Results of the residual stress distributions and magnitudes are presented and discussed. Based on the measurement results, predictive models for residual stress distribution were developed and can be subsequently applied for predicting structural behaviour of the cold-formed HSS IHexHS.