Material properties and residual stresses of cold-formed high-strength-steel circular hollow sections

Owing to the development of material processing technologies, high strength steel plates with yield strengths exceeding 460 MPa are commercially available at present. However, experimental investigations on material properties and residual stress distributions of cold-formed high strength steel circular hollow sections (CHSs) are rather limited. This paper therefore presents an experimental investigation to advance the knowledge in this area. In total, 11 steel circular hollow sections were manufactured from steel plates with the measured yield strength varying from 546.5 MPa to 973.3 MPa. A total of 58 tensile coupons taken from parent plates and hollow tubes were tested to examine the effect of cold-forming process on material properties within the cross-section. When compared with parent metals, strength enhancements were found in Q460 sections, while yield strengths remained nearly the same as parent metal in Q690 sections, and a slight strength reduction by around 1% was noticed in Q960 sections. Basic material parameters in existing material models to obtain stress-strain curves were thoroughly calibrated against the coupon test results. Results indicate that the use of the calibrated parameters can give excellent predictions in terms of stress-strain curves. Residual stress measurements on 2 cold-formed CHSs were performed, with 57 strips extracted and 684 readings taken. The maximum tensile membrane residual stress and maximum tensile bending residual stress on the external surface were observed to be 41% and 32% of the material yield strength. A multilinear predictive model for the distribution of membrane residual stresses in cold-formed high-strength-steel CHSs was subsequently proposed.