Material properties and residual stresses of high strength steel hexagonal hollow sections

This paper presents an experimental investigation on the material properties variation and residual stress distribution within the high strength steel (HSS) hexagonal hollow sections. Three different fabrication routes encompassing welding or combinations of welding and press-braking were employed for fabricating the HSS hexagonal sections. HSS plates of grade Q690 with two thicknesses of 6 mm and 10 mm were used. A total of 76 tensile coupons extracted from the parent plates and the hexagonal hollow sections with different fabrication routes were tested to obtain the static material properties of the parent steel plates and the material properties variation for the hexagonal hollow sections. A new material model describing the material properties for the flat portion was proposed while the existing material model for cold-formed steel was modified for the materials at the press-braked corners. In addition, residual stresses measurements for five HSS hexagonal sections with different fabrication routes and varying section slenderness were subsequently performed. Sectioning method was adopted in this study with 74 strips extracted and more than 898 strain readings obtained. Results of the residual stress distributions and the magnitudes are presented and discussed. Based on the measurement results, predictive models for residual stresses were developed and can be applied to estimate residual stresses for predicting the structural behaviour of the HSS hexagonal hollow sections.