Testing and modelling of residual stresses within Q690 high strength steel press-braked round-ended oval hollow section

Abstract

This research explores the material properties and residual stresses of Q690 high-strength steel (HSS) round-ended oval hollow sections (ROHS), fabricated from steel plates after press-braking and welding. It aims to fill the existing knowledge gap concerning the mechanical properties of this novel section profile. Four Q690 HSS press-braked ROHS were examined, employing both transverse bending and longitudinal welding techniques. In addition to the material properties investigation, membrane and bending residual stresses in the longitudinal direction were assessed. The wire cutting method was utilised to create testing strips, resulting in 60 strips with more than720 strain measurements taken. Complementing the experimental tests, an integrated sequentially-coupled thermo-mechanical analysis was performed by developing an advanced lumped line finite element (FE) model. Solid element was used in simulating both cold-forming and welding process, and birth and death techniques was used to replicate the multi-pass welding and the melting of the welding rod. As a result, an explicit residual stress distribution in the longitudinal direction along the perimeter, resulting from cold-forming process and welding, was established. The collected experimental and simulation results elucidated the levels and distribution characteristics of the residual stresses, leading to the development and proposal of predictive models for residual stresses of the press-braked ROHS containing two different fabrication routes.