Fracture simulation of welded RHS X-joints using GTN damage model

Abstract

A welded rectangular hollow section (RHS) X-joint exposed to tension loading has three typical fracture-related failure modes: Punching shear failure (PSF), Brace failure (BF), and Chord side wall failure (CSWF). Prediction of these failure modes by finite element (FE) simulations requires modelling of the material damage. An appropriate damage model accurately predicts the behaviour of the fracture zone and provides the necessary information to improve design rules for welded high-strength steel (HSS) RHS X-joints based on parametric studies using validated model. In this paper, the parameters of the Gurson-Tvergaard-Needleman (GTN) damage model are calibrated for the base material (BM) and the heat-affected zone (HAZ) of butt-welded cold-formed RHS connections, no fracture appeared in the weld. A computational homogenisation analysis is carried out using representative volume element (RVE) models to calibrate the pressure-dependent yield surface parameters of the GTN damage model, considering the different combinations of the accumulated initial hardening strain and the void volume fraction (VVF) due to a varying stress triaxiality. The critical and final VVFs are calibrated against tensile coupon tests. Finally, the GTN damage models calibrated for BM and HAZ are used in the fracture simulation of nine welded cold-formed RHS X-joints in monotonic tension. The FE model successfully predicts the experimental load-displacement relationships and fractured zone, indicating the calibrated GTN models could effectively be used in parametric study of welded cold-formed RHS X-joints. Finally, possible improvements to the used FE model are outlined for future studies.

Tensile behaviour of welded S700 rectangular hollow section X‐joints

“…The Gurson-Tvergaard-Needleman (GTN) damage model was employed to simulate the fracture of the joint in [7].…”

“…Yan et al [9]- [11] proposed a systematic approach to obtaining the stress-strain relationship of equivalent HAZ, which was further used to calibrate the Gurson-Tvergaard-Needleman damage model for HAZ. Based on the calibrated GTN damage model, a fracture simulation was carried out for the welded HSS RHS X-joints in tension [7].…”

“…The study presented in this paper is a continuation of the work presented in [7]. The calibrated GTN damage model…”

“…Limited studies [7], [8] explicitly consider HAZ in the FE analysis of welded hollow section joints. Lan et al [8] assumed a strength reduction for HAZ in the finite element (FE) analysis of welded RHS T-joint in compression.…”

A macro prediction model for butt-welded (U)HSS connections with softened HAZ

“…where 't' and 'e' in the subscript stand for true and engineering, respectively. Yan et al [33] found that the true stress-strain relationship of HAZ after necking (ultimate strength point) should be generated by the Voce model [34], as shown in Eq. (10), where σ t,V is the true stress predicted by the Voce model.…”