Automotive box section design under torsion: Part 1: Finite element modelling strategy

Abstract

Behaviour under torsion is an important performance-related property of automotive box sections. A previous experimental study has identi®ed joining technique, section thickness and section area as the major in¯uencing factors on the torsional behaviour of box hat sections. Using these test results as the basis, a ®nite element modelling strategy that can simulate the behaviour of adhesively bonded and spot-welded automotive box sections subjected to torsion is presented. The numerical study investigated the eects of material representation, mesh density and layout, and joining technique representation on the stiness, elastic limit and ultimate strength of the box sections. The ®nal model, calibrated and validated against test results obtained from previous work, was used in an extensive study, presented in the companion paper (Part 2), to further the understanding of the behaviour of torsionally loaded box sections and its implications on weight reduction of automotive structures.

Effects of design and adhesive modulus on the torsional stiffness of automotive structures

“…Generally the higher-modulus adhesives give higher torsional stiffnesses. The beams with the high-modulus adhesives are also stiffer than the spot-welded beams, confirming observations from other research [1]. This may be due to a reduction in elastic deformation of the flanges between the spot welds.…”

“…This chamber provides significant torsional stiffness within the vehicle. Although there has been work carried out on the use of adhesives to improve the torsional stiffness of vehicles, it is not until recently that more complex box structures have been investigated [1][2][3]. In these more recent studies, the effects of panel thickness, panel strength, beam section area, and joining method were examined.…”

Automotive box section design under torsion Part 2: Behaviour and implications on weight reduction

“…The ®nite element model was ®rst used to analyse the 32 experimental geometries [4]. Table 1 shows the rate of change in stiness with the three signi®cant continuous factors investigated (sheet thickness, section area and section design), as well as that caused by changing from spot welding to adhesive bonding, estimated from both the experimental and the numerical results.…”

“…From references [3] and [4] it is clear that changing the joining technique used to join box sections from spot welding, at a weld pitch of 50 mm, to adhesive bonding, with a high-modulus adhesive, had a signi®cant eect on the torsional properties of box sections. This section further investigates the eects of joining techniques on the torsional properties of box sections.…”

“…In the work described in the companion paper [4], a ®nite element strategy in modelling automotive box sections was developed, calibrated and validated against the test results obtained from reference [3]. In order to gain a fuller understanding of how the various factors would aect the torsional properties of box sections, the resulting ®nite element model was used to generate further data to augment the experimental database and to investigate factors and levels not covered in the experimental test programme, and this work is reported herein.…”