Finite Element Modelling to Predict Equivalent Stiffness of 3D Space Frame Structural Joint Using Circular Beam Element

Abstract

In automotive industry, thin walled beam is widely used to build vehicles structure. Vehicle structure is built by joining thin walled beams using various welding techniques. The usage of thin walled structure in automotive is important to improve vehicle performance by offering better strength-to-weight ratio. However the application of thin walled structure will cause few drawbacks to vehicle structure. When thin walled beam or structure is loaded with compression load, at certain limit it will undergo local or global buckling. Another problem is when thin walled beam is joined to other thin walled beams, it will show unexpected deformation which called joint flexibility. Both phenomena will cause numerical and analytical model to predict stiffness of structure tend to deviate from experimental result. In vehicle structure fabrication 3D space frame is used a lot. As a case study for this application, area around car bulkhead where cross member, side sill and A pillar are connected to each other at right angle is studied. The intention of this research work is to produce validated finite element model to predict equivalent stiffness of 3D space frame structural joint. Finite element, shell element is most common technique used to model the joined structure. However it is known that shell model cannot produce good result. In this result work, modelling of equivalent stiffness for 3D space frame structural joint is presented. The result shows, using this model the accuracy is about 65%. New modelling technique is proposed to increase the accuracy based on solid model. By introducing circular beam elements at welding area, it is found that accuracy improves up to 90%.