PERFORMANCE OF TENSILE TESTED RESISTANCE SPOT AND LASER WELDED JOINTS AT VARIOUS ANGLES

摘要

The introduction of modern materials has offered engineers tools to develop novel solutions to satisfy the demands of consumers and regulators. Advanced high strength steels combine high strength with good formability and weldability. The increased strength levels allow manufacturers to reduce sheet gauges (thus lowering weight) whilst retaining performance in safety critical areas of the construction. However issues have been reported in literature concerning the failure behaviour of advanced high strength steels. The performance of welded joints is usually evaluated using coupon tests under either normal or shear tensile loading. The actual loading of these joints in an automotive structure may be quite different, especially concerning the angle in which the load is applied. In this report an overview is given of published results on the performance of welded joints in automotive applications. Next the results from a series of resistance spot and laser welded joints in different steel sheet materials (HSLA and DP of varying thickness) subjected to tensile tests under varying loading angles are presented. The focus is on resistance spot welded joints, but the results are compared to similar tests performed with laser welded joints. The performance of the welded joints in terms of failure mode and strength are analysed, and the possible implications for automotive applications are discussed. Finally some work using finite element simulations is presented. Here the characteristics of the base material and welded joints of different grades of materials are evaluated to investigate the differences in performance in tensile testing. It is concluded that the thickness of the materials is the main parameter determining the failure characteristics of materials. The grade (HSLA or DP) is less of a factor determining failure mode. The fact that joints in DP steel perform as well as HSLA steels allows designers and engineers to use the advanced high strength steel without having to worry about unpredictable failure behaviour leading to decreased performance for safety critical applications.