TWI Industrial Member Report Summary 680/July 1999
G R Razmjoo and S A Westgate
Background
The trend for mechanical fastening techniques such as clinching and self-piercing riveting is rapidly increasing in a range of sheet metal industries, particularly for high volume production. They provide a means of achieving fast, reliable joints in a variety of materials and are suitable for automation, similar to resistance spot welding. While many applications, such as domestic appliances, or heating and ventilation, often have relatively limited demand on joint performance, the requirements of the automotive industry are usually more stringent. As well as static performance, there is a need for resistance to fatigue.
The majority of the fatigue data for spot welds and the limited data for the mechanical fasteners have been obtained from single lap joints loaded in tension. However, this method can be inaccurate and misleading. This is because the stress state near the joint in a single lap specimen, which is dominated by the bending moment induced as a result of the eccentric loading, can be different from that in a real member. A standard specimen geometry (the H-specimen) was proposed by the European Working Group 'A K Clinchen' as a more realistic representation of the behaviour of joints in structural elements. This report covers fatigue testing of selected clinching and riveting systems in comparison with spot welding using the H specimens.
Objective
- To evaluate and compare the fatigue and static performance of clinched, self-piercing riveted and spot welded joints in steel and aluminium sheets.