TWI Industrial Member Report Summary 691/1999
S A Westgate and G R Razmjoo
Resistance spot welding is normally considered the most effective and reliable joining method for thin sheet metals in a range of industries. However, rapid growth of alternative joining methods, such as those incorporating mechanical fasteners has been seen during the 1990s. This has been driven by the use of alternative materials (steels with organic, insulating coatings, aluminium alloys, metal/polymer laminates and dissimilar material combinations, etc) whose weldability varies from difficult to virtually impossible.
Sheet metal assemblies are often required to withstand dynamic loading, with constant or variable amplitude loads. Fatigue properties have been evaluated in a number of studies for mechanical fastened joints in various materials. In general, self-piercing riveted and clinched joints are reported to exhibit superior fatigue performance compared to spot-welded joints, despite usually lower static strength. These comparisons, however, are particularly dependent on the type and thickness of the materials being joined, the type and dimensions of the joint, and the loading configuration.
Previous work at TWI involved the use of H-section test sample designs. These were proposed in a European Consortium on fastening (A K Clinchen) as a means of achieving test loading closer to pure shear and peel in the two sample types. However, concern about the cost and effectiveness of such samples had been raised among other researchers in the field, so this report provides comparison of results for simple test samples and H-section samples joined by spot welding, self-piercing riveting and clinching.
Additionally, the report examines the hybrid joining processes rivet-bonding and clinch-bonding for the joining of aluminium to steel. Hybrid processes are a combination of two different joining methods to create a new joining process, with extended capabilities. In this case, the combination of riveting or clinching with adhesive bonding. A study of joint formation and fatigue performance is reported.
- To compare the fatigue performance of single-point lap joints with that of the high cost H-section joints, under shear loading.
- To evaluate the effect of process parameters on the formation of the riveted and clinched joints, and for the equivalent hybrid joints with adhesives, rivet-bonding and clinch-bonding.
- To evaluate the static and fatigue performance of two types of hybrid joints, namely rivet-bonding and clinch-bonding, for joining aluminium alloy to steel sheet.