Experimental and numerical analysis of single-lap joints for the automotive industry

Lap joints are used extensively in the manufacture of cars. In order to determine the effect of using a structural adhesive instead of spot-welding, a detailed series of tests and finite element analyses were conducted using a range of loadings. The adhesive was a toughened epoxy and the adherend was mild steel typical of that used in the manufacture of car bodyshells. The lap joints were tested in tension (which creates shear across the bondline), four-point loading (pure bending) and three-point loading (bending plus shear). Various parameters were investigated such as the overlap length, the bondline thickness and the spew fillet. The major finding is that three-point bending and tension loading are very similar in the way in which they affect the adhesive while the four-point bend test does not cause failure because the steel yields before the joint fails. A failure criterion has been proposed based on the tensile load and bending moment applied to the joint.