A mechanical device for the measurement of combined shear and tension in rocks

Facing the need of a better understanding of spot-weld strength and failure mechanisms of advanced high strength steels, we have developed a novel test for the in situ failure analysis of spot-welded joints. Providing loading conditions similar to the standard cross tension test, this new test is based upon the use of wedges to peel plates apart in a welded sample that has been cut in half, revealing the weld in the scanning electron microscope. We first perform finite element modeling and show why the wedge test approach is suitable for our purpose. We then perform experimental tests and observe failure in the scanning electron microscope chamber. We are able to both follow crack propagation and control the failure mode. As a corollary, this approach enables the use of local strain mapping, using digital image correlation, to measure local strains in the vicinity of the crack path. The wedge test should be valuable for assessing failure processes in spot-welded joints.