Cruciform specimens for in-plane biaxial fracture, deformation, and fatigue testing

Three different types of cruciform specimens, which have been used successfully on the DLR biaxial test rig for investigations in the fields of fracture mechanics, yield surface evaluation, and fatigue of riveted joints are presented in detail. The following three characteristics were required from these specimens: a uniform stress and strain distribution in the central testing regions, low manufacturing costs, and easy mounting in the DLR biaxial test rig. It is shown that the first and the second requirement are in conflict. Because of the uneven stress distribution in the simple and inexpensive fracture mechanics specimen, additional finite-element calculations were needed for a full fracture mechanical characterization. On the other hand, impelling a very uniform stress distribution in the riveted cruciform specimens increased the manufacturing costs considerably. The specimen which satisfies the demands best is the yield locus evaluation specimen of deep drawing steel. It has low manufacturing costs and a very uniform strain distribution in the central testing section.