Stiffness analysis of spot joints as a condition for the numeric modelling - new test methods

Accurate numerical calculation of stresses in structures with a multitude of spot joints continues to be a challenge, especially if local stresses are located in the area of joining positions or if crack endangerment needs to be addressed. In addition to inadequate FE modelling, a major cause for this is the unavailability of exact primary data, which describe the properties of the joints. New methods for determining the stiffness behaviour of joint connections bases on the measurement of the relative displacement of the sheet metals between the joints during applying a load. The measured relative displacement is proportional to the deformations in the joint area. Strain of the test specimen as well as deformations of the load frame or the force measuring cells have no effect in the relative displacement. Two test methods and the necessary measurement technology will be described. On the one hand a method for symmetric joint connections will be shown and on the other hand a method for unsymmetrical pairings of sheets. For the first case a 2- point-shear-load-specimen is used, for the second a 3-point-torsion-test.