Fracture mechanical investigation of preformed metal sheets using a novel CC-specimen

Abstract

Joining is used in many areas of manufacturing where components are formed from individual parts or sheets into complex structures. A simple and common method applied in industry to join dissimilar and coated materials is clinching. This joining process does not require additional joining parts, which saves weight to reduce energy requirements and harmful emissions due to moving masses. In addition, the joining process is carried out without pre-punching and is therefore time-efficient. Damage caused by the joining process or by operational loading can lead to cracks near the joint, to crack propagation due to time-varying loading and subsequently to the complete failure of the component. To avoid these damage cases, knowledge about the fracture mechanical behavior of the clinched connection is required.Within the scope of this paper, a novel CC-specimen for fracture mechanical investigation of preformed metal sheets is developed and investigated. The new specimen geometry is taken directly from a clinched joint in order to identify a possible influence of the outer forming area of the joint on the fatigue crack growth rate. The clinched joint is placed at three different positions and is moved from the radius to the center of the C-shape at 3 mm intervals. In order to investigate the crack growth rate of this new specimen, it is necessary to numerically determine the geometry factor function for the stress intensity factor as well as the calibration curve for the crack length measurement with the direct current potential drop method beforehand. Finally, the results of the crack growth rate tests using the CC-specimen with different positions of the clinched joint are compared with the results of the base material.