Experimental and Numerical Study of Clinched Connections (Experimentele en numerieke studie van clinchverbindingen)

Manufacturing thin-walled structures and products inevitably involves the selection of suited joining techniques. The ongoing search for new, sustainable and innovative lightweight materials puts high demands on joining skills. In order to integrate these new materials in structures, products or vehicles, appropriate joining techniques have to be available. In particular for the joining of lightweight metallic sheets, which can be coated and/or dissimilar, alternative joining techniques have emerged in recent years. Amongst those, clinching -or press-joining- can assemble sheet metal parts by solely relying on local plastic deformation of the combining sheets. Unlike traditional joining techniques, clinching does not use additional material inserts such as a rivet or a bolt, and, as a consequence, the mechanical strength of such a connection highly depends on the final geometry after forming. This work focuses on the so called single stroke round clinch process with a closed die. In addition, the quasi-static mechanical response of joints produced by this technology is studied. This thesis can be divided in three major parts:1. Since clinch forming involves severe plastic deformation, the first part embarks on the identification of plastic material properties at large plastic strains. Two alternative sheet metal material tests are presented. The purpose of these tests is to reveal the plastic material behaviour hidden in the post-necking regime of thin metal sheet.2. In the second part, the complex metal flow during forming is studied with the aid of finite element techniques. Since friction plays an important role in this forming process, a strategy to identify the elements of the tribological system in clinch forming is presented. The predicted final geometry of the joint after forming is systematically compared with experiments.3. The third part concerns the mechanical response of clinched joints to quasi-static loading conditions. To be specific, the capability of finite element techniques to reproduce the experimental results obtained with pull-out tests, single lap shear tests and multi-axial loading of clinched joints is investigated. In addition, analytical models to estimate the shear and pull-out strength of a clinched connection are presented.status: publishe