Computed tomography investigation of the material structure in clinch joints in aluminium fibre-reinforced thermoplastic sheets

Abstract

Recent developments in automotive and aircraft industry towards a multi-material design pose challenges for modern joining technologies due to different mechanical properties and material compositions of various materials such as composites and metals. Therefore, mechanical joining technologies like clinching are in the focus of current research activities. For multi-material joints of metals and thermoplastic composites thermally assisted clinching processes with advanced tool concepts are well developed. The material-specific properties of fibre-reinforced thermoplastics have a significant influence on the joining process and the resulting material structure in the joining zone. For this reason, it is important to investigate these influences in detail and to understand the phenomena occurring during the joining process. Additionally, this provides the basis for a validation of a numerical simulation of such joining processes. In this paper, the material structure in a joint resulting from a thermally assisted clinching process is investigated. The joining partners are an aluminium sheet and a thermoplastic composite (organo sheet). Using computed tomography enables a three-dimensional investigation that allows a detailed analysis of the phenomena in different joining stages and in the material structure of the finished joint. Consequently, this study provides a more detailed understanding of the material behavior of thermoplastic composites during thermally assisted clinching.

Joining Processes for Fibre-Reinforced Thermoplastics: Phenomena and Characterisation

“…This leads to a stabilisation of the neck area of the punch-side sheet [ 18 ]. During the following upsetting phase, the bottom thickness of the TPC decreases with increasing punch movement [ 34 ]. The thinning effect while compression is characterised by a radial material flow.…”

“…The temperature next to the Vicat softening temperature of the matrix just leads to a softening of the thermoplastic PA6 matrix and, therefore, to a more ductile material behaviour. This enables higher degrees of deformation without matrix failure and enables the joining by plastic deformations [ 34 ]. For detailed investigations of the phenomena occurring in the joining process, different stages of the joint formation were analysed with CT ( Figure 15 ).…”

Warmforming Flow Pressing Characteristics of Continuous Fibre Reinforced Thermoplastic Composites

“…Heating above melting temperature on the other hand leads to insufficient undercuts. For a deeper knowledge, in [19], the clinching joint for aluminium-multi-layered unidirectional glass fibre (GF)/polyamide 6 (PA6) sheet is investigated by CT. Since the process temperature is below the melting point, it could be proven that no independent matrix flow processes occur.…”

“…In contrast, in the bottom area and the ring groove fibre fragments can be seen (cf. [19]). For a more detailed description of a clinching process four main phases are defined in [10] for metals and in [11] for composites.…”