Citation: Stephan, R.; Brosius, A. Experimental Measurement Method and Evaluation of an Analytical Approach for Sound Conduction through Multiple Clinched Sheets. Eng. Proc. 2022, 26, 25. https:// doi.org/10.3390/engproc2022026025 Academic Editors: Martin Dix and Verena Kräusel Published: 27 December 2022 Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Proceeding Paper Experimental Measurement Method and Evaluation of an Analytical Approach for Sound Conduction through Multiple Clinched Sheets † Richard Stephan and Alexander Brosius * Department of Forming and Machining Processes, Technische Universität Dresden, 01062 Dresden, Germany * Correspondence: alexander.brosius@tu-dresden.de † Presented at the 28th Saxon Conference on Forming Technology SFU and the 7th International Conference on Accuracy in Forming Technology ICAFT, Chemnitz, Germany, 2–3 November 2022. Abstract: The conduction of structure-borne sound through joints causes energy dissipation. The sound reduction index describes this energy loss as a level decrease in the particle velocity across series-connected damping elements for which the superposition principle applies. This simple model can help to develop a testing method for joints based on this characteristic energy loss. In this paper, this model is experimentally evaluated for multiple in-series clinched aluminium sheets. Samples connected by several clinch points arranged in parallel are investigated experimentally, and the results are discussed. Keywords: clinching; mechanical joining; damping; model; evaluation; dynamics 1. Introduction Clinching is a cost-efficient [1] mechanical joining process that creates a force and form closure [2] between two or more flat partners by forming. The window technique is often used for process monitoring during the clinching process. The force and displacement curves are observed over time and compared with set tolerances [3]. This method allows a rough process control, but not a detailed analysis of property-determining geo- metric values. Particularly important property-determining geometrical parameters are the inter- lock f and the neck thickness t n [4]. These dimensions can only be measured destructively by preparing a microsection or non-destructively by means of radiographic testing [5]. Both methods are relatively time-consuming, cost-intensive and require expert knowledge and handling of samples. Currently, only visual inspection is available as a cost-effective inspection method for clinched joints. However, certain defects cannot be detected by visual inspection. For example, the formation of cracks in the clinch connection is not always visible from the outside [6]. In terms of sustainability and safety, it is necessary to develop suitable testing procedures in order to non-destructively check clinched structures for damage during their lifetime. This is the precondition for a specific repair or service life extension of the structure. A promising approach to address these issues is the transient dynamic analysis (TDA), which combines acoustic analysis with fast signal evaluation and offers the potential to detect quickly and non-destructively irregularities in a clinch joint [7]. The process involves the targeted introduction of sound waves into a joining partner. The characteristic damping of the sound waves in the joint changes their characteristics. These changed, structure-borne sound waves arriving on the other joining partner are detected by means of piezoelectric sensors and then evaluated. Köhler et al. have shown in a numerical study that clinch points with varying bottom thicknesses are different in their dynamic behaviour [8]. This technique has already been practised successfully with regard to bolted joints. Wolf et al. Eng. Proc. 2022, 26, 25. https://doi.org/10.3390/engproc2022026025 https://www.mdpi.com/journal/engproc