# Product Design Analysis with Regard to Recycling and Selected Mechanical Properties
## 1 Introduction
The topic of recycling aluminium alloy automotive sheets connected by self-piercing rivets has been described by [PERSON] et al. [37], [PERSON] et al. [38] and in a review by [PERSON] and [PERSON] [39]. Although the steel rivets used in conventional self-piercing riveting are removed from aluminium alloy sheets during recycling, removal is not required for aluminium alloy rivets. The connected sheets with rivets are directly melted due to the same material--aluminium. A life-cycle assessment model and a life-cycle cost assessment model for car parts connected by techniques such as welding, bonding and riveting are presented in [40]. Here, the environmental and cost impacts of the chosen technique were investigated based on energy consumption and material inflows and outflows. A multi-objective decision-making algorithm was also proposed to identify the most suitable techniques for automotive applications. Optimisation of the roof edge profile recycling process using shape memory alloy connecting elements is described in [41]. The issue of analysing product design from a recycling point of view is reflected in the definition of measures proposed in numerous articles. [PERSON] et al. [42] suggested the Unfastening Effort Index (UFI), which expresses the effort required to disconnect a particular type of fastener. The disconnection time of a fastener can also be estimated from the UFI value. Another formula for estimating the disconnection time was defined by [PERSON] et al. [43]. They distinguish between six categories of dismantling task and sum the dismantling time for each category for a final estimate of the dismantling time. [PERSON] et al. [44] proposed a set of measures to describe product design from dismantling and material properties. The product dismantling properties are assessed in this approach using the following measures: Quantity of Fasteners Index (QFI), Percentage of Fasteners Index (%FI), Type of Fastener Index (TFI), Quantity of Types of Fasteners Index (QFTI) and Accessibility Index (AI). In turn, the product material properties are described by measures, such as Infrastructure Index (II), Material Compatibility Index (MCI), Material Group Index (MGI) and End-of-Life Contamination Index (EoLCI). In contrast to singular assessment measures, aggregate assessment measures can also be found in the literature. [PERSON] [45] and [PERSON] et al. [46] introduced the Total Recycling Rate (TRR), which is the sum of three quantities: Material Diversity (MD), Connection Diversity (CD) and Recycling Target (RT). [PERSON] et al. [47] defined an index of Product Recyclability, which concentrates on recycling properties of the materials used in the product design. This aggregated measure includes compatibility of materials, diversity of materials, recyclability of materials and number of aggregated action levers. This article addresses the issue of product variants [17] and its effects on the recycling process side of the product and on the strength side of the product. The combination of these two aspects has not yet been used in the analysis of connections with fasteners. As an objective, the article set out to investigate how changing the number of fasteners in a connection affects the recycling and mechanical properties of the connection and whether these properties change in parallel. An example of a connection made once as a multi-bolted connection and once as a multi-riveted connection was chosen as the product to be considered. Spatial modelling software (Computer-Aided Design (CAD) type) [48, 49] and Finite Element Method (FEM) calculations [50, 51] were used as engineering tools in the preparation of the article.