# Quality Analysis of Bonded Joints in the Renovation of Plastic Automotive Parts
## 1 Introduction
The aim of the research was to investigate the heat treatment of clinched joints and its combination with adhesive bonding. A parametric study of bonded joints that had a sinusoid shape was developed in a study by [PERSON] [15], who focused his research on joining non-planar test specimens. As a result, the influence of the interface non-planarity between the bonded parts was investigated, which largely influences the strength of the bonded joint. This influence in their research was also supported by finite element analysis. At a lower wavelength and higher wave height, a reduction in the stress at the centre of the bonding layer and, consequently, an increase in the bond strength was achieved. The effect of adhesion and environment on static and transverse impact strength in bonded joints was discussed by [PERSON] [16] because there are few studies combining moisture and its effect on impact toughness. For the experiment, he used single lap joints with different adherends (high-limit elastic steel and a commercial composite). The result demonstrated the sensitivity of adhesive joints with steel adherends to the environment (distilled water, seawater, and distilled water at 40 \({}^{\circ}\)C) and exposure time studied. In both tests, adhesive failures occurred for adhesive joints with steel adherends and the delamination of joints involving the composite. The effect of adhesive thickness, as well as PU adhesive overlap and ageing effects on the mechanical properties of similar and dissimilar single lap joints used in the automotive industry, was investigated by [PERSON] [17]. However, he did not use surface treatment in the bonding methodology, and this was executed to quantify shear strength and stiffness when no surface treatment is applied to the substrates, thereby reproducing typical mass production conditions. The results indicated that the adhesive joints with the composite substrate presented a mixed adhesive/cohesive surface, which led to a damaging effect on the mechanical properties of the single lap joint. The activation of adhesive substrate surfaces by plasma treatment of polypropylene joints used in the automotive industry was studied by [PERSON] [18], who applied this method to polymers that have low surface energy and are widely used in the automotive industry. In his experiment, he used two techniques, namely vacuum and atmospheric plasma, for the treatment of polypropylene substrates and applied polyurethane and methacrylate adhesives for the purpose of forming a bonded joint. In addition to the plasma types, two different gas carriers (air and nitrogen) and different treatment times were investigated. Individual treated and untreated substrates were evaluated using scanning electron microscopy and other analyses, which showed that atmospheric plasma can improve the surface of the substrates using a shorter time. At the same time, another result was the finding that methacrylate and polyurethane cannot crosslink polypropylene substrates without plasma treatment. On the other hand, the treated substrates can create a strong bond with the adhesive because all single lap joints showed substrate failure. According to the author [PERSON] [19], the evaluation of mechanical properties in the form of tensile tests has its importance not only in bonded joints, but also finds its application in the joining of cast magnesium alloys using the welding method. The author [PERSON] [20] in his research dealt with multi-material adhesive joints designed for the automotive industry, choosing a single lap joint for the purpose of the research. As a result, it was found that for small overlaps of the bonded joint, the failure in the strength of the joint, as well as the influence of the geometry or the material used, is not significant, but on the other hand, increasing the overlap increases the load carrying capacity of the joint to a significant extent.