# Quality Analysis of Bonded Joints in the Renovation of Plastic Automotive Parts
## 1 Introduction

Table 2: Adhesives used in automotive repair. materials [42]. The impact strength of bonded joints was studied by [PERSON], who used three different epoxy adhesives in his experiments. At the same time, he used models for numerical calculations, where the result was an increase in impact strength due to increased elastic strain values [43]. Other areas of research include the behaviour of adhesive joints in different environments and monitoring their influence on the mechanical properties of the joint. In these environments, bonded joints can be exposed to various degradation effects, which mainly include temperature, water absorption, salt environment, or wet conditions. All of these affect the bond adhesion and the mechanical properties of the bonded joint [44; 45; 46]. Bonded joints in the automotive industry can be exposed to the same impact loads during their lifetime, which is why impact strength tests have their justification. Design engineers do not know the extent of the effects of impact loads, or they assess their effects only based on assumptions. Nowadays, the methods used to test bonded joints allow us to obtain results that can compare the adhesives used for specific types of bonded joints [47; 48]. The most common method for carrying out impact strength tests of bonded joints is the standard method given in the relevant standard [49]. The main factors during the exposure time of bonded joints are temperature and environmental humidity [50]. This author studied the effect of surface preparation as well as the structure of the bonded joint and the influence of environmental factors on the failure of bonded joints. The materials used were fibre-reinforced plastic (FRP) composites, which were single and sandwich construction. Author [PERSON] [51] improved the chemical bond between the substrate and the adhesive by surface treatment. The use of an insertion element in combination with bonding has been shown to make sense only for those adhesives that have a load capacity just below the yield strength of the substrates. The critical factors that have a significant influence on the strength of the bonded joint are, according to [PERSON] et al. [52], the coefficient of thermal expansion of the adhesive, the shrinkage cure, as well as the change of mechanical properties of the adhesive in combination with temperature. Relative to moisture, its presence in adhesive joints can not only weaken the physical and chemical properties of the adhesive itself, but also the interface between the adhesive and the adherent. The most degraded environment is the exposure of bonded joints to hot and wet environments [53]. Glued joints exposed to this type of environment significantly decrease in strength depending on the time exposed. In the experiments conducted by [PERSON] and [PERSON], where the material was PP filled with glass fibres, it was shown that long exposure times (immersion in water at room temperature) have the effect of significantly reducing the static strength of bonded joints [54; 55]. In the case of defining a bonded joint, one of the main factors is the thickness of the adhesive applied between the materials. Few studies have analysed the effect of adhesive thickness on the strength of the bonded joint. In his work, author [PERSON] indicated the importance of the optimal thickness of the adhesive layer in some types of adhesive joints, where he used simple lap joints in his experiments, and using the FE method, the authors obtained the necessary stresses in the adhesive layer required for the failure of the joint [56]. The analysis of bonded joints and their evaluation through the application of simulation tools was discussed by the author [PERSON] [57] in his work. Just as author [PERSON] [58; 59; 60] has applied simulation tools to predict manufacturing process defects in his work in the milling area, it would be interesting to apply the same simulation tools to the bonding process of polymeric materials and evaluate their strength properties based on the application of the simulation tool.