# Non-Destructive Testing of Joints Used in Refrigerated Vehicle Bodies
###### Abstract
In the paper [9], the authors provide an overview of the current developments in the use of \"smart\" adhesive technology and introduced the reader to early findings on the use of self-healing materials, thermally expandable particles, and nanoparticles, among others, in adhesives and their potential to increase the reliability of adhesive joints. In this work, the possibility of using adhesives in the production of commercial vehicles was confirmed, and the work carried out was also aimed at reducing costs and improving the safety of structures--recycling, healing, or self-healing of bonded structures. The work carried out also included modeling of adhesive joints when joining aluminum [10]. The model developed in work [11] is based on basic mechanical analysis and the application of [PERSON]'s stress equation for single joints, the kind often found in adhesive joints. Non-destructive evaluation of adhesive joints, especially those used in automotive applications, is an important issue. Already at the end of the last century, [PERSON] [12] proposed various non-destructive methods for evaluating adhesive joints. According to [PERSON], the method that provides a fairly good understanding of the properties of an adhesive joint is the ultrasonic method. The quality of adhesive joints using the non-destructive method was also studied in [13]. In this work, three different artificial debondings within composite-adhesive single-lap joints were investigated using ultrasonic immersion pulse-echo technique and induction thermography. Data fusion has been used to increase the performance of different defect detection. Induction thermography NDT performs well with electrically conductive inclusion detection; however, it is not sensitive to nonconductive inclusions. While ultrasonic NDT performs better in detecting release film inclusion, it is an obvious fact that brass inclusion (or any inclusion with high electrical conductivity) is detected better with induction thermography. In the construction of commercial vehicles and buses, adhesives are widely used, mainly polyurethane and polymeric adhesives. In ultrasonic testing, the acoustic properties of adhesives are important, especially acoustic resistivity. Acoustic resistivity is proportional to the density and speed of ultrasonic waves. Polyurethane and polymer adhesives are high-density adhesives. In the case of temperature-controlled vehicle sheathing, there is an adhesive bond between the insulation layer and the steel sheet. The insulation layer is many times less dense than the adhesives, so it has a different acoustic resistance. The acoustic resistance has a significant effect on the reflection and transmission coefficients of ultrasonic waves. Ultrasonic testing of adhesive joints has been conducted for many years. These are mainly tests of steel-adhesive bonds [14], aluminum-adhesive bonds [15], and adhesive joints of composite materials [16; 17]. Ultrasonic evaluation of fatigue damage in adhesive joints is also one of the directions of research conducted by scientists [18]. The quality of adhesive joints was also investigated using non-destructive methods in [19]. Three different types of composite-adhesive joints were examined in this study, utilizing both immersion ultrasonic testing and induction thermography. Similarly, ultrasonic testing was also performed in [20]. In this study, single-layer aluminum adhesive joints were tested in pulse-echo mode. The joints contained defects. The purpose of the test was to increase the probability of detecting defects and to estimate their size. All of these tests involved an adhesive layer that had markedly different acoustic properties from the insulating layer used in temperature-controlled food vehicles. Ultrasonic adhesion bonding has been studied, for example, in the paper [21], B\(\backslash\)but it too had completely different adhesive properties. In this work [21], an automotive putty used in vehicle repair, for example, was studied. As a result of vehicle body vibrations, adhesive joints can be damaged.