# Non-Destructive Testing of Joints Used in Refrigerated Vehicle Bodies
###### Abstract  
This paper focuses on the non-destructive evaluation of adhesive joints used in vehicles designed for transporting food products. The research and analysis were limited to the joints used in connecting elements of the cargo space. Two non-destructive methods were employed in the study: ultrasonic and thermographic techniques. Both methods confirmed the feasibility of evaluating adhesive joints in the construction of food transport vehicles, with the thermographic method proving to be much faster in identifying large areas of deadhesion in the plating. The ultrasonic method, on the other hand, allows for the inspection of sheathting and aluminum profiles. The predefined decibel drop in the height of the first two pulses on the ultrasonic defectoscope screen for areas with high-quality joints was less than 3.5 dB. In contrast, for areas with adhesion-related damage, the decibel drop in the first two pulses exceeded 4.5 dB. ultrasonic testing; thermal imaging method; adhesive joints; refrigerated vehicles +
Footnote †: journal: Applied Sciences  
transport for transporting perishable foodstuffs is described in the Agreement Concerning the International Carriage of Perishable Foodstuffs and Special Means of Transport for this Purpose (ATP) [5]. There are four categories of such vehicles: isothermal, ice cream, refrigerated, and means of transport with heating capabilities. A refrigerated body must guarantee that the cargo maintains the right temperature. A key element in the design of a refrigerated vehicle is a tight and well-insulated body. The construction of an isothermal vehicle is influenced by such factors as the thermal conductivity coefficient, the type of insulation used, the thickness of the insulation and the presence of thermal bridges (e.g., door seals, aggregate mountings, hinges, etc.). The production of isothermal bodies involves the manufacture of insulated walls from sandwich panels, which are formed by foam injection or gluing and then joined together to form a closed, self-supporting box. The walls are joined using an adhesive that is applied to the entire interface. Reinforcing elements may be used (such as screws) to further increase the pressure when gluing the strips [6]. An issue worth exploring is the inspection of the condition of adhesive joints used in ATP vehicle construction. Adhesive joints have numerous advantages: they perfectly dampen vibrations, cause uniform stress distribution and seal the structure. Bonding has two great potential advantages with respect to welding: the speed of application and the absence of thermal distortions [7]. Furthermore, since it presents fewer risks for safety at work, it allows the simultaneous execution of other assembly operations. It is the adhesive joints, which use the phenomena of adhesion and cohesion, that make it possible to produce temperature-controlled food transport bodies. Testing of adhesive joints can be divided into two main groups. These are destructive testing and non-destructive testing. Destructive testing covers many aspects. In [8], the authors showed that the effectiveness of adhesive bonds is notably impacted by the thickness of the cured adhesive layer, underscoring the need for meticulous monitoring within adhesive bonding techniques. A precise adherence to technological protocols and the use of specialized instruments are imperative to ensure the production of high-quality samples meeting the tolerances outlined in relevant standards. For example, the paper [9] modeled adhesive joints and found that the numerical values of maximum load were close to the experimental values, validating the numerical methodology used to predict the lap shear strength and providing the necessary data to explain the obtained behavior. It also noted that the increase of adheren't thickness for CFRP (carbon fiber reinforced plastics) (i.e., from 1.2 mm to 2.1 mm) did not promote a significant increase in joints' strength; thus, a reduction in mass can be achieved without losing the joint efficiency.