# Strength and Ultrasonic Testing of Acrylic Foam Adhesive Tape
## 1 Introduction  
Adhesive joints are increasingly used in modern industry [1; 2; 3]. Testing the reliability of technical objects, including joints, is the subject of many articles [4; 5; 6] and constitutes a major basis for improving manufactured machines and vehicles. A particularly significant share of adhesive joints is observed in the automotive industry [7; 8; 9]. Other joints used in industry include welded joints [10], spot-welded joints [11], ultrasonic welding [12; 13], and soldering [14; 15]. Adhesive joints have numerous advantages, the most important of which include the ability to join different materials with uniform stress distribution, high fatigue life, protection against vibration and noise, weight reduction, and no effect on the structure of the material. However, they also have disadvantages, including the relatively long bonding times of adhesives, their limited mechanical and thermal resistance, the need to follow the rules of manufacturing technology (e.g., sanding, degreasing, surface activation, and ensuring proper temperature and humidity), and their negative impacts on the environment and health. Despite these disadvantages, their share of use in bonding in modern industry is steadily growing. A valuable solution that reduces the disadvantages of adhesive bonding to a limited extent, while retaining its advantages, is the use of tapes covered on both sides with tack adhesive. Manufacturers are replacing traditional adhesives with such tapes in many areas, including fixing side panels in buses, fastening covers and lids, and fixing roof sheathing in buses and door sheathing in railroads. At room temperature, the adhesion of such tapes reaches an initial strength of 50 percent of theshort-term strength after 20 min, and 85 percent of the mechanical strength is secured after 24 h. In the case of polyurethane adhesives used to fix side wall panels or roof sheathing, these periods are many times longer. To a limited extent, hybrid joints are used, which are characterized by the properties of both adhesive and tape joints. The purpose of this research was to evaluate the influence of selected factors on the quality of the tape-steel sheet joint and to assess the possibility of testing the acrylic tape-steel sheet joint using the ultrasonic method. In [16], the literature in the area of hybrid joints using structural adhesives was reviewed, highlighting the scope of their application and presenting the latest developments in the field. Section 1 provided an introduction to the main types of adhesives, categorized by their chemical nature: epoxy, polyurethane, acrylic and cyanoacrylic, anaerobic, and high-temperature adhesives. Seciton 2 outlined the most commonly used hybrid joining (HJ) techniques, including mechanical mounting and bonding, as well as welding and bonding processes. Seciton 3 discussed the use of adhesives in hybrid joining processes, highlighting their performance, benefits, and drawbacks. Finally, the conclusions and perspectives addressed the critical challenges, future prospects, and ongoing research activities. The study concluded that hybrid bonding technology could be a viable solution in various industries for reducing weight and production costs. Hybrid joints were studied in another paper [17]. The tests conducted confirmed the effectiveness of creating hybrid joints for steel sheets using hybrid adhesives. The average shear force of the adhesive joints was 476 N, whereas for sheet metal clinching joints, it was 965 N, indicating a difference of nearly 500 N. The hybrid joint exhibited significantly higher strength compared to both the adhesive and clinching joints alone. For specimens where the clinching joint was made immediately after forming the adhesive joint, the strength was 312% higher than that of the adhesive joint and 154% higher than that of the clinching joint. The study highlighted the importance of timing in forming the clinching joint, showing that it is preferable to form it immediately after the adhesive bond.