# Strength and Ultrasonic Testing of Acrylic Foam Adhesive Tape
## 2 Research
### Ultrasonic Apparatus  
Due to the practical nature of the research, an industrial digital ultrasonic defectoscope USM35 XS ([PERSON], GE Electronic, Boston, MA, USA) was used for the measurements, along with an ultrasonic probe. Because the samples used in the study were small in thickness, a high-frequency probe had to be used so that a short wavelength could be obtained. The wavelength is the quotient of its speed and its frequency. It was assumed that the wavelength should be at least three times smaller than the thickness of the sheet to be tested. Taking into account the above assumptions and the speed of the ultrasonic wave in the steel sheet of about 5940 m/s, it was calculated that the frequency of the wave used should be about 20 MHz. Due to the near-field and dead zone and the impossibility of immersion testing (due to possible degradation of the joint), it was decided to use a head with a water delay line. A probe from GE Electronic with a transducer diameter of 5 mm, designated by the manufacturer as G20 MNK, was selected. This head is equipped with a flexible diaphragm that adapts to the shape of the surface to be tested. The selected ultrasonic probe is shown in Figure 3. The basic parameters of the ultrasonic transducer are shown in Table 2.  
The schematic of the measurement system is shown in Figure 4. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & \\ \hline frequency & 20 & MHz \\ diameter of the transducer & 5.0 & mm \\ effective diameter & 4.5 & mm \\ wave speed of tested material & 5940 & m/s \\ wave length & 0.297 & mm \\ near field & 17.0 & mm \\ the coefficient of decrease of decibels K & 0.87 & - \\ sin the angle of divergence of the beam & 0.06 & - \\ divergence angle degrees & 3.29 & \({}^{\circ}\) \\ distance from the transducer & 20 & mm \\ beam width & 2.3 & mm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters of the ultrasonic transducer used. Figure 3: Ultrasonic probe used in research. Prior to the study, measurement errors were determined experimentally. For this purpose, 30 measurements were taken at a single location, the mean value was determined, and the confidence subinterval was set at 0.95, which allowed the percentage errors to be determined. The results of the calculations are presented in Table 3, while graphically, they are shown in Figure 5. The results of all measurements are presented in Appendix A.  
Figure 4: Measurement stand: (**a**) general view, (**b**) sample and probe model; 1, metal sheet; 2, ultrasonic probe; 3, flexible membrane, 4, adhesive tape; and 5, metal sheet. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Pulse** & **Average** & **Standard** & **Confidence** & **Percent Error** \\
**Number** & **Pulse High** & **Detviation** & **Interval** & **Percent Error** \\ \hline
1 & 80.0 & 0.00 & 0.00 & 0\% \\
2 & 69.2 & 1.55 & 3.17 & 5\% \\
3 & 56.4 & 1.05 & 2.16 & 4\% \\
4 & 44.1 & 1.77 & 3.61 & 8\% \\
5 & 34.5 & 1.41 & 2.88 & 8\% \\
6 & 29.1 & 2.12 & 4.35 & 15\% \\
7 & 28.7 & 3.14 & 6.42 & 22\% \\
8 & 21.9 & 2.63 & 5.38 & 25\% \\
9 & 19.5 & 1.73 & 3.53 & 18\% \\
10 & 15.7 & 1.81 & 3.69 & 23\% \\
11 & 9.8 & 2.21 & 4.51 & 46\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Determination of measurement errors (the complete set of results is available in Appendix A, Table A1). Analyzing the results obtained, it was assumed that for further work, the fifth pulse would be used, since it came from multiple reflections, which increased the accuracy; additionally, the measurement error was about 8 percent, and with subsequent pulses, it increased up to 46 percent. In the tests, a sequence of pulses was obtained on the defectoscope screen, and the heights of all pulses were measured.