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Ultrasonic tests are widely used, both in laboratory and industrial settings, to assess the quality of joints, mainly welded joints. Studies are being carried out on the possibility of ultrasonic evaluation of adhesive joints. This study was conducted using signal analysis in the time and frequency domains. The ultrasonic probes used in the tests were selected on the basis of the properties of the test elements. For example, when testing welded joints, ultrasonic probes with a water delay line bounded by a thin diaphragm were used. Since adhesives have different acoustic properties, it is necessary to evaluate the capabilities of different ultrasonic probes to test adhesive joints. Tests were conducted for two different adhesives (cyanoacrylate and structural) and eight ultrasonic probes with a frequency range of 1.660 to 13.70 MHz. In the literature, no studies have analyzed the use of ultrasonic probes at such different frequencies. Frequency has the greatest effect on the attenuation of ultrasonic waves and the ultrasonic wavelength, and it was noted that the adhesive could cause a 25 percent change in the maximum frequency of the ultrasonic pulse. It was also found that it is necessary to make reference samples before ultrasonic testing of adhesive joints, since specific frequencies can produce erroneous signals for the selected adhesives.

Research into technological processes, such as welding, provides the basis for optimising the strength and quality of PVC joints, which are becoming increasingly important in the context of sustainable construction. The study analysed the influence of welding parameters on the quality and strength of the welds of PVC window profiles reinforced with glass fibre composite. The variable parameters were welding time (21–25 s) and composite milling depth (up to 1 mm). The constant parameters were a welding temperature of 264 °C and a head feed rate of 0.25 mm/s. The results showed that the most favourable results were achieved with a composite milling depth of 1 mm and a melting time of 22 s, which provided the highest average failure load values and met the strength requirements. Additionally, the white welds confirmed that the welding process had been carried out correctly, with no depolymerisation or material degradation occurring. In contrast, milling depths of less than 1 mm or no milling depth at all resulted in problems with dimensional tolerance. In addition, overloading of the welding machine during the welding process was observed for composite milling depths of less than 1 mm and a melting time of 22 s. The results of the study highlight the need for further analysis of the influence of other process parameters, including welding temperature.

Adhesive joints are some of the oldest inseparable connections, and were used much earlier than other non-separable connections (e.g., welded, soldered). Adhesives are widely used in the manufacture of vehicles, household appliances, aircraft, and medicine. One disadvantage of adhesive joints is their long bonding time (amounting, for example, to 72 h for polyurethane adhesives used in bus roof bonding), and another is their production of harmful waste. Tapes that are adhesive coated on both sides are increasingly being used to join parts during production. Such tapes have lower strength than traditional adhesives, but their bonding time is much shorter. In addition, the amount of waste remaining after production is minimized. Tapes, like adhesives, dampen vibrations well and seal the materials being joined. The purpose of this study was to evaluate the influence of selected factors on the quality of tape–steel sheet joints and to assess the possibility of testing acrylic tape–steel sheet joints using ultrasonic methods. It was found that the preparation of a surface for bonding has a significant effect on the quality of the joint, and it was confirmed that non-destructive evaluation of the quality of the tested joints by the ultrasonic method is possible. The decibel drop in the height of the first and fifth pulses obtained on the screen of the ultrasonic defectoscope was proposed as an ultrasonic measure. The highest-quality joints were characterized by a measure in the range of 12 dB, lower-quality areas of about 8 dB, and tape-free areas of about 5 dB. At the same time, it was noted that in the case of proper surface preparation, there was cohesive failure of the joint during breakage.

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 sheathing 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.

The article presents the results of friction and vibroacoustic tests of a railway disc brake carried out on a brake stand. The vibration signal generated by the friction linings provides information on their wear and offers evaluation of the braking process, i.e., changes in the average friction coefficient. The algorithm presents simple regression linear and non-linear models for the thickness of the friction linings and the average coefficient of friction based on the effective value of vibration acceleration. The vibration acceleration signals were analyzed in the amplitude and frequency domains. In both cases, satisfactory values of the dynamics of changes above 6 dB were obtained. In the case of spectral analysis using a mid-band filter, more accurate models of the friction lining thickness and the average coefficient of friction were obtained. However, the spectral analysis does not allow the estimation of the lining thickness and the friction coefficient at low braking speeds, i.e., 50 and 80 km/h. The analysis of amplitudes leads to the determination of models in the entire braking speed range from 50 to 200 km/h, despite the lower accuracy compared to the model, based on the spectral analysis. The vibroacoustic literature presents methods of diagnosis of the wear of various machine elements such as bearings or friction linings, based on amplitude or frequency analysis of vibrations. These signal analysis methods have their limitations with regard to their scope of use and the accuracy of diagnosis. There are no cases of simultaneous use of different methods of analysis. This article presents the simultaneous application of the amplitude and frequency methods in the analysis of vibroacoustic signals generated by brake linings. Moreover, algorithms for assessing the wear of friction linings and the average coefficient of friction were presented. The algorithm enables determination of the time at which the friction linings should be replaced with new ones. The final algorithm analyzes the vibration acceleration signals using both amplitude analysis for low braking speeds, as well as spectral analysis for medium and high braking speeds.

Non-destructive ultrasonic testing can be used to assess the properties and condition of real machine elements during their operation, with limited (one-sided) access to these elements. A methodological question then arises concerning the influence of the material properties of such elements and the condition of their surfaces on the result of ultrasonic testing. This paper attempts to estimate the influence of material hardness and surface roughness on the result of such testing study area testing machine or plant components of unknown exact thickness. Ultrasonic testing was carried out on specially prepared steel samples. These samples had varying surface roughness (Ra from 0.34 to 250.73 µm) of the reflection surface of the longitudinal ultrasonic wave (the so-called reflectors) and hardness (32 and 57 HRC). The ultrasonic measures were the attenuation of the wave, estimated by the decibel drop in the gain of its pulses, and the propagation velocity of the longitudinal ultrasonic wave. Ultrasonic transducers (probes) of varying frequencies (from 2 to 20 MHz), excited by a laboratory and industrial defectoscope were used as the source of such a wave. The results of our research provide a basis for the recommendation of two considered ultrasonic quantities for assessing the material properties of the tested element. This is of particular importance when testing machines or plant components of unknown exact thickness and unknown roughness of inaccessible surfaces, which are the reflectors of the longitudinal ultrasonic wave used for testing. It has been demonstrated that by using the ultrasonic echo technique, it is possible to evaluate the roughness and hardness of the tested elements.

Inseparable joints are widely used in machine and vehicle construction. Hybrid joints include bonding with sheet metal clinching. This combination reduces costs as well as the time of production compared to welded joints. Tests on the samples made of DC01 sheets were carried out. A case study was conducted on four research series. For each series, the shear forces of the joint were measured. The first series consisted of adhesive bonding, and the second and third series consisted of hybrid bonding, during which the sheet metal clinching joint was developed immediately after the completion of adhesive application and after full joint formation. The last test series only includes sheet metal clinching. In the series where bonding was used, the homogeneity of the prepared joints was analysed using the ultrasonic echo technique. The shear strength of the bonded joints was 476 N, whereas the shear strength of sheet metal clinching was 965 N. For the hybrid joint, the average forces were 1085 N (for the specimens in which the lap joint was made after the joint was fully cured) and 1486 N (for the specimens in which the lap joints were made immediately after the adhesive was applied). It was discovered that the clinching of the steel sheets significantly increases the strength of the joint. The stabilisation of the joint causes better crosslinking conditions. This results in an increase in the strength of the hybrid joint.

Adhesive bonding is widely used in modern industry. It has many advantages—the main one being the reduction in production costs. It also has certain limitations. One of the limitations of adhesive bonds is the relatively long bonding time of the joints. The main objective of this research was to determine the possibility of studying the kinetics of adhesive bond formation using a non-destructive ultrasonic method. A research experiment was planned and carried out. Adhesive specimens were prepared, and their quality changes over time were evaluated. In addition, the change in ultrasonic measures during the testing of these bonds was evaluated, as well as the hardness of the adhesive. In this study, the choice of test apparatus was made, in particular ultrasonic probes for the adhesive used and the materials to be bonded. The choice of adhesive was also made, for one in which bonding phenomena occur uniformly throughout the volume. This work examined the changes in the mechanical strength and hardness with time. The tests showed that the greatest changes in mechanical strength occur within the first 24 h after the bond was made. With the mechanical strength reaching 12.6 Mpa after 216 h, the strength in the first 24 h was 10.36 (for bonded steel sheets). For bonded steel discs, the maximum tensile strength was 26.99 Mpa (after 216 h), with a hardness of 22.93 Mpa during the first 24 h. Also, significant changes were observed in the adhesive hardness during the first 24 h. The hardness of the adhesive after 216 h was 70.4 Shore’a on the D scale, while after 24 h it was 69.4 Shore’a on the D scale. Changes in the ultrasonic parameters of the adhesive bond quality were found to occur along with changes in the bond quality.

Adhesive joints are non-separable connections that are used in numerous ways in vehicle construction, particularly in buses. The widespread use of adhesive joints makes it necessary to assess their quality, especially under production conditions. The main goal of this study was to develop a mathematical model to estimate the width of the adhesive path in a plywood-adhesive-closed-profile joint based on selected parameters of the ultrasonic surface wave. A digital ultrasonic flaw detector and Rayleigh wave probes were applied. The test involved evaluating different widths of hybrid adhesive and two-component epoxy adhesive. The tests were conducted on a steel profile from a bus construction. The attenuation of the ultrasonic waves on the steel profile (0.026 db/mm) and the adhesive (0.264 dB/mm) was determined. A one-size-fits-all model for estimating adhesive path width for specific conditions is proposed.

The article presents the results of ultrasonic testing of Ti6Al4V material produced by the conventional method and the laser bed fusion method. Modern manufacturing techniques, such as additive manufacturing, allow the production of parts with complex shapes. It is important to control the condition of such components throughout their lifetime. The purpose of this article was to determine the basic acoustic properties of Ti6Al4V material produced by two different methods—bar drawing and the additive manufacturing method. On this basis, an inspection scheme was developed for adhesive joints, the components of which are made by additive manufacturing technology. The decibel drops in the amplitudes of pulses reflected from the boundary of the adhesive-Ti6Al4V-AM and adhesive-Ti6Al4V joints were determined. The decibel drops for the connection of materials made with additive technology are higher than for the material made in a conventional way. The difference in decibel drop in the amplitudes of the additive manufactured material versus the drawn rod, depending on the ultrasonic head, can be up to 60%. The results of the study provide an important practical guideline for testing adhesive joints of parts made with additive manufacturing technology.