The detection methods for debonding of metal composite plates mainly include eddy current thermal imaging detection, radiographic detection, and ultrasonic detection. Ultrasonic testing technology has become the most commonly used method in non-destructive testing due to its strong penetration ability, safe operation, and easy implementation. The detachment causes discontinuity in the ultrasonic propagation path, resulting in reflection and blocking transmission, which can be identified by signal characteristics. For composite plates with a substrate of steel, composite material of titanium, and a total thickness greater than 4mm, GB/T8547-2019 [6] also stipulates the use of traditional piezoelectric probes to detect non bonded areas using reflected waves, but requires good acoustic coupling between the transducer and the composite plate. Laser ultrasound, as a non-contact excitation technology, is increasingly favored by people. Xia Jia et al. tested steel lead using laser excitation laser reception method.
Connect the structure. Janovsk á et al. used ultrasonic resonance spectroscopy to measure the bonding quality of laser cold spray coatings. Chen Chu et al. used synthetic aperture focusing imaging technology based on phase shift to detect defects. However, optical receiving systems are involved in all experiments, and the detection results are easily affected by the surface roughness of the workpiece and environmental noise. To overcome the above difficulties, a non-contact detection scheme is proposed, which uses pulsed laser to excite broadband ultrasonic waves and utilizes electromagnetic ultrasonic transducers to receive signals.
The quality of the bonding surface directly affects the overall strength of titanium steel composite plates. To effectively evaluate the adhesive performance, a laser electromagnetic ultrasonic non-contact detection scheme for debonding defects was proposed. Based on the principle of laser ultrasonic excitation, longitudinal wave acoustic field directionality, and electromagnetic ultrasonic reception theory, a titanium steel composite plate debonding defect detection system was built. On the substrate side or composite side, a pulsed laser linear spot with a length of 10mm and a width of 0.2mm is used to irradiate the surface of the material to excite ultrasonic waves. An electromagnetic ultrasonic longitudinal wave transducer with a center frequency of 1MHz is used to receive signals at the opposite center on the opposite side. The variation law of signal amplitude during the relative debonding defect movement between the main sound beam and the transducer was explored. According to experimental data, it can be seen that as the length of the transducer being obstructed by the defect increases, the signal amplitude gradually decreases. When the main sound beam and transducer are partially obstructed, the signal amplitude decreases to 0.5 times that of a well bonded state. Therefore, debonding defects can be determined based on the characteristics of signal amplitude changes, and it also indicates that laser electromagnetic ultrasound technology is suitable for non-contact detection of the bonding surface of titanium steel composite plates.
In order to meet the non-contact non-destructive testing requirements for the bonding surface quality of titanium steel composite plates, this paper proposes a pulse laser excitation electromagnetic ultrasonic transducer.
The detection scheme for receiving energy. Discussed the excitation principle and longitudinal wave acoustic field directionality of laser ultrasound under ablation mechanism, and analyzed the longitudinal electromagnetic ultrasound.
The main physical structure of the wave transducer and the theory of ultrasonic reception are described, and a scheme and process for debonding detection of titanium steel composite plates are provided. Using theoretical analysis.
The variation law of signals during the movement of defects relative to the axis of the sound beam was studied through detection experiments, and the results showed that the attenuation of signal amplitude varies with occlusion.
As the length increases, it strengthens. When the amplitude decreases to 1/2 of the reference value, the line connecting the center of the light spot and the center of the transducer is the defect boundary. Overall, the measurement method of pulse laser excitation ultrasonic electromagnetic ultrasonic longitudinal wave transducer receiving signals is sensitive to debonding defects and can effectively identify defect boundaries, making it an effective method for testing the bonding quality of titanium steel composite plates.
