Abstract
We studied the detection and visualization of defects in a test object using a laser ultrasonic guided wave. The scan area is irradiated by a laser generated from a Nd:YAG 532 nm Q-switched laser generator through a galvanometer scanner. The laser irradiation causes the surface temperature to suddenly rise and then become temporarily adiabatic. The locally heated region reaches thermal equilibrium with the surroundings. In other words, heat energy propagates inside the object in the form of elastic energy through adiabatic expansion. This thermoelastic wave is typically acquired by a piezoelectric sensor, which is sensitive in the ultrasonic domain. A single piezoelectric sensor has limited coverage in the scan area, while multi-channel piezoelectric sensors require many sensors, large-scale wiring, and many channeling devices for use and installation. In addition, the sensors may not acquire signals due to their installed locations, and the efficiency may be reduced because of the overlap between the sensing areas of multiple sensors. For these reasons, the concept of a piezoelectric line sensor is adopted in this study for the first time. To verify the feasibility of the line sensor, I- and L-shaped sensors were attached to a steel structure, and the ultrasound signal from laser excitation was obtained. If the steel structure has defects on the back, the ultrasonic propagation image will be distorted in the defect area. Thus, we can detect the defects easily from the visualization image. Three defects were simulated for the test. The results show that the piezoelectric line sensor can detect defects more precisely and accurately compared to a single piezoelectric sensor.
Highlights
Non-destructive testing is carried out in various industries such as aviation, transportation, shipbuilding, and power generation to constantly ensure the safety and maintain the performance of aircraft, machinery, equipment, and structures
The laser ultrasonic guided wave generated absorption and reflection occur in a line verysensor, thin absorbing layer of a solid surfacewas when a atEnergy the object was acquired by the piezoelectric and the visualization algorithm applied hightopower pulse irradiates detect laser and visualize defects.the surface
The ultrasonic waves acquired by the sensor through the signal conditioner and filter were The ultrasonic signal conditioner were waves acquired by the sensor and visualized using ultrasonic propagation and thethe density
Summary
Non-destructive testing is carried out in various industries such as aviation, transportation, shipbuilding, and power generation to constantly ensure the safety and maintain the performance of aircraft, machinery, equipment, and structures. Non-destructive testing has the advantage of being able to inspect the internal conditions without altering the original form or function of the material or product. Non-destructive testing refers to all forms of inspection that identify the existence, condition, and character of defects without destroying, separating or damaging the specimens through special methods exploiting physical phenomena in the materials or products. Many non-contact non-destructive testing systems are being developed for the large-scale inspection of large-sized aircraft structures to ensure worker safety [2,3,4,5]. Non-destructive testing techniques have been developed based on desirable characteristics such as real-time inspection, low cost, high efficiency, and high precision. Laser ultrasonic testing has advantages over UT in that it can be performed in real-time and is non-contact, and does not require a liquid couplant [11,12]. A piezoelectric line sensor using PZT5A3 was adopted to overcome the limitations of
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