Research On Surface Acoustic Wave Technology Detecting Surface Processing Cracks In Metal

Surface acoustic wave detection technology has the capacity of accurately, quick and easily measuring the physical properties in the surface of media, with some advantages that other current testing methods lack of. Therefore, a deep and thorough investigation of this technology will contribute to simplifying the measurement process of surface integrity in industry, saving testing time, improving testing efficiency, and providing a reliable testing method that could assure the quality, safety and lifespan of workpieces.Through theoretical analysis, finite element simulation and experimental measurement techniques, surface acoustic wave detection on surface crack were studied.1. In the theoretical part, the elastic wave equation in a semi-infinite media, and the wave propagation on a layered material, as well as its interaction on phase velocity have been studied, which provided the basis and hypothesis for the further research.2. In the simulation part, by means of establishing a series of models with different size of surface cracks, simulation results and impacts from different physical natures of the load types and different envelope and frequency load functions have been compared and analyzed, then a novel and more real-like load function has been proposed. In the time and frequency domains, the surface acoustic wave propagation in a model with attenuating effect and its influence on the wave amplitude and phase velocity from the surface crack has been studied.3. In the experimental part, after a sensing device suitable to the current laser-generated/PVDF SAW experimental system has been designed and constructed, and then, a series of ultrasonic signals have been detected on a prepared grinded steel sample.Through the above research, the feasibility of detecting surface cracks in steel sample by means of SAW has been proved, and the relation between phase velocity and the diameter of cracks in frequency domain according to the simulation. The experimental testing system and the PVDF sensor has been designed and constructed. Additionally, a series of effective ultrasonic vibration signal has been obtained.