The Study On The Interface Cracks Detection Method In Coating Materials

The coating materials have been widely applied in the aviation, spaceflight and architecture which improve the materials quality of corrosion resistance, heat protection, oxidation-resistance, abrasion resistance, radiation resistance, high strength, light-quality, sealing performance. For the security and safety of coating materials, the requirement of the coating materials quality in engineering is higher and higher. The holes, cracks and interfacial debonding are usually produced in the coating interface, so it is urgent to test the coating interface quality besides the interface strength must be satisfied.It is now the focus and difficulty to detect the coating materials interface cracks by ultrasonic surface wave in the non-destructive test field. A kind of new and simple interface crack detection methods is explored by means of wave propagation and response character in the coating materials. Interface flaws are tested by the composite signal parameter sensitive to the interface cracks by the signal processing technology rather than a directive parameter.The ultrasonic detection technology is widely applied in the NDT field, but the flaw identification in quality is not resolved now because the flaws responding wave is a kind of typical transient pulse signal, wavelet transform has the properties of multi-resolution and high time-frequency resolution, so it's very appropriate for the transient pulse signal processing.The thesis mainly includes there parts: (1) The commonly used and the most advanced non-destructive methods are compared, wavelet package signal processing is put forward. (2) Investigations on the relations between energy and cracks, relative energy feature parameter is put forward and the programmed calculation is carried out. (3) Investigations on the relations between relative energy feature parameter, coating thickness, crack size and the materials character by means of FEA in order to detect the crack location and size in quantification.In the first part, comparison on the popular NDT methods specially the respond signal processing methods in ultrasonic surface wave detection, wavelet package analyses has been applied in the composite materials. Investigation on the signal analysis by wavelet package method.In the second part, wavelet package relative energy feature parameter is carried out based on the wavelet package signal analysis theory. The relation between structure flaws and signal energy is established to prove this parameter sensitivity to cracks.In the third part, investigations on the relations between relative energy feature parameter, coating thickness, crack size and the materials character by means of FEA provides theoretical foundation to measure the crack size.