Research On Nondesturctive Detecting Method For Metal Material Based On Multimodal Signals Of Defects

Along with the rapid development of productivity and the progress of industrial technology, metal materials have been widely used in all walks of life, and play a vital role. In the processing of metal materials, as well as the operating cycle, it will inevitable to produce some defects for many reasons. These defects will have a direct impact on the life and mechanical properties of the material. These defects will gradually develop, deterioration, a nd ultimately will lead to material failure and fracture, even cause a huge loss of life or property. Therefore, it is very important to study the nondestructive testing(NDT) technology of metal materials.In this research, a new method to detect the defects of metallic materials by using photoacoustic signal as the main body, combining with optical signal and ultrasonic signal, is studied. Points included are as follows.First of all, the types and distribution characteristics of metal defects are introduced, which points out the fact that the defects may appear in each position of the material. Also, the principle of optical test, photoacoustic test and ultrasonic test is introduced. The rationality of the multimodal nondestructive testing method is expounded, by analyzing the advantages of the three aspects in the surface, shallow surface and internal defect detection. And then the multimodal NDT method of metal material defects, photoacoustic signal as the main body, combined with the optical signal and ultrasonic signal, is put forward.Secondly, finite element method is used to simulate the process of photoacous tic effect on metal materials. F inite element models are established for the surface impurity defect and the shallow surface crack defects of different sizes. The surface impurity detection method based on laser energy absorption is proposed and verified, by analyzing the initial sound pressure difference between surface impurity and the metal material. Simultaneously, the surface crack size detection method based on surface acoustic wave is proposed and verified, by analyzing the relationship between the surface wave and the crack size.Finally, a multimodal NDT system for metallic defects is built, according to the requirements of the multimodal NDT method for optical signals, photoacoustic signals and ultrasonic signals. The optical, photoacoustic and ultrasonic signals of defects are collected by the multimodal NDT system, and the complete information, including the distribution and size on surface, the depth and internal extension status, etc. of the defect, was obtained through processing and analysis of these signals. Moreover, the wavelet image fusion is used to obtain more accurate and reliable results.This paper expounds and verifies the rationality and feasibility of the NDT based on the multimodal signals of metallic defects from simulation and experiments. It provides a novel, comprehensive and quantitative detection method for N DT of material defects.