Theoretical Research On Photoacoustic Detection Of Crack And Impurity In Composites

Although photoacoustic phenomenon was found by the famous phone inventor A.G.Bell as early as 1880, researches and technologies about photoacoustic boomed because of the development of laser technology until 1970s.Nowadays, there are many detection technologies based on photoacoustic phenomenon, such as photoacoustic spectroscopy, photoacoustic microscopy, etc. These detection technologies have the advantages of non-destructive, high sensitivity, high contrast, etc. They have been widely used in physic, chemical, biomedicine and many other areas.The development of modern industry has higher and higher requirement on materials. By combining different materials through physic or chemical methods, we can get composites which have new characteristics. When component materials and preparation methods change, different composites can have different excellent characteristics such as lightweight, high strength, good heat insulation, corrosion resistance, etc. So composite can meet many special needs, which makes it widely used in aerospace, automobile, building and many other areas.In this work, we study photoacoustic detection of crack and impurity in multilayer composite theoretically. Based on a fully thermally-mechanically coupled model of multilayer composite, we analysis and compare influences of air and liquid film in photoacoustic cell on photoacoustic signals. Taking the Si-Al model, which contain crack or impurity, as the research object, we write a program to calculate the photoacoustic signals and find their variation characteristics with different parameters. Based on large amounts of data, we use program to simulate photoacoustic detection. Random numbers generated by normal distribution function are used as measurements. The depth and width of crack or impurity can be fitted by least squares method. Error analysis is done for those serious distortions to find the distortion causes and the fitting method is improved.