Study On Non-linear Acoustics Characterization Of Cracks In Aluminum Alloy Plate

The ultrasonic testing is one of the main methods of non-destructive testing, which makes use of the influence of the inherent crack on ultrasonic propagation and non-destructively in material and detects interior and superficial condition of the material non-destructively. But the general linear ultrasonic testing technology to small fatigue crack is not satisfied to people, because of the remarkable non-linear characteristic in the crack materials. Ultrasonic time reversed technology is used in this paper to study the non-linear characteristic of the ultrasonic in the aluminum alloy, and provides the theoretical basic to the identification and location in aluminum alloy plate.Acoustic time reversal technology is one kind of adaptive technology. Nonlinear acoustic mainly study on non-linear acoustic equation and a series of nonlinear phenomenon arouse from it. Two technologies that non-linear acoustic and time reversal method are combined in this paper, in order to study the propagation characteristic of ultrasonic in aluminum alloy plate, the main contents contain: determining the testing system composed of arbitrary waveform generation, emission sensor, receiving sensor, oscilloscope, laser vibration meter and so on; analyzing the vibration source characteristics of piezoelectric substrate; applying the different waveform including sine wave, triangular wave, square wave, lamb wave and the characteristics of vibration source; using the intact aluminum alloy plate and the defect plate with crack and porosity defect in the experiment in order to analyze the receiving and focusing waveform in time and frequency domain. In the end, summarizing the testing method combined by non-liner acoustic and time reversal method in the defect detection, giving the method to determine the nature and direct current position of cracks. In addition to, giving the detail experimental data and waveform figures, and introducing the software design method in analysis to experimental waveform and data making use of MATLAB.In addition to, using non-linear time reversal technology as the method to detect the cracks in aluminum alloy, which solve the problems on linear acoustic testing technology undergoing the influence on gain noise acoustic, existence of inhomogeneous volume in the tested object and closure of cracks, establishing the foundation to structure late model of testing and evaluating system.