Numerical Simulation And Experimental Investigation On Material Gradient Test Using Ultrasonic CT Technology

Functionally Graded Material (FGM) will be widely used in the feature because of its excellent thermodynamic property, but the existing test methods of FGM are not complete, and needed further study. This paper managed to detect the internal ingredient and structure of material using ultrasonic computerized tomography, and give a reference to the FGM property test. But the gradient of material will lead to scattering and reflection of ultrasonic wave, which cause attenuation and trace change of the signal. Valid analysis of these phenomena is important for the improvement of test accuracy.This paper studied the procedure of ultrasonic wave transmission in the graded material by finite element method and experiments, and analyzed the factors which influenced test accuracy. Main contents are as follows:1) The theory of CT system was introduced. Speed, accuracy and application field of several kinds of reconstruction algorithms were summarized. Fan beam filter backprojection method was chosen for this study considering the gradient architecture of material and facility of projection data acquisition.2) The finite element model which is suitable for the study of ultrasonic wave transmission in isotropic elastic solid material was built on ANSYS platform. Some key factors which may impact image reconstruction were analyzed, result showed that the gradient of material and the frequency of excitation signal would impact the test result. Some special phenomena appeared in simulation were explained and the valid projection data was collected.3) Fan-beam projection experiment was done with uniformed circle specimen and double-layer circle specimen, and the projection data was used to reconstruction original image. The result shows that the ultrasonic CT system has good accuracy when the specimen is low level non-uniform and the scattering and reflection are weak.