Simulation Of Ultrasonic Propagation Path In Austenitic Stainless Steel Welds

Austenitic stainless steels, as a kind of material with good mechanical properties and great corrosion resistance, are widely used in nuclear power plants, petrochemical industry, food production and medical instruments. In order to prevent potential risks, improve the security, ultrasonic nondestructive inspections are often applied to austenitic welding structures for inner defects. Due to the non-phase-transition feature during the welding process, austenitic welds often result in cylindrical crystals under the impact of heat cycles. The huge size of those cylindrical crystals makes the welds featured with an overall anisotropy and heterogeneity. During the ultrasonic inspection of the austenitic welds, some complicated phenomena would occur such as"beam distortion"and"curved propagation", which severely affects the detection sensitivity and accuracy.In order to solve the prior difficulties during ultrasonic inspections of austenitic welds, a research on the propagation behaviors of ultrasonic in austenitic welds was undertaken by means of simulation methods.To understand better the basic physical process of ultrasonic testing, the radiated acoustic field of ultrasonic transducers was studied first, which in some sense reflects the generation of ultrasonic. In the process, the radiated acoustic fields of different types of transducers were simulated via multi-Gaussian beam model, and a visualized result was given. By comparing with the experimental results, the accuracy of the simulation was verified. On the basis of the above efforts, a programme with friendly graphic user's interface was developed to simulate acoustic fields radiated by different types of transducers.The field distribution of ultrasound propagating in media was researched, during which the reflection/refraction, focusing/defocusing and wave type transition behaviors were simulated when ultrasonic were propagate through plane and curved media boundaries. By means of multi-Gaussian beam model in anisotropic media, the acoustic field change was simulated when ultrasonic was propagating through isotropic/anisotropic borders, and the influence of crystal grain orientation angle upon ultrasonic propagation behaviors was discussed. By analyzing the characteristics of the tissue structures and studying the grain orientations in austenitic welds, a grain orientation recognition algorithm was raised based on the image processing technology. The algorithm was then applied to a macrograph of an austenitic weld to obtain the grain orientation angle distribution of the weld. On that basis, by treating the austenitic weld as multi-layered media, the ultrasonic field in the weld was calculated via multi-Gaussian beam model, and the propagation path of ultrasound was predicted as well. With an experiment where a T/R mode B-Scan was applied, the energy distribution of the destination surface was measured when ultrasonic was propagating through an austenitic weld, and the predicted results were given as well, the comparisons between which demonstrate satisfactory agreement, which verified the reliability of the simulation method.