Research On Key Technologies Of On-line Phased Array Ultrasonic Nondestructive Testing For Small Diameter Bars

As a significant foundation of moden industry, bars are applied in various fields which makes a great contribution to the development of national economy and the modernization of national defense. During the process of forging and rolling, there will be some defects on bars, such as longitudinal crack, transverse crack, and scaly folding. Once bars under high temperature, high pressure, or alternating load, they may fail and cause significant economic losses and casualties. Therefore, it is necessary to carry out nondestructive testing to ensure the quality of bars. Ultrasonic nondestructive testing technology is one of the most effective means to detect the bar defects. Ultrasonic nondestructive testing technology has strong penetration, high resolution, high detection sensitivity and rich information. Also it is harmless to human body. However, with the continuous improvement of social productivity and the rapid development of social economy,the conventional ultrasonic nondestructive testing technology is unable to meet the demand of modern bar defect detection. Phased array ultrasonic nondestructive testing technology is flexible,fast,accurate and easy to electronic. Consequently, it becomes research focus in the field of ultrasonic nondestructive testing. Supported by the National Science Foundation Project "Research on theory and technology of automatic online phased array ultrasonic imaging with high performance for cylindrical components"(NO.51675480), the research on key technologies of on-line phased array ultrasonic nondestructive testing for small diameter bars is put forward. Based on the study of ultrasonic nondestructive testing technology of small diameter bars array and the realization of modeling of the acoustic field of phased array concave linear ultrasonic transducer, This paper simulates and optimizes the parameters of concave linear phased array ultrasonic transducer. What's more, combined with mechatronic technique, an on-line phased array ultrasonic nondestructive testing system for small diameter bars is developed,and related experiments are carried out. This research has laid the necessary theoretical and technical foundation for the automatic ultrasonic nondestructive testing for small diameter bars. The main contents of this thesis are summarized as follows:Chapter 1, the significant position of bars in national economy and social development is introduced and the research status of traditional nondestructive testing technology and ultrasonic nondestructive testing technology is summarized. The application of on-line ultrasonic nondestructive testing of small diameter bars is pointed out to clarify the main research of this paper and indicates the direction for the following chapters.Chapter2, based on Huygens principle, the focusing, deflection and focusing deflection of the beam of phased array ultrasonic transducer are accomplished. The reflection,refraction and wave transformation of ultrasonic wave at the interface between water and steel are analyzed and according to the defect types of the small diameter bars, the corresponding testing methods are put forward. In addition, the sound field modeling of phased array concave linear ultrasonic transducer is completed by analytic method. Based on the optimization target selection of phased array ultrasonic transducer parameters, the influence of adjacent elements corresponding on the central angle, array element width,dynamic array element number, and frequency of linear phased array ultrasonic transducer of concave is studied.Chapter3, the detection method of the profile of the small diameter bars is introduced.On the basis of the envelope extraction of the ultrasonic signal and the temperature compensation of the ultrasonic wave in the coupled water, the contour of the small diameter bars is detected. Detection of sound field on the normal incidence and oblique incidence concave linear phased array ultrasonic transducer module are respectively simulated by CIVA sound field calculation. The defect model of longitudinal crack and transverse crack are set up and the defect detection simulation is carried out by CIVA software defect detection module. It provides further theoretical support for the follow-up research and development.Chapter4, the overall scheme design of on-line phased array ultrasonic nondestructive inspection system for small diameter bars is completed, the objective function of ultrasonic nondestructive testing system is defined, and the overall scheme of the system is designed.Based on the distributed system architecture, the development of the hardware module,software module and the integration of the whole system are completed, and the research and development of the on-line phased array ultrasonic nondestructive inspection system are accomplished. Through the experimental study on the bar with artificial defects, the research content of this paper is confirmed.Chapter5, the main study objective and achievements of the study are concluded, and the improvement space and direction of future research are put forward.