TOFD, ultrasonic time-of-flight diffraction method. Technology for the detection, quantification and localization of material defects.
Time Of Flight Diffraction (TOFD) ultrasonic diffraction time-of-flight method is a method to detect defects by relying on the diffraction energy obtained from the "end angle" and "end point" of the internal structure of the test piece (mainly referring to defects). for the detection, quantification and localization of defects.
TOFD technology was first proposed by Dr. Silk of the National Nondestructive Testing Center in Harwell, UK in the 1970s. Its principle originated from Dr. Silk's research on crack tip diffraction signals. During the same period, the Chinese Academy of Sciences also detected the crack tip diffraction signal, and developed a set of crack height measurement process methods, but did not develop the current TOFD detection technology.
TOFD technology is first of all a detection method, but the instruments that can meet the requirements of this detection method have not yet come out. TOFD requires the probe to achieve a sufficient signal-to-noise ratio when receiving weak diffracted waves. The instrument can record the A-scan waveform throughout the process and form a D-scan spectrum, and the A-scan time value can be converted into a depth value by the method of solving triangles. In the same period, the technical level of industrial flaw detection failed to reach the level that can meet these technical requirements. It was not until the 1990s that the development of computer technology made the digital ultrasonic flaw detector mature, and it became possible to develop a portable and cost-effective TOFD detector.
Since the 1990s, my country began to introduce TOFD detection technology. By 2005, Wuhan Zhongke Innovation Technology Co., Ltd. of the Chinese Academy of Sciences developed the first domestic TOFD special detection equipment. In the development process of TOFD system, the application of computer and digital technology has played a decisive role. Early conventional ultrasonic testing used analog flaw detectors, using shear wave oblique probes or longitudinal wave straight probes for manual scanning. In most cases, single probe detection was used. The instrument displayed A-scan waveforms, and the scanning results could not be recorded. , and cannot be saved as permanent reference data. Since the 1990s, analog instruments have gradually evolved into digital instruments controlled by computers, and then digital instruments have gradually become more sophisticated and complex. They can be configured with probe arrays, automatic scanning devices, and can record and save all scans. Check data for archiving and analysis.
TOFD detection needs to record the complete uncorrected A-scan signal of each detection position. It can be seen that the data acquisition system of TOFD detection is a more advanced and complex digital system, in terms of receiving amplification system, digital sampling, signal processing, information storage, etc. have reached a higher level.