Why is the minimum thickness that can be detected by diffraction time difference ultrasonic testing 12 mm?
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Why is the minimum thickness that can be detected by diffraction time difference ultrasonic testing 12 mm? I would appreciate some advice from fellow sailors.
Calculated based on the minimum diffraction angle.
The diffraction phenomenon is the fundamental physical principle underlying TOFD technology. Explanation of diffraction: The phenomenon in which waves continue to propagate after encountering obstacles or small openings through scattering. According to Huygens’ principle, each point on the wave front in a medium can be regarded as a source that emits secondary waves; the envelope of these secondary waves at any given moment constitutes the new wave front at that time. TOFD working principle: TOFD technology uses two broadband narrow-pulse probes, one for transmission and one for reception, for detection; these probes are arranged symmetrically with respect to the weld centerline. The transmitting probe generates unfocused longitudinal wave beams that strike the workpiece under inspection at a certain angle; some of these beams propagate along the near surface and are detected by the receiving probe, while other beams are reflected off the bottom surface before being detected by the probe. The receiving probe determines the location and height of the defect by detecting the diffraction signals from the tip of the defect as well as their time differences. Calculated based on the minimum reflection angle
Main characteristics of TOFD non-destructive testing: It is a method for detecting defects using ultrasonic diffraction time differences. Its principle differs significantly from that of the commonly used pulse-echo ultrasonic testing method: 1. The defect diffraction signal is independent of the angle of the defect； 2. The error in the quantitative location of defects is independent of the signal amplitude. Please let me know if the above passage is correct.
The diffraction time difference ultrasonic method uses an angled transducer that sends out signals and receives echoes; this results in the formation of direct waves and echoes on the surface of the material, which correspond to detection blind zones. As for 12 mm, this value is likely based on the performance of commonly used TOFD devices.