The difference between transverse wave and longitudinal wave in ultrasonic testing
Reposted from https://www.sohu.com/a/333891059_784717
Ultrasound is a sound wave with a frequency higher than the frequency (20Hz～20KHz) that human ears can hear. Ultrasound is a wave, so it obeys the law of wave transmission during transmission. For example: the ultrasonic wave keeps traveling in a straight line in the material; reflection occurs at the interface of two different materials; the propagation speed obeys the wave transmission theorem: ν=λf (ν is the wave speed, λ is the wavelength, f is the wave frequency).
The greater the speed of the wave traveling in the dielectric material, the greater the rigidity of the dielectric material; on the contrary, the softer the dielectric material. The rigidity of the dielectric material also reflects the strength of the material, so the higher the material strength, the higher the wave speed; the lower the material strength, the lower the wave speed should be. In this way, know the wave speed, that is, know the strength of the material. Some testing equipment uses the principle of ultrasonic reflection for testing.
Wave is the propagation of vibration, propagating through the medium. In the same homogeneous medium, the propagation of vibration is a uniform linear motion, which is characterized by the wave velocity V. Transverse waves and longitudinal waves are two types of waves. Waves are the propagation of vibration and propagate through the medium. Transverse waves are also called "concave-convex waves." Transverse waves are particles whose vibration direction is perpendicular to the direction of wave propagation. A longitudinal wave is a wave in which the vibration direction of the particle is parallel to the propagation direction of the wave.
Ultrasound is still a sound wave, and it is a longitudinal wave propagation method. The propagation of ultrasonic requires a medium. Ultrasound cannot propagate in vacuum.
The difference between transverse wave and longitudinal wave in ultrasonic testing
Longitudinal wave inspection
Transverse wave inspection
Surface wave inspection
In the ultrasonic detection process, the transmission and reception of ultrasonic waves are realized by the probe.
Commonly used transverse wave probes make the longitudinal wave incident on the interface obliquely, and realize transverse wave flaw detection through waveform conversion. When the incident angle is between the first and second critical angles, the longitudinal wave is totally reflected, and only refracted transverse waves are in the second medium.
Relatively speaking, the accuracy of the transverse wave probe will be higher, and when the shape of the detected object is irregular, the longitudinal wave is used for small angle flaw detection. When the detected workpiece is limited by its geometric shape, the probe's movement range is restricted, such as shafts, pins, bolts, etc., to detect axial and transverse defects at the end, or the workpiece is made of coarse grains such as austenitic stainless steel or the thickness of the detected workpiece When the ultrasonic attenuation is very serious, a small-angle longitudinal wave probe is usually considered for detection.
For example, most of the flaw detection of shaft forgings use longitudinal wave straight probes. However, when the length of the shaft is too long or the shaft has multiple shaft sections with unequal diameters, there will be dead zones that cannot be detected by the sound beam scanning, and a small-angle longitudinal wave straight probe should be used for axial detection.