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Ultrasonic testing methods
Jan 09, 2018

Ultrasonic testing methods classified by principle, can be divided into pulse reflection method, penetration method and resonance method.

1. Pulse reflection method

Ultrasonic probe to send pulse wave to be tested pieces, according to the reflected wave to detect defects in the specimen method, known as the pulse reflection method. Pulse reflection method includes defect echo method, bottom wave height method and multiple bottom wave method.

2. penetration method

Penetration method is based on pulse wave or continuous wave through the specimen after the change of energy to determine the defect of a method. Penetration method often use two probes, one received a hair, were placed on both sides of the test probe.

Resonance method

If the sound wave (frequency-adjustable continuous wave) is propagated in the workpiece under test, when the thickness of the specimen is an integer multiple of the half wavelength of the ultrasonic wave, it will cause resonance and the instrument will show the resonance frequency. When there is a defect in the test piece or the thickness of the work piece changes, the resonance frequency of the test piece will be changed. According to the resonance frequency characteristics of the test piece, the method of judging the variation of the defect and the thickness of the work piece is called the resonance method. Resonance method is often used to test the thickness of the specimen.

According to the waveform used in testing, can be divided into longitudinal wave method, transverse wave method, surface wave method, plate wave method, climbing wave method.

A longitudinal wave method

Using a straight probe launch longitudinal wave detection method, known as the longitudinal wave method. At this time, the beam is incident perpendicular to the test surface of the test piece, penetrating the test piece in a constant wave pattern and direction, so it is also called vertical incidence method, referred to as vertical method.

Vertical method is divided into single crystal probe reflection method, dual crystal probe reflection method and penetration method. Common single crystal probe reflection method.

Vertical method is mainly used for casting, forging, rolling and its products of flaw detection, the method of detecting the surface parallel to the defects detected the best. Due to the limitation of blind zone and resolution, the reflection method can only find the defects inside the specimen at a certain distance from the detection surface. When propagating in the same medium, the P-wave velocity is greater than that of the other wave modes, and the penetrating ability is strong and the sensitivity of the grain boundary reflection or scattering is poor. Therefore, the thickness of the detectable workpiece is the largest among all the wave modes and can be used for coarse Flaw detection of crystal materials.

2 wave method

The longitudinal wave through the wedge, water and other media tilt incidental to the probe detection surface, the use of wave conversion to obtain shear wave detection method, known as the shear wave method. Due to penetrating the specimen of the transverse beam and the detection plane acute angle, it is also known as oblique method. This method is mainly used for flaw detection of pipes and welding seams. When other test pieces are flawed, they are used as an effective aid to find defects that are not easily found by the vertical method.

3 surface wave method

The use of surface wave detection method, known as the surface wave method. This method is mainly used for the smooth surface of the specimen. Surface wave wavelength is very short, great attenuation. At the same time, it propagates only along the surface, is responsive to surface coating, greasy, dirty, etc. and is attenuated considerably. Use this feature can be touched by hand oil in the direction of sound beam to touch and observe the height of the defect echo changes, the defect location.

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