Daily Question (20100113) Ultrasonic Testing

Based on their principle, ultrasonic testing methods include pulse reflection method, penetration method, and resonance method. The most commonly used method at present is pulse reflection. Pulse reflection method is a technique that uses an ultrasonic probe to emit pulses into the test specimen, and detects defects in the specimen based on the reflected waves. The penetration method determines the internal condition of a workpiece based on changes in ultrasonic energy. It involves placing the transmitting probe and the receiving probe on two opposite surfaces of the workpiece, respectively. The ultrasonic energy emitted by the transmitting probe is constant; when there are no defects in the workpiece, the energy received at the receiving probe after the ultrasonic waves have penetrated a certain thickness of the workpiece remains constant as well. When the workpiece has defects, the reflected light from these defects reduces the amount of energy received, thereby indicating the presence of defects in the workpiece. The resonance method relies on the principle of resonance; after the probe emits ultrasonic waves at the test piece, the frequency of these sound waves is continuously adjusted to change their wavelength. When the thickness of the test piece is an integer multiple of half the wavelength of the sound waves, a standing wave is generated within the test piece. By measuring the frequency of the ultrasonic waves and the number of resonances, the thickness of the test piece can be calculated.

There are various classification methods for ultrasonic testing: classified by the principle of ultrasonic testing, they include pulse reflection method, penetration method, and resonance method. The most commonly used method at present is pulse reflection. The process of mechanical vibration propagating through a medium is called a wave. The human ear can detect elastic waves with frequencies above 16 hertz and below 20,000 hertz; therefore, elastic waves within this frequency range are also known as sound waves. Elastic waves with a frequency of 10 Hz are known as infrasound, while elastic waves with a frequency higher than 20,000 Hz are called ultrasound. Infrasound and ultrasound are beyond the range of human hearing.

1. Classified by the principle of ultrasonic testing: it includes three methods – pulse reflection method, penetration method, and resonance method. The most commonly used method is pulse reflection. 2. Ultrasonic waves are a type of vibration wave.

There are three methods: pulse reflection, penetration, and resonance. Pulse reflection relies on the echoes from defects and those from the bottom surface to make judgments. It is a longitudinal wave when vertical, and a transverse wave when obliquely incident. The penetration method determines the condition of defects based on their shadows. The resonance method determines the presence of defects by observing the standing waves generated by the object under inspection

It can be divided into ultrasonic flaw detection and ultrasonic thickness measurement, as well as ultrasonic measurement of grain size and stress, etc. In ultrasonic flaw detection, there are the pulse reflection method, penetration method, and resonance method. Pulse reflection method makes judgments based on the echoes from defects and those from the bottom surface; penetration method determines the presence of defects by examining their shadows; whereas resonance method assesses the presence of defects or measures the plate thickness by detecting standing waves generated in the material being inspected. The most commonly used method at present is the pulse reflection method. Pulse reflection testing uses longitudinal waves for vertical inspection and shear waves for oblique inspection. Ultrasonic waves are sent toward one side of the object under inspection, and then the waves reflected back from defects are received on the same side; the condition of the defects is determined based on these echoes. Pulse reflection testing includes longitudinal wave testing and transverse wave testing. The process of mechanical vibration propagating through a medium is called a wave. The human ear can detect elastic waves with frequencies above 16 hertz and below 20,000 hertz; therefore, elastic waves within this frequency range are also known as sound waves. Elastic waves with a frequency of 10 Hz are known as infrasound, while elastic waves with a frequency higher than 20,000 Hz are called ultrasound. Infrasound and ultrasound are beyond the range of human hearing. Characteristics of ultrasonic waves: 1. The ultrasonic wave beam can be focused in a specific direction and propagate in a straight line through the medium, exhibiting good directivity. 2. As ultrasound propagates through a medium, it undergoes attenuation and scattering. 3. Ultrasonic waves undergo reflection, refraction, and wave pattern transformation at the interface between different media. By utilizing these properties, the reflected waves coming back from the defect interface can be obtained, thereby enabling the detection of defects. 4. The energy of ultrasonic waves is much greater than that of sound waves. 5. Ultrasonic waves suffer little transmission loss in solids, allowing for a large detection depth. However, ultrasonic waves are reflected and refracted at heterogeneous interfaces, and in particular, they cannot pass through the gas-solid interface. If the metal contains defects such as pores, cracks, delamination (with gas within these defects) or inclusions, ultrasonic waves will be reflected entirely or partially when they reach the interface between the metal and these defects. The reflected ultrasonic waves are captured by the probe, processed by the circuits inside the instrument, and waveforms at different heights and at regular intervals are displayed on the instrument’s fluorescent screen. The depth, position, and shape of defects within the workpiece can be determined based on the characteristics of the waveform changes.

Pulse reflection method, penetration method, and resonance method – ultrasonic waves have high frequencies and short wavelengths; they can travel in straight lines just like light, which allows us to emit ultrasonic waves in a specific direction. Sound waves are longitudinal waves and can propagate smoothly through human tissues. Ultrasonic waves generate reflected waves when they encounter interfaces between different media. Sound waves are a type of acoustic wave and belong to the category of mechanical waves; they are longitudinal waves that can be detected by the human ear, with a frequency range of 16Hz to 20KHz. Sound waves with a frequency below 16 Hz are called infrasound, while those with a frequency above 20 KHz are known as ultrasonic sound waves.

Ultrasonic testing is primarily used to detect internal defects in test specimens, and it is widely applied. Ultrasonic testing belongs to the reflected wave detection method, that is, it determines the size and location of defects based on the intensity and propagation time of the reflected waves. The frequency range for ultrasonic testing is 0.4–25 MHz, with 1–5 MHz being the most commonly used range. Classified by the principle of ultrasonic testing: it includes three methods—pulse reflection method, penetration method, and resonance method. The most commonly used method at present is pulse reflection. Ultrasonic testing can be applied to butt welds, fillet welds, plates, pipes, bars, forgings, as well as composite materials ； It has a higher detection rate for area-type defects, but a lower detection rate for volume-type defects ； It is suitable for inspecting workpieces with larger thicknesses; it has a low inspection cost, fast speed, and its inspection equipment is easy to carry. Its limitation is that it cannot produce intuitive images of defects, makes qualitative analysis difficult, and has low quantitative accuracy ； There are no direct witness records for the test results ； There are also certain requirements regarding the material and grain size.

Based on their principles, ultrasonic testing can be classified into three methods: pulse reflection method, penetration method, and resonance method. Ultrasonic waves are mechanical waves with high frequencies (frequencies greater than 20,000 Hz) that lie beyond the range of human hearing.

There are three methods: pulse reflection, penetration, and resonance. Pulse reflection relies on the echoes from defects and those from the bottom surface to make judgments. It is a longitudinal wave when vertical, and a transverse wave when obliquely incident. The penetration method determines the condition of defects based on their shadows. The resonance method determines the presence of defects by observing the standing waves generated by the object under inspection

What is the basic principle of ultrasonic flaw detection? Ultrasonic testing is a method for detecting defects in parts, which takes advantage of the ability of ultrasonic waves to penetrate deep into metal materials. As these waves pass from one surface to another, they are reflected at the interface edges. When the ultrasonic beam travels from the surface of the part through a probe into the metal, it is reflected when it encounters defects or the bottom surface of the part; these reflected waves create pulse patterns on a fluorescent screen, and it is by analyzing these pulse patterns that the location and size of defects can be determined. How many categories are there for defects? How to classify? In ultrasonic testing of welds, defects in the weld are generally classified into three categories: point defects, linear defects, and surface defects. In classification, defects with a length of less than 10 mm are referred to as point defects ； Generally, length is not measured; defects smaller than 10 mm are counted as 5 mm. Defects with a length greater than 10 mm are called linear defects. Defects with a length greater than 10 mm and a height greater than 3 mm are called planar defects.