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Based on the existing crack detection methods of fasteners, this paper studies from two aspects of wavelet analysis and electromagnetic pulse nondestructive testing, and summarizes the current status, advantages, and disadvantages of existing crack detection technologies, as well as research hotspots and development directions.

Fasteners are currently widely used in engineering fields such as machinery, construction, bridges, and oil production. As the basic unit of large structural parts, many fasteners will have defects such as cracks, corrosion, pits, and man-made damage in their work, and crack defects account for a very large proportion and harmfulness, which seriously threatens existing structures and The safety and reliability of the organization.

Crack detection is to test and evaluate the mechanical structure to determine whether there are cracks, and then determine the location and degree of cracks. With the rapid development of modern machinery manufacturing, electronic technology and computer technology, non-destructive testing technology has been greatly developed, and crack detection technology has also been rapidly developed. The custom metal stamping parts factory first introduces traditional crack detection methods. On this basis, it summarizes modern nondestructive detection methods based on wavelet analysis and electromagnetic (eddy current) pulses, and points out fastener crack detection methods Hot spots and directions of development.

Non Standard Hexagon Bolt Supplier

1. Traditional crack detection methods

There are many traditional crack detection methods, which can be divided into two categories: conventional detection and unconventional detection. Conventional testing methods include eddy current testing, penetration testing, magnetic particle testing, radiographic testing, and ultrasonic testing; unconventional testing methods include acoustic emission, infrared testing, and laser holographic testing.

(1) Conventional detection methods

At present, the simple detection of cracks in engineering fields such as machinery, construction, and oil extraction generally adopts conventional detection methods. Different inspection methods are adopted for different institutions. For example, ultrasonic inspection is mainly used for the detection of metal plates, pipes and bars, castings, forgings and welds, and concrete construction such as bridges and building construction; the radiographic inspection is mainly used for machinery, Welding, shipbuilding, electronics, aerospace, petrochemical and other fields of castings, welds, etc .; magnetic particle detection is mainly used for metal castings, forgings, and welds; magnetic particle detection is mainly used for metal castings, forgings, and welds Inspection; penetration testing is mainly used for the detection of castings, forgings, welded parts, powder metallurgy parts, and ceramics, plastics, and glass products of non-ferrous and ferrous materials; eddy current testing is mainly used for the detection of conductive pipes, bars, and wires Material sorting. For crack detection of fasteners, ultrasonic testing and eddy current testing can be used. For example, in the experimental study of the optimal eddy current testing parameters for small cracks in fasteners, the best detection parameter section with a linear relationship between the eddy current testing parameters of the small cracks and the phase signal is obtained, which improves the detection accuracy and external type of small cracks in the bar stock. The selection of fastener eddy current testing parameters has an important guiding role. However, there are many interference factors in eddy current testing, which requires special signal processing technology. In addition, there is a Lamb wave (Lamb wave) propagation energy spectrum structure crack detection method, which has the characteristics of strong penetration, high sensitivity, fast and convenient, but sometimes there will be a blind spot, blocking phenomenon occurs, and close cracks cannot be found. It is difficult to qualitatively and quantitatively characterize the defects found. Most of the fasteners are detected by magnetic particle detection and fluorescent flaw detection methods. The relative detection efficiency is relatively high, but it consumes manpower and material resources and damages people's physical health. At the same time, due to the influence of human factors, the phenomenon of missing detection often occurs.

(2) Unconventional detection method

When testing cracks on fasteners, if conventional inspection methods do not achieve the required purpose, consider using non-conventional inspection methods. Non standard hexagon bolt supplier lists three commonly used unconventional crack detection methods.

1) Acoustic emission technology. This technology is the most mature in the crack detection of pressure equipment. It has achieved ideal results in the safety assessment of pressure vessels and pressure pipelines and has also been vigorously developed in the crack detection of aerospace and composite materials. For the diagnosis of rotating machinery cracks, there is a certain degree of development in the detection of rotating shafts, gear fatigue cracks, and bearing cracks. The advantage of acoustic emission is that it is a dynamic detection method. The energy detected by acoustic emission comes from the object to be tested, rather than being provided by non-destructive testing instruments like ultrasound or radiographic testing. Acoustic emission testing is very sensitive to defects and can detect and evaluate the active defect state in the structure as a whole. The disadvantage is that the detection is greatly affected by the material; the detection room is affected by electrical noise and mechanical noise; the positioning accuracy is not high, and the identification of cracks can only give limited information.

2) Infrared detection. Mainly used in power equipment, petrochemical equipment, mechanical processing process detection, fire detection, crop selection, and non-destructive detection of defects in materials and components. The advantage of infrared non-destructive testing technology is that it is a non-contact testing technology, with a high spatial resolution at long distance, safe and reliable, harmless to the human body, high sensitivity, wide detection range, fast speed, and no impact on the measured object. The disadvantage of infrared detection is that because the detection sensitivity is related to the thermal emissivity, it is disturbed by the surface and background radiation of the test piece, affected by the size of the defect, and the depth of the burial. And the location, the interpretation of the test results is more complex, reference standards are required, and the test operator needs to be trained.

3) Laser holographic detection. Mainly used for a honeycomb structure, composite material detection, solid rocket motor shell, insulation layer, cladding layer, and propellant grain interface between defects detection, printed circuit board solder joint quality detection, and pressure vessel fatigue crack detection. It has the advantages of convenient detection, high sensitivity, no special requirements for the measured object, and a quantitative analysis of defects. The disadvantage is that for deeply buried debonding defects, they can only be detected when the debonding area is quite large. In addition, laser holographic testing is mostly carried out in a dark room, and strict vibration isolation measures are required, which is not conducive to on-site testing and has certain limitations.