Method for monitoring ferromagnetic material fatigue crack expansion by variated magnetic signal

A technology of fatigue crack growth and ferromagnetic materials, applied in the direction of analyzing materials, material magnetic variables, measuring devices, etc., can solve problems such as inapplicability, and achieve the effects of simple operation, accurate detection results and good repeatability

Inactive Publication Date: 2008-01-23
ACADEMY OF ARMORED FORCES ENG PLA
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Problems solved by technology

[0006] The present invention is to solve the problem that the only existing acoustic emission technology that can rea

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  • Method for monitoring ferromagnetic material fatigue crack expansion by variated magnetic signal
  • Method for monitoring ferromagnetic material fatigue crack expansion by variated magnetic signal
  • Method for monitoring ferromagnetic material fatigue crack expansion by variated magnetic signal

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Embodiment Construction

[0024] The content of the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments. In a specific embodiment, the material of the component is 18CrNiWA steel.

[0025] Firstly, the ferromagnetic material 18CrNiWA steel, which is the same as the material of the tested component, is selected, and a plate-shaped standard tensile test piece with a central penetration crack is made according to the national standard GB / T6398-2000. The prefabricated central crack is processed by wire cutting technology, the original length is 2a 0 =12mm (as shown in Figure 1). Carry out final heat treatment on the standard sample according to the heat treatment specification of the tested component, in a vacuum of 8×10 -1 Heat to 860°C in Pa WZC-30 type vacuum heat treatment furnace, keep warm for 30 minutes, oil quench, then temper at 180°C, and water cool to room temperature. To obtain a pure initial magnetic state on the surface of the s...

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Abstract

The invention provides a method for monitoring the expansion of fatigue crack in magnetic material by taking use of unusually changed magnetic signals, which pertains to the technical field of non-destructive detection. The method comprises the following procedures: a standard specimen is made with central crack of same material and heat treatment state as an object to be tested; after cycling preset times in fatigue testing, the central crack area of the standard specimen is scanned by a magnetic sensor with fixed liftoff, the normal component Hp(y) signal of the surface stray magnetic field of the scanned area is obtained; the length of the central crack 2a is measured; the max. value Delta Hp(y)max of the self unusually-changed magnetic signal generated by the fatigue crack is extracted as the detection threshold for the cycle numbers; the Delta Hp(y)max and 2a are linearly fit to get the Delta Hp(y)max-2a relationship formula; the object to be tested is inspected by the same liftoff with above magnetic sensor, the measured Delta Hp(y)smax is compared with the detection threshold; the expansion process of the fatigue crack is obtained according to Delta Hp(y)max-2a linear relationship. The invention is easy to operate, with accurate detection results, can monitor the expansion of crack dynamically under an unloaded state.

Description

technical field [0001] The invention relates to a method for monitoring the expansion of fatigue cracks by using spontaneously generated abnormal signals in the geomagnetic field environment, which is suitable for dynamic quality control of ferromagnetic parts bearing fatigue loads and belongs to the technical field of non-destructive testing. Background technique [0002] The surface of ferromagnetic materials in the geomagnetic field will spontaneously generate stray magnetic field signals during processing, manufacturing and service, which can be detected by detecting the normal component H of the stray magnetic field p (y) The zero value point and the maximum value of the magnetic field gradient are used to qualitatively determine the location of the stress concentration of the ferromagnetic material, that is, the potential dangerous area. This is also known as metal magnetic memory detection technology. [0003] The development time of metal magnetic memory detection t...

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Application Information

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IPC IPC(8): G01N27/80G01N27/83G01N3/00
Inventor 徐滨士董世运董丽虹王丹
Owner ACADEMY OF ARMORED FORCES ENG PLA
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