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Online monitoring method for fatigue crack damage propagation of sintered neodymium iron boron

A technology for fatigue damage and fatigue cracks, applied in the field of non-destructive testing, can solve the problems of high environmental requirements, high monitoring costs, and difficult application of optical instrument monitoring methods, and achieve the effects of low requirements, saving monitoring costs, and wide application scenarios

Active Publication Date: 2021-03-16
NANCHANG HANGKONG UNIVERSITY +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, this method needs to build a complex in-situ crack monitoring system, and the monitoring cost is high; and the monitoring process has high environmental requirements, and sufficient light is required to obtain a clearer monitoring picture
In addition, the fatigue fracture of brittle materials is sudden, and the microscopic cracks reach the critical length soon after formation, and enter the crack instability expansion stage almost without going through the crack metastable state expansion stage. The crack growth speed is extremely fast and there is no obvious plasticity before fracture. Therefore, the commonly used optical instrument monitoring method is difficult to apply

Method used

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  • Online monitoring method for fatigue crack damage propagation of sintered neodymium iron boron
  • Online monitoring method for fatigue crack damage propagation of sintered neodymium iron boron
  • Online monitoring method for fatigue crack damage propagation of sintered neodymium iron boron

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Experimental program
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Effect test

Embodiment 1

[0057] The stress energy increased in the step S4 can be expressed as:

[0058]

[0059] Among them, σ is the stress, r1, r2, r3 are the direction cosines of the stress action, α1, α2, α3 are the direction cosines of the magnetization intensity, λ 100 , lambda 111 is the magnetostriction coefficient;

[0060] The sintered NdFeB sample without loading fatigue load history is magnetostrictive and isotropic, then λ 100 =λ 111 =λ σ ; where λ σ is the magnetostriction coefficient under the stress σ, then the increased stress can be expressed as:

[0061]

[0062] Among them, θ is the angle between the stress direction and the magnetization vector direction;

[0063] Assuming that the stress is parallel to the direction of magnetization in the uniaxial tensile test, then there is cos 2 θ=1, then the stress energy is:

[0064]

[0065] According to the energy balance theory based on the basic theory of ferromagnetism, in the geomagnetic field environment where the ma...

Embodiment 2

[0073] The electromagnetic constitutive relation under the air medium obtained in step S5 during the on-line monitoring of fatigue damage is expressed as:

[0074] B=μ 0 H (7)

[0075] Among them, μ σ is the vacuum permeability, B is the magnetic induction of the earth's magnetic field;

[0076] The electromagnetic constitutive relation of a ferromagnetic medium in a magnetic field environment is:

[0077]

[0078] Among them, M(H, σ) is the magnetization change of sintered NdFeB under the action of force-magnetic coupling, and the magnetic induction value B of sintered NdFeB T Analysis of the variation of sintered NdFeB relative permeability μ σ With the evolution process of fatigue damage, the online monitoring of the fatigue damage expansion process of sintered NdFeB is realized.

Embodiment 3

[0080] The judgment phenomenon of fatigue damage accumulation and fatigue fracture in the step S7 is as follows: when the residual value of magnetic induction fluctuates up and down in a small range, it indicates that it is in the process of fatigue damage accumulation; when the residual value of magnetic induction has an obvious upward trend, It shows that fatigue fracture occurs, and after the fatigue fracture behavior ends, the residual value of magnetic induction intensity shows a negative growth phenomenon, and the magnetic induction intensity value drops significantly. is caused by stress relief due to fatigue fracture.

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Abstract

The invention discloses an online monitoring method for fatigue crack damage propagation of sintered neodymium iron boron, and relates to the technical field of nondestructive testing. By means of anonline monitor provided with a high-precision magnetic sensor, on the premise that the monitoring accuracy is guaranteed, the real-time online monitoring process of the fatigue damage propagation process of brittle materials such as sintered neodymium iron boron can be achieved. Meanwhile, the requirement for the monitoring environment is low, and application scenes are wide. According to the monitoring method provided by the invention, the stress concentration condition of sintered neodymium iron boron before fatigue fracture can be reflected on the premise of not damaging the structural integrity of the sintered neodymium iron boron, qualitative analysis is performed on the early fatigue damage accumulation process, the occurrence of sudden brittle fatigue fracture behavior of the sintered neodymium iron boron can be monitored, the problem that an existing optical monitoring system cannot monitor brittle fatigue fracture is effectively solved, and meanwhile a new monitoring method isprovided for the early-stage stress concentration situation in the fatigue damage process.

Description

technical field [0001] The invention relates to the technical field of non-destructive testing, in particular to an online monitoring method for sintered NdFeB fatigue crack damage propagation. Background technique [0002] As the hard magnetic material with the best comprehensive magnetic properties, sintered NdFeB is widely used in communication, medical, aerospace and national military industries. For a long time, people's attention to sintered NdFeB has focused on improving its electromagnetic properties and research on its mechanical and structural properties. There are few studies on mechanical damage, especially the research on the fatigue damage process under the action of dynamic mechanics. In all kinds of complex machinery, parts made of sintered NdFeB are under the action of complex sudden change loads for a long time during service, and fatigue cracks are often easily initiated at stress concentration places such as parts surface and internal defects, which in tu...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01N3/06G01N3/32
CPCG01N3/06G01N3/32G01N2203/0005G01N2203/0073G01N2203/0066G01N2203/0635
Inventor 程强强严毅琪殷金泉孙鹏宇邓强于润桥黄伟荣王勇博刘扬
Owner NANCHANG HANGKONG UNIVERSITY
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