vibratory stress relief equipment effect detection：
Neutron diffraction method: The
detection principle is similar to the X-ray method, but the difference is that neutrons have a strong penetrating ability, so it can detect the residual stress inside a larger solid material. However, the current of the neutron source is weak and the measurement time is long. The neutron diffraction measurement requires a large sample volume and poor spatial resolution (usually the resolution of neutron method is 10mm2, and the resolution of X-ray is 0.1 mm2)[53- 54]. The construction and operation of neutron reactors are expensive, and it is difficult to popularize, and it is impossible to conduct real-time large-scale measurement on industrial sites.
Magnetic method (magnetic measurement method): It is
called Barkhausen Noise Method (BNM). When the ferromagnetic material is subjected to an external excitation magnetic field, the magnetic domain wall will be forced to move back and forth, causing the opposite side Changes in the size of the magnetic domain walls cause changes in the magnetic induction intensity. A kind of noise-like electrical signal can be obtained by measuring the change of magnetic induction intensity by the principle of electromagnetic induction, namely Barkhausen noise (BN). Changes in material stress and magnetic field will affect the BN value. If the stress and the magnetic field in the magnetic domain produce the same effect, the BN value will increase; if the stress and the magnetic field produce the opposite effect in the magnetic domain, the BN value will decrease, resulting in larger measurement errors. The size of the BN value is related to the impurity content and lattice dislocations. This method is only suitable for ferromagnetic materials. The detection accuracy is greatly affected by the material's microstructure, as well as the displacement gap, surface roughness, material remanence and Due to the influence of environmental magnetic field and other factors, the current quantitative calibration and quantitative detection of residual stress are difficult, and the actual field application is also subject to certain restrictions.
Eddy current testing method:
This technology is based on the principle of electromagnetic induction. During the test, the coil connected with alternating current is close to the metal to be tested. Through electromagnetic induction, the alternating magnetic field generated by the AC coil creates an eddy current in the metal to be tested. This eddy current will also generate its own magnetic field inside the metal to be tested. The eddy current magnetic field in turn affects the voltage, impedance, and magnetic field strength of the coil. It can be seen that eddy current testing technology is mainly based on changes in material deformation, resistivity and permeability. The existence of residual stress will cause the resistivity and magnetic permeability of the DUT to change. The use of eddy current to detect residual stress is still in the immature stage. It is generally only found in the laboratory environment and can only detect conductive and magnetic materials that can produce eddy current effects. The scope of application is narrow, it is greatly affected by the external environment, and the detection accuracy is low. Raman spectroscopy: Using the principle of Raman scattering, when the material is under stress, the change of the lattice structure will reflect the change of its vibration frequency, so the frequency shift of the Raman scattering relative to the incident light will also change accordingly. According to the stress and The relationship between the frequency shift of the scattered light Raman spectrum line can calculate the stress inside the crystal.
Ultrasonic method: The
ultrasonic method for detecting residual stress is based on the sonoelastic theory. When the residual stress is generated in the material, the parameters such as the propagation speed, frequency, amplitude, phase and energy of the ultrasonic will change. Compared with other non-destructive testing methods for residual stress, ultrasonic The method has the advantages of fast detection speed, no radiation damage to the human body, low cost, better spatial resolution and a larger detection depth, and can be hand-held and easily carried on-site, and can complete the surface and subsurface macro-residual stress and the state of tension and compression The detection and many other advantages.
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