Spring steel wire will generate residual stress during the process of cold drawing and oil quenching and heat treatment. Moreover, spring wire is formed during the process of manufacturing and shot peening is conducted.High frequency quenching, carburizing, nitrification, etc. are used as surface hardening treatment. As a result of these treatments, residual stress will be generated in the material.The qualitative and quantitative analysis of the residual stress of the material will be an important factor to improve the fatigue properties of the spring.
Residual stress of the spring is usually obtained by the following two methods:
(1) X-ray detection method.X ray detection is a non-destructive testing method. This method can detect residual stress on specific surfaces and sites, but it has certain requirements for surface depth. In other words, only shallow surface can be detected, and the residual stress distribution at deep sites cannot be detected.However, the X-ray detection method is widely used in the detection of spring residual stress due to its reliable data collection, rapid measurement and automatic data processing.
(2) mechanical detection method.The mechanical test method is a failure test test method. This method is a deformation method of material produced by dropping an appropriate corrosion solution on the surface of the tested spring and releasing residual stress on the dissolved surface.Adopt the
Methods: the residual stress is the average value of the dissolved surface. It can't detect the residual stress of a specific surface and site, but it is beneficial to detect the residual stress of the deeper site.
In recent years, the combination of the two methods is widely used in the residual stress testing equipment, which can improve the accuracy of the testing.
(3) detection principle.The principle of the X-ray detection method, when the surface of the multi-crystal encounters the X-ray, the specific X-ray will be diffracted from a specific crystal lattice.The difference of diffraction Angle can be obtained according to the state with or without strain, and then it can be calculated according to the longitudinal elastic modulus and poisson's ratio of the material.The mechanical testing method is the deformation of the material caused by the change of residual stress according to the dissolution of corrosion solution, as mentioned above.