Method for measuring residual stress on surface of metal sample based on micro indentation

Abstract

The invention discloses a method for measuring residual stress on surface of a metal sample based on micro indentation. The method comprises the following steps: performing a micro indentation test on the surface of the sample by utilizing a Vickers microhardness tester, recording the indentation morphology by adopting a scanning electron microscope, and obtaining the nominal projection area and actual projection area of the indentation on the surface of the sample through calculation for diagonal length and side length of the micro indentation; obtaining a strength coefficient and strain hardening index of the material through a standard tensile test; and obtaining a theoretical formula for measuring the residual stress through an indentation method and containing the ratio of the actual projection area to the nominal projection area of the micro indentation, the strength coefficient and strain hardening index based on the hypothesis for the two-dimension isometric residual stress field on the surface of the sample, and further obtaining the residual strain and residual stress on the surface of the sample. The measurement method belongs to basically nondestructive or micro-damage measurement and has the advantages of low measurement cost, simplicity and convenience in operation and high measurement efficiency. If being combined with a portable high-power optical microscope with a distance measurement function, the method can be popularized and applied in the field of engineering.

Description

technical field [0001] The invention relates to a method for measuring residual stress on the surface of a metal structure, which mainly uses a Vickers microhardness tester to leave microindentations on the surface of a sample, and the ratio of the actual projected area of ​​the microindentation to the nominal projected area The residual strain and residual stress in the sample can be determined according to the residual stress measurement formula based on the indentation method based on the indentation response and elastic-plastic contact theory. The invention belongs to the fields of elastic-plastic contact mechanics, engineering materials and indentation residual stress measurement. Background technique [0002] Residual stress is the result of non-uniform elastic deformation or non-uniform elastic-plastic deformation in the material, or it is a reflection of the elastic anisotropy and plastic anisotropy of the material. All processes that can cause inhomogeneous elastic...

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Problems solved by technology

However, in view of the limitations of the application of these methods, the drilling method and X-ray diffraction method are widely used in practice. Although the drilling method is relatively mature, the drilling method needs to destroy the tested sample to remove the residual stress. Release to measure the residual stress value, so it cannot be used in many important engineering structures. At the same time, because the strain gauge is sensitive to temperature, the strain measurement accuracy depends on the bonding technology, and it has high requirements for the drilling process, so it is not necessary It is suitable for measurement in complex environments; when using X-ray diffraction to measure the residual stress of the sample, the test is expensive, and the grain size of the sample is strictly required, that is, the grain size of the sample should not be too large, and the sample should not have a high texture

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