Measuring method of little opening displacement of microcrack

Abstract

The invention discloses a measuring method of little opening displacement of microcrack, belonging to the technical fields of photo mechanics, structural member deformation, displacement measurement and the like. The invention adopts a measuring system mainly consisting of a laser device, a loading device, a test specimen with a microcrack, a light intensity receiving screen and a pattern collecting system. During measurement, laser sends out light with a wave length of lambda; a Fraunhofer diffraction fringe pattern is formed on the receiving screen by the microcrack; an initial light intensity pattern of the microcrack is obtained by the pattern collecting system; the loading device is used for slowly loading the test specimen to open the microcrack; the pattern collecting system is used for recording multiple slit diffraction light intensity patterns of the microcrack on the receiving screen under different loads; digital pattern analysis and relative operation are carried out according to a light intensity pattern so as to finally obtain the little opening displacement amount of the microcrack under different loads. The method has the characteristics of convenient use, high measurement precision and the like. The deformation amount measurement of the microcrack can reach 100 mu epsilon magnitude, and the displacement measurement sensitivity can reach wavelength magnitude.

Description

A Measuring Method for Micro-crack Opening Displacement technical field The invention relates to a method and system for accurately measuring the microcrack opening displacement (nanometer to micron level) of a test piece with microcracks (1 μm to 200 μm) when it is loaded, and belongs to optical mechanics, engineering materials, Component deformation, micro-nano displacement testing technology and fatigue fracture mechanics research fields. Background technique In recent decades, the theory and test technology of linear elastic fracture mechanics have been relatively mature, and have been widely used in the study of brittle failure, fatigue failure and stress corrosion of materials. When a small load is applied to the crack body, a small area yields at the crack tip. However, when the component fails rapidly, sometimes large-scale yielding occurs at the top of the crack. For example, when medium and low-strength steels are used above the transformation temperature where...

AI Technical Summary

Problems solved by technology

However, for the micro-cracks (1 μm ~ 200 μm) of the test piece, the small opening displacement generated during loading, due to the accuracy of the above-mentioned optical displacement measurement technology, few can meet the accuracy and requirements of the crack opening displacement.

For example, the moiré method and the digital image correlation method will be affected by the displacement of the rigid body during measurement, and its resolution for the opening displacement of the micro-crack is not high; The displacement is usually at the lowest estimated reading level of the microscope, resulting in a large error, and a larger error in the measurement of fracture performance

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