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Measuring method of little opening displacement of microcrack

A technology of opening displacement and measurement method, which is applied in the field of fatigue fracture mechanics research, and can solve problems such as the accuracy and requirements of the opening displacement of few cracks, the low resolution of the opening displacement of micro-cracks, and the error of fracture performance.

Inactive Publication Date: 2009-12-23
TSINGHUA UNIV
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  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0005] 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

Method used

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  • Measuring method of little opening displacement of microcrack

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Embodiment approach

[0030] Such as figure 2 As shown, the measurement system of the microcrack opening displacement of the present invention mainly includes a laser 1, a loading device 2 (comprising a common loading frame, a force sensor, etc.), a test piece 3 with a microcrack, and a light intensity Receiving screen 4, image acquisition system 5. The system is mounted on a vibration-isolated table, and the laser emits light at a wavelength of lambda. The test piece with microcracks is placed on the loading device 2, and when the laser light passes through the microcracks, a Fraunhofer diffraction fringe pattern is formed on the light screen receiving screen 4. A slit diffraction light intensity image of the micro-crack is obtained through the image acquisition system 5, and the image is used as an initial light intensity image; the loading device 2 is used for slow loading, and the micro-crack is deformed, so that the crack is opened. At this time, through the image The acquisition camera sys...

Embodiment

[0048] Assuming that the width of the initial tiny crack is 0.10mm, the diffraction fringe pattern obtained from the initial shooting is as follows image 3 shown. After loading, the diffraction fringes produced by the laser passing through the tiny cracks change as follows Figure 4 shown in the table. image 3 The position of the dotted line in the center is the calculated position, and the calculation process is as described in the theory. Select the position of the central point line before and after loading in the diffraction fringe as the calculation area, and perform one-dimensional digital correlation calculation on this area to obtain the result shown in the figure below, and finally perform a linear fitting on the displacement of the fringe to obtain S =0.009627, such as Figure 5 As shown. The final calculation results in ε=0.0097204, so the variation of micro cracks can be calculated as Δa=aε=0.972μm. Through the magnification of the diffraction fringe pattern,...

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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

technical field [0001] 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 [0002] 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 the toughness changes drastically, large-...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01B11/02G01N3/00
Inventor 谢惠民胡振兴王怀喜
Owner TSINGHUA UNIV
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