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A real-time extensometer measurement method based on two-dimensional digital image correlation compensation algorithm

An image correlation and measurement method technology, applied in the direction of measuring devices, instruments, optical devices, etc., can solve problems such as large amount of calculation, easy to be affected by out-of-plane movement, difficult to measure in real time, and achieve high measurement accuracy.

Active Publication Date: 2018-05-29
UNIV OF SCI & TECH OF CHINA
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Problems solved by technology

Usually, the typical measurement accuracy of digital image correlation is about 100 microstrain, while the measurement results of two-dimensional digital image correlation are easily affected by out-of-plane motion, and the relative error can reach more than 20%.
In the non-patent literature "Optical extensometer and elimination of the effect of out-of-planemotions" (Optics and Lasers in Engineering, Vol.65, pp.28-37, 2015), Bai et al. used the rigidity attached to the specimen The virtual strain field of the plate (generated by the out-of-plane motion) compensates the strain field of the deformed specimen, thereby obtaining high-precision compensation results; but this method requires a large amount of calculation and is difficult to measure in real time

Method used

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  • A real-time extensometer measurement method based on two-dimensional digital image correlation compensation algorithm
  • A real-time extensometer measurement method based on two-dimensional digital image correlation compensation algorithm
  • A real-time extensometer measurement method based on two-dimensional digital image correlation compensation algorithm

Examples

Experimental program
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Effect test

Embodiment 1

[0047] Example 1: Using digital image correlation method (including traditional two-dimensional digital image correlation extensometer measurement and compensated extensometer measurement) to monitor strain in aluminum alloy tensile test. The testing process is as follows:

[0048] a) Fix the aluminum alloy specimen with the compensation plate on the tensile testing machine ( image 3 In (a)), the surface of the specimen and the compensation plate (rigid plate) has sprayed artificial speckle, which is convenient for digital image correlation measurement; strain gauges are attached to the back of the specimen.

[0049] b) Adjust the test optical path so that the test piece is perpendicular to the optical axis of the camera and clearly imaged in the camera, and then use the calibration plate to calibrate the camera, so as to determine the principal point position of the camera and the aberration parameters of the lens.

[0050] c) Use the image before loading as a reference ima...

Embodiment 2

[0055] Example 2: Using the out-of-plane displacement test to evaluate the influence of the out-of-plane displacement on the measurement accuracy of the traditional two-dimensional digital image correlation optical extensometer and compensation extensometer. The testing process is as follows:

[0056] a) A flat specimen is fixed on the displacement platform, and the displacement platform is fixed on the anti-vibration platform. The surface of the specimen has sprayed artificial speckles, which is convenient for digital image correlation measurement.

[0057] b) Adjust the test optical path so that the test piece is perpendicular to the optical axis of the camera and clearly imaged in the camera, and then use the calibration plate to calibrate the camera, so as to determine the principal point position of the camera and the aberration parameters of the lens.

[0058] c) After the test starts, first take an image as a reference image, set a line segment (i.e. optical extensomete...

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Abstract

The invention relates to a real-time extensometer measurement method based on a two-dimensional digital image correlative compensation algorithm, and the method comprises the following steps: firstly determining a main point position of a camera and a pixel parameter of a lens through a camera calibration method; secondly solving a compensation parameter in real time in a deformation process of a test piece through employing a two-dimensional digital image correlative compensation algorithm; thirdly calculating a displacement field of an end point of one extensometer through employing a conventional optical extensometer algorithm; fourthly compensating the displacement field of the end point of the extensometer in real time through the compensation parameter obtained in real time, and calculating the linear strain after compensation. The method eliminates the influence of out-of-plane motion and lens aberration on a measurement result, guarantees the measurement precision, and can measure the strain in real time.

Description

technical field [0001] The invention relates to a real-time optical extensometer measurement method based on a two-dimensional digital image correlation compensation algorithm, which belongs to the field of photoelectric detection. Background technique [0002] In actual material experiments and engineering applications, it is often necessary to measure the deformation of materials or specimens. For the strain test in the elastic deformation stage of the specimen, the commonly used test method is the contact measurement method: using electronic strain gauges or mechanical extensometers for measurement. Electronic strain gauges need to be tightly attached to the test piece, while mechanical extensometers need to be clamped on the surface of the test piece, which is complicated to operate and requires certain testing skills. For this reason, an optical extensometer based on digital image correlation has been developed, which has the characteristics of non-contact, high precis...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G01B11/02G01B11/16
CPCG01B11/02G01B11/16
Inventor 张青川徐小海苏勇吕泽乾
Owner UNIV OF SCI & TECH OF CHINA
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