Method for measuring dynamic stress field evolution law of complex heterogeneous structure

Patent metadata

Field	Value
Publication number	US-10648894-B2
Application number	US-201816477850-A
Country	US
Kind code	B2
Filing date	Mar 23, 2018
Priority date	May 27, 2017
Publication date	May 12, 2020
Grant date	May 12, 2020

Abstract

A method for measuring the dynamic stress field evolution law of a complex heterogeneous structure, comprising: preparing a transparent photosensitive resin model of a complex heterogeneous structure by means of three-dimensional (3D) printing technology to serve as a test piece (S101); placing the test piece in a light path of a circularly polarized light dark field, performing continuous stress loading on the test piece, and recording images (S102); acquiring a plurality of continuously changing full-field stress fringe grayscale images according to videos generated by the image recording (S103); then acquiring grayscale value change sequences of pixel points at each position in the images (S104); and finally, calculating full-field fringe orders under continuous loading conditions according to the relation between the grayscale values and the fringe orders so as to calculate full-field stress values under the continuous loading conditions (S105). Thus, it is possible to extract and quantify the global dynamic stress field evolution law of a complex heterogeneous structure subjected to high exterior load under fixed light field conditions.

First claim

The invention claimed is:

1. A method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure, comprising:
manufacturing a transparent photosensitive resin model of a complex heterogeneous structure by 3D printing, to serve as a test piece;
placing the test piece in an optical path of dark-field circularly polarized light, performing continuous stress loading on the test piece and recording the test piece;
obtaining a plurality of full-field stress fringe grayscale images that are continuous, based on a video generated by the recording;
obtaining a sequence of gray values of a pixel at each position in the plurality of full-field stress fringe grayscale images based on the plurality of full-field stress fringe grayscale images that are continuous; and
calculating a full-field fringe order under a continuous loading condition, according to a relationship between gray value and fringe order and sequences of gray values of all pixels in the plurality of full-field stress fringe grayscale images, and calculating a full-field stress value under the continuous loading condition.

2. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 1 , wherein the manufacturing the transparent photosensitive resin model of the complex heterogeneous structure by 3D printing comprises:
obtaining an internal complex pore structure of the complex heterogeneous structure by computed tomography (CT) scanning;
digitally reconstructing the internal complex pore structure to generate a digital model; and
importing the digital model into a 3D printer, and obtaining the transparent photosensitive resin model by printing.

3. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 2 , wherein the calculating the full-field fringe order under the continuous loading condition comprises:
calculating an integer part and a decimal part of a fringe order of a pixel at each position.

4. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 3 , wherein the calculating the integer part of the fringe order of the pixel at each position comprises:
converting the sequence of gray values of the pixel at each position into a curve of change;
calculating an average of peaks and troughs in the curve of change; and
obtaining the integer portion of the fringe order of the pixel at a corresponding position based on a number of troughs below the average.

5. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 2 , wherein the calculating the full-field stress value under the continuous loading condition comprises:
multiplying the full-field fringe order by an optical fringe constant, to obtain the full-field stress value.

6. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 1 , wherein the placing the test piece in the optical path of the dark-field circularly polarized light, performing continuous stress loading on the test piece and recording the test piece comprises:
placing the test piece in the optical path of the dark-field circularly polarized light, performing continuous stress loading on the test piece by a stress loading apparatus, and recording a whole process of change of a full-field stress fringe in the test piece by a high-definition digital video camera.

7. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 6 , wherein the calculating the full-field fringe order under the continuous loading condition comprises:
calculating an integer part and a decimal part of a fringe order of a pixel at each position.

8. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 7 , wherein the calculating the integer part of the fringe order of the pixel at each position comprises:
converting the sequence of gray values of the pixel at each position into a curve of change;
calculating an average of peaks and troughs in the curve of change; and
obtaining the integer portion of the fringe order of the pixel at a corresponding position based on a number of troughs below the average.

9. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 8 , wherein the calculating the decimal part of the fringe order of the pixel at each position comprises:
calculating the decimal part of the fringe order of the pixel at each position according to a cosine function y=I b +I a (1 cos θ) between the curve of change and a wrapped phase difference θ, wherein I b is an intensity of a background light during test, I a is an intensity of a light source, θ is the wrapped phase difference meeting θ=2πx, and x is the decimal part of the fringe order, wherein the cosine function is determined based on a last peak and a last trough in a curve of light intensity change calculated at a pixel under a certain load.

10. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 6 , wherein the calculating the full-field stress value under the continuous loading condition comprises:
multiplying the full-field fringe order by an optical fringe constant, to obtain the full-field stress value.

11. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 1 , wherein the obtaining the plurality of full-field stress fringe grayscale images that are continuous, based on the video generated by the recording comprises:
converting, at a rate of 10 frames per second, the video generated by the recording into a plurality of pictures that are continuous; and
performing image processing on the plurality of pictures, to obtain the plurality of full-field stress fringe grayscale images.

12. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 11 , wherein the calculating the full-field fringe order under the continuous loading condition comprises:
calculating an integer part and a decimal part of a fringe order of a pixel at each position.

13. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 11 , wherein the calculating the full-field stress value under the continuous loading condition comprises:
multiplying the full-field fringe order by an optical fringe constant, to obtain the full-field stress value.

14. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 1 , wherein the obtaining the sequence of gray values of the pixel at each position in the plurality of full-field stress fringe grayscale images based on the plurality of full-field stress fringe grayscale images that are continuous comprises:
extracting gray values of each pixel at a same position in the plurality of full-field stress fringe grayscale images that are continuous, to form the sequence of gray values of each pixel.

15. The method for measuring the evolution of a dynamic stress field in a complex heterogeneous structure according to claim 14 , wherein the calculating the full-field fringe order under the continuous loading condition comprises:
calculating an integer part and a decimal part of a fringe order of a pixel at ea

Assignees

• Univ China Mining

Inventors

• Ju Yang
• Ren Zhangyu
• Wang Li
• Mao Lingtao
• Liu Hongbin

Classifications

• B33Y50/00

  Data acquisition or data processing for additive manufacturing · CPC title

• B29K2995/0026

  Transparent · CPC title

• B29L2031/40

  Test specimens {; Models, e.g. model cars (mannequins B29L2031/7028); Probes} · CPC title

• G06T7/20

  Analysis of motion (motion estimation for coding, decoding, compressing or decompressing digital video signals H04N19/43, H04N19/51) · CPC title

• B33Y80/00 Primary

  Products made by additive manufacturing · CPC title