Method for measuring full-field strain of an ultra-high temperature object based on digital image correlation method

Patent metadata

Field	Value
Publication number	US-11734815-B2
Application number	US-202117388131-A
Country	US
Kind code	B2
Filing date	Jul 29, 2021
Priority date	Oct 10, 2020
Publication date	Aug 22, 2023
Grant date	Aug 22, 2023

Abstract

The present disclosure relates to a method for measuring full-field strain of an ultra-high temperature (UHT) object based on a digital image correlation method. The temperature range is from normal temperature to 3500 degrees Celsius. The method includes the steps of selecting a proper high-temperature-resistant speckle material, tantalum carbide powder, according to the characteristics of the object to be measured. First, polishing a to-be-measured surface of a tungsten test piece to remove an oxide layer, then mixing the tantalum carbide (TaC) powder and absolute ethanol to form a paste according to a mass ratio of 1:2. Making randomly distributed speckles from the mixture on the to-be-measured surface of the test piece which has been processed. In order to improve firmness and stability of the newly made speckles, performing curing treatment to the speckles.

First claim

What is claimed is:

1. A method for measuring full-field strain of an ultra-high temperature (UHT) object based on a digital image correlation method, wherein: reducing interference on camera imaging by strong self-illumination of a high-temperature object by using UHT stability of a speckle material and a proper speckle making process, and meanwhile by way of superimposing double filters, finally realizing accurate measurement of full-field strain of the UHT object, comprising the following steps:
(1) polishing a to-be-measured surface of a test piece level by level to remove an oxide layer, and cleaning by alcohol to remove oily stains;
(2) mixing selected UHT-resistant speckle materials, tantalum carbide powder or chromium carbide powder or hafnium carbide powder, with absolute ethanol according to a mass ratio of 1:21:0.5 to form a paste; the UHT referring to being greater than 2000° C.;
(3) dipping the paste in step (2) by a needle tip to make randomly distributed speckle patterns on the surface of the test piece treated in step (1); or spraying the paste of tantalum carbide mixture on the surface of the test piece by using a spray gun to make randomly distributed speckle patterns;
(4) drying the speckles made in step (3) in room temperature for 6-8 h, to volatilize the ethanol;
(5) curing the test piece and the speckles dried in step (4) in two steps; first step: keeping them in a vacuum environment for 5 minutes at a temperature of 400 degrees Celsius, then cooling down to room temperature; second step: keeping them in a vacuum environment lower than 10 −2 Pa magnitude for 5 minutes at a temperature of 800 degrees Celsius, then cooling down to room temperature;
(6) installing a sample of the test piece cured in step (5) to a test platform;
(7) adjusting the camera to make the test piece be imaged clearly in the camera, calibrating the digital image measuring system by a calibration board, connecting an infrared thermometer with a digital image correlation measurement system by a synchronous trigger software, to ensure that collected temperature data correspond to calculated strain field data one by one;
(8) heating the test piece in step (6) by using an electronic beam scanning heating system to a temperature range of 2000-3500 degrees Celsius;
(9) measuring a temperature of a predetermined region of the to-be-measured surface of the test piece by the infrared thermometer;
(10) consecutively shooting and recording planes with speckle patterns of the test piece in step (9) by using a CCD camera; at a first temperature range of 25-1200 degrees Celsius, realizing the strain measurement by using blue light illumination and a single blue light filter; at a second temperature range of 1200-1800 degrees Celsius, turning off the blue light illumination at the first temperature region, using the high temperature self-illumination of the object to be measured to perform CCD camera illumination to realize strain measurement; at a third temperature range of 1800-3500 degrees Celsius, in order to reduce the interference on the strain measurement due to the strong self-illumination of the high-temperature object, superimposing two blue filters to realize strain measurement;
(11) performing processes based on the digital image correlation method, and calculating the strain field data of the predetermined region in step (9).

2. The method for measuring full-field strain of an ultra-high temperature (UHT) object based on a digital image correlation method according to claim 1 , wherein: the to-be-measured surface processed in step (1) is a surface of various metals, or a surface of ceramic materials; the polishing and cleaning processes remove oxide films and stains on the surface of the test piece.

3. The method for measuring full-field strain of an ultra-high temperature (UHT) object based on a digital image correlation method according to claim 1 , wherein the speckle material in step (2) has a melting point greater than 3500° C. and UHT stability, and keeps chemical stability with the sample materials to be measured in the UHT condition; the speckle materials and the absolute ethanol are evenly mixed according to a mass ratio of 1:21:0.5, thus ensuring the quality of the speckles.

4. The method for measuring full-field strain of an ultra-high temperature (UHT) object based on a digital image correlation method according to claim 1 , wherein the high-temperature speckles made in step (3) should have characteristics of random distribution and a proper size, corresponding to the size of the surface to be measured; the proper size refers to that the size should be 5-10 times of the camera resolution, and the CCD camera resolution refers to that each pixel corresponds to a size of the surface to be measured.

5. The method for measuring full-field strain of an ultra-high temperature (UHT) object based on a digital image correlation method according to claim 1 , wherein in step (5), the vacuum degree during the curing should be lower than 10 −2 Pa magnitude.

6. The method for measuring full-field strain of an ultra-high temperature (UHT) object based on a digital image correlation method according to claim 1 , wherein in step (10), in order to improve the temperature range of the test measurement, two light filtering methods for reducing self-illumination of a high-temperature object are used: (1) turning off the externally added blue light source at the second temperature region of 1200-1800 degrees Celsius, illuminating by the high temperature self-illumination of the test piece; (2) at a higher temperature range, i.e., the third temperature range of 1800-3500 degrees Celsius, still illuminating by the high temperature self-illumination of the test piece, and additionally combining the filters of the two blue light wavebands; reducing the interference on the CCD camera imaging by the high temperature self-illumination by way of filtering twice.

7. The method for measuring full-field strain of an ultra-high temperature (UHT) object based on a digital image correlation method according to claim 1 , wherein in step (10), using a CCD camera to implement two-dimensional strain filed measurement, and meanwhile using two CCD cameras to implement three-dimensional strain filed measurement.

8. The method for measuring full-field strain of an ultra-high temperature (UHT) object based on a digital image correlation method according to claim 1 , wherein in step (10), the two blue light filters are: Bi 440, 420-455 nm; Bi 420, 406-435 nm, respectively, and a narrow-band filtering effect can be obtained through superimposing; reducing the interference on camera imaging by self-illumination of the high temperature object by filtering twice; or selecting a light filter of other wavebands to get the narrow-band filtering effect.

9. The method for measuring full-field strain of an ultra-high temperature (UHT) object based on a digital image correlation method according to claim 1 , wherein in step (11), the strain field calculation method uses an image before heating as a reference image, and matches the heated speckle patterns of the test piece by using a digital image correlation method, so as to calculate a two-dimensional or three-dimensional strain filed.

10. The method for measuring full-field strain of an ultra-high temperature (UHT) object based on a digital image correlation method according to claim 1 , wherein the speckle material is micron tantalum carbide powder, with an average granularity of 1 micron and a purity of 99.9%; or the speckle material can be micron chromium carbide powder, or micron hafnium carbide powder.

11. The method for measuring full-field strain of an ultra-high temperature (UHT) object based on a di

Assignees

• Univ Science & Technology China

Inventors

• Huang Shenghong
• Pan Zhiwei
• Jiang Menglai
• Zheng Zhifeng
• Qiao Meixia

Classifications

• G06T7/001 Primary

  using an image reference approach · CPC title

• G01L1/248 Primary

  using infrared (G01L1/241, G01L1/242 take precedence) · CPC title

• H04N5/72

  Modifying the appearance of television pictures by optical filters or diffusing screens · CPC title

• H04N13/25

  using two or more image sensors with different characteristics other than in their location or field of view, e.g. having different resolutions or colour pickup characteristics; using image signals from one sensor to control the characteristics of another sensor · CPC title

• H04N17/002

  for television cameras · CPC title