Method for Measuring Full-Field Strain of an Ultra-High Temperature Object Based on Digital Image Correlation Method

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).