Development of Three Dimensional Strain Measurement System around Crack Tip by Means of Image Processing

点击翻译按钮获取中文摘要

The grid pattern with space-interval of 20-30mum was described around fatigue crack tip in copper and circular hole machined at the center of stainless steel plate specimen. Then variation of localized strain near crack tip during one load cycling and three dimensional high temperature creep strain around circular hole were successfully measured, where the displacement of grids was measured using an optical microscope as a first step.Subsequently, the image processing technique was introduced to measure the displacement of the grid around the circular hole under high temperature creep loading. The acethylcellulose film replica was taken from the location at which the grid pattern with space-interval of 50mum was described around the circular hole of tensile creep specimen. Then gold-spattering was treated to observe this through scanning electron microscope. The magnification of the dynamic range (DR) was conducted to intensify the contrast of image taken through SEM.Subsequently, the unevenness of brightness was removed by conducting shading correction, and then filter treatment was made.The two-valued image treatment was conducted at brightness of 254 so that the grid was valued at brightness of zero and the background at 255 in the SEM image. Then the spike noise was fully removed through a rank filter. Such treatments were repeated, and then the clear two-valued image was attained. Thus, we obtained a bright prospect to apply the image processing technique to measurement of localized strain around crack tip and high temperature creep strain.