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

在铜疲劳裂纹尖端和在不锈钢试件中心加工的圆孔周围，描述了间距为20-30微米的网格图。首先利用光学显微镜测量了圆孔周围网格的位移，然后利用图像处理技术测量了高温蠕变载荷作用下圆孔周围网格的位移。乙基纤维素膜复制品取自拉伸蠕变试件圆孔周围描绘间隔为50微米的网格图案的位置。然后用金溅射的方法对其进行扫描电子显微镜观察。通过对动态范围(DR)的放大来增强扫描电镜图像的对比度，然后通过阴影校正去除亮度不均匀，然后进行滤波处理，在扫描电子显微镜图像中对亮度为254的二值图像进行二值化处理，从而使网格的亮度为0，背景的亮度为255。然后通过秩滤波完全去除尖峰噪声。重复这样的处理，得到了清晰的二值图像。因此，将图像处理技术应用于裂纹尖端局部应变和高温蠕变应变的测量具有广阔的应用前景。

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.