Issue 30

W. Tao et alii, Frattura ed Integrità Strutturale, 30 (2014) 537-544; DOI: 10.3221/IGF-ESIS.30.64 542 It emerges from the calculation results that target cracks’ circularity is very small, with 90% being below 0.01. This indicates that the boundary shape of the crack range is relatively complex and irregular. The axial ratio of the external ellipse is large. The rate above 7 percent is more than 80%. And it is in accordance with the features in the real cracks observed. The present linear features a slender line while the width-height ratio 80% of the external rectangle is over 2.5. And the reflection of the characteristics of the crack shape is not obvious. In the grayscale image, the gray value of the crack area is smaller, while the gray value of the external rectangle becomes bigger. The differences between them are obvious. And the difference rate above 30 accounts for 85% of the total. In accordance with the situation that some real cracks observed are darker and the background color is lighter. But there are some exceptions because of the gray value of the closed segmentation. Some backgrounds were closed to the gray level of the cracks. The crack has connected into an area and expanded the crack area, including a small amount of non-crack pixels. The average gray of the expanded region is higher than the original average gray of the crack area. This leads to the decline of the grayscale difference. There is a 0 value generated into the calculation results about the image’s feature quantity. This is because several complex image processing results are not satisfactory and the cracks’ target cannot be extracted from the image. The above statistical analysis results show that by selecting several characteristic quantities we can represent the shape and gray feature of the crack area. The difference of the external ellipse is the axis ratio and the range’s gray average value. The gist is that information on the cracks can be extracted from the image tested for these two characteristic quantities. U NDERWATER BRIDGE CRACK CLIP CONNECTION fter extracting the target, we found the target was divided into various discontinuous fragments. This is in conformity with reality. If the connection is not to be restored, it will affect the awareness and application of the target’s nature. Therefore, connecting the fragments is needed. Establishment model N-th   2 N  fracture fragment is assumed to be existed after extracting crack target. The fragments belonging to different parts of the same crack are on the overall trend line. They are ordered from left to right, top to bottom after marking the individual segment. The leftmost, upwards of the left endpoint area, are defined as the 1-th section fragments. The rightmost, downwards, are defined as the N-th section fragments. Set a simple model shown as Fig. 5 (a). (a) (b) Figure 5: (a) Location model; (b) Connecting model of the crack fragment’s endpoint A