PSI - Issue 13

Yanzeng Wu et al. / Procedia Structural Integrity 13 (2018) 890–895 Yanzeng Wu et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig. 2. (a) Configuration of specimen; (b) HAB distribution in the specimen; (c) Case 1: crack tip located near the HAB zone; (d) Case 2: crack tip located in the non- HAB zone.

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Fig. 3. OM micrographs of LMD TC11 alloy. (a) HAB zone in the layer band. (b) non-HAB zone between layer bands.

2.2. Digital Image Correlation procedure To obtain the crack tip information, during the loading and unloading process, one loading cycle is divided into several steps as shown in Fig. 4a, and the images corresponding to each load step were captured from the optical microscope for displacement field calculation by DIC commercial software. In DIC analysis, the image around the crack tip corresponding to 0 N was set as the reference image and the displacement fields of crack tip corresponding to other load conditions can be calculated by comparing one by one. Since CTOD is characterized by the opening displacement near the crack tip, the vertical displacement fields around the crack tip should be obtained from the DIC analysis. A vertical displacement field of crack tip is shown in Fig. 4b, corresponding to the crack length of 2.40 mm and maximum load level. From the vertical displacement fields around the crack tip, CTOD can be obtained by analyzing the relative displacement of the crack flanks. In detail, it is usually characterized by defining the measurement points, such as a pair of points behind the crack tip, as shown in Fig. 4c, the distances along and perpendicular the crack directions are marked as L1, and L2, respectively. In this work, three pairs of points along the crack direction were chosen for CTOD analysis, where the distances from crack tip are L 1 =10, 50, 100 pixel, L 2 =25 pixel. a