PSI - Issue 13

Rui Guo et al. / Procedia Structural Integrity 13 (2018) 2202–2209 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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direction tensile stress value around the crack tips are larger than the yield stress of the local material, indicating the existence of the plastic zone of the crack tips. To study the influence of crack length on the plastic strain around crack tips, the equivalent plastic strain and Y-direction tensile plastic strain of six different length crack tips at the sampling position were extracted. The equivalent plastic strain distributions in 1 mm radius area around crack tips in 6 different lengths is shown in Fig. 6.

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Figure 5 Von Mises Stress distributions around crack tips with different crack lengths (a)a=5mm (b)a=10mm (c)a=15mm (d)a=20mm (e)a=25mm (f)a=30mm

Figure 6 Equivalent strain distributions around crack tips with different crack lengths (a)a=5mm (b)a=10mm (c)a=15mm (d)a=20mm (e)a=25mm (f)a=30mm

As shown in Fig. 6, among the six sampling length cracks, the equivalent plastic strain distribution around the tip of crack with length a=10 mm has the widest range and the largest strain distribution, followed by the crack of a=5 mm. The crack length is from 5mm to 10mm, and the equivalent stress of the crack tip increases with the crack length. When the crack length is 10mm to 30mm, the equivalent stress of the crack tip decreases with the crack length, and reaches the lowest when a=30mm. . In the figure, the equivalent plastic strain of the crack tip of the crack in (c)(d)(e) is uneven on both sides of the seam, and the strain under the seam is commonly large. This phenomenon can be attributed to the upper part of the crack close to the welding interface and the other side of the interface is the base metal A533B, whose yield stress and the power hardening index are relatively large, the plastic strain caused by the welding residual stress is small, which affects the weld metal on the side in contact with it. 4.2 The analysis of fracture parameters of cracks near welding surfaces between A533B and 182 This section mainly studies the cracks in the vicinity of the interface between the base material A533B and the welding consumable182 alloy, the surfacing layer 182 alloy and the base material 316L alloy, and the cladding layer 304 stainless steel and the base material 316L. The sampling position is as shown in Fig. 1(c), and the stress and strain distributions around the cracks are observed. Due to the particularity and complexity of the dissimilar welding structures, the dissimilar components of the dissimilar welds at different locations are emphasized. The three states are simulated and analyzed which are the crack whose tip is close to, at and cross the welding interface. Each sampling position maintains the same x coordinate, and the y coordinate is 1 mm apart from each other. The position of this research object is shown in Figure 5(a). The Von Mises stress distribution at the tip of the three different length cracks at the sampling position is shown in Fig. 7. As shown in Fig. 7, when the crack tip is in the 182 alloy, the equivalent stress distribution is small. As shown in Fig. 7(a) and (c), there is a obvious dividing line in the contour maps of Von Mises stress distribution, the stress is different in the distribution of the two different materials. As shown in Fig. 7(b), when the crack tip is at the interface between 182 alloy and A533B, visible boundary line can be seen passing through the stress distribution contour map around the crack tip. The stress distribution on both sides of the boundary line is asymmetric, and the high stress distribution area on the upper side is larger than that of the lower side. As shown in Fig. 7(c), when the crack tip is in A533B, the high stress region is significantly larger than the crack tip in the 182 alloy, indicating that the stress around crack tip in the base material A533B is larger. Therefore, the crack near the welding interface of the base material A533B and the welding consumable 182 alloy in the safety end welding structure of the nuclear power circuit is driven by the welding residual stress, and the mechanical property non-uniformity of the welding material has an influence on its Von Mises stress distribution.