PSI - Issue 14

Viswa Teja Vanapalli et al. / Procedia Structural Integrity 14 (2019) 521–528 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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been carried out. There are several layers of elements along the thickness of the specimen in FE models as shown in Fig. 5a. It is obser ved that in all the cases, the minimum value of ‘q’ has been obtained at the mid -section of the model across the thickness due to more constraints (closer to plain strain condition). The ‘q’ parameter for all specimens are calculated when the applied J integral in the specimen reaches a value of 220 kJ/m 2 . Similarly, the triaxiality parameters ‘q’ for all six straight pipes are determined by elastic -plastic finite element analyses. Finite element computer code WARP3D (Healy, et al., 2016) is used for this purpose. J-integral along the crack front is also calculated by domain integral method for the increasing load. Fig. 5b shows variation of t riaxiality parameter ‘q’ as a function of distance from crack tip for straight pipe SPBMTWC8-1 for all the six layers of elements along thickness. Layers 1 to layer 6 are numbered from outer diameter to inner diameter of the pipe. These values are plotted for a J-integral value of 220 kJ/m 2 . The minimum value of ‘q’ is for layer 4 and is equal to 0.31878. This procedure is repeated for all the six straight pipes to compute values of ‘q’ and is shown in Table 3. Finite element analyses are conducted on fourteen TPBB specimens using the principle of cohesive zone along crack front. Fig. 4 shows computed a) Load vs. CMOD, (b) Load vs. crack extension and (c) J-R curve in comparison to experimental results for a particular TPBB specimen (T082C) for which dimensions are shown in Table 2. Such results have been obtained by varying the value peak stress ‘T’. The results shown in Fig, 4 are for the most optimal value of ‘T’ for which best comparison between computed and experimental results have been obtained. Fig. 5 shows the variation of ‘q’ along the crack front for a typical TPBB specimen T082C and pipe SPBMTWC8 -1. The geometric details of the TPBB specimens and pipe components along with the fitted cohesive parameters & ‘q’ parameters are tabulated in Table 2. & Table 3. A plot betw een most optimal values of ‘T’ and ‘q’ for all the specimens analyzed here are shown in Fig. 6a. 2.5. Cohesive analyses of TPBB specimens & Pipes to simulate crack propagation

Fig. 4. Comparison of (a) Load vs. CMOD, (b) Load vs. crack extension and (c) J-Resistance curve with experimental result

Fig. 5. ‘q’ vs. distance from cra ck front for (a) T08_2C and (b) SPBMTWC8-1 obtained for various layers along thickness at J~220kJ/m 2 .