PSI - Issue 42

Zeng Chen et al. / Procedia Structural Integrity 42 (2022) 180–188 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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C(T) and SEN(B) specimens, the opening stress values were extracted at the midplane. For 3PB and 5PB specimens, those values were extracted at the layers where the maximum J -integral were found. According to Eq. (1), the crack opening stress under SSY (Small Scale Yielding) is necessary to calculate parameter Q . In this case, all specimens were tested at around the low temperature - 160℃ which is entirely in the lower shelf region according to Figure 1. The C(T) specimen with 25mm thickness and a/W =0.5 at this temperature can be considered to be under SSY conditions. Therefore, the mean value of σ θθ of C(T) specimens at r/(J/σ 0 ) =2 was used in the calculations. The σ θθ of all specimens at r/(J/σ 0 ) =2 were determined and submitted into Eq. (1), then the results of parameter Q are obtained and presented in Figure 8.

Figure 8. Results of parameter Q for 4 specimens

The total volume of all elements whose equivalent stress exceeded the yield stress was extracted from the FEA result and then divided by the thickness to calculate the area of the plastic region at fracture for each model. The mean value of the plastic region area for 25mm C(T) models was used as the reference plastic region at fracture for a standard specimen A ref . The results of parameter φ can be easily obtained by Eq. (2) and are shown in Figure 9.

Figure 9 . Results of parameter φ for 4 specimens

4.3. Comparison and discussion Figure 8 shows the in-plane constraint parameter Q of all specimens. It is found that for the C(T) and SEN(B) specimens which have a large change in the thickness while the a/W ratios are equal, the values of their Q parameters are almost the same and remain stable. It indicates that the in-plane constraint levels of these two specimens are similar and parameter Q cannot quantify the out-of-plane constraint for them. For 3PB and 5PB specimens, it is obvious that their Q parameters are smaller than SEN(B) specimens although they have the same