*3.3. "12321" Model*

When changing the width of 52Mb individually, the *J*-resistance curves of different "12321" models under different material constraints are shown in Figure 10a. It can be found that increasing the width of 52Mb, the *J*-resistance curves of different "12321" models increase and remain steady when the width of 52Mb is up to 16mm. It is similar with the "121" model; the strength of the material 52Mb is higher than the materials A508 and 52Mw, with increasing of the width of 52Mb, the *J*-resistance curve of the model increases. When the width of 52Mb over the effect range of the material constraint, the *J*-resistance curve of the "12321" model is unchanged.

**Figure 10.** The *J*-resistance curves (**a**) and the areas surround by the *εp* = 0.1 isoline (**b**) of different "12321" models with the same *W*52Mw.

The areas surrounded by the *ε<sup>p</sup>* = 0.1 isoline at crack tip at the same *J*-integral (*J* = 1600 kJ/m2) for different "12321" models are shown in Figure 10b, which also reflects the same change rule with the *J*-resistance curves.

When changing the width of 52Mw individually, the *J*-resistance curves of different "12321" models under different material constraints are shown in Figure 11a. It can be found that increasing of the width of 52Mw, the *J*-resistance curves of different "12321" models increase firstly then decrease, and finally remain steady. The model with *W*52Mw = 0 mm has the lowest *J*-resistance curve and the model with *W*52Mw = 16 mm has the highest *J*-resistance curve. When the width of 52Mw up to 32 mm, the *J*-resistance curve of the model will not change by increasing the 52Mw's width.

**Figure 11.** The *J*-resistance curves (**a**) and the areas surround by the *εp* = 0.1 isoline (**b**) of different "12321" models with the same *W*52Mb.

Because the strength of the material 52Mw is higher than the material A508, thus, increasing of the width of 52Mw, the *J*-resistance curve of the model increases firstly. When the *W*52Mw = 16 mm, there exists an optimal width and the model has the highest *J*-resistance curve. Then, the *J*-resistance curves of the models decrease and remain steady at last when the total width of 52Mb and 52Mw over the effect range of the material constraint.

The areas surrounded by the *ε<sup>p</sup>* = 0.1 isoline at crack tip at the same *J*-integral (*J* = 1600 kJ/m2) for different "12321" models are shown in Figure 11b, which also reflects the same change rule with the *J*-resistance curves.
