*3.4. "12324" Model*

When changing the width of 52Mb individually, the *J*-resistance curves of different "12324" models under different material constraints are shown in Figure 12a. It can be found that increasing the width of 52Mb, the *J*-resistance curves of the models increase firstly then decrease, and finally remain steady. The models with *W*52Mb = 0 mm and *W*52Mb = 0.5 mm have the lowest *J*-resistance curves and the model with *W*52Mb = 2 mm has the highest *J*-resistance curve. When the width of 52Mb up to 8 mm, the *J*-resistance curve will not change by increasing the 52Mb's width.

It is the same with "12321" model, because the strength of material 52Mb is higher than the material 52Mw, and increasing the width of 52Mb, the *J*-resistance curves of the models increase firstly. However, the strength of material 52Mb is lower than the material 316L, the *J*-resistance curves of the models do not always increase. When the *W*52Mb = 2 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 width of 52Mb 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 "12324" models are shown in Figure 12b, which also reflects the same change rule with the *J*-resistance curves.

**Figure 12.** The *J*-resistance curves (**a**) and the areas surround by the *εp* = 0.1 isoline (**b**) of different "12324" models with the same *W*52Mw.

When changing the width of 52Mw individually, the *J*-resistance curves of different "12324" models under different material constraints are shown in Figure 13a. It can be found that increasing of the width of 52Mw, the *J*-resistance curves of the "12324" models decrease. When the width of 52Mw is up to 32 mm, the *J*-resistance curves of the models remain steady and will not change with increasing the 52Mw's width. This is because although the strength of material 52Mw is higher than the material A508, it is much lower than the materials 316L and 52Mb. Increasing of the width of 52Mw, the *J*-resistance curves of the models decrease until the total width of 52Mb and 52Mw over the effect range of the material constraint.

**Figure 13.** The *J*-resistance curves (**a**) and the areas surround by the *εp* = 0.1 isoline (**b**) of different "12324" models with the same *W*52Mb.

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 "12324" models are shown in Figure 13b, which also reflects the same change rule with the *J*-resistance curves.

In general, the above results show the effect range of the material constraint. Comparing all the models, it can be found that the effect range of the material constraint is real. The effect range relates to the materials on both sides of the crack. It should be pointed that the effect range is not only related to the adjacent material, but also non-adjacent material. It can be proved by comparing the *J*-resistance curves of the "12321" model and "12324" model. When the two cracks have the same adjacent material and dimensions but different non-adjacent materials, the *J*-resistance curves of the two models are different. That is, the *J*-resistance curves influenced by all the materials within the effect range, no matter whether they are adjacent or not.
