*3.2. "123" Model*

The *J*-resistance curves of different "123" models under different material constraints are shown in Figure 8. It can be found that increasing of the width of 52Mb, the *J*-resistance curves of the models increase firstly then decrease, and finally remain steady. The model with *W*52Mb = 0 mm has the lowest *J*-resistance curve and the model with *W*52Mb = 4 mm has the highest *J*-resistance curve. When the width of 52Mb is up to 16 mm, the *J*-resistance curve will not change with increasing of the 52Mb's width.

**Figure 8.** The *J*-resistance curves of different "123" models.

When the *W*52Mb = 0 mm, the model is the same with the bimetallic welded joint with an interface crack. In this condition, the model has the lowest *J*-resistance curve, which shows that the interface crack in bimetallic welded joint is very dangerous. With increasing of the width of 52Mb, the *J*-resistance curve of the model increases. When the *W*52Mb = 4 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.

The same with the "121" model, when the width of 52Mb up to a value, the *J*-resistance curve of the model is same with the *J*-resistance curve of homogeneous material 52Mb. That is, an effect range also exists. By contrast with the "121" model, the steady value is different and is related to the materials on both sides of the crack.

Figure 9 shows the areas surround by the *ε<sup>p</sup>* = 0.1 isoline at crack tip at the same *J*-integral (*J* = 1600 kJ/m2) for different "123" models. It reflects the same change rule with the *J*-resistance curves. The same change rules can prove each other also.

**Figure 9.** The areas surround by the *εp* = 0.1 isoline at the same *J*-integral for "123" model.
