# Effect Range of the Material Constraint in Different Strength Mismatched Laboratory Specimens
## 3 Results and Discussion
### CT Specimen
#### 3.1.2 Two Kinds of CT Specimens with Deep Crack  
Figure 6 presents the fracture resistance curves and crack propagation paths of the CT-\"121\" and CT-\"1231\" specimens with deep crack under different material constraints. Figure 6a presents the fracture resistance curves of the CT-\"121\" specimens with deep crack.  
It is different with the CT-\"121\" specimens with shallow crack in the Figure 5a. First, the fracture resistance curves have an obvious steady state when the width of the material 52 Mb reaches 16 mm. When the width of the material 52 Mb is longer than 16 mm, the fracture resistance curves of the CT-\"121\" specimens with deep crack no longer change. It means that an effect range of the material constraint exists in the CT-\"121\" specimen with deep crack. When the width of the material 52 Mb is longer than 16 mm, it exceeds the effect range of the material constraint. Second, the fracture resistance curves decrease first when the width of the material 52 Mb changes from 0 mm to 4 mm. This is the same for the SENB-\"1231\" specimen in the previous study of the authors [23]. The decreasing of the fracture resistance curves is related to the high geometry constraints of CT and SENB specimens with deep crack. There exists interaction between geometry constraint and material constraint. The high geometry constraints in the CT and SENB specimens with deep crack strengthen the effect of material constraint and decrease the fracture resistance curve first. When the width of the material 52 Mb is longer than 4 mm, the overall strength and fracture resistance curve of the CT-\"121\" specimen with deep crack increase.  
Figure 5: The fracture resistance curves of CT-\"121\" (**a**) and CT-\"1231\" (**b**) specimens with shallow crack together with the crack propagation paths of CT-\"121\" (**c**) and CT-\"1231\" (**d**) specimens with shallow crack.  
Figure 6b presents the fracture resistance curves of the CT-\"1231\" specimens with deep crack. Similarly, with the CT-\"121\" specimen with deep crack in the Figure 6a, an effect range of the material constraint also exists in the CT-\"1231\" specimen with deep crack.  
Figure 6c,d present the crack propagation paths of the CT-\"121\" and \"1231\" specimens with deep crack. Figure 6c presents that all the cracks propagate straight and have not changed considerably under different material constraints in the CT-\"121\" specimens with deep crack. It is also because that the initial crack located in the center of the material 52 Mb, the strengths of materials at the both sides of the crack are symmetric. Figure 6d presents that the crack propagation paths deviate to the side of material 52 Mw which has a lower strength than material 52 Mb in the process of crack growth. With an increase in the widths of material 52 Mb and material 52 Mw, the deviation becomes more obvious first then remains steady. It is consistent with the fracture resistance curves in the Figure 6b, and means that the effect range of the material constraint exists in the CT-\"1231\" specimen with deep crack. When the total width of the material 52 Mb and material 52 Mw is longer than 16 mm, it exceeds the effect range of the material constraint, and the crack propagation paths no longer change.  
Considering both Figures 5 and 6, it can be concluded that the effect range of material constraint exists in the CT specimen. Not only that, the effect range is influenced by the geometry constraint induced by the crack depth. The high geometry constraint (deep crack) against the plastic deformation at crack tip and reduces the effect range of material constraint. For the CT specimen with shallow crack and low geometry constraint, the effect range is greater than 38.4 mm, and thus the steady state has not been obtained in the Figure 5.