# Effect Range of the Material Constraint in Different Strength Mismatched Laboratory Specimens
## 3 Results and Discussion
### SENT Specimen
#### 3.2.2 Two Kinds of SENT Specimens with Deep Crack  
Figure 8 presents the fracture resistance curves and crack propagation paths of the SENT-\"121\" and SENT-\"1231\" specimens with deep crack under different material constraints. Figure 8a presents the fracture resistance curves of the SENT-\"121\" specimens with deep crack. The fracture resistance curves are related to the strengths of the materials A508 and 52 Mb. Because the strength of the material 52 Mb is higher than the material A508, the increasing of the width of material 52 Mb increases the fracture resistance of the specimen. When the width of material 52 Mb reaches 32 mm, it exceeds the effect range of material constraint, and the fracture resistance curves of the SENT-\"121\" specimens with deep crack no longer change.  
Figure 7: The fracture resistance curves of SENT-\"121\" (**a**) and SENT-\"1231\" (**b**) specimens with shallow crack together with the crack propagation paths of SENT-\"121\" (**c**) and SENT-\"1231\" (**d**) specimens with shallow crack.  
Different from the Figure 8a,b presents that the fracture resistance curves of the SENT-\"1231\" specimens with deep crack decrease first then increase, and finally remain steady with increasing of the widths of material 52 Mb and material 52 Mw. Similarly, with CT-\"121\" and CT-\"1231\" specimens with deep crack in the Figure 6a,b, the decreasing of the fracture resistance curves is also related to the high geometry and material constraints of the SENT-\"1231\" specimen with deep crack. The high constraint decreases the fracture resistance curve first. When the widths of the materials 52 Mb and 52 Mw are longer than 8 mm, the overall strength and fracture resistance curve of the SENT-\"1231\" specimen with deep crack increase. Because the material constraint of the SENT-\"121\" specimen is lower than SENT-\"1231\" specimen, the fracture resistance curves of the SENT-\"121\" specimens in Figure 8a have not decreased.  
Figure 8c presents that all the cracks propagate straight and have not changed considerably under different material constraints in the SENT-\"121\" specimens with deep crack. Similarly, with SENT-\"121\" specimens with shallow crack, it is also because the strengths of materials at the both sides of the crack are symmetric.  
For the SENT-\"1231\" specimen with deep crack, Figure 8d presents that the crack propagation paths deviate to the side of the material 52 Mb which has a higher strength than material 52 Mw in the process of crack growth. It is different with the CT specimens in this study and the SENB specimens in the previous studies [24; 25], and may be related to the loading configuration. The crack bears the bending stress in the CT and SENB specimens, but bears the shearing stress in the SENT specimen. The crack propagation path deviates to the side of high strength under the shearing stress in the SENT specimen.  
Taking into account both Figures 7 and 8, we can arrive to a conclusion that the effect range of material constraint also exists in the SENT specimen.  
Figure 8: The fracture resistance curves of SENT-\"121\" (**a**) and SENT-\"1231\" (**b**) specimens with deep crack together with the crack propagation paths of SENT-\"121\" (**c**) and SENT-\"1231\" (**d**) specimens with deep crack.