3.3.3. Tensile Fracture Morphology of Samples

Figure 12a–e shows the fracture morphology of untreated samples with different carbon contents. After plastic deformation, dimples and tearing ridges appear in the fracture of the sample. Furthermore, as the carbon content increases, the number of dimples increases, indicating that the strength of the samples also increase.

**Figure 12.** Fracture surfaces of the untreated samples: (**a**) A1, (**b**) A2, (**c**) A3, (**d**) A4, and (**e**) A5.

Figure 13a–e shows the fracture morphologies of the units. It can be seen that the fracture morphologies are different from those of the untreated samples. When the carbon content is between 0.15% and 0.37%, more dimples appear in the fracture of the bionic unit, and the dimples become smaller and deeper. Furthermore, as the carbon content increases, the dimples gradually decrease. For the tensile properties of the specimen, the smaller and deeper the dimple, the more energy required to break the sample. When the carbon content is 0.37%, tearing ridges and cleavage planes appear at the fracture of the biomimetic unit, indicating that the sample has a brittle fracture tendency. When the carbon content increases to 0.45–0.55%, the sample experiences a brittle fracture, and the fracture morphology has obvious tearing ridges, cleavage step, and a river pattern, further verifying that the tensile properties are inferior.

**Figure 13.** Fracture surfaces of the units: (**a**) LR-A1, (**b**) LR-A2, (**c**) LR-A3, (**d**) LR-A4, and (**e**) LR-A5.
