*2.2. Sample Preparations*

Figure 4 is a schematic diagram of the experimental sample, where Figure 4a is the tensile sample with a gauge length of 30 mm, a width of 20 mm, and a thickness of 5 mm. Considering the operability of the experiment, a notch with a width of about 0.3 mm and a depth of about 0.5 mm was preset in the middle of the tensile sample specimens to replace the crack equivalent. Figure 4b shows a sample for thermal fatigue test, with a size of 30 mm × 20 mm × 5 mm. A circular hole with a radius of 1.5 mm was formed 1 mm away from the upper edge to suspend the samples during thermal fatigue tests. In order to study the e ffect of unit spacing on the thermal fatigue performance, samples with unit spacings of 3, 5, 7 mm were prepared and labeled as T1, T2, and T3. The aforementioned samples were cut using an electric spark machine (DK7732, Huadong Group, Hangzhou, China). To prevent thermal fatigue and tensile property reduction, due to the surface and side-face roughness, the specimens were mechanically polished progressively by various grits of silicon-carbide-impregnated emery papers prior to laser biomimetic treatment. Oil stains were cleaned with an ultrasonic cleaner containing an acetone solution to form smooth and clean surfaces.

**Figure 4.** Sketch of crack repair. (**a**) Tensile test sample, (**b**) thermal fatigue test sample, and (**c**) the cross section of the sample.

All test samples imitating the anti-crack structure of leaves were fabricated using a solid-state Nd-YAG pulsed laser (XL-500WF, Rofin, Munich, Germany) with a wavelength of 1064 nm and a maximum rated output power of 500 W (Figure 5) [22]. Then, long cracks were segmented into several smaller cracks. In contrast, the structure of the laser remelting zone was obviously di fferent from that of the substrate; thus, the laser remelting zone was defined as a bionic crack blocked unit (unit) for a more convenient discussion. The units were fabricated by a pulse laser with di fferent laser parameters, which are shown in Table 2. Through the work-bench movement, a unit with a length of 3 mm processed by a laser beam was perpendicular to the direction of crack propagation. The unit distance was 2.5 mm. In addition, the untreated specimens were also compared to the laser-treated specimens.



**Figure 5.** The schematic diagram of laser processing.
