*2.3. Sample Preparation*

Using a DK77 electric spark cutting machine produced by Donghua CNC company in China, the fragments of the grey cast iron brake hub were processed into 100 × 20 × 10 mm<sup>3</sup> and 40 × 20 × 10 mm<sup>3</sup> rectangular samples, and a 3 mm round hole was drilled on the upper part of 40 rectangular samples, as shown in Figure 3. The surfaces of the samples were polished with 80#, 360#, 600#, and 1000# sandpaper to remove machining traces.

The bionic sample processing was carried out by the system of controlling the laser source's moving track with a six degree of freedom manipulator (Figure 4). The main part of the system was the Nd: YAG pulse laser generator (XL-500WF, Rofin, Munich, Germany). A pulse beam with a wavelength of 1064 nm and a maximum output power of 300 W was emitted through the YAG crystal. The laser energy transmitted by the optical fiber was dispersed with a Gaussian distribution on the sample surface. The entire experimental laser setup was comprised of a cooling system, a two-dimensional rotating table, a six degree of freedom manipulator, and a servo control system. By adjusting the position coordinates of the manipulator in the *z*-axis direction, precise control of the defocusing amount of the laser spot can be realized, and the spot with the required size can meet the needs of the unit machining. The first mock exam was carried out to adjust the output laser parameters through the laser control cabinet, and ensure that the laser output energy was in accordance with the test requirements and that the size, shape, and organizational structure of the bionic cells in each model laser processing were the same. The laser parameters are shown in Table 2.

**Figure 3.** Bionic specimens with different distance distributions.

**Figure 4.** Schematic diagram of laser processing process.


**Table 2.** Laser parameters.
