磨削速度对碳化硅陶瓷磨削损伤影响机制研究

碳化硅陶瓷高速磨削过程中，磨粒对工件材料强力冲击，应变率剧增、复杂显微结构对应力波传送响应转变，材料力学行为发生变化，目前高速磨削对材料去除机制影响的物理本质认识还不清楚。为此，开展磨削速度对SiC陶瓷磨削裂纹损伤影响机制研究。通过单颗磨粒磨削SiC陶瓷试验，分析了磨削速度对SiC陶瓷磨削表面形貌、磨削亚表面裂纹损伤深度、磨削力和磨削比能的影响规律。试验结果表明，当SiC陶瓷材料以脆性方式去除时，磨削速度对裂纹损伤影响最为显著，随着磨削速度从20 m/s增加到160 m/s，磨削亚表面裂纹损伤深度从12.1μm快速降低到6μm。采用Voronoi法建立了金刚石磨削多晶SiC陶瓷有限元仿真模型，当磨粒切厚为0.3μm，磨削亚表面损伤以微裂纹为主；当磨粒切厚为1μm时，随着磨削速度增加，磨削亚表面裂纹损伤深度从14.7μm降低到4.6μm，磨削亚表面宏观沿晶裂纹逐渐变为微观裂纹。基于位错理论和冲击动力学理论，揭示了高速磨削过程中位错密度的增加和晶界反射应力波对应力场削弱作用是高速磨削SiC陶瓷裂纹损伤“趋肤效应”产生的机理。

Effect of Grinding Speed on Mechining Damage of Silicon Carbide Ceramics

In the high speed grinding of silicon carbide ceramics, the grains have a strong impact on the workpiece, the strain rate increases sharply, the complex microstructure of SiC ceramics alters the response to stress wave transmission, and mechanical behavior changes. The physical essence of the effect of strain rate on the material removal mechanism is not clear during high speed grinding process. Hence, the effect of grinding wheel speed on the grinding crack damage were investigated with the experimental and numerical single diamond grinding tests. The experimental results show that the grinding speed has a significant effect on the ground subsurface crack damage when the SiC ceramics removed in brittle mode. With the grinding speed increasing from 20 m/s to 160 m/s, the depth of subsurface crack damage decreases from 12.1 µm to 6 µm. A finite element model based on typical Voronoi tessellation method has been established for diamond grinding polycrystalline SiC ceramics. It is found that ground subsurface damage is mainly microcracks under the chip thickness of 0.3 µm, and the depth of subsurface crack damage decreases sharply from 14.7 µm to 4.6 µm with the increasing grinding speed under the chip thickness of 1 µm. Based on the principles of dislocation and shock wave dynamics, the mechanism of "skin effect" of subsurface crack damage was analyzed. The increasing dislocation density and reflected stress wave by the grain boundaries, leading to the intensity of stress field rapidly dissipated, were recognized as the dominant factors resulting in the "skin effect" of subsurface damage.