## 4 Discussion
However, it is important to note that the maximum vibration amplitude of the CFRP hub reaches 0.2 um, which is greater than the 0.15 um observed for the steel hub under high vibration frequencies, specifically at 5500 Hz, where the external force is substantial. The reduction in the vibration amplitude of the CFRP hub during free vibrations can be attributed to its superior damping ability compared to that of steel. Notably, the CFRP hub comprises two distinct materials--carbon fiber fabrics and a resin matrix, arranged in a layered structure. These structural differences set the CFRP hub apart from a single-material hub like the steel hub and allow it to absorb vibrations effectively. This outcome can be attributed to the CFRP hub's lower density and elastic modulus, which render it lighter and more conducive to shorter oscillation times. Furthermore, the CFRP hub demonstrates enhanced damping properties, effectively mitigating resonance frequencies and reducing oscillation times during grinding. This observation aligns with the findings of [PERSON] et al. (2013), reaffirming the significance of hub material properties in shaping grinding dynamics. A critical aspect emphasized by the study is the influence of the hub material on the grinding process' longevity and operational stability. The substantial disparity in material density between the steel and CFRP hubs results in distinct thermal fatigue and wear behaviors. Specifically, the higher density of the steel hub can exacerbate thermal fatigue damage in the spindle or wear in the grinding machine's bearing. The subsequent reduction in spindle life has direct implications for power efficiency. Introducing a CFRP hub addresses this challenge by stabilizing the grinding process swiftly and introducing smaller amplitudes in high-speed grinding. Figure 6 displays the measured ground surface roughness, revealing an intriguing comparison between the two materials' hubs. The transition from a peripheral speed of 20 to 100 m/s is associated with a notable improvement in surface smoothness. Specifically, when the steel hub of the grinding wheel grinds at a peripheral speed of 20 m/s, the Rz/Ra ratio stands at 10.8 in the workpiece surface roughness. Simultaneously, the CFRP hub of the grinding wheel, under the same peripheral speed of 20 m/s, records a ratio of 10.2. These values are remarkably similar. However, when the peripheral speed of the steel hub grinding wheel escalates to 100 m/s during the grinding of the WC workpiece, the Rz/Ra ratio surges to 15.03. Conversely, after the CFRP hub of the grinding wheel processes the WC workpiece, the Rz/Ra ratio only reaches 11.29, as indicated in Table 2.  
These outcomes suggest that changes influence the grinding wheel with a CFRP hub in peripheral speed less. In other words, the CFRP hub is better suited for high-speed grinding wheel configurations. Furthermore, the results highlight that the performance of the CFRP grinding wheel exhibits an optimal boundary under usage conditions, typically at a peripheral speed of around 60 m/s. At this speed, the Rz/Ra ratio in the CFRP hub is approximately 4.1, notably smaller than ratios at other speeds. This implies that the CFRP hub performs most effectively at a peripheral speed of roughly 60 m/s, which is the same as the critical speed of high-speed grinding. In contrast, the performance of the steel hub diminishes as peripheral speed increases. In summary, these observations underscore the suitability of the WC material for high-speed machining due to its hardness and brittleness. This finding elucidates how the CFRP hub of the diamond wheel excels in stabilizing the grinding process, mainly when dealing with tough and brittle WC material. It is intriguing that despite working under identical grinding conditions, the grinding wheel with a CFRP hub consistently delivers a finer surface roughness. However, this phenomenon remains inadequately explained when considering factors like the grinding wheel's weight, the material properties of the hub, and the abrasive characteristics alone.