Rock failure modes exist a transition from ductile to brittle with the increase of cutting depths. Further insight into the determination of critical transition depth is of great significance to optimize the design of cutting tools and operational parameters. In the present study, a novel method for identifying rock failure modes is proposed based on the evolution of cutting force. Furthermore, a series of experiments were conducted to validate this method and investigate the critical depth under different experimental conditions. Firstly, we calculate the cutting force difference (ΔF) from peak to valley and its variation rate (Ra). Then, Ra and ΔF are fitted linearly, and the slope of the fitting line (Sl_Ra) is determined. According to the experimental results, rock breakage is a process involving continuous changes in failure modes. At shallow cutting depths, Sl_Ra is close to zero, indicating the domination of ductile failure. Then Sl_Ra rises with the increase of cutting depths, indicating that the proportion of brittle failure becomes higher. Such region is generally defined as a transition region. Once cutting depths exceed the critical depth, effects of ductile failure can be ignored and Sl_Ra tends to be stable. The higher rock brittleness and smaller back rake angles result in a reduction of critical depth. In addition, the critical transition depth can be correlated with some parameters such as the distribution of cuttings and the number of valleys in cutting force. Our current study helps to identify rock failure modes and provides an in-depth understanding about the critical depth.

随着切削深度的增加，岩石破坏模式存在从韧性到脆性的转变。进一步深入了解临界过渡深度的确定，对于优化刀具设计和操作参数具有重要意义。在本研究中，提出了一种基于切削力演化的岩石破坏模式识别新方法。此外，还进行了一系列实验来验证该方法并研究不同实验条件下的临界深度。首先，我们计算从峰到谷的切削力差 (Δ F ) 及其变化率 ( Ra )。然后，线性拟合Ra和ΔF，拟合线的斜率（Sl_Ra ) 确定。根据实验结果，岩石破碎是一个破坏模式不断变化的过程。在浅切削深度处，Sl _Ra接近于零，表明韧性破坏占主导地位。然后Sl _Ra随切削深度的增加而升高，表明脆性破坏的比例变高。这种区域通常被定义为过渡区域。一旦切削深度超过临界深度，延性破坏的影响可以忽略，Sl _Ra趋于稳定。较高的岩石脆性和较小的后倾角导致临界深度减小。此外，临界过渡深度可以与一些参数相关，例如切削力的分布和谷的数量。我们目前的研究有助于识别岩石破坏模式，并提供对临界深度的深入了解。