Cutting force as an index to identify the ductile-brittle failure modes in rock cutting

Abstract

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 (Δ F ) from peak to valley and its variation rate ( Ra ). Then, Ra and Δ F 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.