On the other hand, the indentation process will lead to the damage of rock as well, which is beneficial to the cutting process. As a result, the improvement of indentation helps to enhance the efficiency of PDC bit (He and Xu, 2016 He et al., 2017 Liu et al., 2018 Zhou and Lin, 2013 Zhou and Lin, 2014). On the one hand, the rock failure mode will change from ductile to brittle with the increase of cutting depth. In fact, the indentation of PDC cutters is an important process for rock breaking. The cutting depth remained constant and the process of PDC cutters indention was ignored in these experiments (Cheng et al., 2018). However, the vast majority of these studies only focused on the cutting process, which is the main way to break the rock. On the basis of this, the performance of PDC bit has been improved a lot (Che et al., 2017 Chen et al., 2018 Cheng et al., 2019). A series of single cutter tests and theoretical analyses were conducted to investigate the mechanism of rock breaking. The polycrystalline diamond compact (PDC) bit has been widely used in the oilfield since its introduction in the mid-1970s (Ersoy and Waller, 1997 Warren and Sinor, 1994). The main findings of this paper are helpful to understand the penetration process of the PDC cutter and increase the cutting depth. Moreover, the cracks propagate more easily along the side where the PDC cutter has a larger angle with the rock surface. According to the shape of the damaged zone, the increase of back rake angles will lead to the crack propagation in the process of PDC cutter penetration. The number of AE hit counts has a clear increase trend corresponding to the decrease of penetration force, which indicates the brittle failure dominates at this moment. With the increase of back rake angles, the brittle failure and ductile failure occurs alternately. The results show that when the back rake angles of the PDC cutter is smaller than 20 degrees, the ductile failure is the main way to break the rock. After the experiments, the shape of the damaged zone was analyzed. The variation trend of penetration force and the number of AE hit counts versus penetration depth was recorded in our tests. In this work, laboratory experiments were conducted to investigate this process.
However, this process is ignored in the past because the cutting is the main way to break the rock for the PDC bit. The process of polycrystalline diamond compact (PDC) cutter penetrating into the rock is important for the increase of cutting depth.
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