## 1 Introduction  
Currently, polycrystalline diamond compact (PDC) bits are mainly used for drilling soft to medium hard formations. While in hard abrasive formations serious failures, such as chipping, broken cutter and falling off of the PDC, often occur and the drilling effect is not satisfactory [1; 2; 3; 4], which is difficult to meet the exploration and development needs of unconventional resources in deep formations [5; 6]. To improve the performance of conventional PDC bits in deep formations, a series of approaches has been conducted on the material refinement and the design method supplement, such as increasing the number of cutters and blades [7], optimizing diamond packing [8] and using high-temperature and high-pressure (HT/HP) sintering for higher diamond volume in the PDC layer [9; 10]. However, the actual improvement in field application is not obvious. Efficiently drilling with PDC in hard abrasive formations remains challenging. At present, conventional PDC bits are still not able to completely substitute the roller cone bits in deep formations.  
In the last decade, with the advent of new technologies in manufacturing and depleting the catalyst material (Co) from the diamond structure, the structure of PDC cutting elements is no longer limited to a flat layer, but turns on a tendency to develop into non-planarization. In 2010, Novatek International Company initially proposed the innovative new Stinger conical shaped polycrystalline diamond element (CDE) with a thick synthetic layer (Figure 1a). The conical diamond element delivers improved wear for superior durability, and generated high point loading for effective formation fracture [11]. Later, Schlumberger Company also introduced its innovative cutter-the Axe cutter, which combines a standard cylindrical substrate with a modified ridge diamond layer (Figure 1b). Field tests indicate that this cutter improves drilling performance in terms of rates of penetration (ROP) and footage over the current PDC bits [1]. In 2015, Sifangda Company in China produced an innovative cutter with three cutting edges, called the 3-RDE cutter. Laboratory experiments show that its wear resistance and fatigue resistance are much higher than conventional cutters [12]. In addition, scholars at home and abroad have also carried out some research on non-planar cutters. [PERSON], et al. [13] investigated the influence of back-rake angle, cone apex angle and weight on bit (WOB) on the rock breaking efficiency of conical cutters through experiment and numerical simulation. [PERSON], et al. [14] studied the rock-breaking process of axe cutters and conventional cutters, and found that axe cutters behavior better than conventional cutters in wear resistance, cutting forces required and rock breaking efficiency.  
Although the non-planar cutters have shown certain potential in hard abrasive formations, related design and research are still in their infancy. Furthermore, the current study is mainly focused on the conical cutters or axe cutters. The research on 3-RDE cutters has rarely been reported in the literature. In this paper, based on elastic-plastic mechanics and rock mechanics, a three-dimensional (3D) finite element model of dynamic rock breaking with the innovative 3-RDE cutter has been established, using the extended Drucker-Prager criterion as the rock yield criterion. The accuracy of the numerical model was verified by laboratory experiments. The effects of back-rake angle, cutting depth, rotational angle, and rock properties on rock breaking efficiency were analyzed. The difference of rock breaking mechanism between 3-RDE cutter and conventional cutter was also studied. The research results could provide reference for the design and manufacture of the 3-RDE cutter.