As the development of geothermal resources in medium to deep dry hot rock formations progresses, traditional drilling technologies face numerous challenges posed by high-strength hard rocks. These challenges, including inadequate bit penetration capacity and low rotational cutting efficiency, severely constrain drilling performance. In this context, hydraulic impact hammer drilling technology has demonstrated significant advantages in enhancing drilling speed. To investigate the rock-breaking mechanisms under the coupled effects of impact load magnitude and frequency, deep granite was selected as the research object. Based on dynamic mechanical experimental data obtained under high-temperature and high-pressure conditions (200 °C, 40 MPa), a two-dimensional dynamic numerical model for cone-shaped tooth impact cutting of dry hot rock has been developed by incorporating cohesive elements. This model systematically analyzes the effects of varying impact loads (9 to 12 kN) and impact frequencies (30 to 60 Hz) on rock fragmentation patterns, dynamic response characteristics, and impact energy. The results indicate that the cone-shaped tooth impact cutting exhibits a pronounced “dynamic crushing-shear coupling” feature, with the rock-breaking process undergoing dynamic evolution from local crushing initiation to volume fracturing, eventually leading to shear-mixed destruction. An increase in impact load significantly enhances the system's dynamic response amplitude, leading to a transition in the rock-breaking mode from shallow local crushing to extensive shear-mixed failure, accompanied by a notable increase in the fractured area. Additionally, increasing the impact frequency reinforces the superposition effect of stress waves within the rock and ensures continuous energy input, resulting in a denser dynamic response and further expanding the wedge-shaped fracture zone in front of the tooth tip. Moreover, as both load and frequency increase, the impact damaged area and energy increases significantly, allowing the system's energy to be more efficiently converted into rock damage and fracture energy. This study reveals the mechanisms by which high-frequency and high-energy parameters influence the efficiency of impact rock breaking, providing important theoretical support for the optimization of hydraulic impact hammers and the design of drill bit structures.
Zhou et al. (Mon,) studied this question.
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