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<p>Microwave pretreatment assists mechanical fragmentation of hard rock by inducing thermal cracks and reducing rock strength; however, its effectiveness under dynamic indentation and confining pressure remains poorly understood. In this study, dynamic indentation tests were conducted on microwave-pretreated granite using a split Hopkinson pressure bar (SHPB). The results show that the peak indentation force increases with loading rate, and that a distinct double-peak force–depth response occurs at an impact velocity of 10 m/s. Microwave-induced damage reduces the peak indentation force, alters the fracture process, and enhances fragmentation. With increasing confining pressure from 5 to 15&#xa0;MPa, the fracture mode shifts from splitting to localized crushing, accompanied by a reduction in crater size. Energy analysis indicates that prolonged microwave exposure decreases the mechanical specific energy consumption by up to 60%, whereas higher confining pressure results in increased energy dissipation through plastic deformation and frictional processes. To predict the peak indentation force, a closed-form cavity-expansion model incorporating pressure hardening, thermal softening, and rate hardening was developed. These findings improve the understanding of microwave-assisted dynamic indentation and provide guidance for optimizing microwave exposure time under different confining pressures.</p>

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Rock Failure Characteristics Under Dynamic Indentation Tests of Granite Pretreated by Microwave Heating

  • 期刊论文

  • 发表日期：

    2026年4月9日

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  • Xiaoli Su,
  • Diyuan Li,
  • P. G. Ranjith,
  • Pingkuang Luo,
  • Hao Gong,
  • Quanqi Zhu

摘要

Microwave pretreatment assists mechanical fragmentation of hard rock by inducing thermal cracks and reducing rock strength; however, its effectiveness under dynamic indentation and confining pressure remains poorly understood. In this study, dynamic indentation tests were conducted on microwave-pretreated granite using a split Hopkinson pressure bar (SHPB). The results show that the peak indentation force increases with loading rate, and that a distinct double-peak force–depth response occurs at an impact velocity of 10 m/s. Microwave-induced damage reduces the peak indentation force, alters the fracture process, and enhances fragmentation. With increasing confining pressure from 5 to 15 MPa, the fracture mode shifts from splitting to localized crushing, accompanied by a reduction in crater size. Energy analysis indicates that prolonged microwave exposure decreases the mechanical specific energy consumption by up to 60%, whereas higher confining pressure results in increased energy dissipation through plastic deformation and frictional processes. To predict the peak indentation force, a closed-form cavity-expansion model incorporating pressure hardening, thermal softening, and rate hardening was developed. These findings improve the understanding of microwave-assisted dynamic indentation and provide guidance for optimizing microwave exposure time under different confining pressures.