Existing numerical models cannot well reproduce the fracturing process and reveal the underlying mechanisms of rocks under microwave irradiation. In this work, the electromagnetic-thermal-mechanical multiphysics is decoupled into microwave-induced heating (continuum-based) and thermally-driven fracturing (discontinuum-based), with temperature serving as the key interlink. The rigid-body spring-subset network (RBSSN) model is proposed to calculate the progressive fracturing of rocks under open-ended microwave irradiation, where the individual contacts between adjacent tetrahedral blocks are disassembled into three hypothetical spring-subsets. To depict failure characteristics of large-scale rocks under microwave irradiation, a variable-sized block model is developed by densifying the rigid-blocks near the irradiation. This electromagnetic-thermal-mechanical decoupling framework effectively captures the microwave fracturing process, revealing that microwave irradiation induces tensile-dominant progressive failure and regionalized deterioration (localized damage and macroscopic radial fissure). The fracturing rate of rocks is time-dependent, progressing through silent, violent and slowdown periods of rupturing with extended exposure time. The reason why high-power microwave is more effective in promoting visible fractures under the identical input energy is analyzed by combining the thermal deformation theory and RBSSN simulation. It is found that, power levels should be kept within reasonable scopes to maximize fracturing effects as excessive power densities lead to initiation of numerous microcracks around the high temperature zone and susceptibility to spalling.

中文翻译：

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岩石微波压裂建模：一种连续体-不连续数值方法


现有的数值模型不能很好地再现岩石在微波照射下的压裂过程，也不能揭示岩石在微波照射下的底层机理。在这项工作中，电磁-热-机械多物理场解耦为微波诱导加热（基于连续体）和热驱动压裂（基于不连续体），其中温度是关键的互连。提出了刚体弹簧子集网络 （RBSSN） 模型来计算开放式微波照射下岩石的渐进压裂，其中相邻四面体块之间的单个接触被分解成三个假设的弹簧子集。为了描述微波照射下大型岩石的破坏特征，通过在照射附近致密化刚性块，建立了一种可变尺寸的块体模型。这种电磁-热-机械解耦框架有效地捕捉了微波破裂过程，揭示了微波辐照诱导拉伸主导的渐进性破坏和区域化恶化（局部损伤和宏观径向裂缝）。岩石的破裂速度与时间有关，随着暴露时间的延长，会经历无声、剧烈和缓慢的破裂期。结合热变形理论和 RBSSN 仿真，分析了在相同输入能量下高功率微波更有效地促进可见裂缝的原因。研究发现，功率水平应保持在合理的范围内，以最大限度地提高压裂效果，因为过高的功率密度会导致高温区周围产生大量微裂纹，并容易剥落。