The effect of specimen size on microwave-induced fracturing of rocks has not been well understood. In this study, the experimental tests using open-ended microwave and numerical simulations coupling COMSOL Multiphysics and four-dimensional lattice spring model (4D-LSM) were carried out to investigate the evolution process of microwave-induced cracks, and to elucidate the mechanisms responsible for size-dependent microwave-induced fracturing. The experiments show that with the increase of the specimen dimension, the number of microwave-induced cracks is almost constant, and the total crack length first increases and then decreases, while the maximum crack width and maximum crack depth decrease gradually. A comparison of the experimental and numerical temperature characteristics as well as cracking characteristics indicates that the models established in this study are reasonable in the simulation of the rock fracturing behaviours. The numerical results show that the crack initiation time increases logarithmically with the increase of the specimen dimension. For the small-sized specimens, the microwave-induced cracks started from the outer boundary of the specimen and propagated toward to specimen center and into the depth. For the medium-sized and large-sized specimens, the microwave-induced cracks initiated near the outer boundary of the antenna aperture, and then propagated toward to the center of the specimen and the outer boundary of the specimen. The main reason for the size-dependent of fracturing behavior is that the local fracture energy will dramatically decrease when the crack is approaching the specimen boundary.

中文翻译：

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样品尺寸对闪长岩微波诱导破裂影响的实验研究和数值模拟

样品尺寸对微波诱导岩石破裂的影响尚未得到很好的了解。本研究采用开放式微波和耦合 COMSOL Multiphysics 和四维晶格弹簧模型 (4D-LSM) 的数值模拟进行实验测试，以研究微波诱发裂纹的演化过程，并阐明其机理。用于尺寸相关的微波诱导断裂。实验表明，随着试件尺寸的增加，微波诱发裂纹的数量几乎恒定，裂纹总长度先增加后减小，而最大裂纹宽度和最大裂纹深度逐渐减小。实验温度特性与数值温度特性以及破裂特性的对比表明，本研究建立的模型在模拟岩石破裂行为方面是合理的。数值结果表明，裂纹萌生时间随着试件尺寸的增加呈对数增加。对于小尺寸试件，微波引发的裂纹从试件的外边界开始向试件中心和深度扩展。对于中型和大型试件，微波诱发裂纹在天线孔径外边界附近萌生，然后向试件中心和试件外边界扩展。断裂行为与尺寸相关的主要原因是当裂纹接近试样边界时，局部断裂能将急剧下降。