Marcellus页岩裂缝特性尺寸效应试验与计算
Characterization of Marcellus Shale Fracture Properties through Size Effect Tests and Computations
摘要：
页岩类岩石的力学特性需要了解测量特性的比例，以便能够从小规模实验室测试外推到现场研究。本文分析了Marcellus页岩的尺寸效应，并通过尺寸效应试验获得了其断裂特性。对尺寸逐渐增大的三点弯曲（TPB）试件进行了大量的断裂试验。试验结果表明，名义强度随试件尺寸的增大而减小，并能很好地用Bazant尺寸效应定律（SEL）拟合。结果表明，SEL占试样尺寸和几何形状的影响，允许准确识别材料的初始断裂能，Gf，和有效的断裂过程区（FPZ）长度，参见。所得到的断裂性能进行了验证，使用标准的有限元技术与凝聚力模型的研究标本的数值模拟。观察到显着的各向异性的断裂性能确定在三个主要的缺口方向：避雷器，分频器，和短横向。讨论了所测结构强度和表观断裂韧性的尺寸效应。无论是基于强度的准则，忽略尺寸效应，也不是经典的LEFM，不考虑FPZ的有限性可以预测报告的尺寸效应数据，和准脆性类型的非线性断裂力学，而不是适用。
英文摘要：
Mechanical characterization of shale-like rocks requires understanding the scaling of the measured properties to enable the extrapolation from small scale laboratory tests to field study. In this paper, the size effect of Marcellus shale was analyzed, and the fracture properties were obtained through size effect tests. A number of fracture tests were conducted on Three-Point-Bending (TPB) specimens with increasing size. Test results show that the nominal strength decreases with increasing specimen size, and can be fitted well by Bazant's Size Effect Law (SEL). It is shown that SEL accounts for the effects of both specimen size and geometry, allowing an accurate identification of the initial fracture energy of the material, Gf, and the effective Fracture Process Zone (FPZ) length, cf. The obtained fracture properties were verified by the numerical simulations of the investigated specimens using standard Finite Element technique with cohesive model. Significant anisotropy was observed in the fracture properties determined in three principal notch orientations: arrester, divider, and short-transverse. The size effect of the measured structural strength and apparent fracture toughness was discussed. Neither strength-based criterion which neglects size effect, nor classic LEFM which does not account for the finiteness of the FPZ can predict the reported size effect data, and nonlinear fracture mechanics of the quasibrittle type is instead applicable.
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