Thermo-hydro-mechanical couplings and strain localization in Cosserat continua : application to stability analysis of rapid shear in faults
Thermo-hydro-mechanical couplings and strain localization in Cosserat continua : application to stability analysis of rapid shear in faults
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Cosserat 连续体中的热-水-机械耦合和应变局部化：在断层快速剪切稳定性分析中的应用
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发表时间：
2017
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通讯作者：
H. Rattez
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作者：
H. Rattez
当材料受到大变形时，大多数材料会经历非弹性变形。它通常伴随着这些变形局部化到一个狭窄的区域，导致失败。应变局部化的一个特殊情况是剪切带的形成，这是在岩土材料中观察到的最常见的模式。在地质构造中，它们以非常不同的尺度出现，从俯冲带的千米尺度到断层核内的微米尺度。研究它们的产状和演化对描述地质材料的破坏和模拟成熟地壳断裂的地震滑动具有重要意义。这些断层中的压力和温度条件以及与高度断裂材料内部孔隙水的相互作用突出了地震成核所涉及的不同物理过程的重要性。在这篇论文中，我们研究了剪切带的发生和演化的断层泥考虑到材料的微观结构，诉诸弹塑性Cosserat连续和热-水-力耦合的影响。Cosserat理论的使用介绍了有关的凿微观结构，即晶粒尺寸的信息，并允许正规化的数学问题，在后本地化制度，通过引入内部长度的本构方程。两种方法被用来研究耦合的非线性偏微分方程组：线性稳定性分析和有限元模拟。线性稳定性分析允许研究多物理耦合的机械系统中局部变形的发生。对扰动的主波长的考虑也允许确定局部区域的宽度。此剪切带的厚度被确认为在一定范围内的变形后本地化制度的数值积分。所获得的局部化带的宽度是理解断层行为的关键参数，与实验和现场观察结果一致。此外，数值有限元计算能够模拟地震滑动期间断层泥的力学响应，并深入了解各种物理耦合对能量收支的影响
When materials are subjected to large deformations, most of them experience inelastic deformations. It is often accompanied by a localization of these deformations into a narrow zone leading to failure. One particular case of strain localization is the formation of shear bands which are the most common patterns observed in geomaterials. In geological structures, they appear at very different scales, from kilometer scale for subduction zones, to micrometric scale inside fault cores. Studying their occurrence and evolution is of key importance to describe the failure of geomaterials and model seismic slip for mature crustal faults. The pressure and temperature conditions in these faults and the interaction with the pore water inside a highly fractured materials highlight the importance of different physical processes involved in the nucleation of earthquakes. In this thesis, we study the occurrence and evolution of shear bands inside fault gouges taking into account the material microstructure by resorting to elastoplastic Cosserat continua and also the effect of thermo-hydro mechanical couplings. The use of Cosserat theory introduces information about the gouge microstructure, namely the grain size, and permits to regularize the mathematical problem of in the post-localization regime by introducing an internal length into the constitutive equations. Two approaches are used to study the coupled non-linear partial differential set of equations: linear stability analysis and finite element simulations. Linear stability analysis allows to study the occurrence of localized deformation in a mechanical system with multi-physical couplings. Considerations on the dominant wave length of the perturbations permit also to determine the width of the localized zone. This shear band thickness is confirmed by numerical integration in the post-localization regime for a certain range of deformation. The obtained widths of the localized zone are key parameters for understanding fault behavior, are in agreement with experimental and field observations. Moreover, numerical finite element computations enable to model the mechanical response of a fault gouge during seismic slip and give insights into the influence of various physical couplings on the energy budget