Two-Phase Model of Damage, Shear Localization and Plate Boundary Formation

研究者建议通过他新发展的两相损伤理论来研究岩石圈剪切局部化（由于非线性弱化机制而使固体材料变形集中）和板块边界形成的过程。该理论指出，受损材料（即具有微裂纹和空隙的材料）以其最简单的形式是两相材料（代表固体主体的基体相和代表填充空隙的流体相，如水或空气）。形成微裂纹的能量为裂纹壁的表面能，在两相模型中为相间界面的表面能。初步结果表明，在强剪切作用下，混凝土具有明显的局部脆弱区，在极端剪切作用下，混凝土具有分布破坏（提示裂缝分支失稳等过程）。然而，该理论仍然处于非常基本的形式，并且只在简单的一维几何形状中进行了测试。因此，拟议的项目需要进一步开发和测试，以便1)将其应用于更多与地幔/岩石圈相关的几何形状和条件；2)包括进一步相关的物理。该模型将适用于单轴压缩的情况；压缩折叠和拉伸缩颈；重力驱动的流动（如斜坡和大陆的稳定性）；源汇驱动流（从纯极向流考察环向运动的激励）；对流驱动的运动。要研究和纳入的新物理包括愈合和退火过程；相间反应（如水合作用）；各向异性（考虑孔隙/微裂纹排列）；热力学效应（例如，影响孔隙压力的流体热膨胀、基体材料的热粘性行为和界面表面张力的温度敏感性）；将不可逆耗散热和半可逆存储的变形功作为界面表面能进行分配。该项目将进一步了解岩石圈的基本过程和其他剪切局部化机制，以及构造板块和板块边界的起源。

Bercovici, DavidEAR-0105269 The investigator proposes to study the process of lithospheric shear localization (focussing of deformation in solid materials due to nonlinear weakening mechanisms) and plate boundary formation through his newly developed two-phase damage theory. The theory states that a damaged material (i.e., with microcracks and voids) is, in its simplest form, a two phase material (a matrix phase representing solid host, and a fluid phase representing void-filling material such as water or air). It also states that the energy going into making microcracks is the surface energy of the crack wall, which in the two phase model is the surface energy of the interface between phases. Preliminary results show sharp localized weak zones under intense shear, and distributed damage with extreme shear (suggestive of processes such as crack-branching instabilities). The theory, however, is still in a very basic form and has only been tested for simple one-dimensional geometries. Thus, the proposed project entails further development and testing to 1) apply it to more mantle/lithosphere-relevant geometries and conditions; and 2) include further pertinent physics. The model will be applied to cases of uniaxial compression; compressive folding and tensile necking; gravity-driven flows (as in slope and continent stability); source-sink driven flows (to examine the excitation of toroidal motion from purely poloidal flow); and convectively driven motion. The new physics to be studied and incorporated includes healing and annealing processes; inter-phase reactions (e.g., hydration); anisotropy (to account for pore/microcrack alignment); thermomechanical effects (e.g., fluid thermal expansion which affects pore pressure, thermoviscous behavior of matrix material, and temperature sensitivity of interface surface tension); and partitioning of deformational work between irreversible dissipative heating and semi-reversible storage as interface surface energy. This project will further our understanding of the fundamental processes of lithospheric and other shear localization mechanisms, as well as the origin of tectonic plates and plate boundaries.