Towards a Robust Constitutive Law for Calcite Rocks

建立方解石岩石的稳健本构定律

• 批准号: 0125669
• 负责人: Brian Evans
• 金额: $ 20万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-07-01 至 2005-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0125669&HistoricalAwards=false
• 关键词: Towards; Robust; Constitutive; Law; Calcite

EAR-0125669J. Brian EvansIn this project the investigators focus on crystal plastic mechanisms involving dislocation creep and diffusion flow. Our understanding of the creep strength of calcite rocks, which are usually complex polyphase assemblages, is largely based on data from a few relatively pure limestones and marbles, from single-phase synthetic marbles, or even from single crystals, and, with a few exceptions, only over very small strain increments. Based on experience with deformation of other rocks and ceramics, one might expect rock strength to be highly dependent on dispersed second phases, solute impurities, preexisting porosity, grain size, and grain-size distribution, as well as temperature, pressure, and pore-fluid chemistry. The standard paradigm, steady-state power-law creep, as applied to calcite rocks, typically relates only temperature, stress, strain rate, and for diffusion creep or boundary sliding processes, grain size. Current data from tests on synthetic marbles with and without an added second phase, and on natural rocks suggest that the standard power-law equation fails to predict accurately the stress sensitivity of strain rate observed in conventional triaxial mechanical experiments in the dislocation flow regime. One particular problem may arise if the microstructure in the rock evolves with strain or time. Such structural variables might include average grain size, grain-size distribution, grain orientation, and dislocation structures that scale with grain-size. Previously it has been assumed that grain size had no influence on strength for high-temperature dislocation creep. In materials composed of more than one phase, the average grain size, shape, and distribution of second-phase particles, and the total amount of the second phase may also affect strength. In this work, carefully controlled samples of marble will be synthesized and tested at high temperature and pressure. The investigators intend to systematically investigate the effect on strength of matrix grain size, second-phase content, and solid solutions of magnesium, iron, manganese, and strontium. An important aspect of the work is the correlation of grain and dislocation microstructure with mechanical behavior. High strain experiments will be conducted using loading in simple shear, conventional triaxial extension, and confined torsion. The expanded data set will be used to construct a more robust constitutive law, applicable to a larger set of thermodynamic conditions.

EAR-0125669J。 Brian Evansin该项目研究人员专注于涉及脱位蠕变和扩散流的晶体塑料机制。我们对通常是复杂的多相组合的方解石岩石的蠕变强度的理解主要基于来自一些相对纯净的石灰石和大理石，单相合成大理石甚至单晶体的数据，而少数例外，仅在很小的应变增量中。基于其他岩石和陶瓷变形的经验，人们可能会期望岩石强度高度依赖于分散的第二阶段，溶质杂质，之前的孔隙率，晶粒尺寸和晶粒尺寸的分布以及温度，压力和毛孔 - 流体荧光化的化学。应用于方解石岩石的标准范式，稳态幂律蠕变通常仅关联温度，应力，应变速率，而扩散蠕变或边界滑动过程，晶粒尺寸。来自有或没有增加第二阶段的合成大理石测试的当前数据，并且对自然岩石的质量岩石方程未能准确预测在错位流动状态下常规三轴机械实验中观察到的应变率的应力敏感性。如果岩石中的微观结构随着应变或时间的变化，可能会出现一个特殊的问题。这样的结构变量可能包括平均晶粒尺寸，晶粒大小分布，晶粒取向以及用晶粒大小扩展的位错结构。以前已经假定晶粒尺寸对高温脱位蠕变的强度没有影响。在由多个相组成的材料中，二相颗粒的平均晶粒尺寸，形状和分布以及第二相的总量也可能影响强度。在这项工作中，将在高温和压力下合成精心控制的大理石样品。研究人员打算系统地研究对镁，铁，锰和锶的基质晶粒尺寸，第二阶段含量以及实心溶液的强度的影响。工作的一个重要方面是晶粒和错位微结构与机械行为的相关性。高应变实验将使用简单的剪切，常规三轴延伸和受限的扭转进行高应变实验。扩展的数据集将用于构建更健壮的本构定律，适用于较大的热力学条件。