Strain-rate dependent brittle deformation of rocks during impact cratering: Linking mechanical data and microstructure

撞击过程中岩石的应变率相关脆性变形：力学数据和微观结构的联系

• 批准号: 398025349
• 负责人: Professor Dr. Thomas Kenkmann
• 金额: --
• 依托单位: Fraunhofer-Institut für Kurzzeitdynamik, Ernst-Mach-Institut (EMI)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/398025349?language=en
• 关键词: Strain; rate; dependent; brittle; deformation

During an impact event, the deformation of minerals and rocks is highly dynamic and reaches strain rates of >1000000 per second. The hemispherical attenuation of propagating shock waves causes strain rates and pressures to decrease with distance. A significant volume of the rock -is deformed at elevated strain rates larger than 10 to 100 per second at which the behavior of brittle materials likely becomes rate-sensitive. The aim of this project is to understand and quantify the role of strain rate sensitive brittle deformation of rocks for typical loads experienced during impact cratering in the range from quasi-static to highly dynamic conditions and to associate it with corresponding microstructures within the deformed rock.To accomplish this, we will systematically determine mechanical data (strength, elastic moduli, Poisson ratio) for limestone, claystone, granite, and basalt at strain rates ranging from quasi-static (~0.1 per second) to highly dynamic (1000000 per second) conditions under both compressive and tensile loading. Data are gathered with a triaxial loading frame (0.1-1 per second), a Split-Hopkinson-Pressure-Bar (1-1000 per second), and a Flyer-plate facility (>>1000 per second). We will derive the dynamic increase factors (DIF) of tensile and compressive strength for a given strain rate. The mechanical analyses will be combined with a comprehensive microstructural investigation of the experimentally deformed samples, in particular with respect to fracture topography, crack branching characteristics, fracture density, and the fracture/fragment size-frequency distribution. This will lead to an under-standing of failure mechanisms, energy dissipation and stress resistance of brittle materials at diverse strain rates conditions. We expect to identify a strain-rate dependent structural fingerprint of rocks that can be applied to naturally deformed rocks. This is key to narrow down the physical boundary conditions of deformation in natural settings. We will test and apply our results to samples from Barringer and Chicxulub impact craters.The inferred strain rate dependent dynamic increase factor (DIF) will be implemented into existing numerical models (e.g., the iSALE shock physics code). We will particularly evaluate the role of strain rate dependent deformation for the efficiency of impact cratering. The results of this study can potentially have a great relevance also for other geo-hazards involving rock deformation at medium to high strain rates, in particular seismogenic faulting.

在撞击事件期间，矿物和岩石的变形是高度动态的，应变率达到每秒 >1000000。传播冲击波的半球衰减导致应变率和压力随着距离的增加而减小。当应变速率大于每秒 10 至 100 次时，大量岩石会发生变形，此时脆性材料的行为可能变得对速率敏感。该项目的目的是了解和量化岩石应变率敏感脆性变形对于从准静态到高动态条件下的撞击坑中经历的典型载荷的作用，并将其与变形岩石内相应的微观结构联系起来。为了实现这一目标，我们将系统地确定石灰石、粘土岩、花岗岩和玄武岩在应变率范围从准静态（~0.1/第二）到压缩和拉伸负载下的高动态（每秒 1000000 次）条件。数据通过三轴加载框架（每秒 0.1-1 次）、分离式霍普金森压力杆（每秒 1-1000 次）和飞盘装置（每秒 >1000 次）收集。我们将推导出给定应变率下拉伸和压缩强度的动态增加因子 (DIF)。力学分析将与实验变形样品的全面微观结构研究相结合，特别是在断裂形貌、裂纹分支特征、断裂密度和断裂/碎片尺寸频率分布方面。这将有助于了解脆性材料在不同应变率条件下的失效机制、能量耗散和抗应力能力。我们期望识别出可应用于自然变形岩石的岩石应变率依赖性结构指纹。这是缩小自然环境中变形的物理边界条件的关键。我们将测试我们的结果并将其应用于来自巴林格和希克苏鲁伯陨石坑的样本。推断的应变率相关动态增加因子（DIF）将被应用到现有的数值模型（例如，iSALE 冲击物理代码）中。我们将特别评估应变率相关变形对撞击坑效率的作用。这项研究的结果也可能与涉及中高应变率下岩石变形的其他地质灾害，特别是地震断层活动具有很大的相关性。