Energy Scaling in Rock Cutting

岩石切割中的能量缩放

• 批准号: 1742823
• 负责人: Emmanuel Detournay
• 金额: $ 44.94万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1742823&HistoricalAwards=false
• 关键词: Energy; Scaling; Rock; Cutting

The drive to mechanize the excavation of hard rock in civil or mining engineering projects has brought to the forefront the need to quantify the mechanics of tool-rock interaction. A related issue is the interpretation of the scratch test. This experimental technique has garnered interest lately, because it appears to offer a simple and economical means to measure strength and fracture properties of quasi-brittle materials such as rock, ceramics, and concrete. However, there remain questions on which parameters can be determined in these experiments and how to interpret them from the test data. Therefore, whether predicting the cutting force (mean and fluctuations) to design mechanical excavation equipment and establish the excavation schedule and costs, or interpreting the measured force in controlled scratch experiments, the same fundamental question arises: what is the dependence of the cutting force (i) on the depth of cut and the cutter geometry, and (ii) on the strength and fracture properties of the rock. By recognizing that different regimes of failure take place in rock cutting and therefore that different parameters affect the cutting force depending on the prevailing regime, the research has the potential to develop universal scaling laws for rock cutting. Furthermore, this research has also the potential of informing our understanding of the failure of engineered materials with a grain structure, such as concrete or ceramics. Failure of structures made of these quasi-brittle materials is characterized by scale effects and possible transition between shear- and tensile-dominant failure mechanisms. However, engineering design practice is still rooted in the strength-based approach, despite its restricted range of applicability when dealing with quasi-brittle materials. If successful, the research will result in a simple experimental means for characterization of fracture properties, thus promoting fracture mechanics -- an essential concept for such materials -- to engineering practice. The findings of this research will be incorporated into classroom teaching at both undergraduate and graduate levels, in an effort to equip the next generation of engineers with fundamental knowledge of rock mechanics, fracture mechanics and experimental mechanics. The project addresses the fundamental question of energy scaling in rock cutting, i.e., the dependence of the specific energy - the energy spent per volume of rock removed, on the depth of cut and on the rock properties. Understanding how the specific energy scales (or alternatively how the cutting force scales) is critical for designing mechanical excavators for hard rocks, as well as for interpreting the scratch test - a technique to assess the properties of quasi-brittle materials. The research is grounded on empirical evidence that suggests the existence of three asymptotic regimes in rock cutting. With increasing depth of cut (larger than the rock mean grain size), different modes of failure can indeed be observed: namely, (i) a ductile regime at shallow depth of cut, with the rock intensely sheared in front of the cutter; (ii) a fragmentation regime with the rock breaking into fragments that are distributed according to a power law over a significant range of sizes, and (iii) brittle regime with macroscopic cracks initiating from the tool tip and propagating unstably ahead of the cutter. The research builds on three respective empirical scaling laws for these regimes, which are informed by the available experimental data and insights from numerical simulation and scaling analysis, for the case where the cutter is at least as wide as the rock slab thickness. The main objective of this research is to provide theoretical underpinnings to these empirical scaling laws using theoretical and computational models, as well as to obtain experimental results for the brittle regime, for which the empirical evidence is weakest.

在土木或采矿工程项目中，硬岩开挖机械化的驱动力已经将量化工具-岩石相互作用的力学的需要带到了最前沿。 一个相关的问题是划痕试验的解释。 这种实验技术最近引起了人们的兴趣，因为它似乎提供了一种简单而经济的方法来测量准脆性材料（如岩石，陶瓷和混凝土）的强度和断裂性能。 然而，在这些实验中可以确定哪些参数以及如何从测试数据中解释这些参数仍然存在问题。 因此，无论是预测切削力（平均值和波动）来设计机械挖掘设备并建立挖掘进度和成本，还是在受控划痕实验中解释测量的力，都会出现相同的基本问题：切削力（i）对切削深度和刀具几何形状的依赖性，以及（ii）对岩石的强度和断裂特性的依赖性。 通过认识到，不同的制度发生在岩石切削故障，因此，不同的参数影响的切削力取决于现行制度，研究有可能开发通用的岩石切削比例定律。 此外，这项研究也有可能为我们了解具有颗粒结构的工程材料（如混凝土或陶瓷）的失效提供信息。 由这些准脆性材料制成的结构的失效的特征在于尺度效应和剪切和拉伸主导失效机制之间的可能过渡。 然而，工程设计实践仍然植根于强度为基础的方法，尽管它的适用范围有限，当处理准脆性材料。 如果成功，该研究将为表征断裂性能提供一种简单的实验手段，从而促进断裂力学（此类材料的基本概念）走向工程实践。 这项研究的结果将被纳入本科和研究生阶段的课堂教学中，以使下一代工程师具备岩石力学，断裂力学和实验力学的基础知识。该项目解决了岩石切割中能量缩放的基本问题，即，比能的依赖性--每移除一体积岩石所消耗的能量，取决于切割深度和岩石性质。 了解比能如何缩放（或者切削力如何缩放）对于设计用于硬岩石的机械挖掘机以及解释划痕测试（一种评估准脆性材料特性的技术）至关重要。 这项研究是基于经验证据，表明存在三个渐近制度，在岩石切削。 随着切削深度的增加（大于岩石平均粒度），确实可以观察到不同的破坏模式：即，（i）在浅切削深度处的韧性状态，岩石在刀具前面被强烈剪切;（ii）破碎状态，岩石破碎成碎片，碎片在相当大的尺寸范围内根据幂律分布，和（iii）脆性区域，宏观裂纹从工具尖端开始并在刀具前方不稳定地传播。 该研究建立在这些状态的三个相应的经验标度定律的基础上，这些定律是由可用的实验数据以及数值模拟和标度分析的见解提供的，适用于刀具至少与岩板厚度一样宽的情况。 本研究的主要目的是提供理论基础，这些经验的标度律，使用理论和计算模型，以及获得实验结果的脆性政权，经验证据是最弱的。

项目成果

Application of wavelet to strength log from scratch test

• DOI: 10.1016/j.jrmge.2022.09.002
• 发表时间: 2022-09
• 期刊: Journal of Rock Mechanics and Geotechnical Engineering
• 影响因子: 7.3
• 作者: He Zhang;J. Le;E. Detournay

Experimental Study of Forces Induced in Mechanical Excavation of Rock

岩石机械开挖诱发力试验研究

• DOI: 10.1061/9780784482841.012
• 发表时间: 2020
• 期刊: and Site Characterization
• 作者: John Pultorak, Dmitry Drozdov

An experimental investigation of brittle failure mechanisms in scratch tests of rock

• DOI: 10.1016/j.engfracmech.2022.108827
• 发表时间: 2022-10
• 期刊: Engineering Fracture Mechanics
• 影响因子: 5.4
• 作者: He Zhang;J. Le;E. Detournay