岩石细观损伤破坏的观测研究

利用扫描电镜（ Ｓ Ｅ Ｍ ）,对香港白岗岩等岩样在单轴压缩状态下,进行细观结构（μｍ 尺度）观察,研究其微损伤的萌生、扩展、连接直至破坏的行为,分析了白岗岩等岩石的细观破坏机制及其与宏观力学行为的关系,得到了一些重要的感性认识和若干观察记录．为认识岩爆发生的机理及复杂应力状态下岩石损伤破坏的理论分析提供了实验依据     

准脆性材料断裂过程区中的圆饼微裂纹损伤计算

准脆性工程材料及结构在外力作用下,不仅引起内部缺陷变化和微裂纹的出现及发展,且使得其结构承载能力降低或性能劣化．在其材料失效过程中常存在裂缝与断裂损伤过程区．为研究材料细观缺陷或微裂纹与宏观破坏的规律,通过细观力学方法,对于代表性体积单元RVE中的圆饼型微裂纹的尺寸与密度变化,探讨其宏观断裂过程区力学参量与损伤之间的量化关系．借助宏观断裂过程区的黏聚裂纹模型,将损伤单元RVE嵌入到宏观裂缝端部的断裂过程区中,对其进行联接细观损伤到宏观破坏的力学多尺度研究．文中也通过实验数据,对其理论计算结果进行了算例的讨论与分析．     

Experimental Investigation of Fracture Process Zone in Rocks Damaged Under Cyclic Loadings

Compared with other materials, most rocks generally fail in a brittle fashion rather than exhibiting yielding or purely plastic deformation. However, the initiation and coalescence of micro-cracks in the nonlinear region, known as the ‘fracture process zone’ (FPZ), are the primary reason for fracture propagation in rocks. Different elasticity-related models proposed for determining the features of the FPZ have not achieved an adequate understanding of its various fracture patterns. Based on previous experiments and numerical models, micro-crack density has been shown to be a function of loading history and to vary depending on whether the loading is monotonic or cyclic. The aim of the study reported here was to examine the different patterns of the FPZ under various types of cyclic loading and to quantitatively define damage and fracture patterns through the grains or rock matrix. Considerable laboratory testing was conducted, and fractured samples were investigated by computerised tomography scanning, supported by thin-section analysis. In the study, two different types of cyclic loading were tested: stepped and continuous. A diametral compressive loading was applied at predetermined amplitude and frequency with the continuous cyclic loading. The applied cyclic diametral compressive load was returned to the original level after each step, and at the next step, the amplitude started from zero, with stepped cyclic loading (SCL). An average 30 % strength reduction was found due to the SCL and emergence of high micro-fracture density in the FPZ. We presume that hard rock breakage techniques will be improved, especially for rock-cutting technologies, such as drag bits and oscillating disc cutting, by understanding the effects of cyclic loading on rock strength.     

混凝土断裂过程区的虚拟裂纹粘聚力奇异性

混凝土断裂过程区视为具有粘聚阻力作用的虚拟裂纹，其非线性断裂和尺寸效应特性是与该虚拟裂纹粘聚力分布规律密切相关的。通过得到的粘聚应力分布函数解析结果，对该粘聚力分布特征的分析得知，在基于断裂过程区之外用线弹性场的力学模型上，该粘聚力随距离虚拟裂纹尖点的靠近，仍具有平方根奇异性。从而本文提出一个能够反映裂纹发展状态的粘聚应力奇异性强度参数，它是无粘聚力的线弹性裂纹应力强度因子和表征裂纹张开位移分布多项式参数的函数；因此，该参数可以作为混凝土非线性断裂的一个参量。文中就已有断裂试验测试结果进行了算例分析和相应的讨论。     

细观尺度下岩石热变形破坏的实验研究

利用带扫描电镜的高温疲劳试验机等目前最先进的实验手段,实时观测了在温度和载荷同时作用下岩石在单向压缩和和拉伸中微细观结构的变化、缺陷演化方式和变形破坏过程,针对岩石的热膨胀是不可逆的,即它会受加温历史的影响,加热时和冷却后岩石结构有差异的特点,对岩石在温度载荷作用下的细观结构特征和细观破坏机理进行了较为系统的实验研究。得到了在不同载荷和温度作用下岩石中微裂纹萌生、扩展、断裂破坏等各个阶段清晰的SEM图像和数据。结合实时观测得到的数据和高清晰度图片,分析研究了岩石热细观损伤特性,探讨了载荷和温度的变化对岩石细观结构的影响。     

岩石爆破损伤断裂的细观机理

基于现有岩石爆破机理和岩石细观损伤力学 ,认为岩石爆破损伤断裂过程包含有爆炸应力波的初期动态损伤演化阶段和后期爆生气体作用下的准静态损伤演化阶段 ,并分别建立了这两个阶段的损伤模型和断裂准则 ,阐述了岩石爆破损伤断裂的细观理论。     

焊接热影响区断裂性能试验研究

钢框架梁柱节点在最近几次地震中经历了大量断裂破坏现象。可以采用杆端非线性弹簧模型对这种破坏模式进行数值模拟。为了确定断裂分析模型的参数，本文进行了结构钢（Q235c,Q345c)焊接热影响区断裂性能试验研究，获得了两种材料在焊接热影响区的JR阻力曲线。通过比较不同的断裂准则，考虑了裂纹失稳扩展前的稳态裂纹累计，根据J积分撕裂模量法建立了裂纹失稳的失效评定图。采用两种材料分别制作了一组外形尺寸一致，初始裂纹尺寸不同的单边裂纹焊接板，测出相应的极限拉伸应力，并和理论曲线进行了对比。最后，对于本文研究结果的适用范围做了说明。     

基于内动力的对径压缩岩石拉张破裂演化规律研究

岩石是一种复杂的天然非均匀脆性材料,拉压性能差距较大,拉破坏往往控制着岩石工程整体的稳定性.论文将岩石内部某一点在一定尺度范围内所受内力的差异性定义为内动力,进行了对径压缩岩石拉张破裂裂纹扩展实验.采用高速摄像机捕捉破裂瞬时拉张裂纹扩展过程并用数字散斑软件分析第一主应变演化过程.采用连续-非连续方法模拟对径压缩岩石拉张裂纹扩展过程.从实验结果可以看出：拉张破裂裂纹扩展分为三个阶段：拉张破裂变形累计阶段(宏观无裂纹)、拉张破裂裂纹稳定扩展阶段、拉张破裂裂纹动态张裂阶段.将实验、数值计算结果与解析解进行对比分析,实验与数值计算结果扩展规律基本一致,但是与弹性力学解析解不同.解析解基于均匀性假设,而外载荷及岩石本身是非均匀的.外载荷及岩石本身的非均匀性是裂纹起裂点、扩展路径与解析解不相同的主要原因.综合分析给出拉张破裂裂纹扩展规律：当外载荷作用下内动力超过原子或分子连接力则裂纹扩展,扩展方向与内动力的方向垂直.岩石拉张破裂裂纹扩展演化规律的研究可为岩石工程拉张破坏的预防和控制提供理论依据.     

基于Burgers模型考虑损伤的岩石蠕变全过程研究

岩石蠕变是一个显著的非线性问题，而经典的Burgers 模型是一种线性蠕变模型，必然不能全面地描述岩石蠕变的全过程．当岩石处于高应力水平下的加速蠕变阶段，岩石内部损伤会不断产生和累积，蠕变呈现出明显的非线性特征．为了更好地描述考虑损伤的岩石蠕变全过程，本文假定加速蠕变阶段的损伤演化方程，将损伤引入到Burgers 模型中，提出了一种非线性蠕变损伤模型．然后以乔后盐矿试件蠕变实测数据为分析案例，验证模型在应用于实际工程时的准确性和适用性．最后根据Origin 软件数值拟合的结果，表明本文所提出的非线性蠕变损伤模型能很好地描述岩石蠕变全过程，模型参数取值也在合理范围之内，模型拟合曲线与实验所得数据具有较好的一致性．     

有限宽板中心裂纹断裂过程区的长度和位移公式

对岩石、混凝土和陶瓷等准脆性材料进行断裂分析,有必要研究裂纹前端的断裂过程区所起的作用以及各种因素对它的影响。本文提出分析有限宽中心裂纹板剪切断裂过程区的方法,此方法基于D－B模型的叠加原理,考虑了压剪断裂的摩擦阻力,并将有限板宽影响简化为载荷的修正,以非常简便的方法推导出计算断裂过程区长度和位移的公式,这些公式补充了现有文献只有“无限大”板的解的不足。利用这些公式,分析各种参数对断裂过程区长度和位移的影响变得非常方便。     

Use of Scanning Electron Microscope and the Non-local Isotropic Damage Model to Investigate Fracture Process Zone in Notched Concrete Beams

In this study, a Scanning Electron Microscope (SEM) is used to understand the micro level aspect of the Fracture Process Zone (FPZ) in a concrete beam. It is mainly based on the preparation and analyzing samples which are considered as being a very important part of SEM (poor preparation techniques can lead to erroneous diagnosis of the concrete study). Numerically, the fracture of concrete requires the consideration of progressive damage, which is usually modeled by a constitutive law. This latest relies on numerical methods to obtain adequate solutions. It is shown herein that by using the Object Oriented Finite Element Method (OOFEM), obtained results agreed more or less with those of others researchers. On the other side, experimental results compromise those obtained by the use of the non-local isotropic damage model. It is finally proven throughout this study that the FPZ is defined by two parameters: the length and the width.     

Application of Fractional Differential Equations for Modeling the Anomalous Diffusion of Contaminant from Fracture into Porous Rock Matrix with Bordering Alteration Zone

Solute diffusion from a fracture into a porous rock with an altered zone bordering the fracture is modeled by a system of two diffusion equations (one for the altered zone and another for the intact porous matrix) with different coefficients of effective diffusivity. Since experimental studies of diffusion into rock samples with altered zones indicate that mathematical models of diffusion based on Fick’s law do not adequately describe the concentration field in a sample, fractional order diffusion equations are chosen in this study for modeling the anomalous mass transport in the rocks. In the case of significantly higher porosity of the altered zone (e.g., this is typical for carbonates) the effective diffusivity here can be much higher than the effective diffusivity of non-altered rocks. By introducing a small parameter that is the ratio of effective diffusivities in the non-altered and altered regions and applying the technique of perturbations, approximate analytical solutions for concentrations in the altered zone bordering the fracture and in the intact surrounding rocks are obtained. Based on these solutions, different regimes of diffusion into the rocks with different physical properties are modeled and analyzed. It is shown that, using experimentally obtained data, the orders of the fractional derivatives in the differential equations can be readily calibrated for the every specific rock.     

The Effect of Wettability on Waterflood Oil Recovery in Carbonate Rock Samples: A Systematic Multi-scale Experimental Investigation

Transport in Porous Media - On the basis of a well-based model (Model I) developed in a previous work (Liu and Valkó in SPE J 2019. https://doi.org/10.2118/197049-PA ), in which a fractional...     

二种岩石断裂韧度试样测试的稳定性分析

本文分析了 ISRM 采纳的两种具有人字形切槽的试样在测试过程中裂纹扩展的稳定性问题,计算了它们在不同加载条件和试验机刚度时各自的稳定性因子;指出对岩石等一类脆性材料,加载方式和试验机刚度对测试的稳定性有很大的影响;说明了这两种试样在稳定性方面的差异,并指出它们在稳定性上明显地优于普通直裂纹试样.     

岩石压缩过程应力-应变-磁感强度效应的实验研究

为了弄清岩石挤压产生的磁感强度效应,将钕铁硼Nd-Fe-B磁芯分别植入圆柱形大理岩、石灰岩中,在其周围产生磁场.借助断裂使岩石导磁回路与磁强发生的改变,进行挤压过程中应力、应变和磁感强度三变量测试.研究结果表明:岩石裂隙变化能够引起磁感强度的改变,应力-应变-磁强存在一一对应的数值关系;达到最大应力前,大理岩、石灰岩周围磁感强度出现增大异常的破坏预兆;在岩石裂解阶段,应力-应变曲线与磁强-应变曲线的变化规律具有明确的反对称性.最后还建立了分段表达岩石应力-磁感强度拟合关系式.     

Microcracking and Fracture Process in Cement Mortar and Concrete: A Comparative Study Using Acoustic Emission Technique

This article reports the acoustic emission (AE) study of precursory micro-cracking activity and fracture behaviour of quasi-brittle materials such as concrete and cement mortar. In the present study, notched three-point bend specimens (TPB) were tested under crack mouth opening displacement (CMOD) control at a rate of 0.0004 mm/sec and the accompanying AE were recorded using a 8 channel AE monitoring system. The various AE statistical parameters including AE event rate $ \left( {\frac{dn }{dt }} \right) $ , AE energy release rate $ \left( {\frac{dE }{dt }} \right) $ , amplitude distribution for computing the AE based b-value, cumulative energy (ΣE) and ring down count (RDC) were used for the analysis. The results show that the micro-cracks initiated and grew at an early stage in mortar in the pre peak regime. While in the case of concrete, the micro-crack growth occurred during the peak load regime. However, both concrete and mortar showed three distinct stages of micro-cracking activity, namely initiation, stable growth and nucleation prior to the final failure. The AE statistical behavior of each individual stage is dependent on the number and size distribution of micro-cracks. The results obtained in the laboratory are useful to understand the various stages of micro-cracking activity during the fracture process in quasi-brittle materials such as concrete & mortar and extend them for field applications.     

Computational Modeling of Fluid Flow through a Fracture in Permeable Rock

Laminar, single-phase, finite-volume solutions to the Navier–Stokes equations of fluid flow through a fracture within permeable media have been obtained. The fracture geometry was acquired from computed tomography scans of a fracture in Berea sandstone, capturing the small-scale roughness of these natural fluid conduits. First, the roughness of the two-dimensional fracture profiles was analyzed and shown to be similar to Brownian fractal structures. The permeability and tortuosity of each fracture profile was determined from simulations of fluid flow through these geometries with impermeable fracture walls. A surrounding permeable medium, assumed to obey Darcy’s Law with permeabilities from 0.2 to 2,000 millidarcies, was then included in the analysis. A series of simulations for flows in fractured permeable rocks was performed, and the results were used to develop a relationship between the flow rate and pressure loss for fractures in porous rocks. The resulting friction-factor, which accounts for the fracture geometric properties, is similar to the cubic law; it has the potential to be of use in discrete fracture reservoir-scale simulations of fluid flow through highly fractured geologic formations with appreciable matrix permeability. The observed fluid flow from the surrounding permeable medium to the fracture was significant when the resistance within the fracture and the medium were of the same order. An increase in the volumetric flow rate within the fracture profile increased by more than 5% was observed for flows within high permeability-fractured porous media.     

A new Method for Measuring Mode-I Dynamic Fracture Toughness of Rock under Blasting Loads

Experimental Techniques - Blasting excavation method by using explosive is still widely applied in mining and quarrying, and therefore, rock dynamic fracture toughness under blasting loads is one...     

寒区冻融环境条件下岩石损伤扩展研究探讨

本文借助于岩石材料冻融循环CT扫描实验，对岩石材料在冻融循环条件下损伤扩展特性进行研究，着重探讨了冻融循环次数对岩石材料损伤扩展的影响，并对冻融循环条件下岩石损伤扩展本构关系进行了探讨。     

动态弹塑性断裂韧性测试方法的比较研究

利用示波冲击试验,对动态弹塑性断裂韧性测试的不同方法（单试样法和多试样法）进行了研究．结果表明,单试样法（柔度变化率）测定材料的动态断裂韧性是一种简单、准确、适合于工程应用的好方法