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Inherent microcrack populations have a significant effect on the fracture behaviour of natural rocks. The present study addresses this topic in numerical simulations of uniaxial tension and three-point bending tests. For this end, a rock fracture model based on multiple intersecting embedded discontinuity finite elements is developed. The inherent (pre-existing) microcrack populations are represented by pre-embedded randomly oriented discontinuity populations. Crack shielding (through spurious locking) is prevented by allowing a new crack to be introduced, upon violation of the Rankine criterion, in an element with an initial crack unfavourably oriented to the loading direction. Rock heterogeneity is accounted for by random clusters of triangular finite elements representing different minerals of granitic numerical rock. Numerical simulations demonstrate the strength lowering effect of initial microcrack populations. This effect is substantially stronger under uniaxial tension, due to the uniform stress state, than in semicircular three-point bending having a non-uniform stress state with a clear local maximum of tensile stress.
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本文应用岩石快速加载设备,系统地研究加载速率在10-1～105公斤/厘米2/秒范围内,花岗岩的抗压、抗拉和抗剪破坏特征,得出强度随加载速率变化的规律,并提出了花岗岩的动力破坏准则. 相似文献
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A study of failure properties of granite specimens under compression, tension, shear conditions at different loading rates has been conducted. The tests, having loading rates from 10-1 to 108 kg/cm2/sec, were carried out on a fast loading equipment for rock mechanics teat. It has been found that the strength of the granite specimens increases with the increasing of loading rates. Based on this study and some results from field tests, a criterion of dynamic failure of granite is presented. 相似文献
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This paper deals with numerical modeling of the compressive behavior of granite rock under high strain rate dynamic loading and wide range of confining pressure. For this end, a constitutive model based on damage mechanics and viscoplasticity for rock is formulated and implemented in explicit dynamics FEM. The viscoplastic part is based on a simple power law type yield criterion that incorporates the rate-dependency with a linear viscosity term. Moreover, a Rankine type of tensile cut-off is employed. The damage part of the model is formulated with separate scalar damage variables in tension and compression. The model is calibrated for Kuru granite and validated with the experimental data from dynamic compression tests at the strain rate of 600 1/s up to 225 MPa of confining pressure. The numerical simulations demonstrate that, despite the underlying continuum modeling approach, the model captures the correct experimental failure modes, including the transition from single-to-multiple fragmentation, as well as the dynamic compressive strengths at different confining pressures. 相似文献
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基于图像检索技术的岩石单轴压缩破坏过程CT描述 总被引：1，自引：0，他引：1
基于X射线的CT扫描技术,因其具有多层位、对同一岩石试件可连续、无损扫描等优点,在岩石力学与工程研究中得到了广泛应用。对岩石单轴压缩破坏过程进行实时CT扫描,也是岩石力学研究的重要内容之一。针对三维显微CT试验系统实时监测煤岩单轴压缩破坏过程中,因位移误差会引起扫描层定位不准确,进而影响试验结果这一基本问题,提出了基于图像检索技术的CT扫描图像处理方法。通过对煤岩试样在单轴载荷作用下破坏过程的CT实时监测,并引入基于Manhattan距离的相似性计算方法,检索出岩石试件同一层位在不同应力状态下的相似扫描层。结果表明,采用图像检索的方法,可以有效地减小煤岩在加载破坏过程中位移误差的影响,更好地通过CT图像来描述煤岩在不同应力状态下的微裂纹分布状况和演化规律,从而在细观层次上揭示岩石在单轴压缩条件下破坏的基本规律。 相似文献
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Micromechanical Model for Simulating the Fracture Process of Rock 总被引：25，自引：3，他引：25
Summary A micromechanical model is proposed to study the deformation and failure process of rock based on knowledge of heterogeneity of rock at the mesoscopic level. In this numerical model, the heterogeneity of rock at the mesoscopic level is considered by assuming the material properties in rock conform to the Weibull distribution. Elastic damage mechanics is used to describe the constitutive law of meso-level elements, the finite element method is employed as the basic stress analysis tool and the maximum tensile strain criterion as well as the Mohr-Coulomb criterion is utilized as the damage threshold. A simple method, similar to a smeared crack model, is used for tracing the crack propagation process and interaction of multiple cracks. Based on this model, a numerical simulation program named Rock Failure Process Analysis Code (RFPA) is developed. The influence of parameters that include the Weibull distribution parameters, constitutive parameters of meso-level elements and number of elements in the numerical model, are discussed in detail. It is shown that the homogeneity index is the most important factor to simulate material failure with this model. This model is able to capture the complete mechanical responses of rock, which includes the crack patterns associated with different loading stages and loading conditions, localization of deformation, stress redistribution and failure process. The numerical simulation of rock specimens under a variety of static loading conditions is presented, and the results compare well with experimental results. 相似文献
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基于梯度塑性理论的岩样拉压剪破坏统一失稳判据 总被引：2，自引：2，他引：2
提出了单轴拉伸,直剪及单轴压缩剪切破坏失稳判据的统一形式。首先对de Borst R及Muhlhaus H B关于单轴拉伸试件梯度塑性理论解析解方面的开创性工作进行了回顾、评论,并指出了他们工作的缺憾。受de Borst R等工作的启发,对直接剪切试件进行了分析,得到了快速回跳条件。并发现:岩样的快速回跳条件就是系统(由剪切带及带外弹性岩石构成)的失稳判据。又对单轴压缩岩样剪切破坏进行了分析,得到了其失稳判据。通过对单轴拉伸失稳判据、直接剪切失稳判据及单轴压缩剪切破坏失稳判据的类比,得到了失稳判据的统一形式。统一失稳判据表明:岩石材料的局部化带宽度及压缩或剪切弹性模量越小,软化模量及等效试件高度越大,试件越容易发生失稳破坏。 相似文献
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In nature, there exist several forms of anisotropy in rock masses due to the presence of bedding planes, joints, and weak layers. It is well understood that the anisotropic properties of jointed rock masses significantly affect the stability of surface and underground excavations. However, these critical anisotropic characteristics are often ignored in existing uniaxial dynamic failure criteria. This study investigates the effect of a pre-existing persistent joint on the rate-dependent mechanical behaviours of a rock mass using a particle mechanics approach, namely, bonded particle model (BPM), to realistically replicate the mechanical response of the rock mass. Firstly, in order to capture the rate-dependent response of the jointed rock mass, the BPM model is validated using published experimental data. Then, a dynamic strength model is proposed based on the Jaeger criterion and simulation results. To further investigate the dynamic behaviours, the dynamic uniaxial compressive strength (UCS) for anisotropic rock masses with various joint orientations is investigated by subjecting the BPM models to uniaxial compression numerical tests with various strain rate. The proposed dynamic strength model is validated based on numerical simulation results. Finally, the fragmentation characteristics of the jointed rock masses are analysed, which demonstrate that the failure mode affects the dynamic UCS. This is further confirmed by the analysis of the orientations of microscopic cracks generated by the compression loading. 相似文献
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单轴压缩下绿砂岩长期强度的尺寸效应研究 总被引：1，自引：0，他引：1
岩石的蠕变特性是影响岩体工程稳定性的重要因素,而岩石的长期强度是确定岩体工程长期稳定的一个重要指标。由于岩石材料的非均质性,其长期强度具有明显的尺寸效应。为了研究岩石长期强度的尺寸效应,首先,在幂函数模型基础上,基于损伤力学理论,建立了能够描述岩石蠕变全过程的非线性蠕变损伤模型;然后,把运用该模型计算得到的单轴压缩蠕变数值模拟结果与室内单轴压缩蠕变试验结果进行对比,验证了模型的正确性;最后,采用所提出的模型对7个不同尺寸的岩样进行了单轴压缩蠕变数值模拟,并对岩石长期强度尺寸效应进行了分析。数值模拟结果表明：随着试样尺寸的逐渐增大,岩石长期强度值逐渐减小,当试样尺寸增大到一定程度时,岩石长期强度稳定在一个特定值附近。 相似文献
12.
基于细观损伤有限元方法,模拟分析了刀具在单一动载、动静联合荷载、静态围压条件下动静联合荷载3种情况下岩体破碎的全过程。模型采用黏弹性人工边界剔除了边界应力波反射对模拟结果准确性的影响。数值模拟结果表明：在弹性情况下,静压的存在对岩体内部最小主应力值影响不大,却显著提高了材料内部最大主应力水平,增大了剪应力的大小,导致剪切破坏可能性增加;当有围压存在时,岩体内部受拉区域减少,岩体强度有所提高。单一动载和动静联合荷载破岩时,岩体内部除刀头附近呈现少量压破坏外,破坏均以拉破坏为主;而围压条件下,岩体破碎面积相对减小,裂纹在围压的作用下向两侧自由面延伸,岩体内部破坏形式则趋于多样化,压破坏比重明显增大,整体表现为拉压复合作用。模拟结果还表明,刀头侵入量主要受动载力大小影响,在相同幅值增量下,动载力增加导致的刀头侵入量远大于静压增加所导致的侵入量。相对单一动载和静压作用下的岩石破碎机制来说,动静组合加载破岩的研究还需更为深入的探讨。研究结果可望对岩体破坏机制以及地下工程作业等实际应用提供一定的参考。 相似文献
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层状盐岩力学和变形特性数值试验研究 总被引：7，自引：0，他引：7
对含泥岩夹层层状盐岩力学和变形特性进行有限元分析。首先,用数值试验方法预测含泥岩夹层层状盐岩体宏观等效弹性力学参数,然后,建立层状盐岩复合体细观有限元模型,研究其在单轴和三轴压缩荷载下盐岩、泥岩以及界面细观应力应变场分布特征、应力集中问题,并将上述研究与已有的理论和试验成果进行对比。结果表明,运用细观有限元方法预测层状盐岩宏观弹性力学参数是一种直观有效的方法;泥岩和盐岩力学特性上的不匹配导致在层状盐岩的泥岩夹层中以及界面边缘处存在较为明显的应力集中和差异变形。单轴压缩时,泥岩体由于侧向变形能力差会受到横向拉伸应力作用而盐岩层则相应的受到横向压应力作用,三轴压缩时因围压和偏应力大小不同层状盐岩细观应力应变场分布特征则更为复杂;此方法能更为直观的分析层状盐岩的变形和破损特征,这一分析结果对进一步进行层状盐岩体内油（气）储库硐室稳定性分析提供了理论基础。 相似文献
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介绍了一种可对同一岩石试样分别进行单轴压缩和单轴拉伸实验的试验装置,该装置改变了因岩样不同而导致的压拉试验结果无法进行直接对比分析的现状,为岩石从受压转向受拉或从受拉转向受压的过渡特性的试验研究提供了可能。以云南大姚铜矿紫色砂岩为例,研究了其在压拉试验条件下的变形特性。结果表明：该种岩石从压缩到拉伸阶段弹模变化不大,但压缩泊松比与拉伸泊松比的变化较为复杂。试验同时证明该类岩石的压缩与拉伸并不是截然不同的两种过程,单轴压缩试验的卸载曲线与直接拉伸试验的加载曲线具有很好的连续性。 相似文献
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不同加载速率条件下岩石的力学特性,对于其动载下破裂内在机制的研究具有积极的意义。基于颗粒流理论,通过黏结颗粒模型（bonded particle model,简称BPM）虚拟实现不同加载速率0.001～0.500 m/s下花岗岩单轴压缩和巴西劈裂试验,定量分析加载速率对应力-应变、破裂形态、应变能率及声发射的影响。结果表明：单轴抗压强度和抗拉强度及其对应峰值应变随加载速率增加而非线性增长;单轴压缩作用下,随加载速率增加,试样由单一斜截面破坏向多斜截面破坏转变,且主控裂隙带宽度急剧增大,由裂纹数量及水平向高应变率区域变化规律可明显看出,试样破坏程度随着加载速率增加而逐渐加剧;巴西劈裂作用下试样从一条主控裂隙向多条主控裂隙转变,且裂纹向圆盘试样两侧边缘部分延伸,破坏程度加剧;单轴压缩和巴西劈裂作用下,声发射事件及应变能率均随加载速率增加而呈现出非线性增长趋势。 相似文献
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含孔岩石加载过程的热辐射温度场变化特征 总被引：1，自引：0，他引：1
选择含圆孔岩石作为试样,利用单轴加载试验系统和红外热像仪,并结合数值模拟分析手段,对模型受力及破裂过程的热辐射时空演化特征进行了试验研究。结果表明：含圆孔岩石在加载过程中压、拉应力呈对称分布,导致热像的升温和降温区对称分布,即压应力区升温,拉应力区降温,应力场与红外辐射温度场之间呈很好的对应关系。试件加载后期发生破裂,破裂的性质与红外辐射温度变化有密切关系,剪性破裂辐射温度升高,而张性破裂辐射温度无明显变化。试件最终呈剪性破裂,而该区域的带状升温是岩石破裂失稳的重要红外前兆。试验结果再次揭示,利用热成像技术可以监测岩石的应力与灾变现象。 相似文献
17.
Timo Saksala 《国际地质力学数值与分析法杂志》2013,37(3):309-324
This paper considers numerical modelling of rock fracture induced by dynamic bit–rock interaction in percussive drilling. The work presented here extends the author's earlier research on the topic from the axisymmetric case to 3D case. The numerical method for modelling rock fracture includes a constitutive model for rock and a contact mechanics‐based technique to simulate the bit–rock interaction. The constitutive model is based on a combination of the recent viscoplastic consistency model, the isotropic damage concept and a parabolic compression cap. This model is improved here from its earlier state by calibrating the softening laws using fracture energies GIc and GIIc in tension and compression, respectively. Moreover, the viscosity modulus in tension is calibrated based on the dynamic Brazilian disc test. With these enhancements, the developed method is applied to 3D case of the bit–rock interaction problem assuming one symmetry plane. Single impact with single and multiple‐button bits is simulated. In the latter case, an initial borehole is modelled in order to simulate the usual in‐situ drilling conditions. The different failure types observed in the experiments as well as the interaction between the buttons resulting in chipping are realistically captured in the simulations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
18.
深入研究盐岩受力变形、破坏机制及力学模型,对于保证油气地下储库的安全和稳定具有十分重要的意义。以盐岩在多组围压下的三轴试验为基础,由热力学定律出发,将损伤引入到改进的摩尔-库仑(Mohr-Coulomb)准则中,提出了与围压相关的损伤准则和塑性硬化函数,建立了一种能够描述盐岩力学特性的弹塑性损伤模型,该模型能够反映盐岩的塑性与损伤耦合、应变硬化-软化和围压影响。将研究成果与ABAQUS软件相结合,通过二次开发,编制了相应的计算程序。通过模拟盐岩室内三轴压缩试验表明,数值模拟曲线与试验曲线吻合较好,所建立的力学模型可以较好地描述盐岩在不同围压状态下的力学损伤发展、应变硬化-软化以及脆-塑性转换的力学特征。 相似文献
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与静态岩石破碎过程相比,冲击作用下岩石的应力改变具有时间效应,应力波传播过程中表现出压、拉变化。基于损伤演化原理和有限元数值模拟方法,针对冲击荷载作用下的压头破岩机制进行了模拟分析。为排除边界上反射波的影响,黏弹性边界被纳入计算中。首先论证了黏弹性边界在均质和非均质介质中的计算精度,然后分析了冲击作用下不同均质度的岩石以及砂砾岩的响应规律,结果显示：在弹性情况下,压头与岩石接触边缘以及自由面附近是拉应力分布区,接触边缘拉应力最大。剪应力最高值并不位于接触面附近,而是离接触面有一定距离。较均质岩石主要呈现拉伸破坏模式,先出现赫兹裂缝,然后是径向裂缝和侧向裂缝,拉应力的产生成为诱发裂缝萌生和扩展的主因。当岩石均质度较低时,岩石的破坏形式呈现多元化,剪切破坏比重加大,表现为复杂的拉剪破坏模式。对于砾石粒径较大、含量较多的砂砾岩,砾石和基质的非均匀性不可忽略,冲击下破坏模式以绕粒环行和穿粒破坏为主。总体说来,对于岩石类准脆性材料,应力波传播过程中产生的拉应力是失稳的诱发和扩展的关键。 相似文献
20.
IV级软弱围岩相似材料的试验研究 总被引：1，自引：0，他引：1
以IV级围岩为参照对象,研制可用于隧道围岩稳定性物理模型试验的软弱围岩相似材料。采用的5种原材料（重晶石粉、石膏、细砂、洗衣液和水）,通过直剪试验、无侧限抗压强度试验及三轴压缩试验测得所配相似材料的强度特征和物理力学参数,包括黏聚力c、内摩擦角?、单轴抗压强度Rc、弹性模量E和泊松比?。首先,通过试验分析每种原材料的不同比例对所配相似材料强度特征及物理力学参数的影响,选择适合于模拟IV级围岩相似材料的原材料配比;其次,针对优选的材料配比所配制的相似材料,开展大量的三轴压缩试验,研究在不同围压下该相似材料的强度及其破坏特征。结果表明,含水率减少或石膏含量增加导致Rc、E和c明显增大,而?降低不明显;增加砂含量可增大E 和?,但Rc值减少;石膏含量对相似材料的脆性和延性影响最明显,而含水率对相似材料的强度影响最为突出。试验结果还表明,相似材料在低围压时呈现脆性,在高围压时呈延性;就破坏准则而言,试验所得结果小于Mohr-Coulomb准则,略大于Hoek-Brown准则,但更符合Hoek-Brown准则。研制软岩相似材料的试验数据可为下一步拟开展的隧道围岩稳定性模型试验和数值模拟提供重要的参考和依据。 相似文献