共查询到20条相似文献，搜索用时 78 毫秒
1.
An Example of Realistic Modelling of Rock Dynamics Problems: FEM/DEM Simulation of Dynamic Brazilian Test on Barre Granite 总被引：2，自引：1，他引：1
The scope of this study is to numerically simulate the behaviour of Brazilian disc specimens as observed in laboratory during dynamic, high-strain rate, indirect tensile tests using an innovative combined finite-discrete element method (FEM/DEM) research code. Laboratory experiments using a split Hopkinson pressure bar (SHPB) apparatus were conducted by the authors and the measured indirect tensile strength values were used to verify the FEM/DEM models. In the models the applied boundary conditions, related to the loading rate of the specimen, were matched with the experimental observations. The results of the numerical simulations, including tensile strength and failure time, are in agreement with the laboratory findings. The main failure mechanisms, i.e. tensile splitting along loading axis and shear failure close to loading platens are captured by the numerical model. A linear relationship between tensile strength and loading rate is found for the range of dynamic strain rates tested and simulated. The simulation results are in good agreement with laboratory observations and demonstrate the potential for using FEM/DEM to realistically model dynamic response of rocks. 相似文献
2.
The validity and rationality of the Brazilian disc test have attracted much attention since it was proposed. To verify the validity of four Brazilian disc tests, red sandstone and yellow rust granite were employed. In these experiments, uniaxial tensile tests and four Brazilian disc tests were performed. Meanwhile, the typical location of the Brazilian discs was arranged with gages to detect the crack initiation location. By analyzing the rationality of the four Brazilian disc tests from two aspects, the crack initiation location and the difference between indirect tensile strength and direct tensile strength, it was found that the Brazilian disc tests without cushion and the Brazilian disc tests with two small-diameter steer rods are suitable for determining the indirect tensile strength of rock materials. However, the Brazilian disc tests with arc loading jaws should be carefully adopted to measure the indirect tensile strength due to their overestimation of the indirect tensile strength. Additionally, flattened Brazilian disc tests were found to be not suitable for measuring the indirect tensile strength of rock materials. 相似文献
3.
4.
为分析巴西圆盘劈裂法在层状岩体抗拉强度试验中的适用性,在以往层状岩体巴西圆盘劈裂试验成果分析基础上,选取层理砂岩为试验对象,设计并进行了考虑不同层理角度的砂岩巴西圆盘劈裂试验。分析结果表明,（1）层状岩体抗拉强度的各向异性特点非常明显,层理角度对各种层状岩体的劈裂抗拉强度的影响规律是基本类似的,只是影响程度不一样;（2）不同层理角度圆盘试样的破裂面形状差别较大,其破坏模式可以归纳为直线型、折线型和弧形型;（3）当层理角度0°＜β＜90°时,破裂面的发展规律不能严格满足巴西圆盘劈裂试验力学理论模型的假定,采用式（1）计算得到的劈裂抗拉强度只能是一个近似的值;（4）当圆盘试样加载线两侧的岩石材料、层理结构对称分布时,加载时圆盘内的应力分布可以较好地满足其理论计算模型,其试验结果比较准确。研究成果可为层状岩体抗拉强度的准确测定提供较好的参考。 相似文献
5.
用5种圆盘试件的劈裂试验确定岩石断裂韧度 总被引：5，自引：1，他引：4
用5种不同形状的圆盘试件测定了大理岩张开型断裂韧度。5种圆盘试件分别为平台巴西圆盘、带有中心圆孔的平台巴西圆盘、人字型切槽巴西圆盘、直切槽巴西圆盘和圆孔切槽平台巴西圆盘。加载模式是对径压缩劈裂。介绍了试件的制作方法,提出了用每种圆盘确定断裂韧度的公式。结果表明,含有切槽圆盘的断裂韧度值在0.78～0.91 MPa•m1/2之间,不含切槽圆盘测得的值在1.01～1.04 MPa•m1/2之间。有3种含有切槽圆盘测得的断裂韧度值比较稳定,其中孔槽式平台巴西圆盘能够制作理想的宽度较小的切槽。 相似文献
6.
The development of the Brazilian disc test for determining indirect tensile strength and its applications in rock mechanics are reviewed herein. Based on the history of research on the Brazilian test by analytical, experimental, and numerical approaches, three research stages can be identified. Most of the early studies focused on the tensile stress distribution in Brazilian disc specimens, while ignoring the tensile strain distribution. The observation of different crack initiation positions in the Brazilian disc has drawn a lot of research interest from the rock mechanics community. A simple extension strain criterion was put forward by Stacey (Int J Rock Mech Min Sci Geomech Abstr 18(6):469–474, 1981) to account for extension crack initiation and propagation in rocks, although this is not widely used. In the present study, a linear elastic numerical model is constructed to study crack initiation in a 50-mm-diameter Brazilian disc using FLAC3D. The maximum tensile stress and the maximum tensile strain are both found to occur about 5 mm away from the two loading points along the compressed diameter of the disc, instead of at the center of the disc surface. Therefore, the crack initiation point of the Brazilian test for rocks may be located near the loading point when the tensile strain meets the maximum extension strain criterion, but at the surface center when the tensile stress meets the maximum tensile strength criterion. 相似文献
7.
Three-Dimensional Numerical Investigations of the Failure Mechanism of a Rock Disc with a Central or Eccentric Hole 总被引：3，自引：3，他引：0
The diametrical compression of a circular disc (Brazilian test) or cylinder with a small eccentric hole is a simple but important test to determine the tensile strength of rocks. This paper studies the failure mechanism of circular disc with an eccentric hole by a 3D numerical model (RFPA3D). A feature of the code RFPA3D is that it can numerically simulate the evolution of cracks in three-dimensional space, as well as the heterogeneity of the rock mass. First, numerically simulated Brazilian tests are compared with experimental results. Special attention is given to the effect of the thickness to radius ratio on the failure modes and the peak stress of specimens. The effects of the compressive strength to tensile strength ratio (C/T), the loading arc angle (2α), and the homogeneity index (m) are also studied in the numerical simulations. Secondly, the failure process of a rock disc with a central hole is studied. The effects of the ratio of the internal hole radius (r) to the radius of the rock disc (R) on the failure mode and the peak stress are investigated. Thirdly, the influence of the vertical and horizontal eccentricity of an internal hole on the initiation and propagation of cracks inside a specimen are simulated. The effect of the radius of the eccentric hole and the homogeneity index (m) are also investigated. 相似文献
8.
Summary This paper presents a systematic procedure for determining fracture toughness of an anisotropic marble using the diametral
compression test (Brazilian test) with a central crack on the discs. Additionally, a novel formulation to increase the accuracy
in Stress Intensity Factor (SIF) calculations using Boundary Element Method (BEM) is applied to determine the stress intensity
factors and the fracture toughness of anisotropic rocks under mixed-mode loading. The numerical results show that the SIFs
for both isotropic and anisotropic problems are in good agreement with those reported by previous authors. The marble with
clear white-black foliation from Hualien (in eastern Taiwan), was selected for the Brazilian tests. Diametral loading was
conducted on the Cracked Straight Through Brazilian Disc (CSTBD) specimens to evaluate their fracture toughness. In addition,
a new fracture criterion was developed to predict pure mode I, pure mode II or mixed mode (I–II) fracture toughness of the
anisotropic marble. The new fracture criterion is based on the examination of mode I, mode II and mixed mode (I–II) fracture
toughness for different crack angles and anisotropic orientation.
Authors’ address: Associate Professor Chao-Shi Chen, Department of Resources Engineering, National Cheng Kung University,
No. 1 Dasyue Rd., East District, Tainan 701, Taiwan 相似文献
9.
This research presents the results of laboratory experiments during the investigation of tensile strength–strain characteristics of Brisbane tuff disc specimens under static and diametral cyclic loading. Three different cyclic loading methods were used; namely, sinusoidal cyclic loading, type I and II increasing cyclic loading with various amplitude values. The first method applied the stress amplitude?cycle number (s–n) curve approach to the measurement of the indirect tensile strength (ITS) and fracture toughness (K IC) values of rocks for the first time in the literature. The type I and II methods investigated the effect of increasing cyclic loading on the ITS and K IC of rocks. For Brisbane tuff, the reduction in ITS was found to be 30 % under sinusoidal loading, whereas type I and II increasing cyclic loading caused a maximum reduction in ITS of 36 %. The maximum reduction of the static K IC of 46 % was obtained for the highest amplitude type I cyclic loading tested. For sinusoidal cyclic loading, a maximum reduction of the static K IC of 30 % was obtained. A continuous irreversible accumulation of damage was observed in dynamic cyclic tests conducted at different amplitudes and mean stress levels. Scanning electron microscope images showed that fatigue damage in Brisbane tuff is strongly influenced by the failure of the matrix because of both inter-granular fracturing and trans-granular fracturing. The main characteristic was grain breakage under cyclic loading, which probably starts at points of contact between grains and is accompanied by the production of very small fragments, probably due to frictional sliding within the weak matrix. 相似文献
10.
基于颗粒流程序（particle flow code,PFC）,对不同接触角（2a = 6º～30º）条件下25～1 000 ℃砂岩进行巴西劈裂模拟试验,研究其应力分布和破裂模式,并将巴西劈裂与直接拉伸进行对比。研究表明：（1）巴西劈裂中,面接触加载可以降低端部效应,加载过程中首先在圆盘中部产生拉裂纹,随着荷载的升高,拉裂纹汇集、扩展、贯通。（2）平板点接触巴西劈裂测得的抗拉强度小于直接拉伸强度,其抗拉强度计算公式的修正系数k随温度T的升高线性减小,满足k = −3.303×10−4T+1.468。随着接触角的增大,不同温度处理后巴西圆盘的抗拉强度均呈现出增大的趋势。（3）在2a≥18º时,巴西圆盘可以保证中心起裂;2a = 18º～24º时,圆盘在不同温度下破裂模式稳定;在接触角过大（2a = 30º）时,圆盘在较低温度（≤600 ℃）下会形成倾斜裂纹。（4）结合修正系数和破裂模式分析,推荐接触角为18º～24º时,修正系数在0.802 6～ 0.856 0之间,可以保证所有温度试样中心起裂且破裂模式稳定。 相似文献
11.
M. R. M. Aliha 《Arabian Journal of Geosciences》2014,7(11):4757-4766
Indirect test methods are usually the preferred approach for determining the tensile strength of brittle and quasi-brittle materials such as ceramics, rocks, and concrete. In this paper, the tensile strength of a rock material (Iranian Harsin marble) was obtained indirectly by means of two disc type samples. The test samples were the well-known Brazilian disc and semi-disc specimen under three-point bend loading. Since the existing formula for determining the indirect tensile strength is based on 2-D stress assumption which ignores the effects of specimen thickness, a general 3-D tensile strength formulation was derived for each sample by employing finite element analysis. A series of tensile strength tests were conducted on Harsin white marble using disc and semi-disc specimens with different thicknesses in parallel to finite element analysis. The test results using 3-D formulation showed that the tensile strength of the tested marble depends on the thickness/diameter ratio of the specimen and generally decreases from 11.5 to 7 MPa on increasing the thickness of test samples. The average values of tensile strength were about 8.8 MPa for the Brazilian disc specimen and 9.8 MPa for the semi-disc specimen. The good agreement existing between the results of the two specimens suggests that the semi-disc specimen can also be used for determining the rock tensile strength in addition to using the conventional Brazilian test. 相似文献
12.
Investigating the Effect of Cyclic Loading on the Indirect Tensile Strength of Rocks 总被引：1，自引：1，他引：0
This paper presents the results of laboratory experiments during the investigation of the stress–strain characteristics of
Brisbane tuff disc specimens under diametral compressive cyclic loading. Two different cyclic loading methods were used: namely,
sinusoidal cyclic loading and cyclic loading with increasing mean level. The first method applied the S–N curve approach to the indirect tensile strength (ITS) of rock specimens for the first time in the literature, and the second
method investigated the effect of increasing cyclic loading on the ITS of rock specimens. The ITS of Brisbane tuff disc specimens
was measured using the Brazilian tensile strength test. The reduction in ITS was found to be 33% with sinusoidal loading tests,
whereas increasing cyclic loading caused a maximum reduction of 37%. It is believed that the fracturing under cyclic loading
starts at contact points between strong grains and weak matrices, and that contact points at grain boundaries are the regions
of stress concentration (i.e., indenters). Transgranular cracks emanate from these regions and intergranular cracks sometimes
pass through the contact points. Once cracking begins, there is a steady progression of damage and a general ‘loosening’ of
the rock, which is a precursor to the formation of intergranular cracks. 相似文献
13.
为了完善平台巴西劈裂试验测定岩石抗拉强度的理论基础,基于二维弹性理论,建立对弦载荷下的平台巴西劈裂力学模型,采用应力场叠加法求得圆盘内的应力近似解析解。该应力理论解与有限元数值解一致,证明理论求解的合理性。在此基础上,对比研究了平台加载角对圆盘内应力大小及应力集中程度的影响,其结果表明：平台加载角越大,圆盘加载处的应力集中程度和压拉应力比都急剧降低,而圆盘内的拉应力值和拉伸区却只有一定程度减小;过大或过小的平台加载角都不利于平台巴西试样发生中心拉伸劈裂破坏,其最优平台加载角在20°~30°之间。最后,依据Griffith强度破坏准则,推得岩石抗拉强度的理论计算公式,其结果与已有抗拉强度经验公式及试验所得抗拉强度相符较好。 相似文献
14.
Summary
This paper presents a new approach, combined with the Boundary Element Method (BEM) analysis and the diametrical compression
on a thin disc with a small central hole, referred to as the ring test, for determining the indirect tensile strength of anisotropic
rocks. The stress distribution around the hole can be successfully obtained by the proposed single-domain BEM. The complex
variable function method was used for conveniently computing the tractions and displacements of a two-dimensional anisotropic
body. If we assume that the tensile strength is given by the maximum absolute value of stress in the direction perpendicular
to the loaded diameter at the intersection of loaded diameter and the hole, then from the failure load recorded by laboratory
testing of ring (disc), the indirect tensile strength of rocks could be obtained. A marble from Hualien (Taiwan) with clearly
black-white foliation, which was assumed to be transversely isotropic, was selected to conduct both ring tests and Brazilian
tests for evaluating the tensile strength. The variation of the marble tensile strength with the inclination angle of foliation
and with the hole size was also investigated. In general, the tensile strength of anisotropic rocks determined by ring test
is not a constant, but depends on the elastic properties of rocks, the angle between the planes of rock anisotropy and the
loading direction, the diameter of the central hole, and the contact condition of loading. 相似文献
15.
A relationship between tensile strength and loading stress governing the onset of mode I crack propagation obtained via numerical investigations using a bonded particle model 
下载免费PDF全文
下载免费PDF全文 Numerical models based on the discrete element method are used to study the fracturing process in brittle rock‐like materials under direct and indirect tension. The results demonstrate the capacity of the model to capture the essential characteristics of fracture including the onset of crack propagation, stable and unstable crack growth, arrest and reinitiation of fracturing, and crack branching. Simulations of Brazilian indirect tension tests serve to calibrate the numerical model, relating macroscopic tensile strength of specimens to their micromechanical breakage parameters. A second suite of simulations reveals a linear relationship between the tensile strength of specimens and the loading stress for which mode I tensile crack propagation ensues. Based on these results, a crack initiation criterion for brittle materials is proposed, prescribing the stressing conditions required to induce tensile failure. Such a criterion, if broadly applicable, provides a practical means to rapidly assess the failure potential of brittle materials under tensile loads. 相似文献
16.
层理弱面对层状岩石的力学特性影响较显著，为了研究层理面特性对岩石断裂力学特性的影响，开展了具有不同层理方向的砂岩试样三点弯试验，探讨了砂岩断裂韧度及断裂模式的各向异性。之后基于有限元中的黏聚单元建立了数值模型，采用数值模拟方法研究了层理面强度对各层理角度试样断裂力学行为的影响规律。结果表明：层理方向影响下砂岩的断裂韧度及模式存在各向异性；同一层理方向试样的断裂韧度随层理面强度的增大而增大，且试样的层理面与加载方向夹角越小，断裂韧度受层理面强度变化影响越明显；试样的断裂模式不仅与层理面强度有关，还受层理倾角的控制，层理面与加载方向夹角θ = 0o试样断裂模式基本不受层理面强度影响，θ = 30o试样主要沿层理面张拉或剪切破坏，且沿层理面的破裂长度随层理面强度的降低逐渐增大；层理面强度较大时，θ = 45o试样主要沿层理面张拉破坏，θ = 60o～90o试样主要以贯穿层理的张拉破坏为主；层理面强度较小时，θ = 45o～90o试样均以沿层理面的剪切破坏为主，其中θ = 45o试样沿层理剪切长度最大。另外，通过数值模拟结果分析了层理面强度及方向对试样的起裂角及裂纹扩展路径产生的影响。该研究成果可作为层状岩石断裂力学理论的有益补充。 相似文献
17.
Effect of Rapid Thermal Cooling on Mechanical Rock Properties 总被引：1，自引：1，他引：0
Laboratory tests have been conducted to investigate the effects of rapid thermal cooling on various rock specimens including igneous, sedimentary, and metamorphic rocks. At first, various types of thermal loading were conducted: heating up to 100, 200, and 300 °C, followed by rapid cooling with a fan. In addition, multiple cyclic thermal cooling (10, 15 and 20 cycles) with a maximum temperature of only 100 °C was conducted. Experiments included edge notched disc (END) tests to determine the Mode I fracture toughness, Brazilian disc tests to determine tensile strength, seismic tests to determine P-wave velocity, and porosity tests leading to meaningful results. Even though only small changes of temperature (rapid cooling from 100 °C to room temperature) were applied, the results showed that crack growth occurred in some rock types (granite, diabase with ore veins, and KVS) while crack healing occurred in other rock types (diabase without ore veins, quartzite, and skarn). To better understand the results, 3D transient thermo-mechanical analysis was conducted using the ANSYS program. The results indicated that there was a thin region near the outside of the specimen where large tensile stresses occur and microcracking would be expected, and that there was a large area in the middle of the specimen where lower magnitude compressive stresses occur and crack closure would be expected. It was found that the more heterogeneous and more coarse-grained rock types are more likely to exhibit crack growth, while less heterogeneous and more fine-grained rocks are more likely to exhibit crack healing. 相似文献
18.
Mixed mode fracture experiments were conducted on Harsin marble using two disc-shape samples namely the Brazilian disc (BD)
and the semi-circular bend (SCB) specimens. For each specimen, a complete fracture toughness envelope ranging from pure mode
I to pure mode II was obtained. The experimental results indicate that the mixed mode fracture toughness depends on the geometry
and loading conditions such that for any similar mode mixture, the BD test data were significantly greater than the SCB fracture
toughness results. Therefore, the conventional fracture criteria which present a unique mixed mode fracture curve, fail to
predict the test results. It is shown that a generalized criterion, which takes into account the effects of geometry and loading
conditions, is able to provide individual fracture curves for theses specimens with very good estimates for the test results
obtained from both BD and SCB specimens. The BD and SCB specimens can be suggested as appropriate specimens for obtaining
typical upper bound and lower bound envelopes for mixed mode fracture toughness of rocks. 相似文献
19.
基于P-CCNBD试样的岩石动态断裂韧度测试方法 总被引：2，自引：0，他引：2
预裂的人字形切槽巴西圆盘(Pre-cracked chevron notched Brazilian disc,简称P-CCNBD)是将人字形切槽巴西圆盘(cracked chevron notched Brazilian disc,简称CCNBD)的切槽尖端再稍加切削制成直裂纹前沿的试样。利用霍普金森压杆对P-CCNBD砂岩试样进行径向冲击,完成I型动态断裂试验后再做数值分析得到岩石的动态断裂韧度。为了验证数值模拟的可靠性,先进行了无限平面中一条有限尺寸裂纹表面受冲击拉伸作用的动态有限元分析,结果表明,数值模拟的结果与Shi得到的结果非常吻合。将试验-数值法和他人的准静态法分别确定的砂岩的动态起裂韧度进行对比,两种方法得到的结果有一定的差异。采用试验-数值法,将比较成熟的直裂纹巴西圆盘(cracked straight-through Brazilian disc,简称CSTBD)和P-CCNBD两种试样测得的结果进行对比,两者吻合较好。得到的动态起裂韧度都有随着加载率的增加而增大的加载率效应。分析了准静态法的缺陷,认为试验-数值法得到的结果更为合理。 相似文献
20.
采用中心裂纹圆盘-霍普金森压杆(CCCD-SHPB)试验系统对大理岩中心裂纹圆盘试件进行不同加载速率下的纯Ⅰ型加载试验,研究岩石材料动态断裂韧性的加载速率相关性。考虑到试验中所使用的圆盘试件是带有中心切口的非理想裂纹,结合试件的实际加工情况,提出采用切口尖端形状为小圆弧形的预制裂纹,介绍了试件的制作方法,并利用有限元计算论证了采用这种形状非理想裂纹试件的试验可行性。结果表明,采用圆弧形裂尖、裂纹宽度为1 mm的中心切口非理想裂纹圆盘试件来代替理想裂纹圆盘试件是可行的,误差不超过2.13%。分析试验数据得出：非理想裂纹圆盘试件在纯Ⅰ型加载条件下,其断裂韧度表现出明显的速率相关性,且随着加载速率的增大而增大。 相似文献