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1.
Timo Saksala 《国际地质力学数值与分析法杂志》2010,34(13):1362-1386
This paper presents a damage–viscoplastic cap model for rocks with brittle and ductile behavior under low‐velocity impact loading, which occurs, e.g. in percussive drilling. The model is based on a combination of the recent viscoplastic consistency model by Wang and the isotropic damage concept. This approach does not suffer from ill posedness—caused by strain softening—of the underlying boundary/initial‐value problem since viscoplasticity provides a regularization under dynamic loading by introducing an internal length scale. The model uses the Drucker–Prager (DP) yield function with the modified Rankine criterion as a tension cut‐off and a parabolic cap surface as a compression cut‐off. The parabolic cap is smoothly fitted to the DP cone. The strain softening law in compression is calibrated with the degradation index concept of Fang and Harrison. Thereby, the model is able to capture the brittle‐to‐ductile transition and hardening behavior of geomaterials under highly confined compression, which is the prevailing stress state under a bit‐button in percussive drilling. Rock strength heterogeneity is characterized statistically at the structural level using the Weibull distribution. An explicit time integrator is chosen for solving the FE‐discretized equations of motion. The contact constraints due to the impact of an indenter are imposed with the forward increment Lagrange multiplier method that is compatible with explicit time integrators. The model is tested at the material point level with various uniaxial and triaxial tests. At the structural level confined compression, uniaxial tension tests and a rock sample under low‐velocity impact are simulated. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
2.
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
3.
Numerical modelling of bit–rock fracture mechanisms in percussive drilling with a continuum approach
Timo Saksala 《国际地质力学数值与分析法杂志》2011,35(13):1483-1505
This paper presents a numerical method for continuum modelling of the dynamic bit–rock interaction process in percussive drilling. The method includes a constitutive model based on a combination of the recent viscoplastic consistency model, the isotropic damage concept and a parabolic compression cap. The interaction between the drill bit and rock is modelled using contact mechanics by treating the bit as a rigid body. As the bit–rock interaction in percussive drilling is a transient event, the method is implemented in explicit dynamics FEM. The rock strength heterogeneity is characterized at the mesoscopic level statistically using the Weibull distribution. The bit–rock interaction is simulated under axisymmetric conditions using cylindrical and hemispherical buttons. The choice of the quite complex constitutive model accounting, e.g. for plastic compaction, viscoplastic shear and tensile failure along with induced damage and rate dependency is justified by numerical simulations. Moreover, the quasi‐static and dynamic cases are compared in plane strain simulations. Finally, some results clarifying the discrepancy of opinions found in the literature concerning the side (lateral) crack formation are obtained. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
4.
A numerical study of the influence from pre‐existing cracks on granite rock fragmentation at percussive drilling 
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下载免费PDF全文 Mahdi Saadati Pascal Forquin Kenneth Weddfelt Per‐Lennart Larsson Francois Hild 《国际地质力学数值与分析法杂志》2015,39(5):558-570
The aim of this study is to investigate the effect of pre‐existing, or structural, cracks on dynamic fragmentation of granite. Because of the complex behavior of rock materials, a continuum approach is employed relying upon a plasticity model with yield surface locus as a quadratic function of the mean pressure in the principal stress space coupled with an anisotropic damage model. In particular, Bohus granite rock is investigated, and the material parameters are chosen based on previous experiments. The equation of motion is discretized using a finite element approach, and the explicit time integration method is employed. The pre‐existing cracks are introduced in the model by considering sets of elements with negligible tensile strength that leads to their immediate failure when loaded in tension even though they still carry compressive loads as crack closure occurs because of compressive stresses. Previously performed edge‐on impact tests are reconsidered here to validate the numerical model. Percussive drilling is simulated, and the influence of the presence of pre‐existing cracks is studied. The results from the analysis with different crack lengths and orientations are compared in terms of penetration stiffness and fracture pattern. It is shown that pre‐existing cracks in all investigated cases facilitate the drilling process. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
5.
潜孔锤的钻进过程是一个高度非线性、大变形、破碎岩石的过程,利用非线性有限元程序ANSYS/LS-DY-NA研究了在凿岩过程中,球齿凿入不同空隙率（塑性体积应变）岩石的冲击力特性。结果表明,岩石空隙率对钻头球齿与岩石之间的凿入冲击力幅值有很大影响,随着空隙率的增大,球齿凿入的冲击力显著减小,而对活塞与钻头间冲击力幅值影响甚微。通过ANSYS/LS-DYNA瞬态冲击数值模拟,形象地再现了潜孔锤钻凿系统冲击岩石发生侵入破坏的物理过程,为冲击碎岩瞬态研究提供了一个有效的分析方法。 相似文献
6.
岩石拉伸剪切破裂是一类特殊应力状态条件下的破裂形式,属于同时受垂直于破裂面的法向拉应力和平行于破裂面的剪应力作用的复合破裂模式。在研制的DSC-800电液伺服测控岩石拉伸剪切试验仪的基础上,进行了大量花岗闪长岩和砂岩的拉伸剪切试验,开展了配套的破裂断口三维激光扫描、扫描电子显微镜（SEM）、岩石物理力学性质试验、颗粒流离散元（PFC）数值模拟等相关试验,利用分形理论研究了岩石拉剪破裂面特征,研究了岩石拉剪-压剪全区破裂准则、剪切速率对岩石拉剪破裂强度的影响,采用颗粒流离散元研究了岩石拉剪破裂过程。研究结论如下:（1）岩石拉剪破裂面的宏观与微观分形维数即粗糙度随着拉应力的增加而增大;（2）岩石的微观断裂形式是拉伸破坏和剪切破坏的结合。当拉应力较小时,岩石的微观断裂形式主要表现为剪切破坏,并且随着拉应力的增加,岩石的拉伸破坏形式表现得更加明显;（3）岩石在拉伸剪切区的破裂拉应力与剪应力成线性负相关关系,在拉伸剪切应力区的岩石破裂线斜率比压缩剪切区大,岩石在拉伸剪切应力条件下比压缩剪切应力条件下容易破裂;（4）在岩石拉伸剪切条件下,剪切速率与剪切强度成非线性反相关关系,随着剪切速率的增加,岩石拉剪破裂面粗糙度增加;（5）建立了岩石拉伸剪切PFC数值试验模型,模拟了岩石拉伸剪切破裂过程中的力链演化以及剪切速率对拉剪破裂面粗糙度的影响,获得了与实验室试验一致的结果。 相似文献
7.
This paper presents a novel dynamical model to analyze the long‐term response of a percussive drilling system. This departs from existing approaches that usually consider a single activation and bit/rock interaction cycle for the analysis of the process performance. The proposed model integrates the axial dynamics of an elastic piston and an elastic drill bit, a motion‐dependent pressure law to drive the piston, and a generalized bit/rock interaction law representative of the dynamic indentation taking place at the bit/rock interface. It applies to down‐the‐hole percussive drilling as well as top‐hole, with minor modifications. The model does not account for the angular motion or the hole cleaning, however. The model is first formulated mathematically; then, a finite‐dimensional approximation is proposed for computations. Numerical analyses of the model response, for a low‐size down‐the‐hole percussive system, follow. The period‐1 stationary response for the reference configuration is studied in detail, and parametric analyses assessing the influence on the rate of penetration of the bit/rock interaction parameters, the feed force, and the percussive activation parameters are conducted. These analyses reveal that the multiscale nature of the process is well captured by the model and recover expected trends for the influence of the parameters. They also suggest that a significant increase of the penetration rate can be achieved by increasing the percussive frequency. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
8.
X. Li T. S. Lok D. A. Summers G. Rupert J. Tyler 《Geotechnical and Geological Engineering》2001,19(2):119-136
Experiments have been conducted using an impact method with drop-hammers to obtain the required signals so that a detailed analysis of these data could be undertaken to quantify the drillability index of rocks. The dynamic stress waveform or reflected energy from the rock-drill bit interface is represented as a drillability index. This information enables the assessment of the characteristics of the rock under the bit. The results show that neither the amplitude nor the frequency spectra of the reflected stress wave significantly changes with the type of rock tested. However, the energy reflection coefficient varies with rock hardness. In the process of drilling the rocks, the energy reflection coefficient can increase by approximately 20% when the hardness or penetration resistance index of rock is doubled. This investigation confirmed the variation of reflected energy of rocks. For a single sharp or domed indentor, energy reflection decreases with penetration resistance index of the rock while it increases with this index in actual drilling or testing of percussive bits. In drill bit design and in tests for using a single indentor, a reasonable indentor shape should be adopted to correspond to a high energy reflection coefficient. By contrast, the energy reflection from a drill system or percussive bit should be minimised in practice. 相似文献
9.
井底压差对垂直井井底应力场的影响研究 总被引：1，自引：0，他引：1
井底压差是影响钻井机械钻速的重要因素之一。实践证明欠平衡钻井与常规钻井相比机械钻速有显著提高,不同钻井条件下的井底应力场需要深入地研究。在分析井底岩石所受载荷的基础上,建立了轴对称条件下井底岩石流固耦合模型,并利用有限元方法进行求解,通过对不同井底压差下的井底岩石应力场进行数值模拟计算,针对井壁岩石的理论解和数值模拟结果进行对比验证模型的合理性,并对井底待破碎岩石进行了力学分析。结果表明,数值模拟结果与理论结果相符,验证了模型的正确性;井底待破碎岩石按照应力状态分为3个区域,分别为3向拉伸区、2向压缩区和3向压缩区。井底压差对井底应力场的影响研究为快速高效破岩提供理论基础。 相似文献
10.
Damage‐viscoplastic consistency model for rock fracture in heterogeneous rocks under dynamic loading
Timo Saksala 《国际地质力学数值与分析法杂志》2010,34(10):1041-1062
This paper presents a damage‐viscoplastic consistency model for numerical simulation of brittle fracture in heterogeneous rocks. The model is based on a combination of the recent viscoplastic consistency model by Wang and the isotropic damage concept with separate damage variables in tension and compression. This approach does not suffer from ill‐posedness, caused by strain softening, of the underlying boundary/initial value problem since viscoplasticity provides the regularization by introducing a length scale effect under dynamic loading conditions. The model uses the Mohr–Coulomb yield criterion with the Rankine criterion as a tensile cut‐off. The damage law in compression is calibrated via the degradation index concept of Fang and Harrison. Thereby, the model is able to capture the brittle‐to‐ductile transition occurring in confined compression at a certain level of confinement. The heterogeneity of rock is accounted for by the statistical approach based on the Weibull distribution. Numerical simulations of confined compression test in plane strain conditions demonstrate a good agreement with the experiments at both the material point and structural levels as the fracture modes are realistically predicted. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
11.
Polygonal finite elements are gaining an increasing attention in the computational mechanics literature, but their application in rock mechanics is very rare. This paper deals with numerical modeling of rock failure under dynamic loading based on polygonal finite elements. For this end, a damage-viscoplastic constitutive model for rock based on the Mohr-Coulomb criterion with the Rankine criterion as a tensile cutoff is employed and implemented with the polygonal finite element method. Moreover, the mineral mesostructure or rock is described by randomly mapping groups of polygonal elements representing the constituent minerals into a global mesh and assigning these groups with the corresponding mineral material properties. The performance of the polygonal elements is compared with that of the linear and quadratic triangular and bilinear quadrilateral elements in numerical simulations of controlled shear band formation under uniaxial compression and lateral splitting failure in the dogbone tension test. Numerical simulations of uniaxial tension and compression tests as well as dynamic Brazilian disc test under increasing loading rates demonstrate that the present approach predicts the correct failure modes as well as the dynamic increase in strength of rock. 相似文献
12.
Letícia Fleck Fadel Miguel Jorge Daniel Riera Ignacio Iturrioz 《国际地质力学数值与分析法杂志》2008,32(15):1857-1881
The numerical fracture analysis of non‐homogeneous rock or concrete dowels subjected to shear and compression is described in detail. The method of analysis allows the consideration of scale and rate effects due to material non‐homogeneity and fracture. The proposed approach is verified by comparing numerical predictions with experimental results reported in the literature for a series of small rock samples, since experimental evidence for large bodies is not yet available (2007). Results generated by Monte Carlo simulation using the so‐called discrete element method to model the dowels suggest that a simple three parameters law can be used to predict the relationship between tangential stress at the base and lateral distortion. It is observed that the larger the size of the cubes, the smaller both the peak tangential stress and the rupture distortion. Size effects are also evaluated in samples with vertical restraint. The influence of loading rate is likewise numerically assessed for two sample sizes. The effect is compatible with experimental evidence available for concrete using small samples. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
13.
Modeling 3D thermal fracture propagation by transient cooling using virtual multidimensional internal bonds 下载免费PDF全文
下载免费PDF全文 Thermal fracturing can play an important role in development of unconventional petroleum and geothermal resources. Thermal fractures can result from the nonlinear deformation of the rock in response to thermal stress related to cold water injection as well as heating. Before the rock reaches the final failure stage, material softening and bulk modulus degradation can cause changes in the thermo‐mechanical properties of the solid. In order to capture this aspect of the rock fracture, a virtual multidimensional internal bond‐based thermo‐mechanical model is derived to track elastic, softening, and the failure stages of the rock in response to the temporal changes of its temperature field. The variations in thermo‐mechanical properties of the rock are derived from a nonlinear constitutive model. To represent the thermo‐mechanical behavior of pre‐existing fractures, the element partition method is employed. Using the model, numerical simulation of 3D thermal fracture propagation in brittle rock is carried out. Results of numerical simulations provide evidence of model verification and illustrate nonlinear thermal response and fracture development in rock under uniform cooling. In addition, fracture coalescence in a cluster of fractures under thermal stress is illustrated, and the process of thermal fracturing from a wellbore is captured. Results underscore the importance of thermal stress in reservoir stimulation and show the effectiveness of the model to predict 3D thermal fracturing. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
14.
基于Drucker-Prager（下简称D-P）准则,建立压缩载荷作用下的非贯通节理岩石的弹塑性断裂模型。针对节理岩石小范围屈服翼裂纹尖端塑性区,推导了D-P屈服准则的纯I、纯II及I、II复合型3种翼裂纹无量纲塑性区径长函数,并与Mises准则的塑性区进行对比;结果表明,D-P准则的I型和复合型塑性区较Mises屈服准则的塑性区大,且其II型及I、II复合型塑性区在翼裂纹上下表面不连续。进一步,引入断裂软化因子以表征节理岩石裂隙断裂扩展后的断裂软化规律,考虑非贯通节理岩石复合型断裂软化,是由于节理尖端翼裂纹应变能密度超过最小应变能密度导致其成核扩展引起的,提出用应变能密度的指数函数形式表征断裂软化变量的演化;塑性屈服函数采用Borja等的应力张量3个不变量的硬化/软化函数,反映塑性内变量及应力状态对硬化函数的影响;建立节理岩石的弹塑性断裂本构关系及其数值算法,并用回映隐式积分算法编制了弹塑性断裂模型的程序。以单轴压缩下非贯通节理岩石为例,分析岩石断裂韧度、节理摩擦系数和节理倾角等参数的影响,结果表明,所提出的弹塑性断裂模型与数值和试验结果比较吻合。 相似文献
15.
从岩石宏观裂纹变化出发,研究孕镶金刚石钻头在钻进过程中由于岩体裂纹的影响而造成的断裂问题。运用岩石断裂力学理论,结合钻头实际工作条件,简化应力、水力及裂纹条件,建立了简化的岩石断裂等效模型,从理论上分析了一种新型栅格胎体孕镶金刚石钻头的破岩机理。研究结果表明:与常规的钻头相比,新型钻头的特殊栅格结构能有效提高钻压,比压由原来的68.03 kgf/cm2增加到了113.33 kgf/cm2,提高了将近67 %,使钻头能更有效地压入岩体,产生破碎穴及裂纹;特殊的栅格结构有利于冲洗液的储存,改善了金刚石颗粒的冷却效果,从而以更加有利的拉裂破坏方式破碎岩石。 相似文献
16.
This paper presents a numerical model for predicting the dynamic response of rock mass subjected to large‐scale underground explosion. The model is calibrated against data obtained from large‐scale field tests. The Hugoniot equation of state for rock mass is adopted to calculate the pressure as a function of mass density. A piecewise linear Drucker–Prager strength criterion including the strain rate effect is employed to model the rock mass behaviour subjected to blast loading. A double scalar damage model accounting for both the compression and tension damage is introduced to simulate the damage zone around the charge chamber caused by blast loading. The model is incorporated into Autodyn3D through its user subroutines. The numerical model is then used to predict the dynamic response of rock mass, in terms of the peak particle velocity (PPV) and peak particle acceleration (PPA) attenuation laws, the damage zone, the particle velocity time histories and their frequency contents for large‐scale underground explosion tests. The computed results are found in good agreement with the field measured data; hence, the proposed model is proven to be adequate for simulating the dynamic response of rock mass subjected to large‐scale underground explosion. Extended numerical analyses indicate that, apart from the charge loading density, the stress wave intensity is also affected, but to a lesser extent, by the charge weight and the charge chamber geometry for large‐scale underground explosions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
17.
Characterisation of confinement effect on jointed rock pillars using a Synthetic Rock Mass approach 下载免费PDF全文
下载免费PDF全文 Confinement effect on jointed rock pillars is numerically characterised in this research using a Synthetic Rock Mass (SRM) approach. The SRM is an integrated model incorporating a discrete fracture network within a Particle Flow Code 3D particle assembly. In this paper, the confinement effect on a 3D jointed pillar SRM model is investigated in a series of simulations, including biaxial compression tests and true and conventional triaxial compression tests. The numerical results suggest that the applied confining stresses generally result in higher pillar strengths and ductile post‐peak responses. More brittle post‐peak behaviour is simulated in the biaxial and true triaxial tests when the pillar is confined by a high stress in one lateral direction and by a zero/low stress in the other lateral direction. This phenomenon is attributed to significant lateral pillar dilation in the less confined direction. Detailed pillar failure modes are monitored in the uniaxial and triaxial tests. Axial splitting fractures and long shear zones cutting through the pillar are simulated when the pillar is able to dilate in the direction of least confinement. Localised shearing along joints and failed rock blocks is the dominant failure mode when the pillar dilation is resisted by the applied confining stresses. The pillar remains relatively intact with limited cracking in the pillar core in the highly confined triaxial tests. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
18.
基于复合材料以及连续介质损伤理论,给出了岩石材料的各向异性损伤破坏模型。通过引入与岩石材料单轴加载行为相对应的特征模态构成的四阶对称损伤张量,描述了岩石材料的损伤演化过程,其中对不同主应变方向采用不同的损伤变量,而对同一主应变方向拉压时的损伤则采用不同的损伤变量来描述。在数值模拟岩石破坏过程的程序中,采用了张量分解的方法。将该模型编写用户材料子程序,并嵌入到大型有限元分析程序ABAQUS中,通过ABAQUS/EXPLICIT SOLVER的显式有限元算法求解。利用此程序对岩石材料的单轴压缩进行了数值模拟。 相似文献
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分析了大口径嵌岩钻进面临的主要技术难点,并对目前国内常用的３种大口径嵌岩钻进方法－牙轮／滚刀钻进法、冲击钻进法（包括无循环和反循环）和气动／液动潜孔锤钻进法的技术现状作了介绍,提出了提高我国大口径嵌岩钻进技术水平的建议。 相似文献