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脆性材料I型(张开)-断裂韧性测定的PFC2D和试验研究:一种新方法

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Acta Mechanica Sinica 2024年第2期40卷 116-130页

作者：付金伟 Hadi Haeri Joseph FLabuz Vahab Sarfarazi Pouyan Ebneabbasi MRM Aliha Hamid Reza Karimi Shirin Jahanmiri mohammad fatehi marji School of Civil Engineering and Transportation North China University of Water Resources and Electric PowerZhengzhou450046China Department of Mining Engineering Higher Education Complex of ZarandShahid Bahonar University of KermanKermanIran Department of Civil Environmentaland Geo-EngineeringUniversity of MinnesotaMinneapolis55455USA Department of Mining Engineering Hamedan University of TechnologyHamedanIran Research Scholar Civil Engineering DepartmentIslamic Azad UniversityHamedanIran Welding and Joining Research Center School of Industrial EngineeringIran University of Science and TechnologyNarmakTehranIran School of Civil Engineering Iran University of Science and Technology(IUST)NarmakTehranIran Department of Mine Exploitation Engineering Faculty of Mining and MetallurgyInstitute of EngineeringYazd UniversityYazdIran

在本文研究中,通过利用优势边缘缺口盘型(END)试样,确定了石灰石的断裂韧性,提出了一种新的石灰石归一化相应力、高相变的计算方法.采用柔性有限元法(FEM)对试样的I型(张开)-断裂韧性进行了精确计算,并得到了相应实用公式.在试验中,还... 详细信息

在本文研究中,通过利用优势边缘缺口盘型(END)试样,确定了石灰石的断裂韧性,提出了一种新的石灰石归一化相应力、高相变的计算方法.采用柔性有限元法(FEM)对试样的I型(张开)-断裂韧性进行了精确计算,并得到了相应实用公式.在试验中,还使用含缺口巴西圆盘(NBD)试件,测试了END程序的准确性.为了在数值上重现这些测试并验证断裂韧性测量的正确性,还对END测试进行了离散元分析.数值模拟结果与实验结果吻合良好.然而,END研究所确定的韧性水平低于NBD测试规定的韧性水平,这是因为END石灰石样品中的缺口具有均匀的拉伸应力分布.

关键词：断裂韧性脆性材料实用公式拉伸应力巴西圆盘离散元分析相变归一化

Numerical simulation of fatigue crack propagation in heterogeneous geomaterials under varied loads using displacement discontinuity method

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第3期15卷 702-716页

作者： Rezvan Alizadeh mohammad fatehi marji Abolfazl Abdollahipour Mehdi Pourghasemi Sagand Department of Mining and Metallurgical Engineering Faculty of EngineeringYazd UniversityYazdIran School of Mining Engineering College of EngineeringUniversity of TehranTehranIran

Heterogeneous brittle geomaterials are highly susceptible to cyclic *** contain inherent flaws and cracks that grow under fatigue loads and lead to *** study presents a numerical model for analyzing fatigue in these materials based on the two-dimensional(2D)boundary element method and linear elastic fracture *** process is formulated by coupling the displacement discontinuity method with the incorporation technique of dissimilar regions and the governing equations of *** heterogeneous media are assumed to consist of materials with different properties,and the interfaces are assumed to be completely *** addition,the domains include multiple cracks exposed to constant and variable amplitude cyclic *** stress intensity factor is a crucial parameter in fatigue analysis,which is determined using the displacement field around crack *** incremental crack growth scheme is applied to calculating the fatigue *** growth rate values are employed to estimate the length of crack extension when there are multiple *** interaction between cracks is considered,which also includes the coalescence ***,various structures under different cyclic loads are examined to evaluate the accuracy of this *** results demonstrate the efficiency of the proposed approach in modeling fatigue crack growth and life *** behavior of life curves for the heterogeneous domain was as *** curves illustrate the breakpoints caused by utilizing discrete incremental life *** these points,the trend of the curves changed with the material properties and fatigue characteristics of the new material around the crack tips.

关键词： Fatigue life Crack coalescence Interface Incorporation technique Variable amplitude loading

Simulation of crack coalescence mechanism underneath single and double disc cutters by higher order displacement discontinuity method

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Journal of Central South University 2015年第3期22卷 1045-1054页

作者： mohammad fatehi marji Faculty of Mining & Metallurgy Yazd University

The present research is focused on the numerical crack coalescence analysis of the micro-cracks and cracks produced during the cutting action of TBM disc cutters. The linear elastic fracture mechanics(LEFM) concepts and the maximum tangential stress criterion are used to investigate the micro crack propagation and its direction underneath the excavating discs. A higher order displacement discontinuity method with quadratic displacement discontinuity elements is used to estimate the stress intensity factors near the crack tips. Rock cutting mechanisms under single and double type discs are simulated by the proposed numerical *** main purposes of the present modeling are to simulate the chip formation process of indented rocks by single and double *** effects of specific disc parameters(except speed) on the thrust force Ft, the rolling force Fr, and the specific energy ES are investigated. It has been shown that the specific energy(energy required to cut through a unit volume of rock) of the double disc is less than that of the single disc. Crack propagation in rocks under disc cutters is numerically modeled and the optimum ratio of disc spacing S to penetration depth Pd(i.e. S/Pd ratio) of about 10 is obtained, which is in good agreement with the theoretical and experimental results cited in the literature.

关键词：位移不连续法数值模拟微裂缝高阶机制微裂纹扩展切割岩石贯通

Numerical analysis of confinement effect on crack propagation mechanism from a flaw in a pre-cracked rock under compression

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Acta Mechanica Sinica 2012年第5期28卷 1389-1397页

作者： Amin Manouchehrian mohammad fatehi marji Mining and Metallurgical Engineering Department Yazd University

In many situations rocks are subjected to biaxial loading and the failure process is controlled by the lateral confinement stresses. The importance of confinement stresses has been recognized in the literature by many researchers, in particular, its influence on strength and on the angle of fracture, but still there is not a clear description for the influence of confining stress on the crack propagation mechanism of rocks. This paper presents a numerical pro- cedure for the analysis of crack propagation in rock-like ma- terials under compressive biaxial loads. Several numerical simulations of biaxial tests on the rock specimen have been carried out by a bonded particle model （BPM） and the influ- ence of confinement on the mechanism of crack propagation from a single flaw in rock specimens is studied. For this purpose, several biaxial compressive tests on rectangular spec- imens under different confinement stresses were modeled in （2 dimensional particle flow code） PFC2D. The results show that wing cracks initiate perpendicular to the flaw and trend toward the direction of major stress, however, when the lat- eral stresses increase, this initiation angle gets wider. Also it is concluded that in addition to the material type, the initiation direction of the secondary cracks depends on confine- ment stresses, too. Besides, it is understood that secondary cracks may be produced from both tensile and shear mechanisms.

关键词： Crack propagation Confinement Bonded par-ticle model - Rock Secondary cracks

Fracture analyses of different pre-holed concrete specimens under compression

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Acta Mechanica Sinica 2015年第6期31卷 855-870页

作者： Hadi Haeri Alireza Khaloo mohammad fatehi marji Department of Civil Engineering Sharif University of Technology Member of National Elites Foundation Center of Excellence in Structure and Earthquake Engineering Sharif University of Technology Mine Exploitation Engineering Department Faculty of Mining and Metallurgy Yazd University

Crack propagation processes in specially prepared concrete discs and rectangular specimens containing a single cylindrical hole or multiple holes of varying diameters have been studied both experimentally and numerically. In this research, the cracks coalescence paths in Brazilian disc and rectangular specimens made from rock-like material containing multi-holes are investigated. These concrete specimens are specially prepared from an appropriate mixture of Portland Pozzolana Cement （PPC）, fine sands, and water. The pre-holed Brazilian discs and rectangular specimens are experimentally tested under compression. The breakage load in the ring type disc specimens containing an axial hole with varying diameters is measured and the distribution of the induced lateral stress is obtained. The mechanism of cracks propagation in the wall of the ring type specimens is also stud- ied. In the case of multi-hole Brazilian disc and rectangular specimens, the cracks propagation and cracks coalescence are also investigated. These experiments are numerically modeled by a modified higher order displacement discontinuity method. It has been shown that the corresponding experimental and numerical results are in good agreement with each other. The results presented in this research vali date the accuracy and applicability of these crack analyses procedures.

关键词： Concrete rings Pre-holed Brazilian disc ·Rectangular specimens Crack analyses Coalescence ·Induced lateral stress

On the accuracy of higher order displacement discontinuity method(HODDM) in the solution of linear elastic fracture mechanics problems

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Journal of Central South University 2016年第11期23卷 2941-2950页

作者： Abolfazl Abdollahipour mohammad fatehi marji Alireza Yarahmadi Bafghi Javad Gholamnejad Faculty of Mining and Metallurgical Engineering Yazd University

The higher order displacement discontinuity method(HODDM) utilizing special crack tip elements has been used in the solution of linear elastic fracture mechanics(LEFM) problems. The paper has selected several example problems from the fracture mechanics literature(with available analytical solutions) including center slant crack in an infinite and finite body, single and double edge cracks, cracks emanating from a circular hole. The numerical values of Mode Ⅰ and Mode Ⅱ SIFs for these problems using HODDM are in excellent agreement with analytical results(reaching up to 0.001% deviation from their analytical results). The HODDM is also compared with the XFEM and a modified XFEM results. The results show that the HODDM needs a considerably lower computational effort(with less than 400 nodes) than the XFEM and the modified XFEM(which needs more than 10000 nodes) to reach a much higher accuracy. The proposed HODDM offers higher accuracy and lower computation effort for a wide range of problems in LEFM.

关键词： accuracy higher order displacement discontinuity method LEFM mode Ⅰ stress intensity factor mode Ⅱ stress intensity factor

Experimental and Numerical Study of Shear Fracture in Brittle Materials with Interference of Initial Double Cracks

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Acta Mechanica Solida Sinica 2016年第5期29卷 555-566页

作者： Hadi Haeri Vahab Sarfarazi mohammad fatehi marji Ahmadreza Hedayat Zheming Zhu Young Researchers and Elite Club Bafgh BranchIslamic Azad UniversityBafghIran Department of Mining Engineering Hamedan University of TechnologytiamedanIran Associate Prof. Head of Mine Exploitation Engineering DepartmentFaculty of Mining and MetallurgyInstitution of EngineeringYazd UniversityYazdIvan Department of Civil and Environmental Engineering Colorado School of MinesGoldenColorado 80401USA College of Architecture and Environment Sichuan UniversityChengdu 610065China

A simultaneous experimental and numerical study of shear fracture of concrete-like materials is carried out using Brazilian disc specimens with initial double edge cracks and fourpoint bending beam specimens with double *** interference effects of two cracks/notches are investigated through varied ligament angles and crack *** is shown that shear fracturing paths change remarkably with the initial ligament angles and crack *** cracked specimens are numerically simulated by an indirect boundary element method.A comparison between the numerical results and the experimental ones shows good agreement.

关键词： cracked Fracture overlapped fracturing ligament simultaneous discontinuity cracking specimen shrinkage

Cracks coalescence mechanism and cracks propagation paths in rock-like specimens containing pre-existing random cracks under compression

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Journal of Central South University 2014年第6期21卷 2404-2414页

作者： Hadi Haeri Kourosh Shahriar mohammad fatehi marji Parviz Moarefvand Department of Mining Engineering Science and Research BranchIslamic Azad University Department of Mining and Metallurgical Engineering Amirkabir University of Technology Mine Exploitation Engineering Department Faculty of Mining and MetallurgyInstitution of EngineeringYazd University

The mechanism of cracks propagation and cracks coalescence due to compressive loading of the brittle substances containing pre-existing cracks(flaws)was modeled experimentally using specially made rock-like specimens from Portland Pozzolana Cement(PPC).The breakage process of the specimens was studied by inserting single and double flaws with different inclination angles at the center and applying uniaxial compressive stress at both ends of the *** first crack was oriented at 50° from the horizontal direction and kept constant throughout the analysis while the orientation of the second crack was *** is experimentally observed that the wing cracks are produced at the first stage of loading and start their propagation toward the direction of uniaxial compressive *** secondary cracks may also be produced in form of quasi-coplanar and/or oblique cracks in a stable *** secondary cracks may eventually continue their propagation in the direction of maximum principle *** experimental works were also simulated numerically by a modified higher order displacement discontinuity method and the cracks propagation and cracks coalescence were studied based on Mode I and Mode II stress intensity factors(SIFs).It is concluded that the wing cracks initiation stresses for the specimens change from 11.3 to 14.1 MPa in the case of numerical simulations and from 7.3 to 13.8 MPa in the case of experimental *** is observed that cracks coalescence stresses change from 21.8 to 25.3 MPa and from 19.5 to 21.8 MPa in the numerical and experimental analyses,*** some of the numerical and experimental results with those recently cited in the literature validates the results obtained by the proposed ***,a numerical simulation was accomplished to study the effect of confining pressure on the crack propagation process,showing that the SIFs increase and the crack initiation angles change in this case.

关键词：裂纹扩展传播路径压缩载荷机制标本聚结数值模拟岩样

Comparison of indirect boundary element and finite element methods A case study:Shiraz-Esfahan railway tunnel in Iran

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Frontiers of Structural and Civil Engineering 2012年第4期6卷 385-392页

作者： Amin MANOUCHEHRIAN mohammad fatehi marji Mohsen MOHEBBI Mining and Metallurgical Engineering Department Yazd UniversityYazd 89195Iran

Because of the high importance of transportation tunnels,most precise analyses of stress concentration and displacement around them are essential to provide safety of them as much as ***,various numerical methods such as finite element method(FEM),discrete element method(DEM),finite difference method(FDM)and boundary element method(BEM)have been used extremely in geosciences problems,but among these numerical methods,BEM has been used less than others because the computational algorithm is not so *** paper suggests the implementation of the indirect boundary element method(IBEM)as a formulation of BEM to analyze displacement around Shiraz-Esfahan railway tunnel in Zagros Mountains southwest of *** this purpose,this tunnel has been modeled numerically using two-dimensional fictitious stress method(TWOFS)*** validate the results,they were compared with FEM results as a commonly used numerical *** of current theoretical study have shown that the presented approach using IBEM is reasonably accurate and can be used for analysis of displacement in geosciences *** rock mechanics,for problems with a low ratio of boundary surface to volume,FEM is not very well suited and may be cumbersome,but use of such a proposed IBEM approach can be particularly attractive.

关键词： indirect boundary element method finite element method displacement tunnel case study