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Responses of jointed rock masses subjected to impact loading

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第4期10卷 624-634页

作者： Shabnam Aziznejad Kamran Esmaieli John Hadjigeorgiou Denis Labrie Lassonde Institute of Mining University of Toronto CanmetMINING Natural Resources Canada

Impact-induced damage to jointed rock masses has important consequences in various mining and civil engineering applications. This paper reports a numerical investigation to address the responses of jointed rock masses subjected to impact loading. It also focuses on the static and dynamic properties of an intact rock derived from a series of laboratory tests on meta-sandstone samples from a quarry in Nova Scotia, Canada. A distinct element code(PFC2D) was used to generate a bonded particle model(BPM) to simulate both the static and dynamic properties of the intact rock. The calibrated BPM was then used to construct large-scale jointed rock mass samples by incorporating discrete joint networks of multiple joint intensities into the intact rock matrix represented by the BPM. Finally, the impact-induced damage inflicted by a rigid projectile particle on the jointed rock mass samples was determined through the use of the numerical model. The simulation results show that joints play an important role in the impactinduced rock mass damage where higher joint intensity results in more damage to the rock mass. This is mainly attributed to variations of stress wave propagation in jointed rock masses as compared to intact rock devoid of joints.

关键词： Jointed rock mass Impact loading microcracks Rock damage

Particle simulation of the failure process of brittle rock under triaxial compression

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International Journal of Minerals,Metallurgy and Materials 2010年第5期17卷 507-513页

作者： Ming Xia Ke-ping Zhou School of Resources and Safety Engineering Central South University Changsha 410083 China Ma＇anshan Institute of Mining Research Ma＇anshan 243004 China

In order to investigate the failure process of brittle rock under triaxial compression through both experimental and numerical approaches, the particle simulation method was used in numerical simulations and the simulated results were compared with those of the experiment. The numerical simulation results, such as fracture propagation, microcrack distribution, stress-strain response, and damage patterns, were discussed in detail. The simulated results under various confining pressures （0-60 MPa） are in good agreement with the experimental results. The simulated results reveal that rock failure is caused by axial splitting under uniaxial compression. As the confining pressure increases, rock failure occurs in a few localized shear planes and the rock mechanical behavior is changed from brittle to ductile. Consequently, the peak failure strength, microcrack numbers, and the shear plane angle increase, but the ratio of tensile to shear microcracks decreases. The damage formation during the compression simulations indicates that the particle simulation method can produce similar behaviors as those observed through laboratory compression tests.

关键词： rock mechanics compression testing failure fracture modes simulation microcracks

Multiphase microstructure formation and its effect on fracture behavior of medium carbon high silicon high strength steel

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Journal of Materials Science & Technology 2021年第13期72卷 81-92页

作者： Kui Chen Huabing Li Zhouhua Jiang Fubin Liu Congpeng Kang Xiaodong Ma Baojun Zhao School of Metallurgy Northeastern UniversityShenyang 110819China State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819China School of Chemical Engineering The University of QueenslandBrisbane 4072Australia

This work investigated the evolution of multiphase microstructure and impact fracture behavior of medium carbon high silicon high strength steel subjected to the austempering treatment at 240,360,and400℃.The results show that martensite,bainite,and retained austenite(RA)are the main microstructural phases.The austempering treatments at 360 and 400℃ caused the formation of carbon-poor ferrite in the matrix,and the transformation of ultrafine bainite into coarse lath bainite and granular bainite,respectively.Thick filmy RA was distributed between bainite laths.The polygonal martensiteaustenite islands and blocky RA formed along the grain boundaries.The average carbon concentration in the matrix decreased with the temperature increase,while the impact toughness initially increased and then dropped with temperature.The quasi-cleavage brittle fracture dominated the impact fracture mechanism of the sample austempered at 240℃ by forming tearing surfaces and tearing steps.The microcracks disappeared in the RA on the prior austenite grain boundaries.On the other side,the fracture surface of the sample austempered at 360℃ exhibited ductile fracture with deep dimples and brittle fracture with cleavage river patterns.The polygonal martensite-austenite islands or blocky RA constrained the microcracks.After austempered at 400℃,the brittle fracture was dominant,showing river patterns,and the microcracks propagated through the granular bainite without any resistance.

关键词： Medium carbon high silicon steel Austempering Martensite Bainite Retained austenite microcracks

Stainless steel binder for the development of novel TiC-reinforced steel cermets

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Journal of University of Science and Technology Beijing 2006年第6期13卷 546-550页

作者： Akhtar Farid Materials Science and Engineering School University of Science and Technology BeijingBeijing 100083 China

Steel reinforced TiC composites are an attractive choice for wear resistance and corrosion resistance applications. TiC- reinforced 17-4PH maraging stainless matrix composites were processed by conventional powder metallurgy （P/M）. TiC-reinforced maraging stainless steel composites with 〉97% of theoretical density were fabricated. The microstructure, mechanical and wear properties of the composites were evaluated. The microstructure of these composites consisted of spherical and semi-spherical TiC particles. A few microcracks appeared in the composites, showing the presence of tensile stress in the composites produced during sintering. Typical properties, namely, hardness and bend strength were reported for the sintered composites. After heat treatment and aging, the increase of hardness was observed. The increase of hardness was attributed to the aging reaction in the 17-4PH stainless steel. The precipitates appeared in the microstructure and were responsible for the increase in hardness. The specific wear behavior of the composites was strongly dependent on the content of TiC particles, the interparticle spacing, and the presence of hard precipitates in the binder phase.

关键词： TiC-based cermets binder phase maraging stainless steel aging microcracks

Porothermoelastic response of an oil sand formation subjected to injection and micro-fracturing in horizontal wells

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Petroleum Science 2020年第3期17卷 687-700页

作者： Botao Lin Han Meng Jingjun Pan Sen Chen State Key Laboratory of Petroleum Resources and Prospecting&College of Petroleum Engineering China University of PetroleumBeijing 102249China Oil Production Technology Research Institute PetroChina Xinjiang Oilfield CompanyKaramay 834000XinjiangChina

Stimulation of unconsolidated formations via horizontal wells has seen its vast implementation in the recent development of heavy oil reservoir to save the time and cost of preheating the reservoir before the steam-assisted gravity drainage(SAGD)process.A mathematical approach was proposed in this research that fully couples the hydraulic,mechanical and thermal responses of unconsolidated sandstone formations and also applies failure criteria for describing either shear dilation or tensile parting mechanism that generates microcracks.The approach was implemented to predict the porothermoelastic response of a pair of SAGD wells subject to injection and subsequent micro-fracturing using hot water.It was found that the predicted bottom hole pressures(BHPs)match closely with the field observed data.An elliptical dilation zone developed around the dual wells with relatively high pore pressure,porosity,permeability and temperature,implying good interwell hydraulic communication between both wells.The activation of microcracks dramatically accelerated the dissipation of pore pressure across the entire formation depth and also facilitated heat convection in between the dual wells,though to a lesser extent.In summary,the approach provides a convenient means to assist field engineers in the optimization of injection efficiency and evaluation of interference among multiple horizontal wells.

关键词： Porothermoelastic response Unconsolidated sandstone Injection Micro-fracturing microcracks Oil sand

Research on fabric characteristics and borehole instability mechanisms of fractured igneous rocks

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Petroleum Science 2013年第2期10卷 212-218页

作者： Liu Xiangjun Zhu Honglin Liang Lixi State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Southwest Petroleum University

There are favorable exploration prospects in igneous rock reservoirs. However, problems of borehole instability occur frequently during drilling igneous formations, which is a serious impediment to oil and gas exploration and production. The lack of systematic understanding of the inherent instability mechanisms is an important problem. A series of experiments were conducted on several igneous rock samples taken from the sloughing formations in the Tuha area in an attempt to reveal the inherent mechanisms of wellbore instability when drilling in fractured igneous rocks. Research methods involved slurry chemistry, analysis of micro-geological features （Micro-CT imaging, SEM）, and rock mechanics testing. The experimental results indicated that clay minerals were widely distributed in the intergranular space of the diagenetic minerals, crystal defects, and microcracks. Drilling fluid filtrate would invade the rock along the microcracks. Tile invasion amount gradually increased over time, which constantly intensified the hydration and swelling of clay minerals, leading to changes in the microscopic structure of igneous rocks. Primary and secondary microcracks can propagate and merge into single cracks and thus reducing rock cohesion and the binding force along cleavage planes. Based on this result the authors propose that a key towards solving wellbore instability in igneous formations is that specific micro-geological characteristics of the igneous rocks should be taken into consideration in the design of antisloughing drilling muds.

关键词： Igneous rocks microcracks clay minerals hydration instability

Analysis of surface microcracks in low-carbon steel produced via twin-roll strip casting

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Baosteel Technical Research 2019年第2期13卷 24-31页

作者： YANG Xiaoping FANG Yuan SHI Bi Research Institute Baoshan Iron & Steel Co.Ltd.Shanghai 201999China Shanghai Engineering Research Center of Strip Casting and Rolling Shanghai 201999China

In this study,morphological and microstructural analyses were conducted on net-shaped microcracks appearing on the surface of low-carbon steel manufactured via twin-roll strip casting. The fractograph and microscale distribution of elements in the cracked region were also analyzed. Results revealed that the cracked surfaces were characterized by slight pits,along with inclusions composed of manganese and silicon oxide distributed along both the sides of the cracks. Fractograph analysis revealed that the crack and smooth dendrite surfaces were oxidized. These phenomena indicate that microcracks on the cast strip surface form at the hightemperature stage of the solidification process during twin-roll casting and rolling. microcracks were present in each region with pits in the cast strip and extended along the dendrite interface because of the combined effects of phasechange stress,thermal stress,mechanical stress,and fractional crystallization during the solidification process.

关键词： strip casting low-carbon steel microcracks

A THEORY OF EFFECTIVE THERMAL CONDUCTIVITY FOR MATRIX-INCLUSION-MICROCRACK THREE-PHASE HETEROGENEOUS MATERIALS BASED ON MICROMECHANICS

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Acta Mechanica Solida Sinica 2000年第2期13卷 179-187页

作者： Zhang, QJ Zhai, PC Li, Y Wuhan Univ Technol State Key Lab Adv Technol Mat Synth & Proc Wuhan 430070 Peoples R China

The effective thermal conductivity of matrix-inclusion-microcrack three-phase heterogeneous materials is investigated with a self-consistent micromechanical method (SCM) and a random microstructure finite element method(RMFEM). In the SCM, microcracks are assumed to be randomly distributed and penny-shaped and inclusions to be spherical, the crack effect is accounted for by introducing a crack density parameter, the effective thermal conductivity is derived which relates the macroscopic behavior to the crack density parameter. In the RMFEM, the highly irregular microstructure of the heterogeneous media is accurately described, the interaction among the matrix-inclusion-microcracks is exactly treated, the inclusion shape effect and crack size effect are considered. A Ni/ZrO2 particulate composite material containing randomly distributed, penny-shaped cracks is examined as an example. The main results obtained are: (1) the effective thermal conductivity is sensitive to the crack density and exhibits essentially a linear relationship with the density parameter: (2) the inclusion shape has a significant effect on the effective thermal conductivity and a polygon-shaped inclusion is more effective in increasing or decreasing the effective thermal conductivity than a sphere-shaped one; and (3) the SCM and RMFEM are compared and the two methods give the same effective property in the case in which the matrix thermal conductivity A, is greater than the inclusion one lambda(2). In the inverse case of lambda(1) < lambda(2), the two methods as the as the inclusion volume fraction and crack density are low and differ as they are high. A reasonable explanation for the agreement and deviation between the two methods in the case of lambda(1) < lambda(2) is made.

关键词： effective thermal conductivity heterogeneous materials microcracks micromechanics

Numerical simulation of evolution-induced catastrophe

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Science China Mathematics 1995年第4期38卷 462-471页

作者：卢春生柯孚久白以龙夏蒙棼 Laboratory for Nonlinear Mechanics of Continuous Media Institute of Mechanics Chinese Academy of Sciences Beijing 100080 China Department of Applied Mathematics and Physics Beijing University of Aeronautics and AstronauticsBeijing 100080 Physics Department.Center of Nonlinear Science Peking University.Beijing 100871.China.

A numerical simulation of damage evolution in a two-dimensional system of microcracks is presented. It reveals that the failure is induced by a cascade of coalescences of microcracks, and the fracture surface appears fractal. A model of evolution-induced catastrophe is introduced. The fractal dimension is found to be a function of evolution rule only. This result could qualitatively explain the correlation of fractal dimension and fracture toughness discovered in experiments.

关键词： microcracks numerical simulation fractal dimension evolution-induced catastrophe.