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Numerical and experimental investigation on hydraulic-electric rock fragmentation of heterogeneous granite

International Journal of Mining Science and Technology 2024年第1期34卷 15-29页

作者： Xiaohua Zhu Ling He Weiji Liu Yunxu Luo Youjian Zhang Wuji Tang School of Mechatronic Engineering Southwest Petroleum UniversityChengdu 610500China School of Mechanical Engineering Sichuan University of Science and EngineeringYibin 643002China

Hydraulic-electric rock fragmentation(HERF)plays a significant role in improving the efficiency of high voltage pulse rock breaking.However,the underlying mechanism of HERF remains unclear.In this study,considering the heterogeneity of the rock,microscopic thermodynamic properties,and shockwave time domain waveforms,based on the shockwave model,digital imaging technology and the discrete element method,the cyclic loading numerical simulations of HERF is achieved by coupling electrical,thermal,and solid mechanics under different formation temperatures,confining pressure,initial peak voltage,electrode bit diameter,and loading times.Meanwhile,the HERF discharge system is conducive to the laboratory experiments with various electrical parameters and the resulting broken pits are numerically reconstructed to obtain the geometric parameters.The results show that,the completely broken area consists of powdery rock debris.In the pre-broken zone,the mineral cementation of the rock determines the transition of type CⅠcracks to type CⅡand type CⅢcracks.Furthermore,the peak pressure of the shockwave increased with initial peak voltage but decreased with electrode bit diameter,while the wave front time reduced.Moreover,increasing well depth,formation temperature and confining pressure augment and inhibit HERF,but once confining pressure surpassed the threshold of 60 MPa for 152.40,215.90,and 228.60 mm electrode bits,and 40 MPa for 309.88 mm electrode bits,HERF is promoted.Additionally,for the same kind of rock,the volume and width of the broken pit increase with higher initial peak voltage and rock fissures will promote HERF.Eventually,the electrode drill bit with a 215.90 mm diameter is more suitable for drilling pink granite.This research contributes to a better microscopic understanding of HERF and provides valuable insights for electrode bit selection,as well as the optimization of circuit parameters for HERF technology.

关键词： Hydraulic-electric rock fragmentation Shockwave Thermodynamics microcracks Weak Linear Parallel Bond Model

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Effects of seepage pressure on the mechanical behaviors and microstructure of sandstone

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第6期16卷 2033-2051页

作者： Xuewei Liu Juxiang Chen Bin Liu Sai Wang Quansheng Liu Jin Luo State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China Faculty of Engineering China University of GeosciencesWuhan430074China Key Laboratory of Safety for Geotechnical and Structural Engineering of Hubei Province School of Civil EngineeringWuhan UniversityWuhan430072China

Surrounding rocks of underground engineering are subjected to long-term seepage pressure,which can deteriorate the mechanical properties and cause serious disasters.In order to understand the impact of seepage pressure on the mechanical property of sandstone,uniaxial compression tests,P-wave velocity measurements,and nuclear magnetic resonance(NMR)tests were conducted on saturated sandstone samples with varied seepage pressures(i.e.0 MPa,3 MPa,4 MPa,5 MPa,6 MPa,7 MPa).The results demonstrate that the mechanical parameters(uniaxial compressive strength,peak strain,elastic modulus,and brittleness index),total energy,elastic strain energy,as well as elastic strain energy ratio,decrease with increasing seepage pressure,while the dissipation energy and dissipation energy ratio increase.Moreover,as seepage pressure increases,the micro-pores gradually transform into meso-pores and macro-pores.This increases the cumulative porosity of sandstone and decreases P-wave velocity.The numerical results indicate that as seepage pressure rises,the number of tensile cracks increases progressively,the angle range of microcracks is basically from 50-120to 80-100,and as a result,the failure mode transforms to the tensile-shear mixed failure mode.Finally,the effects of seepage pressure on mechanical properties were discussed.The results show that decrease in the effective stress and cohesion under the action of seepage pressure could lead to deterioration of strength behaviors of sandstone.

关键词： Rock mechanics Mechanical property Seepage pressure Numerical simulation microcracks

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Swelling behaviors of heterogeneous red-bed mudstone subjected to different vertical stresses

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第5期16卷 1847-1863页

作者： Kang Huang Zhangjun Dai Chengzeng Yan Fei Yu Wei Zhang Shanxiong Chen State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China University of Chinese Academy of Sciences Beijing100049China Faculty of Engineering China University of GeosciencesWuhanChina International Joint Research Center for Deep Earth Drilling and Resource Development China University of GeosciencesWuhan430074China

In this study,the axial swelling strain of red-bed mudstone under different vertical stresses are measured by swell-under-load method,and the microstructure of mudstone after hygroscopic swelling is studied by mercury intrusion porosimetry(MIP).The weakening coefficient and Weibull distribution function are introduced into the coupling model of mudstone moisture diffusion-swelling deformation-fracture based on finite-discrete element method(FDEM).The weakening effect of moisture on mudstone's mechanical parameters,as well as the heterogeneity of swelling deformation and stress distribution,is considered.The microcrack behavior and energy evolution of mudstone during hygroscopic swelling deformation under different vertical stresses are studied.The results show that the axial swelling strain of mudstone decreases with increase of the vertical stress.At low vertical stresses,moisture absorption in mudstone leads to formation of cracks caused by hydration-induced expansion.Under high vertical stresses,a muddy sealing zone forms on the mudstone surface,preventing further water infiltration.The simulation results of mudstone swelling deformation also demonstrate that it involves both swelling of the mudstone matrix and swelling caused by crack expansion.Notably,crack expansion plays a dominant role in mudstone swelling.With increasing vertical stress,the cracks in mudstone change from tensile cracks to shear cracks,resulting in a significant reduction in the total number of cracks.While the evolution of mudstone kinetic energy shows similarities under different vertical stresses,the evolution of strain energy varies significantly due to the presence of different types of cracks in the mudstone.The findings provide a theoretical basis for understanding the hygroscopic swelling deformation mechanism of red-bed mudstone at various depths.

关键词： Heterogeneous red-bed mudstone Self-sealing band Matric swelling and crack expansion FDEM microcracks Energy evolution

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In-situ investigation on the microstructure evolution of Mg-2Gd alloys during the V-bending tests

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Journal of Materials Science & Technology 2022年第36期131卷 167-176页

作者： Chao He Jianxin Zhou Yan Yang Bin Jiang Ming Yuan Zhihua Dong Yanfu Chai Weijun He Guangsheng Huang Dingfei Zhang Fusheng Pan State Key Laboratory of Mechanical Transmissions College of Materials Science and EngineeringChongqing UniversitySha Zheng Street 174#Sha Ping Ba DistrictChongqing 400044China National Engineering Research Center for Magnesium Alloys Chongqing UniversityChongqing 400044China School of Mechanical and Electrical Engineering Shaoxing UniversityShaoxing 312000China School of Chemistry and Materials Science Hubei Engineering UniversityXiaogan 432000China

In this work,the in-situ observation of the microstructure in the Mg-2Gd(wt%)alloys during V-bending tests was operated.The microstructure and texture evolutions were characterized by the in-situ electron backscatter diffraction(EBSD),scanning electron microscopy(SEM)and the high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)technique.The results revealed a unique microcracks nucleation mechanism in the Mg-Gd alloys compared with the traditional Mg alloy(AZ31 alloy).The microcrack was nucleated at the grain boundary for the Mg-2Gd alloy and in the intragranular for the AZ31 alloy during the bending process.This difference mode between the Mg-Gd and the AZ31 alloys was mainly attributed to the more random topology of the grain boundary network,the lower grain boundary cohesion and the enhanced hinder ability for the dislocations due to the segregated Gd atoms in the Mg-Gd alloy.Furthermore,the microcracks that had a large angleθwith the extruded direction(ED)in the Mg-Gd alloys were preferred nucleated since grain boundaries had the larger normal stress during the bending process.

关键词： Magnesium In-situ V-bending Microstructure Texture microcracks

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Application of ultrasonic surface waves in the detection of microcracks using the scanning heating laser source technique

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Chinese Optics Letters 2012年第11期10卷 40-43页

作者：李加董利明倪辰荫沈中华张宏超 Faculty of Science Nanjing University of Science and Technology Faculty of Science Nanjing University of Aeronautics and Astronautics

This letter reports the application of the scanning heating laser source technique to detect microcracks that may be undetected by conventional methods. In the proposed approach, we monitor changes in the transmitted surface acoustic waves （SAWs） as a heating source is scanned over the crack. The experimental system for microcrack detection by a scanning heating laser source is obtained by exploiting the strong dependence of the transmission efficiency of acoustic pulses on the state of the contacts, whether open or closed, between the crack faces. Microeracks can be detected successfully by confirming the heating position at the point of maximal improvement of the transmission efficiency of the SAWs.

关键词： Acoustic surface wave devices Heating Lasers microcracks Scanning Surface waves Ultrasonic testing

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Two species of microcracks

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Applied Geophysics 2014年第1期11卷 1-8,115页

作者： Stuart Crampin 高原 British Geological Survey School of GeoSciences University of Edinburgh Institute of Earthquake Science China Earthquake Administration

We identify two interrelated but independent species of microcracks with differentorigins and different distributions. One species is the classic high-stress microcracksidentified in laboratory stress-cells associated with acoustic emissions as microcracks openwith increasing stress. The other species is the low-stress distributions of closely-spacedstress-aligned fluid-saturated microcracks that observations of shear-wave splitting （SWS）demonstrate pervade almost all in situ rocks in the upper crust, the lower crust, and theuppermost 400 km of the mantle. On some occasions these two sets of microcracks may beinterrelated and similar （hence ＇species＇） but they typically have fundamentally-differentproperties, different distributions, and different implications. The importance for hydrocarbonexploration and recovery is that SWS in hydrocarbon reservoirs monitors crack alignmentsand preferred directions of fluid-flow. The importance for earthquake seismology is that SWSabove small earthquakes monitors the effects of increasing stress on the pervasive low-stressmicrocrack distributions so that stress-accumulation before, possibly distant, earthquakes canbe recognised and impendin~ earthquakes stress-forecast.

关键词： crack-induced anisotropy, fluid-saturate microcracks, shear-wave splitting, stress-forecastin~ earthquakes, two species of microcracks

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Identification methods for anomalous stress region in coal roadways based on microseismic information and numerical simulation

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International Journal of Mining Science and Technology 2017年第3期27卷 525-530页

作者： Liu Chao Li Shugang Cheng Cheng Cheng Xiaoyu College of Safety Science and Engineering Xi'an University of Science & Technology Xi'an 710054 China Key Laboratory of Western Mine Exploitation and Hazard Prevention Ministry of Education Xi'an University of Science & Technology Xi'an 710054 China

It is believed that the microseismicity induced by mining effect and gas gradient disturbance stress is a precursor to the essential characteristics of roadway unstability. In order to effectively identify and evaluate the stability of coal roadways in the process of mine development and extraction, a microseismic monitoring system was deployed for the study of the stress evolution process, damage degree and distribution characteristics in the tailgate and headgate. The mine under study is the 62113 outburst working face of Xin Zhuangzi coalmine in Huainan mining area. The whole process of microfractures initiation,extension, interaction and coalescence mechanisms during the progressive failure processes of the coal rock within the delineated and typical event clusters were investigated by means of a two dimensional realistic failure process analysis code(RFPA2D-Flow). The results show that the microseismic events gradually create different-sized event clusters. The microseismicity of the tailgate is significantly higher than that of the headgate. The study indicates that the greater anomalous stress region matches the area where microfractures continuously develop and finally connect to each other and form a fissure zone.Due to the mine layout and stress concentration, the ruptured area is mainly located on the left shoulder of the tailgate roof. The potential anomalous stress region of the coal roadway obtained by numerical simulation is relatively in good agreement with the trend of spatial macro evolution of coal rock microfractures captured by the microseismic monitoring system. The research results can provide important basis for understanding instability failure mechanism of deep roadway and microseismic activity law in complex geologic conditions, and it ultimately can be used to guide the selection and optimization of reinforcement and protection scheme.

关键词： Microseismic monitoring technology Numerical simulation Anomalous stress region Event clusters microcracks

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Microstructural characterization and mechanical behavior analysis of 7075-T6 aluminum subjected to simulated lightning strikes

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Chinese Journal of Aeronautics 2021年第12期34卷 39-50页

作者： Luis Henrique SANTOS Weslei Patrick Teodosio SOUSA Sara Silva Ferreira DE DAFE Pedro Americo Magalhaes JUNIOR Department of Mechanical Engineering Pontificia Universidade Catolica de Minas GeraisBelo Horizonte 30535-901Brazil

Aircrafts damages caused by lightning strikes have been known since the early days of aviation.However,the physical effects on the aircraft structure are still being investigated.This work seeks to evaluate the lightning strike effects in the aluminum alloy 7075-T6.Samples were submitted to lightning strike simulation in laboratory and the damages evaluated through characterization techniques.Ultrasound and profilometry tests have shown material loss to 0.272 mm depth in the damaged region.In addition,it was detected the material accumulation occurrence in the damage vicinity of the region.Below the damage,it was found a region where metallurgical changes were identified.The tensile and microhardness tests results have shown reduction in the percentage elongation and hardness increasing in the material affected by lightning.These results are corroborated by the X-Ray Diffraction(XRD)and Rietveld Method(red line)that indicated an increasing in dislocation density and micro-deformation in the material matrix.Optical microscopy results have shown the presence of microcracks on the normal and cross-section surface of the samples damaged.The Energy Dispersive X-Ray Spectroscopy(EDXS)and Electron Backscattered Diffraction Test(EBSD)found coarse intermetallic phases and precipitates compounds with dimensions greater than 1 lm in length.They were responsible for nucleation of the microcracks that propagate along the material grain boundaries.

关键词： Aircraft structure Characterization techniques Lightning strikes Precipitates microcracks

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TiC-Maraging stainless steel composite:microstructure, mechanical and wear properties

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Rare Metals 2006年第6期25卷 630-635页

作者： Akhtar Farid Khadijah Ali Shah Syed Javid Askari School of Material Science and Engineering University of Science and Technology Beijing Beijing 100083 China

Particulate TiC reinforced 17-4PH and 465 maraging stainless steel matrix composites were processed by conventional powder metallurgy （P/M）. TiC-maraging stainless steel composites with theoretical density 〉97% were produced using conventional P/M. The microstructure, and mechanical and wear properties of the composites were evaluated. The microstructure of the composites consisted of （core-rim structure） spherical and semi-spherical TiC particles depending on the wettability of the matrix with TiC particles. In TiC-maraging stainless steel composites, 465 stainless steel binder phase showed good wettability with TiC particles. Some microcracks appeared in the composites, indicating the presence of tensile stresses in the composites produced during sintering. The typical properties, hardness, and bend strength were reported for the composites. After heat treatment and aging, an increase in hardness was observed. The increase in hardness was at- tributed to the aging reaction in maraging stainless steel. The specific wear behavior of the composites strongly depends on the content of TiC particles and their interparticle spacing, and on the heat treatment of the maraging stainless steel.

关键词： TiC-maraging stainless steel composites aging wear powder metallurgy microcracks

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NEW DESCRIPTION OF MICROCRACK DAMAGE BASED ON CONSERVATION LAWS

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Acta Mechanica Sinica 2002年第5期18卷 429-440页

作者：陈宜亨 School of Civil Engineering and Mechanics Xi'an Jiaotong UniversityXi'an 710049China

This paper presents a new description for brittle solids with micro- cracks under plane strain assumption.The basic idea is to extend the conservation laws such as the J_j-vector and M-integral analysis used in single crack problems to strongly interacting crack problems.The M-integral contains two distinct parts.One of them is a summation from the well-known relation between the M-integral and the stress intensity factors(SIF)at both tips of each crack.The other,called as the additional contribution,is obtained from the two components of the J_j-vector and the coordinates of each microcrack center in a global system.Of great significance is the clarification of the confusion about the dependence of the M-integral on the origin selection of global coordinates,provided that the vector vanishes at infinity and that the closed contour chosen to calculate the integral and the vector encloses all the microcracks completely.The M-integral is equivalent to the decrease of the total potential energy of the microcracking solids with the strong interaction being taken into account.The M-integral analysis,from a physical point of view,does play an important role in evaluating the damage level of brittle solids with strongly interacting microcracks.

关键词： damage microcracks conservation laws M-integral

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