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strength properties and evolution laws of cracked sandstone samples in re-loading tests

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International Journal of Mining Science and Technology 2020年第2期30卷 251-258页

作者： Yijiang Zong Lijun Han Qinbin Meng Yingchao Wang State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining&TechnologyXuzhou 221116China School of Transportation Engineering Jiangsu Vocational Institute of Architectural TechnologyXuzhou 221116China

To study the strength properties and evolution laws of cracked sandstone samples in re-loading tests,strength and damage evolution properties of intact sandstone samples were first analyzed through the triaxial compression tests carried on TAW-2000 microcomputer control electro-hydraulic servo rock triaxial test *** evolution models were established based on dilatancy properties realizing the real-time and quantitative evaluation of samples damage state in loading *** this basis,samples with different damage were obtained by pre-peak,peak point,post-peak and residual strength stage unloading tests in the loading process of intact *** characteristics of the stress-strain curves and strength evolution laws were studied through the re-loading tests of samples with different damage under different stress *** experimental results showed that the slope of stress-strain curves,peak strength and residual strength of cracked samples increased linearly with confining pressure and decreased linearly with *** equivalent cohesion decreased with damage in the exponential decay *** mechanics properties of samples transformed from strain softening to strain hardening with damage.

关键词： Rock mechanics Damage Re-loading strength characteristics Strain hardening

strength and failure characteristics of sandstone containing two circular holes filled with two types of inclusions under uniaxial compression

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Journal of Central South University 2017年第11期24卷 2487-2495页

作者： DU Ming-rui JING Hong-wen SU Hai-jian ZHU Tan-tan CHEN Min-liang State Key Laboratory for Geomehanics&Deep Underground Engineering(China University of Mining and Technology) Xuzhou 221116China

Plate shaped sandstones containing two fabricated circular holes that were filled with gypsum and high-strength concrete respectively were prepared for studying the effects of ligament length L ligament incline angle α, as well as filling modes on their strength properties and failure modes. The results show that the initial cracks can be categorized as wing crack, axial tensile crack and curved tensile crack. The failure modes of ligaments can be categorized as mode of single inclined crack, mode of single axial crack and mode of two parallel cracks. The final failure modes of all specimens can be categorized as the tension-shear mixed failure and shear failure. The strength of inclusions shows little influence on the final failure modes of specimens, while the failure modes vary with L and α. When α is a fixed value, the peak strength σc and elastic modulus Ec of tested specimens increase firstly with increasing L and reaches to the maximum value at L of 16 mm, then declines. When L is a fixed value, σc declines firstly and then turns to increase as α increases to 75° from 45°, while Ec increases linearly. The axial stress σp performs the similar variation trends with those of σc versus increasing L and α when ligaments fail.

关键词： sandstone two circular holes inclusions uniaxial compression failure modes strength properties

strength behaviour of sandstone subjected to polyaxial state of stress

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International Journal of Mining Science and Technology 2017年第6期27卷 889-897页

作者： Rukhaiyar Saurav Samadhiya Narendra Kumar Department of Civil Engineering Indian Institute of Technology Roorkee Roorkee 247667 India

The paper presents an experimental investigation on the strength behaviour of natural rock subjected to polyaxial state of stress. The polyaxial tests were conducted on cubical specimens of sandstone obtained from the Shivpuri district in Madhya Pradesh state of India, The specimens having nominal dimensions of100 mm x 100 mm x 100 mm were tested using a polyaxial testing machine. Twenty-five combinations of intermediate and minor principal stresses were applied and the specimens were loaded till failure occurs. It was observed that the intermediate principal stress has a substantial effect on the strength of the Shivpuri sandstone. A database of rock strength under various combinations of σ_2 and σ_3 was obtained for the Shivpuri sandstone. The database was used to study the predictability of five most commonly used strength criterion. Root mean square error(RMSE), average absolute relative error percentage(AAREP) and coefficient of accordance(COA) were used as indices for the measure of goodness of fit. It was observed that the least error in the prediction was shown by modified Mohr Coulomb criterion followed by modified Weibols and Cook criterion. A probability analysis of the error in prediction was also done.

关键词： Polyaxial testing Sandstone strength criterion Modified Mohr-Coulomb criterion Modified Weibols and Cook criterion

strength, strain capacity and toughness of five dual-phase pipeline steels

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Journal of Iron and Steel Research International 2021年第6期28卷 752-761页

作者： Yi Ren Xian-bo Shi Zhen-guo Yang Yi-yin Shan Wei Ye Gui-xi Cai Ke Yang State Key Laboratory of Metal Material for Marine Equipment and Application Anshan 114009LiaoningChina CAS Key Laboratory of Nuclear Materials and Safety Assessment Institute of Metal ResearchChinese Academy of SciencesShenyang 110016LiaoningChina Institute of Metal Research Chinese Academy of SciencesShenyang 110016LiaoningChina

The effect of microstructures on strength,strain capacity and low temperature toughness of a micro-alloyed pipeline steel was *** various dual-phase microstructures,namely,acicular ferrite and a small amount of(around 2 vol.%)polygonal ferrite(AF+PF),polygonal ferrite and bainite(PF+B),polygonal ferrite and martensite/austenite islands(PF+M/A),polygonal ferrite and martensite(PF+M)and elongated polygonal ferrite and martensite(ePF+M),have been *** results show that AF+PF microstructure has high yield strength and excellent low temperature toughness,whereas its yield ratio is the *** ferrite-based dual-phase steels,PF+B,PF+M/A and PF+M microstructures show better strain capacity and low temperature *** strain capacity and low temperature toughness of ePF+M microstructure are the worst due to its high *** relationship between microstructure,strength,strain capacity and toughness has been *** on the results,the optimum microstructure for a better combination of strength,strain capacity and toughness is suggested to be the one having appropriate polygonal ferrite as second phase in an acicular ferrite matrix.

关键词： Pipeline steel Dual-phase microstructure strength Strain capacity Toughness

strength and Wear Behavior of Mg Alloy AE42 Reinforced with Carbon Short Fibers

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Acta Metallurgica Sinica(English Letters) 2019年第1期32卷 31-40页

作者： Sabbah Ataya Naser A.Alsaleh Mohamed M.El-Sayed Seleman Metallurgical and Materials Engineering Department Faculty of Petroleum and Mining Engineering Suez University Department of Mechanical Engineering College of Engineering Al Imam Mohammad Ibn Saud University

In addition to the advantage of the lightweight of magnesium alloys, magnesium composites have moderate strength and elastic modulus. The proposed application of magnesium composites as diesel truck pistons makes it necessary to assess their wear performance. Little research data have been discussed on wear behavior of Mg alloy AE42 matrix and its composites. Thus, this paper reports wear behavior of magnesium alloy AE42(Mg–Al–Mn—RE; rare earth) and its composite AE42-C, which contains 23 vol% of randomly oriented carbon short fibers. Materials characterization, including density measurements, hardness testing, microstructures investigation, and compression testing at temperatures of 25, 150,and 300 °C, were conducted. Wear tests were performed under various loads and sliding distances. Wear mechanisms were also proposed based on the examination of worn surfaces using optical microscopy and scanning electron microscopy equipped with EDX(energy-dispersive X-ray spectrometry) analysis system. The hardness of AE42-23 vol% C composite is twice the hardness of the Mg matrix alloy AE42. Significant improvements to yield stress and compressive strength at temperatures of 25, 150, and 300 °C of the composite versus the AE42 alloy are achieved. Wear resistance of the composite is improved considerably versus that of the Mg alloy AE42 at the various sliding distances. Smearing of graphite on the worn surface produces a lubricating film that delays change from mild to severe wear of the composite, especially at high loads. EDX analysis of the worn surface shows oxidation of the matrix alloy at higher wear loads, and this mechanism decreases in the presence of carbon fibers under the same loads. Abrasive wear, oxidation, and plastic deformation are the dominant wear mechanisms for the alloy matrix AE42, whereas mainly abrasive wear is the wear mechanism of AE42-23 vol% C composite under the proposed testing conditions.

关键词： Magnesium composites Carbon short fibers Compressive strength Wear resistance Wear mechanisms

strength-Toughening Model of Eutectic Ceramic Composite with Inherent Defects

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Chinese Journal of Mechanical Engineering 2014年第4期27卷 754-760页

作者： FU Yunwei ZHANG Long NI Xinhua LIU Xiequan CHEN Cheng ZHAO Siyuan Department of Vehicle and Electric Engineering Ordnance Engineering College Department of Ground Artillery Wuhan Ordnance Non-commissioned Officers Academy

strengthening and toughening mechanisms in composite ceramics is complex. A change in a single parameter induces multiple property variations. The multiple changes in properties are often incompletely represented in theoretical models. This incompleteness in the parameter chosen fails to explain the mechanism of failure in composite ceramics. The exponential toughness function is used to represent the pull-out toughening mechanism, which dominates the crack growth resistance curve（R-curve）. The strengthening-toughening model is established based on the Mori-Tanaka method（M-T method）. The influence of inherent defects on toughness function and strength is analyzed by using this model. The theoretical result is compared with the experiment data. This model exactly reflects the change in strength. The theoretical result indicates that defects change the toughness function. Moreover, micro-cracks increase toughness size ac, and the strength of crack instable extensions acutely decreases as defect content increases. This presented model establishes the relationship among the important mechanical parameters of defect, strength, elastic modulus, and the R-curve.

关键词： inherent defects pull-out toughening toughness function strength

strength and thermal behavior of low weight foam geopolymer using circulating fluidized bed combustion fly ash

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Journal of Central South University 2015年第9期22卷 3633-3640页

作者：刘泽邵宁宁秦俊峰孔凡龙王春雪王栋民 Research Institution of Concrete and Eco-materials School of Chemical and Environmental Engineering China University of Mining & Technology

A comparative study of the influence of elevated temperature on foam geopolymer using circulating fluidized bed combustion fly ash（CFA） was reported. Foam geopoymers were prepared with different amounts of foam agent and different Si O2/Al2O3 molar ratios of 3.1, 3.4, and 3.8. The mechanical, thermo-physical properties and microstructure of the foam geopolymers before and after exposure to elevated temperature of 800, 1000, and 1200 ℃ were investigated. The specimen with Si O2/Al2O3 molar ratio of 3.8 exhibits the highest compressive strength, better microstructure and dimension stability before and after firing. Carnegeite, nepheline, and zeolite crystalline phases appearing after exposure may contribute to the good post-exposure strength. Low weight foam geopolymer using CFA can increase strength and maintain higher stability as high as 1000 ℃.

关键词： foam geopolymer circulating fluidized bed combustion fly ash thermal analysis microstructure strength

strength criterion effect of the translator and destabilization model of gas-bearing coal seam

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International Journal of Mining Science and Technology 2019年第2期29卷 327-333页

作者： Gang Wang Rui Wang Mengmeng Wu Cheng Fan Xiang Song Mine Disaster Prevention and Control-Ministry of State Key Laboratory Breeding Base Shandong University of Science & Technology College of Mining and Safety Engineering Shandong University of Science & Technology Department of Civil and Architectural Engineering City University of Hong Kong

Coal seam destabilization inflicts damage to equipment, causes property loss and personnel casualties,and severely threatens mining safety and efficient production. To further understand this destabilization based on the basic theory of Lippmann seam destabilization, a mathematical model was introduced for gas pressure distribution by considering intermediate principal stress and support ***, we established a translation model suitable for the entire roadway coal seam with rocky roof and floor by applying the unified form of yield criterion in the state of plane strain. We also obtained the analytic expressions of coal seam stress distribution on both sides of the roadway and the widths of plastic and disturbance zones. Afterward, we analyzed several typical cases with different material yield criteria, obtained the plastic zone widths of the coal seam under different gas pressures, and assessed the effects of support resistance, roadway size, and coal strength on coal seam destabilization. Results showed that: the results obtained on the basis of Wilson and Mohr–Coulomb criteria are considerably conservative, and the use of Druker–Prager criteria to evaluate the rockburst-induced coal seam destabilization is safer than the use of the two other criteria; coal seam stability is correlated with gas pressure;and high-pressure gas accelerates the coal seam destabilization.

关键词： Coal seam destabilization strength criterion effect Gas Stress distribution

strength and failure characteristics of brittle jointed rock-like specimens under uniaxial compression:Digital speckle technology and a particle mechanics approach

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International Journal of Mining Science and Technology 2018年第4期28卷 662-670页

作者： Rihong Cao Hang Lin Ping Cao School of Resources and Safety Engineering Central South University State Key Laboratory for Geo Mechanics and Deep Underground Engineering China University of Mining & Technology

The strength and failure characteristics of most natural rock mass are influenced by discontinues such as fissures, joints, and weak surfaces. In the present study, the strength and failure behavior of ubiquitous- joint rock-l!ke specimens under uniaxial loading have been investigated by DIC （digital image correlation） and discrete element numerical method （PFC2D）. The results are obtained. Firstly, the UCSJ of spec- imens with γ= 15° or 30° shows similar tendency while α goes from 0° to 75°. With γ= 45° or 60°, the UCSJ of specimens increases when α goes from 0° to 30° and decreases after α goes beyond 30°. With γ=75°, the peak UCSJ value is reached when α=0°. The UCSJ value shows an increasing trend when α goes from 60° to 75°. Secondly, the ubiquitous-joint specimens present different failure modes for various levels of α and γ（β-α）. Based on the experimental results, the failure mode of ubiquitous-joint specimens can be classified into three categories： stepped path failure, failure through parallel plane, and failure through cross plane.

关键词： Ubiquitous-joint Digital speckle correlation technique PFC2D strength Failure mode