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Dynamic strength of rock with single planar joint under various loading rates at various angles of loads applied

Journal of Rock Mechanics and Geotechnical Engineering 2018年第3期10卷 545-554页

作者： Pei-Yun Shu Hung-Hui Li Tai-Tien Wang Tzuu-Hsing Ueng Institute of Mineral Resources Engineering National Taipei University of Technology Department of Environmental Information and Engineering Chung Cheng Institute of TechnologyNational Defense University Department of Civil Engineering National Taiwan University Department of Materials and Mineral Resources Engineering National Taipei University of Technology

Intact rock-like specimens and specimens that include a single, smooth planar joint at various angles are prepared for split Hopkinson pressure bar（SHPB） testing. A buffer pad between the striker bar and the incident bar of an SHPB apparatus is used to absorb some of the shock energy. This can generate loading rates of 20.2-4627.3 GPa/s, enabling dynamic peak stresses/strengths and associated failure patterns of the specimens to be investigated. The effects of the loading rate and angle of load applied on the dynamic peak stresses/strengths of the specimens are examined. Relevant experimental results demonstrate that the failure pattern of each specimen can be classified as four types： Type A, integrated with or without tiny flake-off; Type B, slide failure; Type C, fracture failure; and Type D, crushing failure. The dynamic peak stresses/strengths of the specimens that have similar failure patterns increase linearly with the loading rate, yielding high correlations that are evident on semi-logarithmic plots. The slope of the failure envelope is the smallest for slide failure, followed by crushing failure, and that of fracture failure is the largest. The magnitude of the plot slope of the dynamic peak stress against the loading rate for the specimens that are still integrated after testing is between that of slide failure and crushing failure. The angle of application has a limited effect on the dynamic peak stresses/strengths of the specimens regardless of the failure pattern, but it affects the bounds of the loading rates that yield each failure pattern, and thus influences the dynamic responses of the single jointed specimen. Slide failure occurs at the lowest loading rate of any failure, but can only occur in single jointed specimen that allows sliding.Crushing failure is typically associated with the largest loading rate, and fracture failure may occur when the loading rate is between the boundaries for slide failure and crushing failure.

关键词： Dynamic strength Failure pattern Rock with single planar Loading rate Angle of load applied

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Dynamic strength behavior of a Zr-based bulk metallic glass under shock loading

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Chinese Physics B 2015年第6期24卷 461-465页

作者：俞宇颖习锋戴诚达蔡灵仓谭叶李雪梅吴强谭华 Laboratory for Shock Wave and Detonation Physics Research Institute of Fluid PhysicsChinese Academy of Engineering Physics

Dynamic strength behavior of Zr51Ti5NiloCu25A19 bulk metallic glass （BMG） up to 66 GPa was investigated in a series of plate impact shock-release and shock-reload experiments. Particle velocity profiles measured at the sample/LiF window interface were used to estimate the shear stress, shear modulus, and yield stress in shocked BMG. Beyond confirm- ing the previously reported strain-softening of shear stress during the shock loading process for BMGs, it is also shown that the softened Zr-BMG still has a high shear modulus and can support large yield stress when released or reloaded from the shocked state, and both the shear modulus and the yield stress appear as strain-hardening behaviors. The work provides a much clearer picture of the strength behavior of BMGs under shock loading, which is useful to comprehensively understand the plastic deformation mechanisms of BMGs.

关键词： shock loading Dynamic strength bulk metallic glass

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Analysis on the turning point of dynamic in-plane compressive strength for a plain weave composite

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Defence Technology（防务技术） 2024年第2期32卷 485-495页

作者： Xiaoyu Wang Zhixing Li Licheng Guo Zhenxin Wang Jiuzhou Zhao Department of Astronautic Science and Mechanics Harbin Institute of TechnologyHarbin150001China AECC Commercial Aircraft Engine Co LTDShanghai201108China

Experimental investigations on dynamic in-plane compressive behavior of a plain weave composite were performed using the split Hopkinson pressure bar. A quantitative criterion for calculating the constant strain rate of composites was established. Then the upper limit of strain rate, restricted by stress equilibrium and constant loading rate, was rationally estimated and confirmed by tests. Within the achievable range of 0.001/s-895/s, it was found that the strength increased first and subsequently decreased as the strain rate increased. This feature was also reflected by the turning point(579/s) of the bilinear model for strength prediction. The transition in failure mechanism, from local opening damage to completely splitting destruction, was mainly responsible for such strain rate effects. And three major failure modes were summarized under microscopic observations: fiber fracture, inter-fiber fracture, and interface delamination. Finally, by introducing a nonlinear damage variable, a simplified ZWT model was developed to characterize the dynamic mechanical response. Excellent agreement was shown between the experimental and simulated results.

关键词： Plain weave composite Dynamic strength Quantitative criterion Turning point Failure mechanism

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Characteristics of dynamic strain and strength of frozen silt under long-term dynamic loading

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Research in Cold and Arid Regions 2011年第6期3卷 478-484页

作者： ShuPing Zhao Wei Ma GuiDe Jiao XiaoXiao Chang State Key Laboratory of Frozen Soil Engineering Cold and Arid Regions Environmental and Engineering Research Institute Chinese Academy of SciencesLanzhouGansu 730000China Civil and Engineering Department Lanzhou UniversityLanzhouGansu 730000China

The dynamic swain and strength of frozen silt under long-term dynamic loading are studied based on creep tests. Three groups of tests are performed (Groups I, II, and III). The initial deviator stresses of Groups I and II are same and the dynamic stress ampli- tude of Group II is twice as that of Group I. The minimum value of dynamic stress in Group IlI is near zero and its dynamic stress amplitude is larger than those of Groups I and II. In tests of all three groups there are similar change trends of accttmulative sWain, but with different values. The accumulative swain curves consist of three stages, namely, the initial stage, the steady stage, and the gradual flow stage. In the tests of Groups I and II, during the initial stage with vibration times less than 50 loops the strain ampli- tude decreased with the increase of vibration times and then basically remained constant, fluctuating in a very small range. For the tests of Group III, during the initial and steady stages the sWain amplitude decreased with the increase of vibration times, and then increased rapidly in the gradual flow stage. The Dynamic strength of frozen silt decreases and trends to terminal Dynamic strength as the vibration times of loading increase.

关键词： frozen silt long-term dynamic loading accumulative strain strain amplitude residual strain Dynamic strength

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Dynamic strength of rocks and physical nature of rock strength

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Journal of Rock Mechanics and Geotechnical Engineering 2009年第1期1卷 1-10页

作者： Qihu Qian Chengzhi Qi Mingyang Wang Engineering Institute of Engtneerlng Crops PLA University of Science and Technology Nanjing 210007 China School of Civil and Communication Engineering Beijing Institute of Civil Engineering andArchitecture Beijing 100044 China

Time-dependence of rock deformation and fracturing is often ignored.However,the consideration of the time-dependence is essential to the study of the deformation and fracturing processes of materials,especially for those subject to strong dynamic loadings.In this paper,we investigate the deformation and fracturing of rocks,its physical origin at the microscopic scale,as well as the mechanisms of the time-dependence of rock strength.Using the thermo-activated and macro-viscous mechanisms,we explained the sensitivity of rock strength to strain rate.These mechanisms dominate the rock strength in different ranges of strain rates.It is also shown that a strain-rate dependent Mohr-Coulomb-type constitutive relationship can be used to describe the influence of strain rate on dynamic rock fragmentation.A relationship between the particle sizes of fractured rocks and the strain rate is also proposed.Several time-dependent fracture criteria are discussed,and their intrinsic relations are discussed.Finally,the application of Dynamic strength theories is discussed.

关键词： rock dynamics deformation and fracturing time-dependence Dynamic strength criteria of fracturing

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Strain-Rate Dependency of a Unidirectional Filament Wound Composite under Compression

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Computer Modeling in Engineering & Sciences 2023年第12期137卷 2149-2161页

作者： Stepan Konev Victor A.Eremeyev Hamid M.Sedighi Leonid Igumnov Anatoly Bragov Aleksandr Konstantinov Ayaulym Kuanyshova Ivan Sergeichev Skolkovo Institute of Science and Technologies Center for Materials TechnologiesMoscowRussia National Research Lobachevsky State University of Nizhny Novgorod Nizhny NovgorodRussia Dipartimento di Ingegneria Civile Ambientale e Architettura(DICAAR)Universitàdegli Studi di CagliariCagliari(CA)Italy Mechanical Engineering Department Faculty of EngineeringShahid Chamran University of AhvazAhvazIran Drilling Center of Excellence and Research Center Shahid Chamran University of AhvazAhvazIran

This article presents the results of experimental studies concerning the dynamic deformation and failure of a unidirectional carbon fiber reinforced plastic(T700/LY113)under compression.The test samples were manufactured through the filament winding of flat plates.To establish the strain rate dependencies of the strength and elastic modulus of the material,dynamic tests were carried out using a drop tower,the Split Hopkinson Pressure Bar method,and standard static tests.The samples were loaded both along and perpendicular to the direction of the reinforcing fiber.The applicability of the obtained samples for static and dynamic tests was confirmed through finite elementmodeling and the high-speed imaging of the deformation and failure of samples during testing.As a result of the conducted experimental studies,static and dynamic stress-strain curves,time dependencies of deformation and the stress and strain rates of the samples during compression were obtained.Based on these results,the strain rate dependencies of the strength and elasticity modulus in the strain rate range of 0.001-6001/s are constructed.It is shown that the strain rate significantly affects the strength and deformation characteristics of the unidirectional carbon fiber composites under compression.An increase in the strain rate by 5 orders of magnitude increased the strength and elastic modulus along the fiber direction by 42%and 50%,respectively.Perpendicular loading resulted in a strength and elastic modulus increase by 58%and 50%,respectively.The average strength along the fibers at the largest studied strain rate was about 1000MPa.The obtained results can be used to design structural elements made of polymer composite materials operating under dynamic shock loads,as well as to build models of mechanical behavior and failure criteria of such materials,taking into account the strain rate effects.

关键词： High strain rate composites filament winding Dynamic strength Split Hopkinson Pressure Bar compression

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System dynamics in structural strength and vibration fatigue life assessment of the swing bar for high‐speed maglev train

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International Journal of Mechanical System dynamics 2022年第2期2卷 178-189页

作者： Feng Guo Feifei Hu Shengchuan Wu Feng He Jianxin Liu Xingwen Wu State Key Laboratory of Traction Power Southwest Jiaotong UniversitySichuanChengduChina School of Mechanical Engineering Southwest Jiaotong UniversitySichuanChengduChina

High‐speed maglev trains are subjected to severe dynamic loads,thus posing a failure hazard.It is necessary to account for the vehicle dynamics to improve the structural strength and fatigue life assessment approach under harsh routes and super high‐speed grades.As the most critical load‐carrying part between the vehicle body and levitation frames,the swing bar was taken as an example to demonstrate the significance of vehicle dynamics to integrate classical structural strength and fatigue life with the service conditions.A multiphysics‐coupled dynamic model of an alpha improvement scheme for an electromagnetic suspension maglev train capable of 600 km/h was established to investigate the complex dynamic loads and fatigue spectra.Using this model,the structural strength and fatigue life of the wrought swing bars were investigated.Results show only a slight effect on the structural strength and fatigue life of swing bars by the super high‐speed grades.The nonaxial bending moments caused by the uncompensated relative displacement between the vehicle body and bolsters are identified as the decisive factors.The minimum safety factor of the structural strength for wrought swing bars is 1.33,while the minimum fatigue life is 34 years.Both match the design requirements but are not conservative enough.Therefore,further verification and optimization are recommended to improve the design of swing bars.

关键词： vibration fatigue life Dynamic strength levitation frame high‐speed maglev train time‐domain stepwise fatigue assessment(TSFA)

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Investigation of the influence of intermediate principal stress on the dynamic responses of rocks subjected to true triaxial stress state

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International Journal of Mining Science and Technology 2021年第5期31卷 913-926页

作者： Wei You Feng Dai Yi Liu Hongbo Du Ruochen Jiang State Key Laboratory of Hydraulics and Mountain River Engineering College of Water Resource and HydropowerSichuan UniversityChengdu 610065China

Precisely understanding the dynamic mechanical properties and failure modes of rocks subjected to true triaxial stress state(σ1>σ2>σ3,whereσ1,σ2,andσ3 are the major principal stress,intermediate principal stress,and minor principal stress,respectively)is essential to the safety of underground engineering.However,in the laboratory,it is difficult to maintain the constant true triaxial stress state of rocks during the dynamic testing process.Herein,a numerical servo triaxial Hopkinson bar(NSTHB)was developed to study the dynamic responses of rocks confronted with a true triaxial stress state,in which lateral stresses can maintain constant.The results indicate that the Dynamic strength and elastic modulus of rocks increase with the rise of intermediate principal stressσ2,while the dynamic elastic modulus is independent of the dynamic strain rate.Simulated acoustic emission distributions indicate that the intermediate principal stressσ2 dramatically affects dynamic failure modes of triaxial confined rocks.Asσ2 increases,the failure pattern switches from a single diagonal shear zone into two parallel shear zones with a small slant.Moreover,a recent triaxial Hopkinson bar experimental system using three bar pairs is also numerically established,and the measuring discrepancies are identified between the two numerical bar systems.The proposed NSTHB system provides a controllable tool for studying the dynamic triaxial behavior of rocks.

关键词： Triaxial Hopkinson bar Intermediate principal stress Dynamic strength Failure modes Numerical simulation True triaxial stress

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dynamic failure of dry and fully saturated limestone samples based on incubation time concept

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Journal of Rock Mechanics and Geotechnical Engineering 2017年第1期9卷 125-134页

作者： Yuri V. Petrov Ivan V. Smirnov Grigory A. Volkov Andrei K. Abramian Anatoliy M. Bragov Stanislav N. Verichev Saint Petersburg University Universitetskaya nab. 7-9 Saint Petersburg 199034 Russia Institute of Problems of Mechanical Engineering Russian Academy of Sciences Bolshoj pr. 61 V.O. Saint Petersburg 199178 Russia Lobachevsky State University of Nizhni Novgorod Prospekt Gagarina 23 Nizhny Novgorod 603950 Russia Allseas Engineering B.V. Poortweg 12 Delft 2612 PA The Netherlands

This paper outlines the results of experimental study of the dynamic rock failure based on the comparison of dry and saturated limestone samples obtained during the dynamic compression and split tests. The tests were performed using the Kolsky method and its modifications for dynamic splitting. The mechanical data(e.g. strength, time and energy characteristics) of this material at high strain rates are obtained. It is shown that these characteristics are sensitive to the strain rate. A unified interpretation of these rate effects, based on the structuraletemporal approach, is hereby presented. It is demonstrated that the temporal dependence of the dynamic compressive and split tensile strengths of dry and saturated limestone samples can be predicted by the incubation time criterion. Previously discovered possibilities to optimize(minimize) the energy input for the failure process is discussed in connection with industrial rock failure processes. It is shown that the optimal energy input value associated with critical load, which is required to initialize failure in the rock media, strongly depends on the incubation time and the impact duration. The optimal load shapes, which minimize the momentum for a single failure impact, are demonstrated. Through this investigation, a possible approach to reduce the specific energy required for rock cutting by means of high-frequency vibrations is also discussed.

关键词： Dynamic strength Incubation time criterion Split Hopkinson pressure bar(SHPB) test Tensile strength Compressive strength Water-saturated limestone Vibration-assisted rock cutting

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Effect of Cyclic Loading Frequency on Undrained Behaviors of Undisturbed Marine Clay

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海洋工程：英文版 2004年第4期18卷 643-651页

作者：陈云敏姬美秀黄博 Geotechnical Institute Zhejiang University Hangzhou 310027 China

Based on a series of cyclic triaxial tests, the effect of cyclic frequency on the undrained behaviors of undisturbed marine clay is investigated. For a given dynamic stress ratio, the accumulated pore water pressure and dynamic strain increase with the number of cycles. There exists a threshold value for both the accumulated pore water pressure and dynamic strain, below which the effect of cyclic frequency is very small, but above which the accumulated pore water pressure and dynamic strain increase intensely with the decrease of cyclic frequency for a given number of cycles. The Dynamic strength increases with the increase of cyclic frequency, whereas the effect of cyclic frequency on it gradually diminishes to zero when the number of cycles is large enough, and the Dynamic strengths at different frequencies tend to the same limiting minimum Dynamic strength. The test results demonstrate that the reasons for the frequency effect on the undrained soil behaviors are both the creep effect induced by the loading rate and the decrease of sample effective confining pressure caused by the accumulated pore water pressure.

关键词： cyclic triaxial test undisturbed marine clay effect of cyclic frequency dynamic strain pore water pressure Dynamic strength creep effect

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