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Material embrittlement in high strain-rate loading 被引量:10
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作者 Xiuxuan Yang Bi Zhang 《International Journal of Extreme Manufacturing》 2019年第2期53-71,共19页
Material embrittlement is often encountered in machining,heat treatment,hydrogen and lowtemperature conditions among which machining is strain-rate related.More strain-rate evoked embrittlement is expected in material... Material embrittlement is often encountered in machining,heat treatment,hydrogen and lowtemperature conditions among which machining is strain-rate related.More strain-rate evoked embrittlement is expected in material loading processes,such as in high-speed machining and projectile penetration.In order to understand the fundamental mechanisms of the strain-rate evoked material embrittlement,this study is concerned with the material responses to loading at high strain-rates.It then explores the strain-rate evoked material embrittlement and fragmentation during high strain-rate loading processes and evaluates various empirical and physical models from different researchers for the assessment of the material embrittlement.The study proposes strain-rate sensitivity for the characterization of material embrittlement and the concept of the pseudo embrittlement for material responses to very high strain-rates.A discussion section is arranged to explore the underlying mechanisms of the strain-rate evoked material embrittlement and fragmentation based on dislocation kinetics. 展开更多
关键词 EMBRITTLEMENT strain rate strain-rate sensitivity DISLOCATION
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Strain-rate Sensitivity of Aluminum 2024-T6/TiB_2 Composites and Aluminum 2024-T6 被引量:1
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作者 朱德智 郑振兴 CHEN Qi 《Journal of Wuhan University of Technology(Materials Science)》 SCIE EI CAS 2015年第2期256-260,共5页
Strain-rate sensitivities of 55vol%-65vol% aluminum 2024-T6/TiB2 composites and the corresponding aluminum 2024-T6 matrix were investigated using split Hopkinson pressure bar method. The experimental results showed th... Strain-rate sensitivities of 55vol%-65vol% aluminum 2024-T6/TiB2 composites and the corresponding aluminum 2024-T6 matrix were investigated using split Hopkinson pressure bar method. The experimental results showed that 55vol%-65vol% aluminum 2024-T6/TiB2 composites exhibited significant strain-rate sensitivities, which were three times higher than the strain-rate sensitivity of the aluminum 2024-T6 matrix. The strain-rate sensitivity of the aluminum 2024-T6 matrix composites rose obviously with increasing reinforcement content(up to 60%), which agreed with that from the previous researches. But it decreased as the ceramic reinforcement content reached 65%. After high strain rates compression, a large number of dislocations and micro-cracks were found inside the matrix and the Ti B2 particles, respectively. These micro-cracks can accelerate the brittle fracture of the composites. The aluminum 2024-T6/Ti B2 composites showed various fracture characteristics and shear instability was the predominant failure mechanism under dynamic loading. 展开更多
关键词 composite materials mechanical properties dynamic compression strain-rate sensitivity
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PRINCIPAL COMPONENT DECOMPOSITION BASED FINITE ELEMENT MODEL UPDATING FOR STRAIN-RATE-DEPENDENCE NONLINEAR DYNAMIC PROBLEMS 被引量:1
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作者 GUO Qintao ZHANG Lingmi TAO Zheng 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2008年第5期70-74,共5页
Thin wail component is utilized to absorb impact energy of a structure. However, the dynamic behavior of such thin-walled structure is highly non-linear with material, geometry and boundary non-linearity. A model upda... Thin wail component is utilized to absorb impact energy of a structure. However, the dynamic behavior of such thin-walled structure is highly non-linear with material, geometry and boundary non-linearity. A model updating and validation procedure is proposed to build accurate finite element model of a frame structure with a non-linear thin-walled component for dynamic analysis. Design of experiments (DOE) and principal component decomposition (PCD) approach are applied to extract dynamic feature from nonlinear impact response for correlation of impact test result and FE model of the non-linear structure. A strain-rate-dependent non-linear model updating method is then developed to build accurate FE model of the structure. Computer simulation and a real frame structure with a highly non-linear thin-walled component are employed to demonstrate the feasibility and effectiveness of the proposed approach. 展开更多
关键词 strain-rate-dependent Finite element model updating Nonlinear dynamics Response surface
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Effects of Calcium and Yttrium on Microstructure and Mechanical Properties of High Strain-Rate Rolled AZ91D Magnesium Alloy
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作者 SHEN Yanjin 《Journal of Donghua University(English Edition)》 EI CAS 2018年第2期149-153,共5页
Effects of calcium( Ca) and yttrium( Y) on microstructure and mechanical properties of high strain-rate rolled AZ91 D magnesium alloy were studied. High strain-rate rolling can improve the strength and plasticity of m... Effects of calcium( Ca) and yttrium( Y) on microstructure and mechanical properties of high strain-rate rolled AZ91 D magnesium alloy were studied. High strain-rate rolling can improve the strength and plasticity of magnesium alloy sheets.Additions of Ca and Y into AZ91 D can refine grains and modify the size and the distribution of the precipitated phases. After solution treatment( 418 ℃ and 20 h) and high strain-rate rolling( heating at420 ℃ for 10 min firstly and then rolling from 10 mm to 2 mm in thickness via a single pass),the tensile strength of the AZ91 D-0. 2%Ca alloy was 1. 3% higher than that of the AZ91 D-0. 4 D%Y alloy,and the tensile strength of the AZ91 D-0. 2%Ca-0. 4%Y alloy was about 8. 3% and 6. 9% higher than those of the AZ91 D-0. 4%Y and the AZ91 D-0. 2%Ca alloys respectively. 展开更多
关键词 HIGH strain-rate rolling magnesium alloy microstructure mechanical properties TENSILE strength GRAIN size
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A QUASI-FLOW CONSTITUTIVE MODEL WITH STRAIN-RATE DEPENDENCE
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作者 胡平 申国哲 杨光 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2004年第3期283-291,共9页
In this paper,the proposed is a quasi-flow constitutive model with strain-rate sen- sitivity for elastic plastic large deformation.The model is based on the Quasi-flow Corner theory, and is suitable for the sheet meta... In this paper,the proposed is a quasi-flow constitutive model with strain-rate sen- sitivity for elastic plastic large deformation.The model is based on the Quasi-flow Corner theory, and is suitable for the sheet metal forming process simulation with a variable punch machine velocity. Uniaxial tensile tests and deep-drawing tests of a circular blank with square punch are carried out and numerically simulated.The consistency between the experimental and the numerically simulated results shows the validity of the present new constitutive model. 展开更多
关键词 strain-rate sensitivity quasi-flow constitutive model sheet metal forming
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Advanced test methods of material property characterization:high strain-rate testing and experimental simulation of multiaxial stress states
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作者 Reinhard BARDENHEIER 《Baosteel Technical Research》 CAS 2010年第S1期122-,共1页
Optimum utilization of the loading capability of engineering materials is an important and active contribution to protect nature's limited resources,and it is the key for economic design methods.In order to make u... Optimum utilization of the loading capability of engineering materials is an important and active contribution to protect nature's limited resources,and it is the key for economic design methods.In order to make use of the materials' resources,those must be known very well;but conventional test methods will offer only limited informational value.The range of questions raised is as wide as the application of engineering materials,and partially they are very specific.The development of huge computer powers enables numeric modelling to simulate structural behaviour in rather complex loading environments-so the real material behaviour is known under the given loading conditions.Here the art of material testing design starts.To study the material behaviour under very distinct and specific loading conditions makes it necessary to simulate different temperature ranges,loading speeds, environments etc.and mostly there doesn't exist any commonly agreed test standard.In this contribution two popular,non-standard test procedures and test systems will be discussed on the base of their application background,special design features as well as test results and typically gained information:The demand for highspeed tests up to 1000 s^(-1) of strain rate is very specific and originates primarily in the automotive industry and the answers enable CAE analysis of crashworthiness of vehicle structures under crash conditions.The information on the material behaviour under multiaxial loading conditions is a more general one.Multiaxial stress states can be reduced to an equivalent stress,which allows the evaluation of the material's constraint and criticality of stress state.Both discussed examples shall show that the open dialogue between the user and the producer of testing machines allows custom-tailored test solutions. 展开更多
关键词 economic design numeric modelling simulation high strain-rate testing strain- rate sensitivity CRASHWORTHINESS multiaxial stress state material constraint equivalent stress state
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A revisit of strain-rate frequency superposition of dense colloidal suspensions under oscillatory shears
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作者 李俊杰 程璇 +1 位作者 张颖 孙尉翔 《Journal of Central South University》 SCIE EI CAS CSCD 2016年第8期1873-1882,共10页
Strain-rate frequency superposition(SRFS) is often employed to probe the low-frequency behavior of soft solids under oscillatory shear in anticipated linear response. However, physical interpretation of an apparently ... Strain-rate frequency superposition(SRFS) is often employed to probe the low-frequency behavior of soft solids under oscillatory shear in anticipated linear response. However, physical interpretation of an apparently well-overlapped master curve generated by SRFS has to combine with nonlinear analysis techniques such as Fourier transform rheology and stress decomposition method. The benefit of SRFS is discarded when some inconsistencies of the shifted master curves with the canonical linear response are observed. In this work, instead of evaluating the SRFS in full master curves, two criteria were proposed to decompose the original SRFS data and to delete the bad experimental data. Application to Carabopol suspensions indicates that good master curves could be constructed based upon the modified data and the high-frequency deviations often observed in original SRFS master curves are eliminated. The modified SRFS data also enable a better quantitative description and the evaluation of the apparent structural relaxation time by the two-mode fractional Maxwell model. 展开更多
关键词 strain-rate frequency superposition medium amplitude oscillatory shear linear viscoelasticity fractional Maxwell model
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Energy Absorption of Pultruded Glass-Graphite/Epoxy Hybrid Composites under High Strain-Rate Induced Transverse Tension
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作者 Damian Stoddard Suman Babu Ukyam +1 位作者 R. Mantena Prabhakar Arunachalam Rajendran 《Open Journal of Composite Materials》 2018年第2期43-53,共11页
This paper focuses on the dynamic tensile response of glass-graphite/epoxy composites illustrating improvement in energy absorption through hybridization. The dynamic response and energy absorption characteristics of ... This paper focuses on the dynamic tensile response of glass-graphite/epoxy composites illustrating improvement in energy absorption through hybridization. The dynamic response and energy absorption characteristics of pultruded hybrid combinations of glass and graphite fibers in an epoxy matrix subjected to induced transverse tension at high strain-rate in a modified Split Hopkinson Pressure Bar (SHPB) apparatus, are presented. Transverse tensile strength was determined by diametral compression of disc samples (Brazilian indirect tensile test method). Diametral crack initiation and strain to failure were monitored with a Shimadzu HPV-2 high-speed video camera at a recording speed of 500,000 fps and Digital Image Correlation (DIC). Adequate measures were taken to ensure that initiation of specimen failure occurred at the exact center of the disc specimen, and propagated through the diameter along the compressive loading axis, for the induced transverse tension tests to be valid. A study of the strength and specific energy absorption demonstrates the benefits of hybridization. Under induced transverse tensile loading condition, the pure glass/epoxy (GL60) exhibited higher strength than pure graphite/epoxy (GR60). Pure graphite/epoxy (GR60) has higher specific energy absorption capacity than pure glass/epoxy (GL60) in transverse tension. Among all hybrids, GR30 has the highest specific energy absorption under transverse tension. Overall, hybrid GL48, with 48% low-cost glass fibers in the inner core and 12% high-cost graphite fibers in outer shell, was found to exhibit better performance under induced transverse tension at high strain-rates, showing the benefits of hybridization. 展开更多
关键词 Pultruded Composites HYBRIDS HIGH strain-rate SHPB Dynamic Energy Absorption BRAZILIAN Disc Indirect Tensile Test
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Dynamic Response of Pultruded Glass-Graphite/Epoxy Hybrid Composites Subjected to Transverse High Strain-Rate Compression Loading
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作者 Mohammad Afrough Tejas S. Pandya +1 位作者 Seyed Soheil Daryadel Prabhakar Raju Mantena 《Materials Sciences and Applications》 2015年第11期953-962,共10页
In a previous study, the energy absorption and dynamic response of different combinations of cylindrical fiber-reinforced pultruded hybrid composite samples made of unidirectional glass and graphite fiber/epoxy, were ... In a previous study, the energy absorption and dynamic response of different combinations of cylindrical fiber-reinforced pultruded hybrid composite samples made of unidirectional glass and graphite fiber/epoxy, were investigated under longitudinal compression loading. It was found that placing glass fibers in the inner core of composites resulted in a higher ultimate compressive strength and specific energy absorption. In this study, the dynamic responses of pultruded glass-graphite/epoxy hybrid specimens with rectangular cross-section subjected to transverse compression loading are reported. Crack initiation and propagation was monitored using a high-speed video camera, and the effects of hybridization were analyzed. It was found that the location of glass or graphite fibers inside the pultruded composites has no significant effect on the ultimate compressive strength under such transverse compression loading. The energy absorption in all the hybrid specimens was almost identical. Graphite/epoxy composite showed higher specific energy absorption due to its lower density, and glass/epoxy composite had the lowest specific energy absorption. 展开更多
关键词 Pultruded Composites HIGH strain-rate Compression Loading SHPB Energy Absorption TRANSVERSE Loadings
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Dynamic recrystallization of electroformed copper liners of shaped charges in high-strain-rate plastic deformation
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作者 WenhuaiTian QiSun 《Journal of University of Science and Technology Beijing》 CSCD 2002年第5期343-346,共4页
The microstructures in the electroformed copper liners of shapedcharges after high-strain-rate plastic deformation were in-vestigated by transmission electron microscopy(TEM). Meanwhile, theorientation distribution of... The microstructures in the electroformed copper liners of shapedcharges after high-strain-rate plastic deformation were in-vestigated by transmission electron microscopy(TEM). Meanwhile, theorientation distribution of the grains in the recovered slug wasexamined by the electron backscattering Kikuchipattern(EBSP)technique. EBSP analysis illustrated that unlike theas-formed electro- formed copper liners of shaped charges the grainorientations in the recovered slug are distributed along randomly allthe directions after undergoing heavily strain deformation athigh-strain rate. Optical microscopy shows a typicalrecrystallization structure, and TEM exam- ination revealsdislocation cells existed in the thin foil specimen. These resultsindicate that dynamic recovery and recrystallization occur duringthis plastic deformation process, and the associated deformationtemperature is considered to be higher than 0.6 times the meltingpoint of copper. 展开更多
关键词 ELECTROFORMATION high-strain-rate deformation dynamic recovery andrecrystallization transmission electron microscopy
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MICROSTRUCTURAL CHARACTERISTICS ASSOCIATED WITH HIGH- STRAIN-RATE PLASTIC DEFORMATION IN THE ELECTROFORMED COPPER LINER OF SHAPED CHARGES 被引量:4
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作者 A.L. Fan W.H. Tian +1 位作者 Q. Suns B.S. Wang 《Acta Metallurgica Sinica(English Letters)》 SCIE EI CAS CSCD 2005年第5期620-626,共7页
The microstructures of electroformed copper liners of shaped charges that had undergone high-strain-rate deformation were observed by optical microscopy (OM) and scanning electron microscopy (SEM). Meanwhile, the ... The microstructures of electroformed copper liners of shaped charges that had undergone high-strain-rate deformation were observed by optical microscopy (OM) and scanning electron microscopy (SEM). Meanwhile, the orientation distribution of the grains in the recovered jet was examined by electron backscattering Kikuchi pattern (EBSP) technique. EBSP analysis reveals that the fibrous texture observed in the as-electroformed copper liners disappeared after explosive detonation deformation. OM observation shows that the microstructure evolves system- atically from the jet center to its perimeter during cooling from high temperatures after explosive detonation deformation. This microstructural characteristic is similar to that of solidification, i.e. there exist equiaxed grains in the center of the jet and significant columnar grains around the equiaxed grains. The result reveals that there is melting-related phenomenon in the jet center. Corresponding microhardness variations from the jet center to its perimeter is also determined. All the phenomena can be explained by a strong gradient of temperature across the section of the jet during plastic deformation at high-strain-rate. 展开更多
关键词 JETTING ELECTROFORMATION microstructure hardness ultra-high strain rate deformation
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Comparison of microstructures in electroformed and spin-formed copper liners of shaped charge undergone high-strain-rate deformation 被引量:4
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作者 范爱玲 李树奎 +1 位作者 田文怀 王富耻 《中国有色金属学会会刊:英文版》 EI CSCD 2007年第6期1447-1450,共4页
The as-formed and post-deformed microstructures in both electroformed and spin-formed copper liners of shaped charge were studied by optical microscopy(OM), electron backscattering Kikuchi patterns(EBSP) technique and... The as-formed and post-deformed microstructures in both electroformed and spin-formed copper liners of shaped charge were studied by optical microscopy(OM), electron backscattering Kikuchi patterns(EBSP) technique and transmission electron microscopy(TEM). The deformation was carried out at an ultra-high strain rate. OM analysis shows that the initial grains of the electroformed copper liner are finer than those of the spin-formed copper liners. Meanwhile, EBSP analysis reveals that the fiber texture exists in the electroformed copper liners, whereas there is no texture observed in the spin-formed copper liners before deformation. Having undergone high-strain-rate deformation the grains in the recovered slugs, which are transformed from both the electroformed and spin-formed copper liners, all become small. TEM observations of the above two kinds of post-deformed specimens show the existence of cellular structures characterized by tangled dislocations and subgrain boundaries consisting of dislocation arrays. These experimental results indicate that dynamic recovery and recrystallization play an important role in the high-strain-rate deformation process. 展开更多
关键词 微观结构 高疲劳率变形 动态恢复
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Comparison of the historic seismicity and strain-rate pattern from a dense GPS-GNSS network solution in the Italian Peninsula 被引量:3
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作者 Giuseppe Casula Maria Giovanna Bianchi 《Geodesy and Geodynamics》 2016年第5期303-316,共14页
We present a dense crustal velocity field and corresponding strain-rate pattern computed using Global Positioning System(GPS)- Global Navigation Satellite System(GNSS) data from several hundred permanent stations ... We present a dense crustal velocity field and corresponding strain-rate pattern computed using Global Positioning System(GPS)- Global Navigation Satellite System(GNSS) data from several hundred permanent stations in the Italian Peninsula. GPS data analysis is based on the GAMIT/GLOBK 10.6 software, which was developed and maintained mainly by Massachusetts Institute of Technology(MIT), using tools based on the distributed-sessions approach implemented in this package. The GPS data span the period from January 2008 to December 2012 and come from several different permanent GPS networks in Italy. The GLOBK package implemented in the last version of the GAMIT package is used to compute the position time-series and velocities registered in the International Terrestrial Reference Frame(ITRF) 2008. The resulting high-density intra-plate velocity field provides indications of the tectonics of the Mediterranean region. A computation of the strain-rate pattern from GPS data is performed and compared with the map of the epicentral locations of historical earthquakes that occurred in the last 1000 years in the Italian territory, showing that, in general, higher crustal deformation rates are active in regions affected by seismicity of greater magnitude. 展开更多
关键词 GPS Strain rate Distributed sessions TECTONICS
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Strain-rate effect on initial crush stress of irregular honeycomb under dynamic loading and its deformation mechanism 被引量:4
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作者 Peng Wang Zhijun Zheng +1 位作者 Shenfei Liao Jilin Yu 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2018年第1期117-129,共13页
The seemingly contradictory understandings of the initial crush stress of cellular materials under dynamic loadings exist in the literature, and a comprehensive analysis of this issue is carried out with using direct ... The seemingly contradictory understandings of the initial crush stress of cellular materials under dynamic loadings exist in the literature, and a comprehensive analysis of this issue is carried out with using direct information of local stress and strain. Local stress/strain calculation methods are applied to determine the initial crush stresses and the strain rates at initial crush from a cell-based finite element model of irregular honeycomb under dynamic loadings. The initial crush stress under constant-velocity compression is identical to the quasi-static one, but less than the one under direct impact, i.e. the initial crush stresses under different dynamic loadings could be very different even though there is no strain-rate effect of matrix material. A power-law relation between the initial crush stress and the strain rate is explored to describe the strain-rate effect on the initial crush stress of irregular honeycomb when the local strain rate exceeds a critical value, below which there is no strain-rate effect of irregular honeycomb. Deformation mechanisms of the initial crush behavior under dynamic loadings are also explored.The deformation modes of the initial crush region in the front of plastic compaction wave are different under different dynamic loadings. 展开更多
关键词 Cellular material Constant-velocity compression Direct impact Cross-sectional stress Initial crush stress Strain rate effect
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Effects of grain size and Al addition on the activation volume and strain-rate sensitivity of CoCrFeMnNi high-entropy alloy
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作者 H.T.Jeong W.J.Kim 《Journal of Materials Science & Technology》 SCIE EI CAS CSCD 2023年第12期242-252,共11页
The activation volume(V∗)and strain-rate sensitivity exponent(m)of CoCrFeMnNi and Al_(0.5)CoCrFeMnNi high entropy alloys(HEAs)with various grain sizes(ranging between 2.4 and 356μm)were measured at different strain r... The activation volume(V∗)and strain-rate sensitivity exponent(m)of CoCrFeMnNi and Al_(0.5)CoCrFeMnNi high entropy alloys(HEAs)with various grain sizes(ranging between 2.4 and 356μm)were measured at different strain rates and strain levels at room temperature.As the strain rate decreased,the plastic strain decreased,and the grain size increased,V∗increased.The enhanced solid-solution strengthening by addition of aluminum decreased V∗.The Hassen plot was modified to capture the grain-size depen-dence of V∗by considering the grain-size dependence of the dislocation density.As the plastic strain increased,the strain rate decreased,and the grain size decreased,m decreased.The behavior of m could be quantitatively predicted by using equations derived for the grain-size-dependent V∗and flow stress.The difference in the grain-size dependence of m between conventional face centered cubic(FCC)metals and FCC HEAs over the nanograin size range could not be explained in terms of a relatively large Hall-Petch slope of the FCC HEAs compared with that of the FCC conventional metals,but was explainable in terms of a substantially higher probability of activation of grain-boundary diffusion-controlled grain-boundary-sliding mechanism at nanograin sizes in the FCC conventional metals than in the FCC HEAs. 展开更多
关键词 Grain size High entropy alloys Activation volume strain-rate sensitivity Solid solution
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Early Detection of Regional and Global Left Ventricular Myocardial Function Using Strain and Strain-rate Imaging in Patients with Metabolic Syndrome 被引量:6
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作者 QinWang Qi-Wei Sun +7 位作者 Dan Wu Ming-Wu Yang Rong-Juan Li Bo Jiang Jiao Yang Zhi-An Li YingWang Ya Yang 《Chinese Medical Journal》 SCIE CAS CSCD 2015年第2期226-232,共7页
Background:Strain and strain-rate imaging (SRI) have been found clinically useful in the assessment of cardiac systolic and diastolic function as well as providing new insights in deciphering cardiac physiology and... Background:Strain and strain-rate imaging (SRI) have been found clinically useful in the assessment of cardiac systolic and diastolic function as well as providing new insights in deciphering cardiac physiology and mechanics in cardiomyopathies,and identifying early subclinical changes in various pathologies.The aim of this study was to evaluate the regional and global left ventricular (LV) myocardial function in metabolic syndrome (MS) with SRI so that we can provide more myocardial small lesions in patients with MS,which is robust and reliable basis for early detection of LV function.Methods:Thirty-nine adults with MS were enrolled in the study.There was a control group of 39 healthy adults.In addition to classic echocardiographic assessment of LV global functional changes,SRI was used to evaluate regional and global LV function.Including:Peak systolic strain (S),peak systolic strain-rate (SR-s),peak diastolic strain-rate (SR-e).Results:There were no statistically significant differences between MS and controls in all traditional parameters of LV systolic function.On the other hand,significant differences were observed between MS and the control group in most of the parameters of S,SR-s,SR-e in regional LV function.Multiple stepwise regression analyses revealed that S and SR significantly were negatively correlated with blood pressure,waist circumference,fasting plasma glucose,uric acid,suggesting that risk factories were relevant to regional systolic dysfunction.Conclusion:In MS with normal LV ejection fraction,there was regional myocardial dysfunction,risk factors contributed to the impairment of systolic and diastolic function of the regional myocardium.Assessment of myocardial function using SRI could be more accurate in MS patient evaluation than conventional echocardiography alone. 展开更多
关键词 Metabolic Syndrome Regional Left Ventricular Function Strain and strain-rate Imaging
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Unveiling the underlying mechanism of forming edge cracks upon high strain-rate rolling of magnesium alloy 被引量:5
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作者 Biwu Zhu Xiao Liu +4 位作者 Chao Xie Jing Su Pengcheng Guo Changping Tang Wenhui Liu 《Journal of Materials Science & Technology》 SCIE EI CAS CSCD 2020年第15期59-65,共7页
In the current study,high strain-rate rolling(≥10 s-1) has been successfully employed to produce Mg-3 A1-1 Zn alloy sheets to a high reduction of 82% with a fine grain structure in a single pass.The underlying mechan... In the current study,high strain-rate rolling(≥10 s-1) has been successfully employed to produce Mg-3 A1-1 Zn alloy sheets to a high reduction of 82% with a fine grain structure in a single pass.The underlying mechanism of forming primary and secondary edge cracks has been investigated.It is found that dynamic recrystallization(DRX) induced by subgrains tends to blunt cracks,while twinning-induced D RX is mainly observed around sharp crack tips.The motion of emitted dislocations from blunted cracks is inhibited by the DRX grain boundaries.This,on one hand,increases local work hardening,and on the other hand,causes stress concentration alo ng grain boundaries especially in the triple junctions leading to the formation of secondary cracks. 展开更多
关键词 Edge crack Secondary crack High strain-rate rolling AZ31 magnesium alloy Dynamic recrystallization
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Experimental study of dynamic mechanical properties of reactive powder concrete under high-strain-rate impacts 被引量:8
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作者 JU Yang1,2,LIU HongBin1,SHENG GuoHua1,3 & WANG HuiJie1 1 State Key Laboratory of Coal Resources and Safe Mining,Beijing Key Laboratory of Fracture and Damage Mechanics of Rocks and Concrete,China University of Mining and Technology,Beijing 100083,China 2 Department of Mechanical and Manufacturing Engineering,University of Calgary,2500 University Drive,AB T2N 1N4,Canada 3 School of Resources and Civil Engineering,Northeastern University,Shenyang 110004,China 《Science China(Technological Sciences)》 SCIE EI CAS 2010年第9期2435-2449,共15页
The dynamic mechanical properties of reactive powder concrete subjected to compressive impacts with high strain rates ranging from 10 to 1.1×102 s-1 were investigated by means of SHPB (split-Hopkinson-pressure-ba... The dynamic mechanical properties of reactive powder concrete subjected to compressive impacts with high strain rates ranging from 10 to 1.1×102 s-1 were investigated by means of SHPB (split-Hopkinson-pressure-bar) tests of the cylindrical specimens with five different steel fiber volumetric fractions.The properties of wave stress transmission,failure,strength,and energy consumption of RPC with varied fiber volumes and impact strain rates were analyzed.The influences of impact strain rates and fiber volumes on those properties were characterized as well.The general forms of the dynamic stress-strain relationships of RPC were modeled based on the experimental data.The investigations indicate that for the plain RPC the stress response is greater than the strain response,showing strong brittle performance.The RPC with a certain volume of fibers sustains higher strain rate impact and exhibits better deformability as compared with the plain RPC.With a constant fiber fraction,the peak compressive strength,corresponding peak strain and the residual strain of the fiber-reinforced RPC rise by varying amounts when the impact strain rate increases,with the residual strain demonstrating the greatest increment.Elevating the fiber content makes trivial contribution to improving the residual deformability of RPC when the impact strain rate is constant.The tests also show that the fiber content affects the peak compressive strength and the peak deformability of RPC in a different manner.With a constant impact strain rate and the fiber fraction less than 1.75%,the peak compressive strength rises with an increasing fiber volume.The peak compressive strength tends to decrease as the fiber volume exceeds 1.75%.The corresponding peak strain,however,incessantly rises with the increasing fiber volume.The total energy Edisp that RPC consumed during the period from the beginning of impacts to the time of residual strains elevates with the fiber volume increment as long as the fiber fraction is not larger than 2%.It turns to decrease if the fiber volume exceeds 2%.The added fibers make various contributions to enhancing the capability of RPC to consume energy at different loading stages.If the fiber fraction is not larger than 2%,the added fibers make more contribution to enhancing the energy consumption ability of RPC in the period before the peak strain than in the period after the peak strain.The impact strain rate,however,distinctively affects the total energy that RPC consumed and the energy consumed in the different loading periods.The higher the impact strain rate,the more the energy consumed in the stages and therefore the higher the dynamic impact toughness.The empirical relationships of the peak compressive strength,corresponding peak strain,residual strain,total consumed energy and the energy consumed in the varied periods with the impact strain rate and the fiber fraction are derived.Four generalized forms of the dynamic impact stress-strain responses of RPC are formulated by normalizing stresses and strains as the generalized coordinates and by taking account of the influences of impact strain rates and fiber volumetric fractions. 展开更多
关键词 impact REACTIVE powder concrete (RPC) high strain rate DYNAMIC strength energy CONSUMPTION DYNAMIC STRESS-STRAIN response
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高温高应变率下钛合金Ti6Al4V的动态力学行为及本构关系 被引量:2
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作者 杨东 姜紫薇 郑志军 《高压物理学报》 CAS CSCD 北大核心 2024年第1期74-84,共11页
采用分离式霍普金森压杆实验技术,研究了钛合金Ti6Al4V在温度为25~800℃、应变速率为2 000~7 000 s-1的冲击压缩下的动态力学行为和微观组织演变,分析了其力学响应的温度依赖性和应变率敏感性,构建了可准确表征材料塑性流动行为的修正Jo... 采用分离式霍普金森压杆实验技术,研究了钛合金Ti6Al4V在温度为25~800℃、应变速率为2 000~7 000 s-1的冲击压缩下的动态力学行为和微观组织演变,分析了其力学响应的温度依赖性和应变率敏感性,构建了可准确表征材料塑性流动行为的修正Johnson-Cook模型。结果表明,Ti6Al4V具有显著的应变硬化、应变率强化、应变率增塑和温度软化效应。随着加载温度和应变率的升高,材料的应变硬化效应减弱。温度敏感性随加载温度的升高而显著降低。应变率敏感性因子与加载温度呈负相关,随真实应变的增大呈下降趋势。高温高应变率下细小等轴α相、拉长型α相和块状α相取代初始等轴α相成为Ti6Al4V微观组织的典型特征。考虑率-温耦合作用和绝热温升影响的修正Johnson-Cook模型能够准确地预测Ti6Al4V的塑性流动应力-应变响应。 展开更多
关键词 高温 高应变率 钛合金 动态力学行为 本构关系 Johnson-Cook模型
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泸定M S6.8地震震前变形特征及鲜水河断裂南东段地震活动性 被引量:1
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作者 申星 梁洪宝 宋成科 《大地测量与地球动力学》 CSCD 北大核心 2024年第1期69-74,共6页
针对鲜水河断裂带南东段的历史地震活动性和近10 a该断裂带上发生的中小震群展布特征,利用GNSS观测数据给出2022年泸定M S6.8地震震源区及周边区域的速度场、应变率场,识别此次地震震前的变形特征。GNSS速度场显示,鲜水河断裂带南东段... 针对鲜水河断裂带南东段的历史地震活动性和近10 a该断裂带上发生的中小震群展布特征,利用GNSS观测数据给出2022年泸定M S6.8地震震源区及周边区域的速度场、应变率场,识别此次地震震前的变形特征。GNSS速度场显示,鲜水河断裂带南东段走滑速率约为10 mm/a,区域整体运动为ES向,与断裂构造运动具有一致性;应变率场结果显示,发震断裂仍存在较强的剪切应变积累,汶川特大地震后随着应变能不断释放,龙门山断裂带的卸载作用间接影响鲜水河断裂带的南东段,该断裂长期处于应变积累高值的过渡区,现今仍具有较高的断层闭锁状态,该地区的地震活动趋势和地震危险性值得进一步关注和研究。 展开更多
关键词 泸定6.8级地震 鲜水河断裂带 地震活动性 应变率场
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