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1.
《原子与分子物理学报》2020,(4)
本文采用分子动力学模拟研究了FeCoCrCuNi高熵合金裂纹和孔洞结构在不同轴向拉伸速率下的力学与微观结构演化机理.结果表明:应变速率越高FeCoCrCuNi裂纹结构对应更高的过冲应变和过冲应力,其主要原因是高拉伸速率会导致高强度的BCC结构及孪晶结构的生成,而BCC结构及孪晶结构的产生进而会抑制应力的下降,通过应力-应变曲线,可知FeCoCrCuNi裂纹模型在轴向应力作用下表现为塑性形变.对于不同尺寸的孔洞FeCoCrCuNi裂纹模型的应力结构分析,可以得出:孔洞尺寸越大, FeCoCrCuNi裂纹结构对应的过冲应变和过冲应力越小,其主要原因是大尺寸的孔洞造成孔洞之间产生裂纹的,进而会影响这个材料的屈服应变和屈服强度. 相似文献
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本文采用分子动力学方法研究了FeCoCrCuNi高熵合金裂纹及孔洞模型结构在不同轴向拉伸应变速率下的力学与微观结构演化机理. 结果表明:应变速率越高FeCoCrCuNi裂纹结构对应更高的过冲应变和过冲应力,其主要原因是高拉伸速率会导致高强度的BCC结构及孪晶结构的生成,而BCC结构及孪晶结构的产生进而会抑制应力的下降,通过应力-应变曲线,可知FeCoCrCuNi裂纹模型在轴向应力作用下表现为塑性形变. 对于不同尺寸的孔洞FeCoCrCuNi裂纹模型的应力模拟与结构分析,可以得出:孔洞尺寸越大, FeCoCrCuNi裂纹结构对应的过冲应变和过冲应力越小,其主要原因是大尺寸的孔洞造成孔洞之间产生裂纹的,进而会影响这个材料的屈服应变和屈服强度. 相似文献
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"采用分子动力学模拟的方法,运用镶嵌原子模型,研究了经过刻划后的单晶铜纳构件在不同拉伸速度条件下的力学行为. 通过原子位图、缺陷原子透视图、径向分布函数及应力-应变关系研究加工后纳构件在拉伸负载作用下的变化特性,并与理想单晶铜纳构件进行对比分析.模拟结果表明,加工后的纳构件的屈服强度较理想纳构件的屈服强度有明显下降,屈服强度随着刻槽深度的增加而下降,而且屈服强度对刻槽方向和拉伸速度敏感;纳结构在拉伸负载作用下,其应力应变关系出现了双峰形式,即工作硬化现象,二次屈服后表现为Z字形逐波下降形式.刻划深度、刻划 相似文献
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利用分子动力学方法, 对本课题组率先采用金属催化的气相合成法制备出的高纯度单晶钨纳米线进行拉伸变形数值模拟, 通过分析拉伸应力-应变全曲线及其微观变形结构, 揭示出单晶钨纳米线的拉伸变形特征及微观破坏机理. 结果表明: 单晶钨纳米线的应力-应变全曲线可分为弹性阶段、损伤阶段、相变阶段、强化阶段、 破坏阶段等五个阶段, 其中相变是单晶钨纳米线材料强化的重要原因; 首次应力突降是由于局部原子产生了位错、孪生等不可逆变化所致; 第二次应力突降是发生相变的材料得到强化后, 当局部原子再次产生位错导致原子晶格结构彻底破坏而形成裂口、且裂口不断发展成颈缩区时, 材料最终失去承载能力而断裂. 计算模拟得到的单晶钨纳米线弹性模量值与实测值符合较好.
关键词:
分子动力学
应力应变曲线
微观机理
单晶钨纳米线 相似文献
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利用MTS材料试验机和分离式Hopkinson压杆(SHPB)实验装置对非退火状态Ta-10W合金进行了准静态和动态压缩实验,给出了材料的静态压缩屈服强度和应变率在700~3 100 s-1范围内的动态压缩应力-应变曲线,并获得了不同应变率下材料的动态屈服强度。通过对实验结果的分析可以发现,非退火状态Ta-10W合金具有较好的韧性,在所进行的实验中试件表面均未出现可见裂纹;试件材料具有较高的静、动态屈服强度,静态屈服强度达到930 MPa,动态屈服强度在1 GPa以上,在所进行的700~3 100 s-1应变率范围内,材料的动态屈服强度随应变率的增加略有提高。 相似文献
8.
热处理对Li2O-Al2O3A-SiO2系统玻璃性质的影响 总被引:1,自引:0,他引:1
测量了线性升温热处理后Li2 O Al2 O3 SiO2 系统零膨胀微晶玻璃V0 2的性质变化。在一个较小的温度区间内 ,玻璃物理性质由于相变而出现显著变化。折射率增加 175× 10 -4、密度增加 0 .0 94g/cm3 、热膨胀系数降低4 1× 10 -7/℃、努普 (Knoop)硬度增加 18.6MPa、线收缩达 1.12 %。短波区透射率随着热处理温度的升高先出现下降而后再次上升。实验结果为大尺寸微晶玻璃毛坯的晶化工艺过程提供有实用意义的建议 相似文献
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基于遥测技术的风力机叶片动态应变特征实验研究 总被引:1,自引:0,他引:1
采用旋转机械应力应变无线遥测技术,在直流式低速风洞开口段对风力机叶片运行状态中的应力应变特性进行了实验研究,结果表明:在相同尖速比下,叶片各截面沿展向向外位置增加应变值逐渐减小,随着风速的增加,压力面的应变值增加幅度大于吸力面,叶根处应变增加幅度大于叶尖,并在0.55R到0.75R段应变拟合曲线略微凸起,主要是气动力在该截面区作用的效果;在相同风速下,叶片各截面沿展向向外位置增加应变值逐渐减小,且各截面的应变值随着尖速比的增加而增大,叶根较叶尖增加幅值更明显,叶根部位所受离心力增加较快;相同翼面处前缘点的应变值大于后缘点的应变值。为开展大型风力发电机组叶片动态应变检测积累了可鉴借的经验。 相似文献
11.
V. A. Pozdnyakov 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(12):1708-1721
A classification of the structural states of materials with a mixed nano-and microcrystalline structure is proposed. Theoretical analysis of the structural mechanisms and peculiarities of plastic flow of singlephase and two-phase nanostructured metals and alloys with a bimodal size distribution of grains and phases is performed. The effect of grain-boundary and dislocation mechanisms of plastic flow on the specific features of the deformation behavior and plasticity of nanocrystalline materials is analyzed. A microstructural model of strain hardening of a material with two-scale nano-and micrograin structure is proposed and the condition for the loss of plastic flow stability of such a material is investigated. The dependence of the yield strength and uniform strain of nanocrystalline materials with a two-scale structure on the grain size and the ratio of the volume fractions of the nano-and microstructural components is calculated. 相似文献
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Motion of a small charged absorbing body (micrograin) immersed in a stationary weakly ionized high pressure plasma environment is considered. It is shown that the total frictional (drag) force acting on the grain can be directed along its motion, causing the grain acceleration. At some velocity, the forces associated with different plasma components can balance each other, allowing free undamped superfluid motion of the grain. The conditions when such behavior can be realized and the possibility of a superconductive grain current are discussed in the context of complex (dusty) plasmas. 相似文献
13.
The cosmic ray extensive air showers in the knee energy region have been studied by the North Bengal University array. The
differential size spectra at different atmospheric depths show a systematic shift of the knee towards smaller shower size
with the increase in atmospheric depth. The measured values of spectral indices at below and above the knee are −2.45 ±0.03
and −2.91 ±0.05 respectively. Measurements at different atmospheric depths correspond to the same values within the error
limits both for below and above the knee. The present experimental results have been compared with similar such experiments 相似文献
14.
Titanium dioxide (titania) particles were prepared by a water-in-oil emulsion system, and studied for the photodecomposition property of methylene blue. Microemulsion (ME) consisted of water, cyclohexane or octane, and surfactant, such as polyoxyethylene (10) octylphenyl ether (TX-100), polyoxyethylene lauryl ether, or bis (2-ethylhexyl) sodium sulfosuccinate. Titanium tetraisopropoxide (TTIP) was dropped into the ME solution and then titania particles were formed by the hydrolysis reaction between TTIP in the organic solvent and the water in the core of ME. It was found that ME could be classified to the reversed micelle (RM) region and the swelling reversed micelle (SM) region according to the water content. The water droplets in RM were almost monodispersed, where the water content was small. On the other hand, the water droplets in SM had a size distribution, although most of the water molecules associated with surfactant molecules. The size of the particles prepared in the RM region was smaller than the ME size. In contrast, the size of the particles formed in the SM region was larger than the ME size, and coagulation of the particles was observed within a few hours. The smallest diameter of the particles was 2 nm in the system of cyclohexane with TX-100 surfactant when the molar ratio of water to surfactant was 2. Titania particles prepared in this condition were collected as amorphous powder, and converted to anatase phase at less than 500 K, which is lower than the ordinal phase transition temperature. These anatase phase titania particles only showed a significant photodecomposition of methylene blue by illumination with a Xenon lamp. 相似文献
15.
《Physics letters. [Part B]》1988,213(2):107-110
The GCM mass parameters for the heavy odd-nuclei region within the mean-field hamiltonian approximation have been calculated. The influence of the energy window size, the level crossing and the projection onto good particle number effects have been analyzed. 相似文献
16.
Multipolar plasmon optical excitations at spherical gold nanoparticles and their manifestations in the particle images formatted
in the particle surface proximity are studied. The multipolar plasmon size characteristic: plasmon resonance frequencies and
plasmon damping rates were obtained within rigorous size dependent modelling. The realistic, frequency dependent dielectric
function of a metal was used. The distribution of light intensity and of electric field radial component at the flat square
scanning plane scattered by a gold sphere of radius 95 nm was acquired. The images resulted from the spatial distribution
of the full mean Poynting vector including near-field radial components of the scattered electromagnetic field. Monochromatic
images at frequencies close to and equal to the plasmon dipole and quadrupole resonance frequencies are discussed. The changes
in images and radial components of the scattered electromagnetic field distribution at the scanning plane moved away from
the particle surface from near-field to far-field region are discussed. 相似文献
17.
The local heating of glass by a focused femtosecond laser pulse and cooling of an irradiated region are numerically modeled. The structural modifications that change the optical properties of glass are assumed to occur within a bulk region whose temperature after irradiation exceeds the glass transition temperature. The shape of the modified region obtained from the calculations coincides with that known from experimental data available. The size of this region is determined by the spatiotemporal dynamics of the laser beam under multiphoton absorption conditions. The heating of glass is maximal in front of a thin lens used for the beam focusing. 相似文献
18.
《Physics letters. [Part B]》1988,206(3):399-403
Nuclear transparency is described within a model of two interpenetrating fluids. The formation of the midrapidity region is included by the energy leak-out from the fragmentation regions. The space-time picture of the collision, the baryon multiplicity distribution and maximum temperatures as well as the effects of target size and deconfinement time scale are discussed. 相似文献
19.
A. D. Lucas 《Optical and Quantum Electronics》1974,6(2):153-160
Preparation of silicon avalanche photodiodes by a planar method in epitaxial PP+ silicon slices limited charge collection to carriers generated in or close to the depletion region. Reducing the effective size of the zero-field absorption region surrounding the depletion region by this method, resulted in the output signal current of the device reproducing the input light pulse shape, within 15 ns. When illuminated with monochromatic radiation, the shot noise of a detector prepared in epitaxial material was less than that observed with a device fabricated in homogeneous material, due to the reduced signal current. 相似文献
20.
Chawanya T 《Chaos (Woodbury, N.Y.)》2003,13(3):982-989
The characteristics of long lasting but not perpetual chaotic states appear in a wide parameter region in a globally coupled overcritical tent map system are exhibited. The lifetime of the transient state has essential relevance with the system size. In some parameter region, the lifetime saturates at a certain level, while in another region it seems to diverge as the size of the system grows. In order to uncover the dynamical structures in large system size limit, the dynamics of one-body distribution is investigated as an idealized model for the infinitely large coupled map system. Obtained numerical results indicate the correspondence between the characteristics of long transient behavior in finite size system and that of the attractor or the ruin of attractor in the idealized model. 相似文献