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1.
The damping capacity of three materials subjected to narrow-band strain fluctuations is investigated, the material effectively undergoing sinusoidal strain with randomly varying amplitude. For this case, a theoretical relationship is established between the expected value of the energy dissipated per unit volume of the material per period of the narrow-band process and the r.m.s. value of the strain history. This is expressed in terms of material damping constants obtained from harmonic damping measurements. The theoretical relationship is checked against experimental results from narrow-band random experiments on three different materials over low and intermediate stress ranges. Good agreement is found.  相似文献   

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硅基锗薄膜选区外延生长研究   总被引:1,自引:0,他引:1       下载免费PDF全文
汪建元  王尘  李成  陈松岩 《物理学报》2015,64(12):128102-128102
利用超高真空化学气相沉积系统, 基于低温Ge缓冲层和选区外延技术, 在Si/SiO2图形衬底上选择性外延生长Ge薄膜. 采用X射线衍射、扫描电镜、原子力显微镜、拉曼散射光谱等表征了其晶体质量和应变等参数随图形尺寸的变化规律. 测试结果显示, 位错密度随着图形衬底外延窗口的尺寸减小而减少, Ge层中的张应变随窗口尺寸的增大先增大而后趋于稳定. 其原因是选区外延Ge在图形边界形成了(113)面, 减小了材料系统的应变能, 而单位体积应变能随窗口尺寸的增加而减少; 选区外延厚度为380 nm的Ge薄膜X射线衍射曲线半高宽为678", 表面粗糙度为0.2 nm, 表明选区生长的Ge材料具有良好的晶体质量, 有望应用于Si基光电集成.  相似文献   

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王广海 《物理学报》2008,57(1):259-263
The formation and mechanical properties of amorphous copper are studied using molecular dynamics simulation. The simulations of tension and shearing show that more pronounced plasticity is found under shearing, compared to tension. Apparent strain hardening and strain rate effect are observed. Interestingly, the variations of number density of atoms during deformation indicate free volume creation, especially under higher strain rate. In particular, it is found that shear induced dilatation does appear in the amorphous metal.  相似文献   

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The formation and mechanical properties of amorphous copper are studied using molecular dynamics simulation. The simulations of tension and shearing show that more pronounced plasticity is found under shearing, compared to tension. Apparent strain hardening and strain rate effect are observed. Interestingly, the variations of number density of atoms during deformation indicate free volume creation, especially under higher strain rate. In particular, it is found that shear induced dilatation does appear in the amorphous metal.  相似文献   

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Knowledge of defects generation, their mobility, growth rate, and spatial distribution is the cornerstone for understanding the surface and structural evolution of a material used under irradiation conditions. In this study, molecular dynamics simulations were used to investigate the coupled effect of primary knock-on atom (PKA) energy and applied strain (uniaxial and hydrostatic) fields on primary radiation damage evolution in pure aluminum. Cascade damage simulations were carried out for PKA energy ranging between 1 and 20 keV and for applied strain values ranging between ?2% and 2% at the fixed temperature of 300 K. Simulation results showed that as the atomic displacement cascade proceeds under uniaxial and hydrostatic strains, the peak and surviving number of Frenkel point defects increases with increasing tension; however, these increments were more prominent under larger volume changing deformations (hydrostatic strain). The percentage fraction of point defects that aggregate into clusters increases under tension conditions; compared to the reference conditions with no strain, these increases are around 13% and 7% for interstitials and vacancies, respectively (under 2% uniaxial strain), and 19% and 11% for interstitials and vacancies, respectively (under 2% hydrostatic strain). Clusters formed of vacancies and interstitials were both larger under tensile strain conditions, with increases in both the average and maximum cluster sizes. The rate of increase/decrease in the number of Frenkel pairs, their clustering, and their size distributions under expansion/compression strain conditions were higher for higher PKA energies. Overall, the present results suggest that strain effects should be considered carefully in radiation damage environments, specifically for conditions of low temperature and high radiation energy. Compressive strain conditions could be beneficial for materials used in nuclear reactor power systems.  相似文献   

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根据任意方向的应变公式,分析了材料力学基本实验中应变片粘贴方向、位置误差对测量结果的影响。  相似文献   

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The effect exerted by an electron beam with an energy of 0.5 MeV on the deformation of polycrystalline aluminum (99.5%) and copper (99.5%) under uniaxial tension at a rate of 2 × 10?4 s?1 in the temperature range from 40 to 100°C has been investigated. It has been established that the plasticity of the metal increases under irradiation with an electron beam: the level of the flow stress and the strain hardening coefficient in the irradiated state decrease, whereas the total resource of plasticity of the material increases. A mechanism of an increase in the plasticity of metals has been proposed. This mechanism is based on the radiation-induced generation of nonlinear strongly localized excitations of the crystal lattice, namely, discrete breathers, whose lifetime is significantly longer than the relaxation time of phonons. The interaction of discrete breathers with dislocations can stimulate the detachment of dislocations from stoppers and, consequently, an increase in the plasticity of the material.  相似文献   

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ZnO nanoparticles and Cu-doped ZnO nanoparticles were prepared by co-precipitation method. Also, a part of the pure ZnO nanoparticles were annealed at 750 °C for 3, 6, and 9 h. X-ray diffraction studies were carried out and the lattice parameters, unit cell volume, interplanar spacing, and Young’s modulus were calculated for all the samples, and also the crystallite size was found using the Scherrer method. X-ray peak broadening analysis was used to estimate the crystallite sizes and the strain using the Williamson–Hall (W–H) method and the size–strain plot (SSP) method. Stress and the energy density were calculated using the W–H method assuming different models such as uniform deformation model, uniform strain deformation model, uniform deformation energy density model, and the SSP method. Optical absorption properties of the samples were understood from their UV–visible spectra. Photocatalytic activities of ZnO and 5 % Cu-doped ZnO were observed by the degradation of methylene blue dye in aqueous medium under the irradiation of 20-W compact fluorescent lamp for an hour.  相似文献   

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