First-principles study of the structural,elastic, and optical properties for Sr0.5Ca0.5TiO3

A detailed theoretical study of the structural, elastic, and optical properties for Sr0.5Ca0.5TiO3 is carried out by first- principles calculations. The band structure exhibits a direct bandgap of 2.08 eV at the F point in the Brillouin zone. The bulk modulus, shear modulus, Young＇s modulus, and Poisson＇s ratio are derived based on the calculated elastic constants. The bulk modulus B = 153 GPa and shear modulus G = 81GPa are in good agreement with available experimental data. Poisson＇s ratio v = 0.275 suggests that Sr0.sCa0.sTiO3 should be classified as being a ductile material. Using the electronic band structure and density of states, we analyze the interband contribution to the optical properties. The real and imaginary parts of the dielectric function, as well as the optical properties such as the optical absorption coefficient, refractive index, extinction coefficient, and energy-loss spectrum are calculated. The static dielectric constant ε1 （0） and the refractive index n（0） are also investigated.     

First-principles study of the electronic structure and optical properties of cubic Perovskite NaMgF_3

The structural, electronic, and optical properties of cubic perovskite NaMgF3 are calculated by plane-wave pseudopo- tential density functional theory. The calculated lattice constant a0, bulk modulus B0, and the derivative of bulk modulus B~ are 3.872/~, 78.2 GPa, and 3.97, respectively. The results are in good agreement with the available experimental and theo- retical values. The electronic structure shows that cubic NaMgF3 is an indirect insulator with a wide forbidden band gap of Eg = 5.90 eV. The contribution of the different bands is analyzed by total and partial density of states curves. Population analysis of NaMgF3 indicates that there is strong ionic bonding in the MgF2 unit, and a mixture of ionic and weak covalent bonding in the NaF unit. Calculations of dielectric function, absorption coefficient, refractive index, electronic energy loss spectroscopy, optical reflectivity, and conductivity are also performed in the energy range 0 to 70 eV.     

拉压模量不同材料的圆孔扩张问题

本文建立了拉、压模量不同材料的圆孔扩展理论，分析了有关参数对圆孔扩张时应力、位移以及塑性区的发展规律的影响。     

YBCO高温超导材料的动态模量

本利用动态激光散斑测振技术测量超小型物体振动特性的实验系统，研究了１２３ＹＢ－ＣＯ温超导体的动态力学性能，运用谱分析仪和时间域分析方法了动态响应信号，识别出了超导体梁的前五阶频率和模态，并根据基频计算了材料的动态模量，为小尺寸脆性功能材料的力学性能测试提供了一种有效的实验方法。     

材料复切变模量的测量方法

本文介绍材料切变模量及损耗因子的测量方法，着重讨论了测量中的一些技术问题．     

有关力学谱和内耗工作的综合与回顾

本文广泛地收集了有关内耗,力学谱,超声衰减方面的专著及会议文集.反映了20世纪在此领域的英文,俄文出版的书籍.也列出了历次国际会议及前苏联,乌克兰,中国的国内会议.文中包括了点缺陷,电,声子,位错,晶界,电畴等诸方面在内的内耗与力学谱工作.     

KH2PO4和(CH3NHCH2COOH)CaCl2在高压下的状态方程与相变

 在活塞圆筒式p-V关系测量装置上，研究了KH₂PO₄（KDP）和(CH₃NHCH₂COOH)CaCl₂［Tris-sarcosine calcium chloride（TSCC）］在室温下、4.5 GPa内的p-V关系。实验结果表明：KDP在2.1 GPa左右有一个相变；TSCC在0.8 GPa和3.2 GPa左右各有一个相变。本工作还给出了它们在相变前后的状态方程，以及它们的格临爱森参数γ₀、体积模量B₀和B₀的压力导数B₀'。     

实用NbTi/Cu超导股线、绞线拉伸及疲劳性能研究

对NbTi/Cu超导股线、绞线开展了一系列常温力学特性实验研究,包括准静态加卸载、芯丝裂纹扩展及轴向疲劳。实验发现:超导股线加载过程具有明显的阶段性,经过初始加卸载循环"锻炼"后,残余应变不随卸载应力增加而增加;疲劳前期芯丝内部无裂纹,疲劳后期裂纹呈指数型增长直至最终破坏;绞线杨氏模量、疲劳寿命均与扭转节距有关。疲劳过程中,采用循环周期内耗散能定性评估材料内部损伤程度。     

蠕变损伤问题的有效模量法及差分解

本文在蠕变损伤问题中，以有效模量法将损伤变量引入本构方程，给出相应非线性问题的差分解；并将结果与一维实验数据及有效应力法的结果进行了比较。     

复合材料模量估算的力学模型

在计算复合材料的模量时，被广泛应用的力学模型是等应力和等应变假设．本文改进了这些力学模型，推导出层合复合材料、单向纤维增强复合材料和颗粒增强复合材料模量的计算式．引入一个反映受力方向与复合材料组元连续性等的调节参量，可将其归纳成一个普遍式．