聚氨酯泡沫塑料胞体结构特性的确定

通过扫描电镜和显微镜观察相结合的手段，确定 了聚氨酯泡沫塑料胞体结构特性，其中包括不同密度的聚氨酯泡沫塑料的胞体结构形态，胞体尺寸及其分布情况，胞体的椭球度及泡沫塑料的孔隙度等重要的材料几何参数。这些参数的确定不仅为提高泡沫兼的质量和改进本文提供了必要的实验数据，也为研究聚氨酯泡沫兼的力学性能提供了重要的物理参数。在扫描电镜和显微镜观察结果的基础上，本文提出了一种确定泡沫塑料密度的方法，结果与实测     

AN/MAA共聚物泡沫塑料泡体结构研究

通过烘箱自由发泡制备丙烯腈(AN)/甲基丙烯酸(MAA)共聚物泡沫塑料,讨论了该泡沫塑料泡孔平均孔径随泡沫塑料密度变化的规律,研究了成核剂和应力对泡沫塑料泡孔尺寸的影响,通过光学显微和电子扫描显微观察了该泡沫塑料的整体结构和微观结构.结果表明: AN/MAA共聚物泡沫塑料泡孔平均孔径随密度的增加而减小;碳酰胺能起到成核剂的作用,显著减小泡沫塑料泡孔尺寸;可发泡共聚物的应力发白现象能改善其发泡成核效果并使泡孔孔径大大减小;该共聚物泡沫塑料具有高闭孔率、各向同性的特征,其泡壁为三至七边形,泡棱由三个泡壁相交而成,泡壁体积分数随密度的增加而减小.     

泡沫塑料包装衬垫的非线性弹性模型

本文分析了泡沫塑料包装衬垫缓冲性能的基本特征,比较了几种弹性衬垫模型的缓冲性能,提出了建立泡沫塑料包装衬垫弹性模型的一些原则。还实际测试了两种国产泡沫塑料材料的静态应力应变关系,根据上述原则和实测数据建立了泡沫塑料包装衬垫的非线性弹性模型并拟合了模型参数。     

二维机织复合材料弹性常数的有限元法预测

为了预测二维机织复合材料的弹性性能,建立了有限元力学分析模型。基于二维机织复合材料的几何特征,建立了参数化的单胞模型;考虑了织物纤维束呈现出的各向异性材料特征,将有限元中材料主方向转化到纤维屈曲方向,建立其力学分析有限元模型;分析了单胞边界面保持平面假设的不足,提出了对于二维机织复合材料通用的周期边界条件,获得了更为准确的二维机织复合材料的工程弹性常数。结果表明:织物衬垫单胞边界面,在单向拉伸载荷和纯剪切载荷下,呈凹凸翘曲变形,即为周期边界;应用给出的织物参数化几何建模方法与有限元求解方法,可以精确地获得工程弹性常数,数值计算结果与实验值吻合较好。      

陶瓷弹性常数的超声动态测量

介绍了材料的声速与弹性模量之间的关系及脉冲重迭法测量声速的基本原理。给出了若干典型工程陶瓷的测量结果,并对结果的误差进行了分析,论证了超声法测量陶瓷材料的弹性常数具有制备样品用料节省,测试重复性好等一为列优点。声学技术不失为一种可取的测量陶瓷弹性常数的方法。     

具有溯源性的原子力显微镜探针法向弹性常数标定系统

原子力显微镜(AFM)悬臂梁探针的弹性常数在微纳米尺度力学测试中十分重要,其准确程度直接影响力学测量结果的可靠性,故需对其进行精确标定.因天平法的测量结果可溯源,本文在已有天平法的基础上,研制了一套新型标定系统.该系统将AFM测头与超精密电磁天平相结合.微悬臂梁在精密位移台的带动下接触天平并产生弯曲,接触力由天平测得,微悬臂梁的弯曲量由光杠杆检测,并通过反馈系统进行精确控制,最后根据胡克定律计算出弹性常数.利用本系统对4种不同型号商用微悬臂梁探针的法向弹性常数进行了标定,标定结果表明本系统具有良好的测量重复性.通过进行不确定度分析,得到测量结果的相对标准不确定度优于2%.     

纳米压痕结合有限元法确定ZnO纳米带的弹性常数

本文结合纳米压痕和有限元法确定了横观各向同性ZnO纳米带各方向上的弹性常数。在正向分析过程中,用ABAQUS有限元软件的压电模式大量模拟了纳米带/硅基底体系的压痕实验,得到无量纲方程的具体形式。在反向分析过程中,通过对沉积在硅基底上的ZnO纳米带进行纳米压痕实验,将相关实验数据代入无量纲方程,确定横观各向同性ZnO纳米带各方向上的弹性常数为ET=35GPa,EL=49GPa和GL=5GPa。     

考虑单向复合材料复杂微观结构的细化单胞模型

通用单胞模型常被应用在复合材料细观力学分析上。但原始的通用单胞模型存在求解量大、计算效率低的问题。该文对其改进,建立了以子胞界面细观应力为未知量的细化单胞模型。利用该模型研究复杂的微观结构包括纤维截面形状/排列方式,界面相材料属性/几何厚度,夹杂/空隙对单向纤维复合材料宏观弹性常数的影响。通过与其他研究方法和试验数据对比证实了该预测模型具有更高的计算效率,计算精度和更广泛的普适性。该文模型子胞划分更细致,克服了原始通用单胞模型无法分析复杂微观结构的不足。有望将损伤力学引入该模型中建立一个有力的分析工具,来进行复合材料结构宏/细观多尺度损伤力学分析。     

通过渐近均匀化方法求解多孔材料弹性常数时局部函数的确定

采用渐近均匀化方法建立具有规则排列微结构的多孔材料弹性本构关系的问题中,需要求解定义在单胞上的局部问题以确定弹性常数。本文给出了求解局部问题的数值方法。算例表明,本方法具有实用价值、准确、简单。     

高密度硬质聚氨酯泡沫塑料的断裂特性

制备不同密度的硬质泡沫聚氨酯塑料,实验研究了材料的拉伸和冲击性能。断口的扫描电镜现察显示,材料的断裂基本上属于脆性断裂,但局部存在明显的塑性形变,这是与材料的有机大分子的特殊结构相关。材料的断裂原因在于材料中相邻泡体互通构成的结构缺陷．根据断裂力学的一般原理。确定了材料断裂韧性的预测的可行方法。并得到实验结果的验证。     

玻璃纤维对硬质聚氨酯泡沫塑料增强机理的探讨

研究了硬质聚氨酯泡沫塑料的微观结构形态，通过实验探讨了玻璃纤维对聚氨酯泡沫塑料的增强作用，并分析了增强泡沫塑料的压缩破坏机理。     

Higher order elastic constants of rare earth metals: gadolinium,dysprosium and erbium

The expressions for the second and third order elastic constants of the rare earth metals, gadolinium dysprosium and erbium have been worked out and their values have been determined. The present theoretical values are compared with the experimentally observed results. It is also suggested that the third order elastic constants of these metals may be measured using ultrasonic technique under high pressures.     

LiNbO3和LiTaO3晶体电子结构、平面声波和光折射特性

本研究基于密度泛函理论的第一性原理超软赝势平面方法计算了LiNbO₃和LiTaO₃的晶格参数、电子结构和弹性常数, 并利用Christoffel方程研究了二者平面声波特征。结果表明: 两者的理论计算晶格参数和弹性常数与实验值接近, 禁带宽度分别为3.78和3.98 eV, 导带底和价带顶主要由O-2p和Nb-4d(Ta-5d)态电子贡献。化学键理论揭示Li和Nb(Ta)与O原子之间有两种成键类型。 电荷布局分析结果显示有两种相应的重叠布居数, Nb(Ta)-O键呈现强共价键作用, 并且Nb-O(Ta-O)键长小于Li-O键长。LiNbO₃和LiTaO₃晶体平面声波有两支横波和一支纵波, 纵波速度大于横波速度, 在xy平面呈现六重对称性, 在xz和yz平面各向异性程度强于xy平面, 沿[001]、晶向上两支横波振动速度相等。最后利用模守恒赝势(Norm-conserving)计算了介电常数和静态折射率, 计算表明LiNbO₃晶体的折射性能和非寻常光(e光)离散程度均强于LiTaO₃晶体。     

Shear moduli for non-isotropic, open cell foams using a general elongated Kelvin foam model

Equations for calculating the shear modulus of non-isotropic, open cell foams in the plane perpendicular to the rise direction and in a plane parallel to the rise direction are derived using an elongated Kelvin foam model. This Kelvin foam model is more general than that employed by previous authors as the size and shape of the unit cell are defined by specifying three independent cell dimensions. The equations for the shear compliances are derived as a function of three unit cell dimensions and the section properties of the cell edges. From the compliance equations, the shear modulus equations are obtained and written as a function of the relative density and two unit cell shape parameters. The dependence of the two shear moduli on the relative density and the two shape parameters is demonstrated.     

On the effective elastic properties of matrix composites: Combining the effective field method and numerical solutions for cell elements with multiple inhomogeneities

The work is devoted to calculation of effective elastic constants of homogeneous materials containing random or regular sets of isolated inclusions. Our approach combines the self-consistent effective field method with the numerical solution of the elasticity problem for a typical cell. The method also allows analysis of detailed elastic fields in the composites. By the numerical solution of the elasticity problem for a cell, integral equations for the stress field are used. Discretization of these equations is carried out by Gaussian approximating functions. For such functions, elements of the matrix of the discretized problem are calculated in explicit analytical forms. If the lattice of approximating nodes is regular, the matrix of the discretized problem proves to have the Toeplitz structure. The matrix-vector products with such matrices may be carried out by the Fast Fourier Transform technique. The latter strongly accelerates the process of iterative solution of the discretized problem. Results are given for 2D-media with regular and random sets of circular inclusions, and compared with existing exact solutions.     

用几何平均模型计算多晶材料的X射线弹性常数

推导出几何平均模型并使用这个模型计算了 Ｃｕ和ＴｉＮ 的弹性矩阵和 Ｘ射线弹性常数,计算的结果处于 Ｖｏｉｇｔ和 Ｒｅｕｓｓ模型所定义的多晶材料弹性常数的有效区间内．与 Ｈｉｌｌ、Ｋｒｏｎｅｒ模型的计算结果的最大相对误差小于 ４％,ＴｉＮ［４２２］方向杨氏模量的计算值为 ４２４．３ＧＰａ,与其实验值４１１±４５Ｇｐａ基本一致     

玻璃纤维增强硬质聚氨酯泡沫塑料的微观结构及破坏机理研究

本文探讨了玻璃纤维增强硬质聚氨酯泡沫塑料的微观结构形态;分析了增强泡沫塑料的拉伸破坏机理;并对增强用最佳纤维长度进行了初步探讨.      

Self-consistent one-particle 3D unit cell model for simulation of the effect of graphite aspect ratio on Young’s modulus of cast-iron

The graphite phase of ferritic cast-iron was assumed to consist of randomly oriented, rotationally symmetric, ellipsoidal inclusions of same dimensions. Accordingly, a self-consistent one-particle 3D unit cell model was developed to simulate the effect of graphite aspect ratio on cast-iron elastic constants. The cube shaped unit cell is made up of an inner rotational ellipsoid of graphite surrounded by Fe–2.5%Si matrix in a concentric outer ellipsoid of the same aspect ratio as the inner graphite ellipsoid in order to model the desired graphite content. The remainder of the unit cell is filled up by the cast-iron compound, the elastic behaviour of which is determined self-consistently. In order to obtain elastic properties, the unit cell was subjected to uniaxial loading. Calculations of stress and strain distributions, in dependence on the orientation of the graphite ellipsoid, were carried out by the finite element method using 3D elements. Finally, updated values of Young’s modulus and Poisson’s ratio were derived by employing Hooke’s law. This procedure was repeated, using the updated elastic constants as new input, to get a self-consistent convergent solution. The results are compared with finite element calculations using a conventional one-particle 3D unit cell model with multiphase elements, and an analytical solution given in the literature. Comparison with experimental data shows the relatively wide range of validity and the superiority of the self-consistent method.