聚酰胺非晶相弹性性质预测

聚合物基复合材料宏观有效力学性质的确定需要复合材料中各个组分的基本力学性质。采用基于拓扑的关联指数法对11种典型聚酰胺非结晶相的体积模量、泊松比、杨氏模量、剪切模量等弹性性能进行了预测。结果表明,当温度从1K逐步增加到(Tg-20)K时,体积模量、杨氏模量和剪切模量随温度的增加呈指数规律减小;而泊松比则呈线性增加。当温度在玻璃化温度Tg附近(Tg-20)相似文献   

基于五相球模型确定含涂层空心微球复合材料的有效模量

利用推广的五相球模型得到了含涂层空心微球填充复合材料的有效体积模量、剪切模量和杨氏模量预测的理论公式。分析了复合材料有效模量同空心微球壁的厚度、填充体积分数、涂层厚度等参数的关系。为了说明本文结果的有效性, 将五相球模型退化为不含涂层空心球填充复合材料的情况, 并与文献中的实验数据进行对比。算例计算表明: 涂层较薄时, 填料体积分数越大, 空心微球壁相对越厚, 弹性模量就越大。当填料体积分数最大时, 在空心微球壁相对最薄处, 弹性模量最低。      

基于RVE方法的磁流变弹性体力学行为的预测

磁流变弹性体是一种在不同磁场条件下力学性能可控的智能材料。磁流变弹性体的模量为无磁场下材料的模量和磁场诱导产生的模量之和。运用基于周期性边界条件的代表性体积单元法,用理论和有限元两种方法对比研究了无磁场下磁流变弹性体的宏观弹性模量和剪切模量。通过引入Maxwell应力张量,研究了磁流变弹性体在不同磁感应强度下对磁场诱导产生的弹性模量和剪切模量的影响。用RVE的方法证明了,磁流变弹性体由于磁场诱导产生的弹性模量是负数,但总的弹性模量是正数,且其大小随磁感应强度的增大而增大。而其初始剪切模量则始终为正数,其大小随着磁场强度的增大而增大,这与偶极子理论推导得到的结论一致。     

高孔隙度泡沫塑料的一种近似非线性本构关系

根据高孔隙度泡沫塑料杨氏模量满足平方律关系的理论和实验结果，并通过对泡沫塑料泊松比的合理近似，在假设基体材料服从幂律本构关系的基础上，研究了高孔隙度泡沫塑料的非线性本构行为，得到了用于非线性本构关系的应变势函数，给出了描述高孔隙度泡沫塑料非线性力学行为的一种有效，合理的本构关系的形式。此外，由此得到的泡沫塑料屈服应力与前人按照量纲分析方法得到的低密度闭孔泡沫塑料的结果相一致。     

等效介质理论在各向同性复合材料的弹性性能上的应用

本文介绍了我们不久前发展的一套应用于复合材料性能的等效(有效)介质理论,并且把它合理地扩展到研究二相各向同性复合材料的弹性性能。作为例子,我们计算了含球状空隙及含球状刚性微粒固体的剪切模量,得到这两个情况下模量与掺入物体积比的直接关系式。计算结果并与实验比较,得到很好的符合。     

水对硬质聚氨酯-酰亚胺泡沫泡孔结构与性能的影响

采用PI预聚体法合成硬质聚氨酯-酰亚胺泡沫塑料,分析了发泡剂水对泡沫塑料密度、表面粉化程度以及力学性能的影响。运用幂次法则建立了力学性能与密度之间的关系,并利用体视显微镜和偏光显微镜对泡沫塑料的泡孔结构进行了研究。结果表明,硬质聚氨酯-酰亚胺泡沫塑料的密度、抗压强度与压缩模量、冲击强度以及泡孔棱厚随水用量的增加逐渐减小;孔径和表面粉化程度随水用量的增加而逐渐增大;密度与抗压强度、压缩模量、冲击强度之间的密度指数分别为1.78,1.55和0.72。     

平压平模切版中聚氨酯泡沫塑料的应用研究

研究了钢刀周长、钢刀连接点等因素对钢刀与纸板摩擦力的影响,测试了多种聚氨酯泡沫塑料的性能,得出了聚氨酯弹垫的压缩模量与硬度的关系,并通过分析得出了小面积封闭钢刀处聚氨酯弹垫的压缩模量的计算公式.研究结果将有助于包装企业正确选用模切弹垫.     

从纳米水化硅酸钙到水泥净浆弹性性能多尺度递推模型

混凝土具有多尺度结构特征,其力学性能受到不同水化产物组分及微观结构的影响。基于分子动力学方法、化学计量法和均质化方法,建立了从纳米尺度水化硅酸钙（C-S-H）到水泥净浆弹性性能多尺度递推模型,其计算结果与实验数据吻合较好。基于该模型的计算结果可得：C-S-H凝胶中44%的孔隙率致使其体积模量、剪切模量和杨氏模量分别降低了约66%、53%和55%。当水灰比从0.3变化至0.5时,水泥净浆的体积模量、剪切模量和杨氏模量分别降低了约39%、30%和32%;LD C-S-H和毛细孔的体积分数分别增大了13%和20%。水化产物中C-S-H的体积分数越大,或水泥熟料中硅酸三钙的质量分数越大,水泥净浆的弹性参数越大。该模型为水泥基材料微观调控提供了指导。     

复合材料圆管构件的等效模型研究

本文针对任意壁厚的复合材料圆管构件的等效弹性模量和剪切模量提出了高阶理论计算方法，它考虑了构件的横向剪切效应以及层合材料的三维本相关系，并且对三种缠绕方式的等效模量进行了预测，预测结果与经典层合报理论和实验的预测结果吻合较好，该方法可用于复合材料杆件结构的设计中。     

水下含气泡橡胶材料的隔声性能的仿真

针对水下含气泡橡胶材料的隔声性能进行了研究。利用以往文献中Kelvin-Voigt粘弹性模型,得到材料动态等效体积模量、等效剪切模量及等效纵波声速随频率变化的关系,通过传递矩阵法数值计算、分析了不同孔隙率、孔径的情况下．材料的隔声性能、等效声速的变化。仿真结果表明,气泡的孔径、孔隙率的变化对复合材料的隔声性能都有显著的影响。该结果对水下隔声材料的设计有一定的参考意义。     

Acoustic investigation of porous silicon layers

Porous silicon (PS) layers are formed on p⁺ -type silicon wafers by electrochemical anodization in hydrofluoric acid solutions. Microechography and acoustic signature, V(z), have been performed at 1.5 GHz and 600 MHz, respectively, in order to study the elastic properties of PS layers. The thicknesses of PS layers were measured and longitudinal, shear and Rayleigh velocities and Young's modulus were obtained as a function of porosity. Equations showing the porosity dependence of bulk wave velocities and Young's modulus have also been proposed.     

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.     

泡沫塑料杨氏模量所满足的微分方程和一些近似解的讨论

本文通过复合材料力学中的微分法和微观力学分析直接导出了泡沫塑料杨氏模量和泊松比所满足的微分方程组，并通过对方程组的讨论得到了泡沫塑料杨氏模量理论预测的近似公式。这些公式形式简单，与实验符合较好，便于工程应用。     

The relations between the shear modulus, the bulk modulus and Young's modulus for porous isotropic ceramic materials

A relation between the shear modulus and Young's modulus of isotropic porous ceramics has been derived based on the Mori–Tanaka mean-field approach. The applicability of the relation has been evaluated using the experimental values available in the literature for the shear modulus, the bulk modulus and Young's modulus of porous ceramics prepared using various processing techniques and powder sizes. It is also shown that the ratio of the shear to Young's modulus of porous ceramics can be approximated by a constant value of 0.391.     

硬质聚氨酯泡沫塑料压缩力学性能

研究了三种密度不同的聚氨酯泡沫塑料的低速压缩力学性能，用ＳＥＭ分析了初始胞体结构，确定了胞体尺寸及结构特性。     

Critical reevaluation of the prediction of effective Poisson's ratio for porous materials

An equation has been derived for the prediction of the Poisson's ratio of porous materials having ribbon like pores. The equation fits the data of silica gel with ribbon like pores quite well for the whole range of porosity. For spherical pores, a relation derived by previous researchers showed an anomalous variation in Poisson's ratio with porosity. It has been shown that it was due to the mathematical form of the function chosen to describe the relation between the bulk and Young's moduli with porosity. In this analysis, a modified form of the function to describe Young's and bulk modulus with porosity has been suggested for spherical pores. The derived relation for variation of Poisson's ratio with porosity shows good agreement with the prediction by self consistent theory.     

Shear and mode II fracture of PUR foams

Polyurethane (PUR) foam materials are widely used as cores in sandwich composites, for packing and cushioning. They are made of interconnected networks of solid struts and cell walls incorporating voids with entrapped gas. The main characteristics of foams are lightweight, high porosity, high crushability, and good energy absorption capacity. Fracture toughness in mixed mode loading is of particular interest because foam cracking weakens the structure’s capacity for carrying loads.Present paper assesses the shear elastic (shear modulus) and mechanical (shear strength) properties of polyurethane foams. Also, three different types of specimens were used to determine mode I and mode II fracture toughness. The shear modulus, shear strength and fracture toughness increases with increasing foam density. Also the effect of loading direction and loading speed is investigated. The authors propose a micromechanical model to estimate fracture toughness based on the tensile strength of the solid material and the topology of the cellular structure.     

含孔隙混凝土复合材料有效力学性能研究

混凝土、岩石等工程材料是典型的多孔介质材料,孔隙或微裂纹的存在对材料的弹性模量及强度等力学参数产生很大影响。该文基于三相球模型确定了含孔隙复合材料的有效体积模量,提出采用空心圆柱形杆模型推导得到了含孔隙复合材料有效剪切模量的理论公式,并在各向同性材料的假设条件下确定了材料的有效弹性模量及泊松比;推导并得到了含孔隙材料的有效抗拉、抗压强度及有效抗剪强度与孔隙率之间的定量关系公式,并进一步得到了含孔基质在达到有效强度时的临界应变与孔隙率之间的定量关系。结果表明该文方法能较好的预测含孔混凝土材料的有效力学性能,且公式简单,易于应用。     

Strength and elastic modulus of a porous brittle solid: An acousto-ultrasonic study

The strength and elastic modulus of a porous brittle solid such as gypsum have been studied using an acousto-ultrasonic technique. Acousto-ultrasonics has been found to be a sensitive indicator of strength and porosity which are linearly related to some powers of a stress wave factor. New equations for porosity dependence of ultrasonic velocity, elastic modulus and strength of brittle solids have been proposed.