轻质环氧复合材料的制备与性能研究

制备了一种以空心玻璃微珠为填充材料的轻质环氧复合材料,确定了材料的固化工艺,并对不同型号的空心玻璃微珠进行了筛选.研究了玻璃微珠填充量对材料密度及力学性能的影响.研究发现,复合材料的密度随空心玻璃微珠填充量的加大呈现先降低后略有升高的趋势;拉伸强度和压缩强度均随填充量的增加而减小;拉伸弹性模量和压缩弹性模量随着填充量提...     

基于ANSYS的PE-HD实壁管性能与尺寸的关系

采用ANSYS逆向模拟分析高密度聚乙烯(PE-HD)实壁管的环刚度测试过程,研究了管材环刚度为6.3时其规格尺寸如直径和壁厚与原材料性能之间的关系,并分析了标准YD/T 841.2-2008的合理性。结果表明,材料的泊松比对管材最大变形量影响较小;材料的弯曲弹性模量越大,管材最大变形量越小;管材环刚度达到6.3时所需要的原材料弯曲弹性模量值与其径厚比成正比直线关系;标准YD/T 841.2-2008中关于某些壁厚的规定存在不合理性,即按照标准中规定的某些壁厚尺寸,生产PE-HD实壁管所用原材料无法达到环刚度为6.3时所需要的弯曲弹性模量值。     

玻璃微珠——微小空心填充剂

一、什么叫玻璃微珠玻璃微珠以玻璃和陶瓷为原料,壁厚2微米,粒径10—250微米,非常细小,富于流动性,是完全中空的珠状填充剂。用肉眼看,它像白色的砂粒;而在显微镜下,是透明、无机的空心球粒。将玻璃微珠和塑料或无机粘结剂配合后,在配合物中形成细小的单个气泡。因其重量轻,故和其它填充剂相比,其强度较高(按重量比),能制成机械加工性能、耐热性能和绝缘性能都优良的塑性薄层材料。这种材料广泛地用作电气设备,海洋用机械等。     

玻璃微珠填充改性PA6的研究

通过对玻璃微珠填充聚酰胺6(PA6)应力-应变行为、力学性能、熔融与结晶特性的研究，发现部分试样在拉伸过程中出现二次屈服(或二次成颈)现象。玻璃微珠的加入，同时起到增强和增刚作用，但体系的韧性有所下降，玻璃微珠粒径越小，增强、增刚效应越显著。随玻璃微珠含量增大，屈服强度增大，在玻璃微珠含量10％～15％时出现最大值，而后略有降低；弹性模量、弯曲强度和弯曲模量则呈线性增长。玻璃微珠粒径与含量对材料的熔融与结晶特性的影响都较小，表明界面作用与比表面积对材料力学性能的变化影响更大。     

空心微珠填充聚丙烯复合材料的研究

研究了空心微珠含量、粒径以及改性剂对聚丙烯复合材料性能的影响。研究结果表明,当空心微珠填充量在0－30％（质量,下同）之间时,空心微珠／聚丙烯复合材料的常温和低温下的缺口冲击强度、拉伸性能、弯曲性能都显著提高,当加入改性剂时,提高得更加显著。当空心微珠含量为20％时材料的性能提高到实验中的最大值,弹性模量提高了83％。同时,通过材料的DSC轨迹分析研究了材料的热性能,并进行了扫描电镜分析。空心微珠填充聚丙烯不仅能提高聚丙烯材料的力学性能和热性能,而且可以降低聚丙烯复合材料的成本。     

GB/HDPE复合材料拉伸性能及介电性能研究

采用小粒径玻璃微珠（GB）与HDPE熔融共混,研究了玻璃微珠用量及表面处理对复合材料拉伸性能及介电性能的影响。研究结果表明,无论玻璃微珠表面处理与否,GB／HDPE复合材料的拉伸强度和拉伸弹性模量均随着玻璃微珠用量的增加而增大;经过偶联剂KH550和EB151处理的玻璃微珠与HDPE复合后,拉伸强度和拉伸弹性模量有一定的提高。复合材料的介电常数随玻璃微珠用量增加呈现增大的趋势,经过改性的复合材料的介电常数比未经改性的有所增加,而玻璃微珠的添加和界面改性对介电损耗的影响不大。     

HGB/EP复合泡沫材料界面破坏模拟研究

空心玻璃微珠(HGB)/环氧树脂(EP)复合泡沫材料是一种新型的结构功能双重材料,其两种材料相互间的黏结性能对复合材料的力学性能有较大的影响。通过设计玻璃与环氧树脂的黏结力实验测得了黏结力与变形的关系。建立玻璃微珠与环氧树脂的数值模拟模型,采用实验所得数据在其间设置黏结单元,对六种情况下的模型施加拉伸和压缩均布载荷进行数值模拟,考察两种材料间界面的变形和破坏情况,研究了界面破坏时复合泡沫材料所受的极限载荷,分析了极限载荷随玻璃微珠半径及填充比的变化规律,发现其与相关文献实验结果一致。     

空心微珠填充CPU性能的研究

以PEA/TDI-100/MOCA体系为基础,研究了空心微珠填充聚氨酯材料的合成工艺及力学性能,并探讨了空心微珠用量对聚氨酯材料耐热性能和耐水性能的影响。结果表明,硬段含量对聚氨酯材料的力学性能有显著影响;偶联剂种类及用量对空心微珠填充聚氨酯弹性体有影响;空心微珠能够提高聚氨酯弹性体的热稳定性。     

环氧树脂基固体浮力材料的研制及表征

采用空心玻璃微珠填充环氧树脂研制固体浮力材料。间苯二胺 (MPD)、顺丁烯二酸酐 (MA)、二氨基二苯砜(DDS)及 593四种固化剂对比研究表明,MPD和DDS环氧树脂固化体系轴向压缩强度可达 210MPa。γ 氨丙基三乙氧基硅烷(KH—550)偶联剂在无机玻璃微珠与有机环氧树脂的复合过程中,可增加环氧树脂与微珠之间的亲合,电镜照片观察到微珠与环氧树脂间无界面沟隙,粘结界面均匀。空心玻璃微珠质量填充量为 25%时,复合材料密度降低至 0. 61g/cm3,轴向压缩强度仍能保持在 40MPa以上。     

玻璃微珠填充聚丙烯复合材料的力学性能

研究了玻璃微珠填充聚丙烯中玻璃微珠含量及粒径大小对复合材料力学性能的影响。结果表明,填充体系随着微珠体积分数V_f的增加,拉伸弹性模量E_c和冲击强度S_(IC)呈非线性函数形式增大,而拉伸屈服强度σ_(yc) 则相反,在相同条件下,小粒径微珠填充体系的E_c和σ_(yc)稍高于大粒径微珠填充体系。在V_f为0～20％的范围内,复合材料的S_(IC)为纯聚丙烯的1.4倍。     

Effect of composition and high-temperature annealing on the local deformation behavior of silicon oxycarbides

Silicon oxycarbides with varying compositions were investigated concerning their elastic and plastic properties. Additionally, the impact of thermal annealing on their elastic properties was assessed. Phase separation of SiOC seems to have no significant impact on Young’s modulus (high values of β-SiC compensate the low values of the vitreous silica matrix) and hardness. However, it leads to an increase in Poisson’s ratio, indicating an increase in the atomic packing density. The phase composition of SiOC significantly influences Young’s modulus, hardness, brittleness and strain-rate sensitivity: the amount of both β-SiC and segregated carbon governs Young’s modulus and hardness, whereas the fraction of free carbon determines brittleness and strain-rate sensitivity. Thermal annealing of SiOC glass-ceramics leads to an increase in Young’s modulus. However, the temperature sensitivity of Young’s modulus and Poisson’s ratio is not affected, indicating the glassy matrix being stable during thermal annealing. A slightly improved ordering of the segregated carbon and the β-SiC nanoparticles upon thermal annealing was observed. It is suggested that this is responsible for the increase in Young’s modulus.     

单搭接接头峰值应力数值模拟的正交法分析

运用正交试验法研究了几个主要力学和几何参数如泊松比,弹性模量和被粘物厚对单搭接接头Von Mises等效应力的影响。有限元分析结果的极差分析、方差分析和最优方案的工程平均等结果表明:被粘物厚对单搭接接头Von Mises等效应力影响最大,弹性模量次之,泊松比影响程度最小。分析可知:高的泊松比、低弹性模量和被粘物厚的增大会使得Von Mises等效应力值显著降低。     

Elastic Modulus of Fibers Spun from the Binary Polymer Blends

Abstract

Among mechanical properties of polypropylene fibers, spun from the blend of medium molecular weight CR-polymer with added high molecular weight polymer in the composition range of. 10-50 wt%, special interest is focused on the elastic modulus in this paper. In the case of two-phase composite system, the resultant modulus is a function of the moduli of the individual pure components, the volume of the weight fraction, the geometry and packing of the disperse phase and the Poisson ratio of the matrix. In present paper only several representative equations for the calculation of elastic properties of a two-phase systems are presented. This present work is concerned with applicability of those theories to the specific case, drawn polypropylene fibers spun from blend of different polymer grades. Predicted elastic modulus calculated from the Kleiner's simplex equation is compared with the elastic modulus of drawn fibers determined from the stress vs. strain curve.     

Adhesion of a rigid punch to a confined elastic layer revisited

The adhesion of a punch to a linear elastic, confined layer is investigated. Numerical analysis is performed to determine the equivalent elastic modulus in terms of layer confinement. The size of the layer relative to the punch radius and its Poisson’s ratio are found to affect the layer stiffness. The results reveal that the equivalent modulus of a highly confined layer depends on its Poisson’s ratio, whereas, in contrast, an unconfined layer is only sensitive to the extent of the elastic film. The solutions of the equivalent modulus obtained from the simulations are fitted by an analytical function that, subsequently, is utilized to deduce the energy release rate for detachment of the punch via linear elastic fracture mechanics. The energy release rate strongly varies with layer confinement. Regimes for stable and unstable crack growth can be identified that, in turn, are correlated to interfacial stress distributions to distinguish between different detachment mechanisms.     

The effect of interlayers on the transverse stresses in fiber composites

Numerical results are given of calculations of the radial, transverse, and shear stresses in the matrix surrounding a cylindrical inclusion in plane strain perpendicular to the cylinder axis, this being taken as a model of a fiber composite under transverse loading. It is shown that the presence of an interlayer on the fiber at a thickness which is a small fraction of the fiber diameter can significantly affect the stress concentrations in the matrix. The interlayer-fiber ‘composite’ can be ‘matched’ to the matrix by suitable choice of interlayer elastic moduli. In particular, if the shear modulus of the interlayer is smaller than that of the matrix and its Poisson's ratio is very small, the stress concentrations in the matrix are considerably reduced and the composite should be less subject to failure by delamination.     

Modeling of elastic properties and conductivity of partially sintered ceramics with duplex microstructure and different grain size ratio

The elastic constants and conductivity of partially sintered single-phase and two-phase ceramics (exemplified by alumina ceramics and alumina-zirconia composites, respectively) with different grain size ratio (from 1:1 to 1:4) are investigated by numerical modeling. The relative elastic moduli of partially sintered two-phase ceramics are shown to be relatively similar to those of single-phase ceramics, whereas the relative conductivity is significantly lower, because of the higher phase contrast. The more the grain size ratio deviates from unity, the higher is the initial packing fraction, and the lower are the relative elastic moduli and conductivity of the partially sintered ceramics. The porosity dependence of the Poisson ratio shows a decreasing trend which is only very weakly affected by the grain size ratio. Correlations between relative Young’s modulus and relative conductivity lie between upper and lower cross-property bounds. For single-phase materials the correlation lies below, for two-phase materials above, the Pabst-Gregorová cross-property relation.     

Hertzian-Crack Suppression in Ceramics with Elastic-Modulus-Graded Surfaces

Hertzian (spherical) indentation experiments were carried out in a graded alumina-glass composite whose Young's modulus increased with depth beneath the indented surface. An in situ processing method involving impregnation of a dense, fine-grained alumina by an aluminosilicate glass was employed to fabricate such a composite. With this technique, a monotonic, unidirectional variation in Young's modulus of as much as 50% was introduced over a distance of approximately 2 mm, while keeping the coefficient of thermal expansion and the Poisson ratio for the glass and the alumina nearly the same. The macroscopically graded, elastic composite so produced with nearly full density has essentially no macroscopic, long-range residual stresses following processing. The unidirectional variation in Young's modulus under the indenter is shown to fully suppress the formation of Hertzian cone cracks. Without these elastic-modulus gradients, cone-crack formation was observed in bulk glass and alumina. Finite-element analyses of spherical indentation on elastically graded substrates were also performed to develop a quantitative understanding of the experimental trends. It is reasoned that the present innovations, involving functionally graded surfaces and their in situ processing, provide new possibilities for enhancing certain contact-damage resistance characteristics in various ceramic materials for a broad range of engineering applications. Furthermore, this contact-damage-resistance phenomenon in functionally graded ceramics is elastic in nature, and is, therefore, likely to be immune to mechanical fatigue within the elastic limit.     

Longitudinal Strain Dependent Variation of Poisson’s Ratio for HTPB Based Solid Rocket Propellants in Uni‐axial Tensile Testing

Poisson’s ratio of HTPB based composite propellant is estimated at break using double dumbbell specimens as per ASTM D638 Type IV standard and its value obtained by change in the volume of specimens is calculated as approximately 0.25. This major finding contradicts the behaviour of solid rocket propellants in respect of Poisson’s ratio, which is reported to be 0.5. Further, Poisson’s ratio varies almost linearly with strain even in linear portion of stress‐strain curve in uni‐axial tensile testing as per theoretical calculations. It must be noted that no change in volume does not necessarily indicate constant Poisson’s ratio equal to 0.5. SEM scan indicates that the rate of reduction of Poisson’s ratio with longitudinal strain accelerates after dewetting due to the formation of vacuoles. Bilinear variation of Poisson’s ratio with longitudinal strain is observed. One slope is valid in pre‐dewetting region, calculated from close form solution and other slope is valid for post‐dewetting region, which is measured at break. Measurement of Poisson’s ratio at various longitudinal strains indicates uni‐linear variation and not a bilinear variation with a kink. It is also observed that Poisson’s ratio is different along different lateral directions of the propellant specimen. Poisson’s ratio in two orthogonal directions perpendicular to longitudinal axis is calculated as 0.17 and 0.30. As ASTM Specimen has rectangular cross‐section of approximate size 6×4 mm, the directional behavior of Poisson’s ratio may be attributed to initial dimensions. Prismatic propellant specimen with square cross‐section of 115×6×6 mm dimension do not show any variation in respect of Young’s modulus, tensile strength and percentage elongation as compared to ASTM specimen. Directional behavior of Poisson’s ratio with almost similar numerical value is again observed, thus ruling out dependence of this behavior on different initial dimensions of propellant cross‐section. The propellant slurry flow during vacuum casting, directional curing and orientation of specimen with respect to web of the cast propellant are mainly responsible for this directional behaviour of Poisson’s ratio for the composite propellants. Composite propellants behave as compressible material in most of the region and near failure region or at higher strains; Poisson’s ratio is not anywhere close to 0.5, instead it is close to 0.25.     

On the prediction of graphene’s elastic properties with reactive empirical bond order potentials

The elastic properties of graphene as described by the reactive empirical bond order potential are studied through uniaxial tensile tests calculations at both zero temperature, with a conjugate gradient approach, and room temperature, with molecular dynamics simulations. A perfect linear elastic behavior is observed at 0 K up to ≈0.1% strain. The Young’s modulus and Poisson’s ratio obtained with this potential are of ≈730 GPa and 0.39, respectively, with little chirality effects. These values differ significantly from former estimations, much closer to experimental values. We show that these former values have certainly been obtained by neglecting the effect of atomic relaxation, leading to a severe inaccuracy. At larger strains, an extended apparent linear domain is observed in the stress–strain curves, which is relevant to Young’s modulus calculations at finite temperature. Our molecular dynamics simulations at 300 K have allowed obtaining the following, chirality dependent, apparent Young’s moduli, 860 and 761 GPa, and Poisson’s ratios, 0.12 and 0.23, for armchair and zigzag loadings, respectively.     

The transverse elastic modulus of fiber-reinforced composites as defined by the concept of interphase

A theoretical expression for the prediction of the transverse elastic modulus in fiber-reinforced composites was developed. The concept of interphase between fibers and matrix was used for the development of the model. This model considers that the composite material consists of three phases, that is, the fiber, the matrix, and the interphase. The latter is the part of the polymer matrix lying at the close vicinity of the fiber surface. In the present investigation it was assumed that the interphase is inhomogeneous in nature with continuously varying mechanical properties. Different laws of variation of its elastic modulus and Poisson ratio were taken into account in order to define the overall modulus of the composite. Thermal analysis method was used for the estimation of the thickness of the interphase. The results obtained were compared with the respective values of other models as well as with experimental data. © 1993 John Wiley & Sons, Inc.