钢纤维／聚合物复合材料性能研究

以HDPE和ABS为基体树脂，钢纤飨为填充材料制备了钢纤维／聚合物复合材料，研究了钢纤维含量和长径比对复合材料导电性能，力学性能和导热性能的影响，考察了重复加工次数与纤维长径比和复合材料性能的关系。     

LDPE/不锈钢纤维电磁屏蔽材料的性能研究

以不锈钢纤维作为导电填料，添加到低密度聚乙烯（LDPE）中，制备了一种电磁屏蔽材料。分析了不锈钢纤维的加入对复合材料电磁性能、导电性能和力学性能的影响。结果表明，LDPE/不锈钢纤维复合材料的电磁屏蔽效能与不锈钢纤维的长径比成正比，添加了长径比大的不锈钢纤维的LDPE的导电性能更佳。随着不锈钢纤维用量的增加，LDPE／不锈钢纤维复合材料的拉伸强度和断裂伸长率都有较大幅度的下降。     

铜纤维长径比的分布对复合材料性能的影响

以ＨＤＰＥ为基材，选用冷拉法铜纤维为填料，建立了长径比的测定方法，采用概率和数理统计证明纤维长度的分布状态符合正态分布，成型加工条件对铜纤维的长径比和分布有明显革影响，不同长径的铜纤维对复合材料的性能影响也不同。     

工艺条件对沥青炭纤维/ABS树脂复合材料导电性及力学性能的影响

研究了单螺杆挤出机挤出温度及螺杆转速对沥青炭纤维填充ＡＢＳ树脂复合材料导电性及力学性能的影响。结果表明,纤维经挤出后,纤维长度有不同程度的降低,长径比减小,随着挤出的升高及螺杆转速的降低,纤维长径比增大,挤出条件对复合材料电性能及力学性能的影响主要可归结为长径比对材料的影响,随着长径比增加,复合材料的导电性及拉伸强度均有增大。此外,复合材料导电性及拉伸强度随复合材料中纤维填加量的增多而增大。     

纤维增强聚合物发泡体的研究进展

纤维增强聚合物发泡体是一种新型的三相复合材料，纤维增强发泡体可以大大提高发泡体的弹性模量和压缩模量，提高材料的破坏强度，也显著地降低了材料的收缩率，因而可用于结构性材料。纤维增强发泡体中纤维特性，长径比，用量，与基体的粘合状态，泡孔的大小，形状，发泡密度等因素对发泡体系的性能均有影响，其中粘合是非常生要的。过长的纤维由于结构缠结对聚合物发泡体的增强并不理想。     

挠度对大长径比复合材料壳体缠绕成型质量影响研究

大长径比复合材料缠绕成型壳体在成型过程中会产生挠度。本文针对挠度对壳体的缠绕线型、缠绕张力和固化残余应力的影响开展研究。通过解析计算和数值仿真建立大长径比复合材料壳体几何模型和有限元模型。分别采用测地线缠绕方法探究挠度对纤维缠绕线型的影响;采用正轴偏轴应变转换方法探究挠度对纤维缠绕张力的影响;采用CHILE本构模型探究挠度对纤维缠绕固化残余应力的影响。通过对大长径比复合材料壳体的仿真分析发现,挠度对纤维缠绕线型影响较小,挠度对纤维缠绕张力有一定的影响,张力随着壳体挠度位移值的增大而增大,挠度对纤维缠绕固化残余应力有一定的影响,且在壳体周向规律分布。     

晶须长径比对复合材料力学行为影响的模拟

在单向晶须增强树脂基复合材料的轴对称模型和已有研究成果基础上,利用有限元分析方法,研究该类复合材料中晶须长径比的变化对材料整体力学行为的影响.结果表明:1)晶须长径比对晶须应力作用明显大于对基体的影响;2)晶须的长径比h/r≤30时,随着晶须长径比的增大,发生在晶须端部处的集中应力急剧增加;但当长径比h/r≥30时,长径比的进一步增加对集中应力影响不大;3)随着晶须长径比的增大,界面剪切应力减小,分布曲线下移;但当长径比h/r≥30时,长径比的进一步增加对剪切应力影响不大;4)随着晶须长径比的增加,复合材料的拉伸强度逐渐增大.     

剑麻纤维增强聚乳酸可降解复合材料力学性能

采用正交实验的方法,以纤维长径比、纤维含量和纤维的处理方式为因素,以剑麻纤维增强聚乳酸可降解复合材料的力学性能包括拉伸强度、拉伸模量、弯曲强度、弯曲模量和冲击强度为指标,运用极差和方差分析方法,探讨复合材料力学性能影响因素的敏感性,得到复合材料力学性能最佳的优化方案.     

尼龙短纤维增强PVC流动性研究

用尼龙-6短纤维增强PVC,研究了纤维长径比、用量、表面处理及纤维与基体树脂共混条件对复合材料流动性的影响。发现用自制的封闭异氰酸酯增粘体系(TDI)处理纤维所得复合材料的流动性优于用其它增粘体系。     

短纤维直径对橡胶复合材料性能的影响

制备了 3种具有不同直径、相同长径比及其分布的涤纶短纤维增强氯丁橡胶基复合材料。对屈服强度及伸长率、断裂强度及伸长率以及撕裂强度等力学性能的研究发现 :在相同长径比及其分布情况下 ,与传统混合法则不同的是屈服强度和伸长率不相等 ,也不是只取决于短纤维的直径 ,而是受直径和长度的共同作用 ;在相同的纤维体积分数时 ,复合材料的断裂强度基本相同 ,而断裂形变和撕裂强度随纤维直径的减小而增大     

High-Temperature Flow Behavior of SiC-Glass Composites in Compression and Tension

The high-temperature flow behavior of different borosilicate composites was investigated in compression and tension. The flow behavior of composites changed from Newtonian to non-Newtonian as the volume fraction and aspect ratio of reinforcements increased. Generally, platelet/particulate composites exhibited higher tensile elongations compared with short fiber/whisker composites. The tensile ductility increased with decreased volume fraction of reinforcements and temperature. Cavitation in these samples varied across the length, and maximum cavitation occurred near the fracture zone.     

Rheological behaviour of borosilicate composites with metallic and non-metallic dispersions

Silicate matrix composites are potential candidates for high-temperature applications. In the present investigation, the effect of metallic (Cu) and non-metallic (SiC particulates, platelets, short fibres and whiskers) additions on the rheological behaviour of borosilicate matrix composites has been evaluated. The hot-pressed composites were tested both in compression and tension in the temperature range of 625–725°C. SiC reinforced composites tested in compression exhibited varying degree of strengthening and strain rate sensitivity depending on the volume fraction and morphology of reinforcements. The degree of strengthening and strain rate sensitivity depends on the volume fraction and morphology of reinforcements. Strengthening effect increased with the volume fraction and aspect ratio of reinforcements. The flow behaviour of composites changed from Newtonian to non-Newtonian with strain rate sensitivity index value changing from unity to 0.48. A similar trend was seen in the rate sensitivity of copper composites. However, copper additions decreased the strength of the composites at lower temperatures because of the softer copper phase. Pre-oxidation of copper particles had certain strengthening effect on the composite. The apparent viscosity of SiC reinforced composites increased with volume fraction and aspect ratio of reinforcements. However, in particulate composites, the viscosity found to increase with particle size. The mechanical/hydrodynamic interactions among the particulates appeared to be responsible for such a behaviour. With increasing strain rate, the viscosity decreased progressively confirming the shear thinning of the composites. The tensile ductility of the composites with 40 vol% reinforcements was evaluated at 700°C. While 400% elongation was observed in SiC particulate, platelet and copper composites, in short fibre/whisker composites, the tensile elongation values were only 150%. Further, the elongation of SiC platelet and copper composites improved by decreasing temperature and volume fraction of reinforcements, and also elongation values >500% were recorded. The tensile ductility of borosilicate composites was limited by onset and growth of cavities nucleated at the reinforcement/matrix interfaces.     

Filler fraction effect on creep response of crosslinked polyester matrix with mineral filler

The effect of a particle marble filler on the creep response of a crosslinked polyester matrix before and after physical aging is described. Composites with various filler–polyester matrix percentages are prepared by applying mixing technology, curing at room temperature, and postcuring above the glass‐transition temperature. Two groups of specimens of identical composition are studied. The first group is tested 1 month after preparation (relatively nonaged), whereas the second group is tested after 13 years of storage at stable room temperature and humidity, at current atmospheric pressure, and in the absence of direct light (aged). The two groups of specimens (aged and nonaged) are subjected to creep measurements. The modulus of elasticity and the creep compliance are determined, plotted against the filler volume fraction, and fit by empirical equations. A simple mechanical model is proposed to fit the compliance curves, and good agreement between the measured and predicted values is shown. The mechanical behavior of the composites is also described, using empirical equations that fit the relation between the composite/matrix ratio of the deformation characteristics and the filler volume fraction. A crucial matrix influence is proposed to fit the compliance curves, and good agreement between the measured and predicted values is shown. Experimentally established natural regularities can be used to predict the creep compliances of composites from a less demanding experimental program. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3329–3335, 2003     

Small-angle X-ray study of particulate reinforced composites

Small-angle X-ray scattering technique can be used to quantify the microvoids structure within a particulate reinforced composite. An expression for the correlation function of three-phase systems has been derived in terms of the correlation function of the individual phases. By using this expression and the scattered intensities from the damaged and the undamaged composites; it has been show that the volume fraction and the chord length of the microvoids can be obtained, provided no damage occurs to the reinforcement particles. In cases where the microvoids are preferentially oriented within the composites, an approximation scheme based on a linear transformation method has also been developed to measure the aspect ratio of the microvoids provided the volume fraction of these microvoids is much smaller than the other two phases.     

Computation of Effective Steady‐State Creep of Porous Ni–YSZ Composites with Reconstructed Microstructures

This paper investigates the effective steady‐state creep response of porous Ni–YSZ composites used in solid oxide fuel cell applications by numerical homogenization based on three‐dimensional microstructural reconstructions and steady‐state creep properties of the constituent phases. The Ni phase is found to carry insignificant stress in the composite and has a negligible role in the effective creep behavior. Thus, when determining effective creep, porous Ni–YSZ composites can be regarded as porous YSZ in which the Ni phase is counted as additional porosity. The stress exponents of porous YSZ are the same as that of dense YSZ, but the effective creep rate increases by a factor of 8–10 due to porosity. The relationship of creep rate and volume fraction of YSZ computed by numerical homogenization is underestimated by most existing analytical models. The Ramakrishnan–Arunchalam creep model provides the closest approximation among all analytical models.     

Computer simulation of the electrical conductivity of polymer composites containing metallic fillers

In this study, a theoretical basis for the use of conductive composites was established. A percolation simulation program was used to determine critical area fractions for dispersions of rectangles in two dimensions. Both the aspect ratio and orientations of the rectangles were varied independently, and the simulation results were used to predict the effect of these parameters on the critical concentration of conductive flakes in a filled polymer. Above a certain aspect ratio defined as the “scaling limit,” the critical area fraction for rectangles was inversely proportional to aspect ratio. The scaling limit was smallest for a set of randomly oriented rectangles, and its value became larger as greater degrees of alignment were imposed. The smallest critical area fractions belonged to high aspect ratio, randomly oriented rectangles. The predictions of percolation theory were compared with results for dispersions of nickel-coated mica in fine glass powder and in compression molded polyethylene. The critical volume fraction of mica was inversely proportional to flake aspect ratio over the range of aspect ratios tested. Electromagnetic interference (EMI) shielding effectiveness was examined for composites containing both aligned and randomly oriented flakes. For a given filler loading, the shielding effectiveness of the aligned flake composites was substantially lower than that of the composites containing randomly oriented flakes.     

Structure-property relationships in nanocomposites

A numerical finite-difference model is presented for the study of the factors controlling the properties of composites reinforced with platelets and fiber-like nano-inclusions. The approach provides a comprehensive treatment of the dependence of composite modulus and strength on the shape of the inclusions and the interrelated effects of their orientation, volume fraction, aspect ratio, modulus and interfacial properties with the matrix. At the same volume fraction, we find that platelets are generally more efficient than fibers in improving composite modulus. This is rationalized through our model finding that fibers have a typically low critical aspect ratio value, which puts an upper limit to their reinforcement potential. Platelets also turn out to be superior to fibers in all nanocomposites characterized by a poor orientation of the inclusions. We also find that low interfacial adhesion and poor dispersion of the inclusions lead to a decrease in reinforcement efficiency. Turning to comparison with experiment, a good agreement is found between our model predictions and modulus data on nanocomposites reinforced with montmorillonite platelets and carbon nanotubes.     

Theoretical determination of the optimal fiber volume fraction and fiber-matrix property compatibility of short fiber composites

Although the question of minimum or critical fiber volume fraction, beyond which a composite can then be strengthened due to addition of fibers, has already been dealt with by several investigators for both continuous and short fiber composites, a study of maximum or optimal fiber volume fraction at which the composite reaches its highest strength has not been reported. The present analysis has investigated this issue for short fiber case based on the well-known shear lag (the elastic stress transfer) theory. Using the relationships obtained, the minimum spacing between fibers is determined upon which the maximum fiber volume fraction can be calculated. The effects on the value of this maximum fiber volume fraction due to such factors as the mechanical properties of the fiber and matrix, the fiber aspect ratio, and fiber packing forms are discussed. Furthermore. Combined with the previous analysis on the minimum fiber volume fraction, this maximum fiber volume fraction is used to examine the property compatibility of fiber and matrix in forming a composite. This is deemed to be useful for composite design. Some examples are provided as well to illustrate the results.     

Carbon nanotube functionalization effects on thermal properties of multiwall carbon nanotube/polycarbonate composites

The thermal properties of composites based on polycarbonate (PC) filed with ultraviolet/ozone (UVO) treated multiwall carbon nanotubes (MWCNTs) in low limit (less than 0.01) volume fractions have been investigated. The composites were prepared in the form of films of relatively small thickness (23–33 μm) with random orientation of treated MWCNTs. Functionalization of MWCNTs has been confirmed through Fourier transform infrared measurements. Thermal conductivity was obtained by measuring both of thermal diffusivity and thermal effusivity using photoacoustic technique. The results reveal that the addition of UVO treated MWCNTs lead to enhance both the thermal diffusivity and thermal effusivity of the composites. Insertion of 0.95% MWCNTs into PC improves the thermal conductivity of the composites by ∼22%. This enhancement is reasonable using such low content of MWCNTs of moderate aspect ratio. The experimental results were analyzed using a simple model concerning some relevant parameters such as volume fractions, interfacial thermal resistance, aspect ratio, and nonstraightness of nanotubes. An interface thermal resistance in the low limit of about 2.1 × 10⁻⁸ m²K/W has been estimated. In the light of these results, the role of MWCNTs functionalization on the overall thermal transport properties of MWCNTs‐polymer composites has been discussed. POLYM. COMPOS., 36:1242–1248, 2015. © 2014 Society of Plastics Engineers     

Temperature-dependent fracture strength of whisker-reinforced ceramic composites: Modeling and factor analysis

In this study, a temperature-dependent fracture strength model for whisker-reinforced ceramic composites was developed. This model considers the strength degradation of both whisker and ceramic matrix at elevated temperatures, as well as the evolution of residual thermal stress with temperature. It was verified by comparison with the available flexural strengths of five types of whisker-reinforced ceramic composites at different temperatures, and good agreement between the model predictions and the experimental data is obtained. Moreover, based on the established model, we systematically analyzed the effects of six influencing factors, including the volume fraction and the aspect ratio of whisker, the Young's modulus of matrix and whisker, the thermal expansion coefficient difference and the stress-free temperature, on the temperature-dependent flexural strengths of whisker-reinforced ceramic composites. Some new insights which could help optimize and improve the temperature-dependent fracture strength of whisker-reinforced ceramic composites are obtained.