The Mechanical Properties and Chemical Resistance of Short Glass-Fiber-Reinforced Epoxy Composites

ABSTRACT

Epoxy–short glass fiber composites were prepared by directly blending two-pack system of Araldite (CY-230) and hardner (HY-951) with short glass fibers. The short glass fiber content was varied from 2% to 10% by weight of the total matrix. These composites were then characterized for morphology using scanning electron microscopy, mechanical properties, that is, tensile and flexural properties and resistance toward various chemicals. The epoxy-glass fiber composites showed improved tensile and flexural properties but increased dispersion among the properties with increasing fiber content. Several reasons to explain these effects in terms of reinforcing mechanisms were discussed. These composites were stable in most chemicals but were completely destroyed in concentrated sulfuric acid, nitric acid, and pyridine.     

Correlating Electrical Resistance Change with Mechanical Damage in Woven SiC/SiC Composites: Experiment and Modeling

Silicon carbide (SiC) fiber‐reinforced SiC matrix composites are inherently multifunctional materials. In addition to their primary function as a structural material, the electric properties of the SiC/SiC composites could be used for the sensing and monitoring of in situ damage nucleation and evolution. To detect damage and use that information to further predict the useful life of a particular component, it is necessary to establish the relationship between damage and electrical resistance change. Here, two typical SiC/SiC composites, melt infiltrated (MI), and chemical vapor infiltrated (CVI) woven SiC/SiC composites, were tested to establish the relationship between the electrical response and mechanical damage in unload–reload tensile hysteresis tests. Compared to the 55% resistance increase seen for CVI composites, the MI SiC/SiC composites exhibit a maximum resistance change in 450% in response to mechanical loading (damage), which is the highest sensitivity known among various composites. An analytic model accounting for fiber breakage and matrix cracks was developed to link the electrical resistance to mechanical damage in the composites. The predictions from the models agree well with the experimental data for both composites with high and low conductive matrices. The residual resistance change after unloading is also correlated to the loading history by the analytical relationship. This study demonstrates that resistance change is sensitive to damage in a predictable manner and can be used to improve the reliability of damage assessment of SiC/SiC composites.     

聚甲基丙烯酸丁酯／炭黑导电复合材料在有机蒸气中的电阻响应

研究了由原位聚合法制备的聚甲基丙烯酸丁酯／炭黑（PBMA／CB）复合材料在有机溶剂蒸气中的电阻响应。结果表明，复合材料在有机溶剂蒸气中的电阻响应显著依赖于聚合物基体与有机溶剂的相容性，而且其电阻响应程度大小可以由聚合物摹体和有机溶剂之间的三维溶度参数差之和（△δ^2）来衡量；温度会显著影响复合材料在有机溶剂蒸气中的电阻响应时间，对电阻响应程度也有一定程度的影响，这一结果与聚合物基体的玻璃化转变温度有关；复合材料对有机蒸气的最大电阻响应程度随有机蒸气分压呈现指数级增长；自然老化会导致复合材料电阻响应程度的下降，但恢复性能显著提高，负蒸气系数效应（NVC）强度减弱。PBMA／CB复合材料可以作为气敏材料用于检测有机溶剂蒸气。     

MAH接枝改性PP基木塑复合材料抗老化性能研究

利用MAH和DCP接枝改性PP,再加入一定比例的木粉、助剂制得PP基木塑复合材料.通过对比KH550共混改性PP基木塑复合材料、纯PP材料在经过2400 h紫外光加速老化试验后的吸水性能、拉伸强度、弯曲强度、冲击强度.结果显示:MAH接枝改性PP的WPS吸水率、吸水厚度膨胀率比纯PP材料更大.老化前后MAH接枝改性PP...     

Microcellular Foamed Wood‐Plastic Composites by Different Processes: a Review

Wood fiber reinforced polymer composites represent a relatively small but rapidly growing material class, extensively applied in interior building applications and in the automotive industry. The polymer‐wood fiber composites utilize fibers as reinforcing filler in the polymer matrix and are known to be advantageous over the neat polymers in terms of the materials cost and mechanical properties such as stiffness and strength. Wood fiber reinforced polymer composites are microcellularly processed to create a new class of materials with unique properties. Most manufacturers are evaluating new alternatives of foamed composites that are lighter and more like wood. Foamed wood composites accept screws and nails like wood, more so than their non‐foamed counterparts. They have other advantages such as better surface definition and sharper contours and corners than non‐foamed profiles, which are created by the internal pressure of foaming. This paper represents a review on microcellular wood fiber reinforced polymer composites obtained by different processes (batch, injection molding, extrusion, and compression molding process) and includes an overview of foaming agents (physical and chemical) and the foaming of wood fiber‐polymer composites (changes in phase morphology, formation of polymer‐gas solution, cell nucleation, and cell growth control).

     

Boron Nitride–Aluminum Nitride Ceramic Composites Fabricated by Transient Plastic Phase Processing

BN–AlN ceramic composites have been successfully fabricated by a novel process referred to as transient plastic phase processing (TPPP). The process used BN as both the reactant phase and the matrix and Al as the transient plastic phase. The products AlN and AlB₁₂ were regarded as the reinforcing phases. With the addition of Al powder in BN, both the mechanical and thermal properties were improved. Relatively high green density (2.03 g/cm³, 82.0% of theoretical density (TD)) and as-sintered density (2.18 g/cm³, 92.6%TD), high bending strength (106 MPa), and high thermal conductivity (72 W/(m·K)) were attained for one kind of BN–AlN composite. A low thermal expansion coefficient of 2.0 × 10⁻⁶/K was also achieved.     

造粒工艺对PP基木塑复合材料的耐老化性能影响研究

材料耐老化性能对于提高木塑复合材料的使用寿命至关重要.本文采用正交试验法研究木粉粒径、挤出温度、挤出机喂料速度、挤出机主机频率四个因素对PP基木塑复合材料的耐老化性能影响程度大小.实验结果显示4个因素对老化后材料静曲强度和色差影响程度大小为:木粉粒径>挤出机主机频率>挤出温度>挤出机喂料速度.最佳造粒工艺条件是:木粉粒...     

Monitoring Charge Exchange in P3HT-Nanotube Composites Using Optical and Electrical Characterisation

Charge exchange at the bulk heterojunctions of composites made by mixing single wall nanotubes (SWNTs) and polymers show potential for use in optoelectronic devices such as solar cells and optical sensors. The density/total area of these heterojunctions is expected to increase with increasing SWNT concentration but the efficiency of solar cell peaks at low SWNT concentrations. Most researchers use current–voltage measurements to determine the evolution of the SWNT percolation network and optical absorption measurements to monitor the spectral response of the composites. However, these methods do not provide a detailed account of carrier transport at the concentrations of interest; i.e., near or below the percolation threshold. In this article, we show that capacitance–voltage (C–V) response of (metal)-(oxide)-(semiconducting composite) devices can be used to fill this gap in studying bulk heterojunctions. In an approach where we combine optical absorption methods with C–V measurements we can acquire a unified optoelectronic response from P3HT-SWNT composites. This methodology can become an important tool for optoelectronic device optimization.     

Transient Plastic Phase Processing of Titanium–Boron–Carbon Composites

Ceramic/ceramic composites in the Ti-B-C system were fabricated by a novel process referred to as transient plastic phase processing (TPPP). The basic concept is based on the following reaction:

• "soft" transient plastic matrix

• + reactant phase → hard matrix

• + reinforcement phase

where the transient plastic phase is a phase with a wide range of stoichiometry and a yield point that is a strong function of that stoichiometry. The reactant phase is one that will react with the transient phase in such a way so as to shift the composition of the latter toward its harder and more refractory composition. The composite is formed in two stages: In the first, pressure is applied to shape and fully densify the reactants while the transient phase is soft, i.e., before reaction. Once the reactants are densified, the reaction is allowed to proceed, forming a new phase and rendering the matrix more refractory. If the volume change upon reaction is small, then the density of the final compact will remain near theoretical. Using this approach ceramic/ceramic composites in the Ti─B─C system were hotpressed to full density and complex shapes at temperatures as low as 1600°C.     

Ambient- and High-Temperature Properties of Titanium Carbide–Titanium Boride Composites Fabricated by Transient Plastic Phase Processing

Ambient- and high-temperature properties of a class of titanium carbide-titanium boride composites that have been produced by transient plastic phase processing are presented. The composites produced are comprised of Ti₃B₄, TiB₂, and TiC_0.65 at their equilibrium composition (34.5, 30.5, and 34.9 vol%, respectively), and the Ti₃B₄ phase in these composites occurs either as equiaxed grains or as platelets, depending on the starting mixture composition. Measurements of the ambient- and high-temperature flexure strength and fracture toughness, thermal shock susceptibility, oxidation resistance, and wear resistance of this class of composites are presented. The role of various microstructural parameters—such as the morphology of the Ti₃B₄ phase, the length scale of the microstructure, and the volume fraction of borides—on these properties has been identified.     

无损监测技术在复合材料中的应用研究

本文利用JF2107B型自动介电分析仪对环氧/玻璃纤维复合材料的固化历程进行了研究。研究了升温速率、固化剂含量对复合材料介电性能的影响。结果表明,以1.25℃/min、2.5℃/min、5℃/min三种速率进行线性升温,随升温速率增加,tgδ曲线向左移动,损耗峰出现较早,表明固化反应提前了。环氧/玻璃纤维复合材料中,固化剂含量为65%时,tgδ与固化度分别为0.0538和98.5%。树脂固化终点的tgδ值与固化剂含量呈抛物线关系,有最小极值,最小极值点的配比为最佳配比,其C点tgδ值最低,固化度最高。     

Oxidation Resistance of Alumina–Titanium Nitride and Alumina–Titanium Carbide Composites

The presence of TiC or TiN paritcles in an Al₂O₃ matrix affects the thermal stability of the composites in oxidizing environments. In isothermic oxidation tests at 700°, 800°, 900°, 1000°, and 1100°C for up to 20 h, two different oxidation regimes have been observed at T < 900°C and at 900°C ≤ T ≤ 1100°C. At low temperatures ( T < 900°C), the oxidation follows a phase-boundary reaction; the reaction product initially consists of aggregates of submicrometer needlelike TiO₂ rutile crystals that subsequently grow and coalesce. When a continuous TiO₂ rutile layer is formed ( T ≥ 900°C), the oxidation kinetics change to parabolic, and the diffusion of O₂ through a thick TiO₂ layer is proposed as the governing step.     

通过压裂裂缝监测解释来预测储层产量

水力压裂是油气井增产、注水井增注的一项重要技术措施[1].水力压裂实时监测及解释技术是确保压裂施工取得理想效果的关键性手段,也是水力压裂技术的最新进展和发展趋势.压裂井裂缝参数是决定压裂效果最主要的因素,优选压裂参数可以提高效益,节约成本[2].本文主要讲了通过地层闭合应力分析、施工摩阻分析和净压力拟合分析来进行进行裂缝参数解释,从而得出储层的产量预测.     

Electrical Properties of Boron Nitride Matrix Composites: II, Dielectric Relaxations in Boron Nitride–Silicon Carbide Composites

A low-frequency Maxwell–Wagner relaxation, resulting from space-charge buildup, was observed when BN–SiC composites were subjected to an ac current. This paper discusses the Maxwell–Wagner relaxation and information that it reveals about the microstructure of the composite. A modified Maxwell–Wagner equation for the real part of the permittivity is used to model the data. SiC has a higher dielectric constant than that of BN. The microstructure of these composites is anisotropic, with BN platelets preferentially oriented perpendicular to the hot-pressing direction. Samples measured in this direction exhibit a lower dielectric constant than those measured parallel to the hot-pressing direction. In regard to frequency response, the permittivity of BN shows no dependence on frequency, whereas frequency dependence is seen with increasing SiC content.     

木塑复合材料的研究进展

木塑复合材料(WPC)是一种新型环保材料,具有优异的综合性能,近几年得到了迅速发展。本文就该材料的原料组成、加工工艺、性能及应用等国内外技术现状进行了全面阐述,总结了前人的研究结果,分析了不足并展望了未来。     

Electrical Resistance of SiC Fiber Reinforced SiC/Si Matrix Composites at Room Temperature during Tensile Testing

The implementation of Ceramic Matrix Composites necessitates the understanding of stress‐dependent damage evolution. Toward this goal, two liquid silicon infiltrated SiCf reinforced SiC composites were tensile tested with electrical resistance (ER) monitoring as well as acoustic emission to quantify matrix cracking. ER was modeled using a combination of resistors in series and parallel to model transverse matrix cracks and fiber/matrix segments between matrix cracks. It is shown that resistance change is sensitive to transverse matrix crack formation and stress‐dependent debonding length. The model appears to be accurate up to the stress for matrix crack saturation.     

Study of Water Absorption Behavior in Wood Plastic Composites by Using Neutron Radiography Techniques

Abstract

Neutron radiography (NR) technique has been adopted to study the water absorption behavior of different kinds of wood plastic composites (WPC). The cold neutron radiography facility (CNRF) of Japan Research Reactor (JRR‐3M) was used in this work. Profiles of the absorbed water thickness of the samples are easily observed and measured from the radiography images. A small difference between NR image data and the measured data has been observed. That water absorption in these composites increases with time is clearly observed from the NR images.     

Titanium–Silicon–Nitrogen Composites with High Wear Resistance in Water and in Artificial Sea Water

Titanium–silicon–nitrogen (Ti-Si-N) composites were produced from a mixture of Si₃N₄, titanium nitride (TiN), and titanium by spark plasma sintering to develop wear-resistant materials with good environmental and biological compatibilities in water and sea water. The Ti-Si-N composite consisted of Si₃N₄, TiN, and titanium metal-rich particles coated with TiSi _x . Results of sliding tests in water and in artificial sea water showed that the wear resistance of the Ti-Si-N composite was much better than that of the titanium metal.     

Mullite—Alumina Composites by Extrusion

The rheological properties of a paste containing chopped alumina fiber and particulate silica suspended in a gelled boehmite liquid phase have been evaluated using a physically based extrusion model. When sintered, the paste formed a mullite-alumina fiber composite. Extrudates with fiber volumes up to 30% in the sintered product were prepared. During extrusion, the pressure drop was largely independent of extrudate velocity, fiber length, and the fiber concentration. All pastes showed significant yield behavior leading to good postextrusion shape retention. For any given fiber length, it was shown that there exists a critical volume fraction above which fiber-fiber interactions are so great that both yield and wall shear stresses increase. At these high concentrations of fiber, inhomogeneities also increase. Up to the critical volume fraction, dispersed wet fibers produced lower extrusion parameters than when dry fibers were used as the starting material. The observed behavior is explained in terms of low viscosity liquid formation above the yield point of the boehmite gel.     

木材及木塑复合材料的阻燃性能研究进展

木材阻燃机理主要有覆盖理论、热理论、不燃气体冲淡理论、自由基捕集理论、炭量增加和挥发物减少理论;人造板阻燃处理主要是在生产工序中添加阻燃剂和成板处理两种方法,高压处理法是目前最重要的工业化方法;以FRW阻燃剂、BL-环保阻燃剂为代表的磷-氮-硼系阻燃剂仍旧是木材阻燃剂的主流。对于木塑复合材料的阻燃研究尚处于起步阶段,一般采用对木纤维和基体分别阻燃的手段;研制高效膨胀型木材阻燃剂和将纳米技术应用于木材阻燃剂制造,开发阻燃效率高、低烟、低毒、环境友好等多功能复合阻燃剂将是今后阻燃剂研究领域的发展方向。