Tensile properties of multilayer-connected biaxial weft knitted fabric reinforced composites for carbon fibers

Multilayered-connected biaxial weft knitted (MBWK) fabric reinforced composites have excellent tensile properties. Three kinds of different fabrics reinforced composites are used in this paper, which are three-layer-connected biaxial weft knitted fabric, four-layer-connected biaxial weft knitted fabric and five-layer-connected biaxial weft knitted fabric. The tensile properties of MBWK fabrics reinforced composites are studied with 0° and 90° directional testing with different carbon fiber volume fractions. The results show that the carbon fiber volume fraction has significant effect on tensile strength of MBWK fabrics reinforced composites. The linear correlation between tensile strength and carbon fiber volume fraction is very well in the certain range, and failure analyses are also available by means of sample debris examination to identify the failure modes and the fracture surfaces.     

Tensile properties of VGCF reinforced carbon composites

Carbon composites based on vapor grown carbon fibers prepared by a fixed catalyst method were fabricated using a pitch infiltration technique. The composites have both unidirectional and bi-directional fiber reinforcement, and different fiber volume fractions ranging from 25% to 56%. Specimens were prepared from these composites for tensile testing at room temperature, and tensile modulus and strength were determined. The composite modulus was then used to estimate the fiber modulus.     

Aligned ramie fiber reinforced arylated soy protein composites with improved properties

To enhance the strength, ramie fibers aligned in vertical (V), horizontal (H) as well as both vertical and horizontal (X) directions were used to reinforce soy protein materials (SC), coded as VSC, HSC and XSC. The soy protein isolate was arylated with 2,2-diphenyl-2-hydroxyethanoic acid through the process of “dip-coating”, coded as SC-B. The SC and SC-B composite films were characterized by Fourier transform infrared spectra, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile testing. Substantial improvement in the water uptake (from 100% to 25%) and the increased modulus (from 125 to 942 MPa) of the VSC-B composite were observed. This could be attributed to the formation of phase separation induced hydrophobic microparticles of DPHM on the surface of the SC-B films upon arylation, leading to the hydrophobicity. The thermal stability of the arylated composites increased compared to non-arylated ones. The VSC-B materials exhibited the highest water resistance and mechanical properties compared to HSC-B and XSC-B. Therefore, the arylation of SPI and alignment of the ramie fibers in the composites played an important role in the improvement of mechanical properties. This work provided a novel idea to improve the water resistance and modulus by reinforcing the protein matrix with natural fibers.     

Tensile properties of elephant grass fiber reinforced polyester composites

Elephant grass stalk fibers were extracted using retting and chemical (NaOH) extraction processes. These fibers were treated with KMnO₄ solution to improve adhesion with matrix. The resulting fibers were incorporated in a polyester matrix and the tensile properties of fiber and composite were determined. The fibers extracted by retting process have a tensile strength of 185 MPa, modulus of 7.4 GPa and an effective density of 817.53 kg/m³. The tensile strength and modulus of chemically extracted elephant grass fibers have increased by 58 and 41%, respectively. After the treatment the tensile strength and modulus of the fiber extracted by retting have decreased by 19, 12% and those of chemically extracted fiber have decreased by 19 and 16%, respectively. The composites were formulated up to a maximum of 31% volume of fiber resulting in a tensile strength of 80.55 MPa and tensile modulus of 1.52 GPa for elephant grass fibers extracted by retting. The tensile strength and the modulus of chemically extracted elephant grass fiber composites have increased by approximately 1.45 times to those of elephant grass fiber composite extracted by retting. The tensile strength of treated fiber composites has decreased and the tensile modulus has shown a mixed trend for the fibers extracted by both the processes. Quantitative results from this study will be useful for further and more accurate design of elephant grass fiber reinforced composite materials.     

Hemp yarn reinforced composites – II. Tensile properties

Whereas the first paper is addressing the characteristics of textile hemp yarn, this second paper is addressing the tensile properties of aligned hemp yarn composites under influence of a number of experimental variables: hemp yarn type, fibre volume fraction, thermoplastic matrix type, process temperature, conditioning humidity, and loading direction relative to the fibre direction. Altogether, the results show that aligned hemp yarn composites demonstrate the good potential of plant fibres as reinforcement in composites for structural components. The tensile performance of the hemp yarn composites is excellent. As an example, a fibre volume fraction of 0.48 results in a stiffness of 28 GPa and an ultimate stress of 280 MPa. It is demonstrated that the influence of experimental variables is well understood and can be quantitatively described.     

Flexural properties of fully biodegradable alpha-grass fibers reinforced starch-based thermoplastics

This work has the aim of study the flexural properties of alpha-grass reinforced starch-based composites. The composite materials contain alpha-fibers in the range from 5 to 35 wt%. The reinforcing fibers were submitted to an alkali treatment to create a good interphase between the fibers and the matrix. It was observed that a mild 2.5 h cooking process was enough to create a good interphase, while longer periods rendered lesser improvements. The surface charges of the fibers and the matrix were determined by polyelectrolyte titration, and it was found that after the alkaline treatment both were similar. The composite materials were injection molded and tested under flexural conditions. All the flexural properties of the studies composites increased linearly with the reinforcement contents. The micromechanics of the flexural modulus and strength were studied and compared with that of tensile modulus and strength. It was established that the efficiency factors for the tensile and flexural properties were statistically similar. Three different methods were used to compute the intrinsic flexural strength from the available data. Finally the Weibull theory was used to study the best prediction of the standard deviation of the intrinsic flexural modulus.     

Preparation and properties of polyamide 6 thermal conductive composites reinforced with fibers

The majority of inorganic particles-filled thermal conductive composites highlight thermal conductivity in detriment of mechanical properties. In this work, magnesium hydroxide (Mg(OH)₂), alumina (Al₂O₃) and flake graphite-filed polyamide 6 (PA6) composites prepared by twin-screw extruder, were reinforced with carbon and glass fibers separately. Effects of fiber type and content on thermal conductivity, mechanical properties and heat deflection temperature (HDT) of the PA6-based composites were investigated. The results showed that the thermal conductivity of the composites improved with increasing carbon fiber content, while decreased slightly with glass fiber loading. Furthermore, strength, modulus and HDT of the PA6-based composites increased with the increase of fiber content. The reinforcing effects of the two fibers on the thermal and mechanical properties of the composites were compared and interpreted in this paper. By incorporating simultaneously high thermal conductive fillers and high-strength fibers, the combined composites hold a good potential in heat dissipation applications.     

表面处理玄武岩纤维增强水泥基复合材料力学性能

为提高玄武岩纤维(BF)与水泥基体的界面结合力和桥接作用,分别采用HCl溶液(0~2.0mol/L)和NaOH溶液(0~2.0mol/L)对BF表面进行刻蚀糙化处理,研究纤维表面处理对BF增强水泥基复合材料的力学性能影响规律。结果表明:随着HCl溶液浓度增加,BF/水泥复合材料抗折强度与弯曲强度均先增加后降低,挠度呈现缓慢增加趋势,而抗压强度变化幅度较小;当HCl溶液浓度为1mol/L时,BF/水泥复合材料的强度与韧性最佳;碱处理BF后,BF/水泥复合材料的力学性能随NaOH浓度增加而显著降低,且复合材料韧性无明显改善;BF经HCl溶液腐蚀后的质量保留率变化规律与NaOH溶液腐蚀后的变化规律接近,而经HCl溶液腐蚀后BF强度保留率大于NaOH溶液腐蚀后的BF强度保留率。     

Tensile and compressive properties of flax fibres for natural fibre reinforced composites

Mechanical properties of standard decorticated and hand isolated flax bast fibres were determined in tension as well as in compression. The tensile strength of technical fibre bundles was found to depend strongly on the clamping length. The tensile strength of elementary flax fibres was found to range between 1500 MPa and 1800 MPa, depending on the isolation procedure. The compressive strength of elementary flax fibres as measured with a loop test lies around 1200 MPa. However, the compressive strength can be lowered severely by the decortication process. The standard decortication process induces kink bands in the fibres. These kink bands are found to contain cracks bridged by microfibrils. The failure behaviour of elementary flax fibres under compression can be described as similar to the failure behaviour of a stranded wire.     

Tensile and thermomechanical properties of short carbon fiber reinforced polyamide 6 composites

In this study, carbon fiber (CF) reinforced polyamide 6 (PA6) composites were prepared by using melt mixing method. Effects of fiber length and content, on the mechanical, thermal and morphological properties of CF reinforced PA6 composites were investigated. Fiber length distributions of composites were also determined by using an image analyzing program. It was seen that the maximum number of fibers were observed in the range of 0–50 μm. Mechanical test results showed that, increasing CF content increased the tensile strength, modulus and hardness values but decreased strain at break values of composites. DSC results showed that T_g and T_m values of composites were not changed significantly with increasing CF content and length. However, heat of fusion and the relative degree of crystallinity values of composites decreased with ascending CF content. DMA results revealed that storage modulus and loss modulus values of composites increased with increasing CF content.     

Fabrication and properties of short carbon fibers reinforced copper matrix composites

Short carbon fibers (SCFs) reinforced copper matrix composites have been produced by a new electrodeposition plus cold press and sintering technique. SCFs were copperized directly by the new method, and the electrodeposit had a loose porous structure. The coating thickness is uniform, and can be controlled by appropriate parameters. A model representing the growth process of these electrodeposits was presented. SCFs were distributed homogeneously, and no defects were found in the Cu/SCFs composites. The effects of SCFs volume fraction on mechanical, physical, thermal, and tribological properties of the composites were discussed.     

气相生长碳纤维增强水泥基复合材料的制备及性能

研究了脱油沥青(De-oiled asphalt)基气相生长碳纤维(VGCFs)增强水泥基复合材料的制备方法及其性能。以脱油沥青作原料,采用化学气相沉积法(CVD)制备出气相生长碳纤维,以此纤维制备水泥基功能复合材料。结果表明:低含量VGCFs的碳纤维增强水泥基复合材料具有良好的抗压强度和导电性能,在VGCFs的掺量由0增至0.6 %范围内,随着VGCFs掺量的增加,碳纤维增强水泥基复合材料的电阻率下降,抗压强度提高。当VGCFs为0.4 %时,VGCFs水泥基复合材料电阻率降低2个数量级,从3.25 ×105 Ω·cm 降为1.49 ×103 Ω· cm ,抗压强度提高28.8 %,为最佳掺量。      

竹纤维增强聚乳酸复合材料热老化性能

采用氢氧化钠和异氰酸酯处理的界面调控方法对竹纤维(BF)增强聚乳酸(PLA)复合材料界面进行调控,通过注射成型工艺制备BF/PLA复合材料。利用FTIR、XRD、凝胶渗透色谱及SEM等分析手段研究了BF/PLA复合材料热老化性能。研究发现: 热老化过程中PLA分子链中的C O不断水解,分子链的C—O断裂生成聚合度更低的小分子量的PLA,PLA结晶度减小,PLA与BF的接合界面被破坏,拉伸强度和冲击强度随老化时间的增加逐渐降低。BF/PLA复合材料在80℃热老化16天后拉伸强度和冲击强度分别降低了75%和77.6%,在100℃热老化32 h后拉伸强度和冲击强度分别降低了80.3%和83.4%。温度对BF/PLA复合材料老化影响显著,温度越高,老化速度越快。     

Tensile deformation mechanism of polyamide 6,6/SEBS-g-MA blend and its hybrid composites reinforced with short glass fibers

Short glass fiber (SGF) reinforced polyamide 6,6 hybrid composites toughened with maleated styrene-ethylene butylenes-styrene (SEBS-g-MA) elastomer were prepared by compounding and subsequent injection molding. The hybrids were reinforced with 5, 10, 15, 20 and 30 wt% SGF. The matrix of the hybrids consisted of 80 wt% PA6,6 and 20 wt% SEBS-g-MA. Dilatometery was employed to characterize the deformation mechanisms of tough PA6,6/SEBS-g-MA 80/20 blend and its hybrid composites under uniaxial tension. Dilatometric responses showed that both cavitation and shear yielding occur in PA6,6/SEBS-g-MA 80/20 blend during deformation. And the cavitation deformation prevailed over shear yielding in this blend after the initial elastic deformation. Moreover, the volume strain was observed to increase considerably with increasing SGF content for the hybrids investigated. SEM examination revealed that microvoids originated from the debonding of glass fiber from the PA6,6 matrix were responsible for the cavitation strain in the hybrids. Consequently, cavitation deformation predominated over shear yielding in hybrids.     

Characterization of interfacial and mechanical properties of “green” composites with soy protein isolate and ramie fiber

Environment-friendly fiber-reinforced composites were fabricated using ramie fibers and soy protein isolate (SPI) and were characterized for their interfacial and mechanical properties. Ramie fibers were characterized for their tensile properties and the parameters for the Weibull distribution were estimated. Effect of glycerol content on the tensile properties of SPI was studied. Interfacial shear strength (IFSS) was determined using the microbond technique. Based on the IFSS results and fiber strength distribution, three different fiber lengths and fiber weight contents (FWC) were chosen to fabricate short fiber-reinforced composites. The results indicate that the fracture stress increases with increase in fiber length and fiber weight content. Glycerol was found to increase the fracture strain and reduce the resin fracture stress and modulus as a result of plasticization. For 10% (w/w) of 5 mm long fibers, no significant reinforcement effect was observed. In fact the short fibers acted as flaws and led to reduction in the tensile properties. On further increasing the fiber length and FWC, a significant increase in the Young's modulus and fracture stress and decrease in fracture strain was observed as the fibers started to control the tensile properties of the composites. The experimental data were compared to the theoretical predictions made using Zweben's model. The experimental results are lower than the predicted values for a variety of reasons. However, the two values get closer with increasing fiber length and FWC.     

Tensile properties and thermal expansion of discontinuously reinforced aluminium composites at subambient temperatures

The effects of temperature on the mechanical properties and thermal expansion of two discontinuously reinforced aluminium composites have been determined over the range 300–100 K. Silicon carbide particulate-reinforced 2009 and 6092 aluminium alloys were studied by tensile testing, in which both longitudinal and transverse strains were recorded, and by thermal expansion measurements. The test results clearly show that cooling to 100 K induces plastic flow in the aluminium alloy matrices due to the thermal expansion difference between aluminium and silicon carbide. At very low temperatures, the linear region of the stress-strain curve is greatly reduced or eliminated and the Poisson’s ratio, ν, increases. For the higher yield strength 2009 matrix composite, ν increases from a room-temperature value of 0.28 to 0.35 at 100 K. For the lower-strength 6029 matrix composite, ν increases from a room-temperature value of 0.33 to a value of 0.5 at 100 K. A Poisson’s ratio of 0.5 is the value characteristic of plastic flow in an incompressable material. Changes in yield strength, Young’s modulus and thermal expansion with decreasing temperature are also consistent with thermally induced plastic flow in the composite matrix. This revised version was published online in November 2006 with corrections to the Cover Date.     

Tensile and flexural properties of snake grass natural fiber reinforced isophthallic polyester composites

Natural fiber composite materials are one such capable material which replaces the conventional and synthetic materials for the practical applications where we require less weight and energy conservation. The present paper, which emphasis the importance of the newly identified snake grass fibers which are extracted from snake grass plants by manual process. In this paper, the tensile properties of the snake grass fiber are studied and compared with the traditionally available other natural fibers. The mixed chopped snake grass fiber reinforced composite is prepared by using the isophthallic polyester resin and the detailed preparation methodology is presented. Fiber pull-outs on the fractured specimen during the physical testing of the composites are also investigated. The experimental evidence also shows that the volume fraction increases the tensile, flexural strength and modulus of the snake grass fiber reinforce composite.     

织物形式对苎麻纤维渗透率及其复合材料力学性能的影响

采用树脂传递模塑工艺(RTM)研究了三种典型苎麻纤维织物结构(平纹、 斜纹和缎纹)对树脂流动性的影响, 并研究了三种苎麻纤维织物结构对其增强酚醛树脂复合材料的拉伸性能和层间剪切性能的影响。结果表明, 苎麻纤维织物树脂渗透率主要受纤维屈曲和流道面积的影响。斜纹和缎纹苎麻织物的纤维屈曲较小且流道面积较大, 其织物的树脂渗透率较大, 同时, 较小的纤维屈曲使其增强的复合材料拉伸性能也较优。然而, 不同织物形式对苎麻纤维织物/树脂复合材料的层间性能影响不大。     

织物形式对苎麻纤维渗透率及其复合材料力学性能的影响

采用树脂传递模塑工艺(RTM)研究了三种典型苎麻纤维织物结构(平纹、斜纹和缎纹)对树脂流动性的影响,并研究了三种苎麻纤维织物结构对其增强酚醛树脂复合材料的拉伸性能和层间剪切性能的影响.结果表明,苎麻纤维织物树脂渗透率主要受纤维屈曲和流道面积的影响.斜纹和缎纹苎麻织物的纤维屈曲较小且流道面积较大,其织物的树脂渗透率较大,同时,较小的纤维屈曲使其增强的复合材料拉伸性能也较优.然而,不同织物形式对苎麻纤维织物/树脂复合材料的层间性能影响不大.     

Tensile properties and thermal expansion behaviors of continuous molybdenum fiber reinforced aluminum matrix composites

The tensile properties and thermal expansion behaviors of continuous molybdenum fiber reinforced aluminum matrix composites (Mo_f/Al) have been studied. The Mo_f/Al composites containing different volume percents of Mo fibers were processed by diffusion bonding. The strengths of unidirectional Mo_f/Al composites were close to the rule-of-mixtures. The strengths of 0°/90° dual-directional composites increased with fiber content, while those of 45°/135° composites remained relatively low. The coefficients of thermal expansion (CTEs) of the composites decreased as the fiber content increased, close to the values of Mo fibers. With increasing temperature, the CTEs of unidirectional composites increased, while those of dual-directional composites decreased due to large accumulated thermal stresses. The CTEs of 45°/135° composites were lower than those of 0°/90° composites because of contraction effect. At temperatures above 250 °C, the CTEs of the dual-directional composites gradually increased due to matrix yielding and interfacial decohesion.