Application of continuously-monitored single fiber fragmentation tests to carbon nanotube/carbon microfiber hybrid composites

To assess the effect of carbon nanotube (CNT) grafting on interfacial stress transfer in fiber composites, CNTs were grown upon individual carbon T-300 fibers by chemical vapor deposition. Continuously-monitored single fiber composite (SFC) fragmentation tests were performed on both pristine and CNT-decorated fibers embedded in epoxy. The critical fragment length, fiber tensile strength at critical length, and interfacial shear strength were evaluated. Despite the fiber strength degradation resulting from the harsh CNT growth conditions, the CNT-modified fibers lead to a twofold increase in interfacial shear strength which correlates with the nearly threefold increase in apparent fiber diameter resulting from CNT grafting. These observations corroborate recently published studies with other CNT-grafted fibers. An analysis of the relative contributions to the interfacial strength of the fiber diameter and strength due to surface treatment is presented. It is concluded that the common view whereby an experimentally observed shorter average fragment length leads to a stronger interfacial adhesion is not necessarily correct, if the treatment has changed the fiber tensile strength or its diameter.     

Influence of fiber content on the mechanical and thermal properties of Kenaf fiber reinforced thermoplastic polyurethane composites

The aim of this paper is to study the influence of fiber content on mechanical (i.e. tensile, flexural, impact, hardness and abrasion resistance) and thermal (i.e. TGA) properties of Kenaf bast fiber reinforced thermoplastic polyurethane (TPU) composites. The composite was prepared by melt-mixing method, followed by compression molding process. Different fiber loadings were prepared; namely, 20%, 30%, 40%, and 50% weight percent. A 30% fiber loading exhibited the best tensile strength, while modulus increased with increase of fiber content, and strain deteriorated with increase of fiber content. Flexural strength and modulus increased with increase of fiber loading. Increase of fiber loading resulted in decline in impact strength. Hardness increased by addition of 30% fiber content. Abrasion resistant decreased with increase of fiber loading. Fiber loading decreased thermal stability of the composite.     

Hybridization effect on the mechanical properties of curaua/glass fiber composites

The aim of this paper was to evaluate the effect of hybridizing glass and curaua fibers on the mechanical properties of their composites. These composites were produced by hot compression molding, with distinct overall fiber volume fraction, being either pure curaua fiber, pure glass fiber or hybrid. The mechanical characterization was performed by tensile, flexural, short beam, Iosipescu and also nondestructive testing. From the obtained results, it was observed that the tensile strength and modulus increased with glass fiber incorporation and for higher overall fiber volume fraction (%V_f). The short beam strength increased up to %V_f of 30 vol.%, evidencing a maximum in terms of overall fiber/matrix interface and composite quality. Hybridization has been successfully applied to vegetable/synthetic fiber reinforced polyester composites in a way that the various properties responded satisfactorily to the incorporation of a third component.     

Enhanced mechanical properties of multiscale carbon fiber/epoxy composites by fiber surface treatment with graphene oxide/polyhedral oligomeric silsesquioxane

Graphene oxide (GO) and polyhedral oligomeric silsesquioxane (POSS) grafted carbon fiber (CF) was demonstrated to reinforce the mechanical properties of fiber composites. Such a fiber composite was prepared by grafting POSS onto the CF surface using GO as the linkage. The presence of GO linkage and POSS could significantly enhance both the area and wettability of fiber surface, leading to an increase in the interfacial strength between fibers and resin. Compared with the desized CF composites, the grafted CF composites fabricated by compression molding method exhibited 53.05% enhancement in the interlaminar shear strength. The changed surface morphology, surface composition and surface energy were supposed to be related with the interfacial performance of unidirectional composites, as revealed by scanning electron microscopy, atomic force microscope, dynamic contact angle test and X-ray photoelectron microscopy charaterizations.     

Influence of processing methods and fiber length on physical properties of kenaf fiber reinforced soy based biocomposites

Biocomposites from kenaf fiber and soy based bioplastic were fabricated by extrusion, followed by injection or compression molding. The impact of fiber length and the processing method on the thermal and mechanical properties of the composites were characterized with dynamic mechanical analysis (DMA) and mechanical properties measurements. The morphology was studied with optical and electron microscopy. Compression molded specimens have a similar modulus to injection molded specimens at room temperature, but exhibit a higher heat deflection temperature (HDT) and notched Izod impact strength. The improved HDT and impact strength are derived from an increase in modulus at high temperature and fiber bridging effects, respectively. The modulus, impact strength and HDT of kenaf fiber reinforced soy based biocomposites increase with increases in fiber length, fiber content and fiber orientation. Through microscopy observations, it was found that the fractured fiber length on the impact fracture surface increased with increasing fiber length and fiber content. This indicates that the role of fiber bridging effects is predominant on impact strength of the biocomposites.     

Dynamic mechanical and thermo-gravimetric analysis of Sansevieria cylindrica/polyester composite: Effect of fiber length,fiber loading and chemical treatment

The Sansevieria cylindrica (SC) fiber reinforced polyester matrix composites (SCFRPCs) were fabricated using compression molding machine. The influences of fiber length, fiber loading and chemical treatments of SCFRPCs over the mechanical and thermal stability were analyzed at different temperatures. The dynamic characteristics such as storage, loss modulus and damping were significantly influenced by the increase in fiber length and fiber loading but not in a geometric progression. Among various chemical treatments, the potassium permanganate treated SCFRPCs show the maximum increase in storage and loss modulus values. This result concluded that in addition to the reinforcing element (fiber length and wt% of fiber) the interfacial bonding between the fiber and the matrix plays a vital role in restricting the molecular mobility which was apparent from the storage modulus values. Efficient stress transfer at the interface is necessary to produce better dynamic properties rather than having more interfacial region. The change in morphology of cleaned and roughened SC fiber and the degree of interfacial adhesion between the fiber and matrix were studied using scanning electron microscope (SEM). The weight loss of SCFRPCs were also studied under varying temperatures with the help of thermo-gravimetric analysis (TGA).     

国产CCF300碳纤维单向织物液体成型工艺性及其复合材料力学性能

选取国产碳纤维CCF300所制备的2种单向织物,单向无纬织物U3160及单向无屈曲织物KUC160,分别对其预成型体进行压缩特性和渗透特性测试,以研究2种单向织物的液体成型工艺性,并采用树脂传递模塑(RTM)工艺制备2种单向织物/双马来酰亚胺树脂基复合材料,测试并对比其面内力学性能。结果表明:预成型体压缩试验中,嵌套效应受压力及织物层数影响较大,压力越高、层数越多,嵌套效应越显著。U3160织物的嵌套效应较KUC160织物更为明显,在较高压力下,KUC160织物预成型体的纤维体积分数较U3160织物的下降了约20%。渗透率测试结果表明:相比U3160织物,KUC160织物0°方向的渗透率较高,而90°方向的渗透率有所降低;这是由于经编线的绑缚作用能促进0°方向的宏观流动,而阻碍90°方向的微观渗透。此外,KUC160织物的经编线与U3160织物的纬向纱线的导流作用也对渗透率有影响。力学性能试验结果表明:相比U3160织物增强复合材料,KUC160织物增强复合材料0°方向的拉伸、弯曲和压缩性能均有所下降,拉伸强度和弯曲模量降幅最大,分别约为11%和21%;而层间剪切强度有小幅提高,增幅约为8%。      

Controlled growth of CuO nanowires on woven carbon fibers and effects on the mechanical properties of woven carbon fiber/polyester composites

The effect of CuO nanowires on the improvement of the mechanical properties of woven carbon fiber (WCF)-based polyester resin composite was studied. The composite was manufactured by the vacuum-assisted resin transfer molding (VARTM) process. CuO nanowires were grown on woven carbon fiber sheets in subsequent steps of seeding followed by growth. Scanning electron microscopy (SEM) showed the growth of CuO nanowires on the surface of the carbon fibers; this growth increased with the number of seeding cycles and the length of the growth time. The concentration of the growth solution did not have a significant effect. The maximum amount of growth occurred for 8 seeding cycles with a 60 mM growth solution and a growth time of 8 h. An analysis of the percent weight change, along with X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, supported the above findings. The crystalline peak height of the CuO nanowires increased with the nanowire growth. The new absorption peaks arising in the FTIR spectra also indicated growth of CuO nanowires on the WCF. The mechanical properties in terms of tensile strength, modulus, and impact resistance improved significantly after the growth of nanowires on the carbon fibers: the modulus and strength improved by up to 33.1% and 42.8%, while the impact energy absorption increased by 136.8% relative to bare WCF.     

剑麻/聚丙烯复合材料的冲击性能及其预测

采用注塑工艺制备剑麻纤维增强聚丙烯复合材料,研究纤维含量、长度及其分布、不同基体树脂和相容剂类型等对复合材料冲击性能的影响。分析单纤维强度的分散性,采用修正的Weibull分布模型估算临界纤维强度,并对复合材料的冲击强度进行预测。结果表明：剑麻/聚丙烯的冲击强度随纤维含量增加而升高,树脂基体的性质对冲击强度具有显著的作用;界面层为刚性层的相容剂MAPP对冲击强度具有负作用,而界面层为柔性层的相容剂PP-g-GMA对冲击强度具有提高作用;同等含量下,使用PP-g-GMA后复合材料的冲击强度比使用MAPP提高21.7%。通过KH550硅烷溶液处理后的纤维与PP-g-GMA反应,在界面处引入更加柔性的界面层,使冲击强度比引入MAPP提高50.7%。将纤维取向因子引入冲击强度模型后,预测值与实测值符合较好。     

Notched behavior of prepreg-based discontinuous carbon fiber/epoxy systems

The elastic behavior and failure response of discontinuous carbon fiber/epoxy laminates produced by compression molding of randomly-oriented preimpregnated unidirectional tape is characterized. Commercial applications for this type of material form already exist, such as Hexcel HexMC^®. Complex relationships between unnotched and notched tensile strengths are observed, and show this material to be particularly notch-insensitive. A parametric study on the effect of specimen thickness, width, diameter/width ratio, and hole size yields fundamental information on the behavior of this material.     

Bamboo fiber reinforced thermoplastic molding made of steamed wood flour

To improve the mechanical property of moldings made of steamed wood flour, layered wood moldings reinforced with steam-exploded bamboo fiber was prepared. Setting the bamboo fiber weight fractions at 25, 50, and 75%, and number of layers at three-, five-, and seven-layered wood moldings were prepared by compression molding. The results of tensile test showed that the tensile strength as well as Young’s modulus increased along with the increase in the bamboo fiber fractions. Where the bamboo fiber content was 75%, the tensile strength became approximately 3.8 to 5.8 times greater, and the tensile Young’s modulus became approximately 2.5 times greater when compared to moldings of 100% wood flour. This fact shows that bamboo fiber is effective to improve the mechanical property of wood moldings. In addition, the tensile strength also increased as the number of layers increased. This result suggested that interfacial shear stress was produced between the layers of bamboo fiber and wood flour.     

Effects of fiber orientation and anisotropy on tensile strength and elastic modulus of short fiber reinforced polymer composites

An experimental study was conducted to investigate anisotropy effects on tensile properties of two short glass fiber reinforced thermoplastics. Tensile tests were performed in various mold flow directions and with two thicknesses. A shell–core morphology resulting from orientation distribution of fibers influenced the degree of anisotropy. Tensile strength and elastic modulus nonlinearly decreased with specimen angle and Tsai–Hill criterion was found to correlate variation of these properties with the fiber orientation. Variation of tensile toughness with fiber orientation and strain rate was evaluated and mechanisms of failure were identified based on fracture surface microscopic analysis and crack propagation paths. Fiber length, diameter, and orientation distribution mathematical models were also used along with analytical approaches to predict tensile strength and elastic modulus form tensile properties of constituent materials. Laminate analogy and modified Tsai–Hill criteria provided satisfactory predictions of elastic modulus and tensile strength, respectively.     

Dependence of tensile properties of abaca fiber fragments and its unidirectional composites on the fragment height in the fiber stem

Properties of natural fiber vary with its growth conditions even with different parts of the fiber. The main objective of this work is to study the effect of the fragment height in the fiber stem (FHFS) on the mechanical properties of abaca fibers and their unidirectional composites. Abaca fibers were cut into sequent fragments, and their unidirectional epoxy composites were fabricated by means of a compression molding technique. Tensile tests of fibers as well as composites were conducted, followed by the physicochemical analysis such as morphology, density, chemical compounds, and crystal structure. The results showed that the tensile strength and Young’s modulus of abaca fiber greatly increased to the maximum at about 1.0 m from the bottom and then slightly decreased with the increasing FHFS. This can be attributed to the different physicochemical properties caused by FHFS. Different to fiber, the tensile strength of composites presented a remarkable decrease with increasing FHFS due to the different stochastic nature of fiber which is varied with FHFS.     

Mechanical behavior of carbon fiber reinforced polyamide composites

The purpose of this work is to compare tensile, compressive and interlaminar shear properties of different carbon reinforcement/polyamide composites obtained by interfacial polymerization and hot compression molding techniques. Two types of composite matrices were studied: polyamide 6 and polyamide 6/6, both reinforced by fabric and unidirectional carbon fibers. The effects of the fiber volume fraction and the matrix on mechanical properties were analyzed through tensile, interlaminar shear and compressive tests. In general, the results have shown a slight increase of the composite elastic modulus, tensile and compressive strength with the increase of carbon fiber content. The microscopic damage development within selected composites during the loading has been observed through optical and scanning electron microscope techniques and has shown that shear failure at the fiber/matrix interface has been mostly responsible for damage development, initiated at relatively low stress.     

Renewable resource based biocomposites from natural fiber and polyhydroxybutyrate-co-valerate (PHBV) bioplastic

Renewable resource based green biocomposites were prepared using a bacterial polyester i.e., poly(hydroxybutyrate-co-valerate) (PHBV) and natural bamboo fiber. Fabrication of the biocomposites was carried out by injection molding following extrusion compounding of PHBV and bamboo fiber with 30 or 40 wt.% fiber. The mechanical, thermo-mechanical and morphological properties of the biocomposites were evaluated. Little variation in the thermo-mechanical and impact properties was observed when the fiber content was varied. The tensile modulus of biocomposites at 40 wt.% fiber improved by 175% as compared to that of neat PHBV. The theoretical tensile modulus of the biocomposites was calculated using Christensen’s equations and compared with the experimental results. It was found to be in near approximation to the experimental data. The storage modulus was affected slightly by the variation of fiber content from 30 to 40 wt.% in biocomposites. The heat deflection temperature of PHBV increased by 9 °C at 40 wt.% of fiber reinforcement. Morphological aspects and thermal stability were studied using scanning electron microscopy and thermo-gravimetric analysis, respectively. In addition, a comparative analysis of bamboo fiber–PHBV with wood fiber–PHBV biocomposites was performed. Statistical analysis of both biocomposites was carried out by performing a two-way ANOVA on their tensile and flexural moduli in order to evaluate the effect of fiber type and content in the PHBV matrix.     

短切碳纤维增强尼龙66复合材料注塑成型工艺模拟

采用毛细管流变仪和自制小型模具,对不同质量分数的短切碳纤维增强尼龙66(CF/PA66)复合材料颗粒进行了熔体流动性能分析和注塑成型工艺模拟,实现少量原料快速模拟CF/PA66的注塑成型工艺参数。研究表明:短切CF/PA66复合材料的熔体属于幂律流体,熔体黏度随温度、压力和CF质量分数变化显著,当温度和压力升高到临界值后熔体流变特性从假塑性区进入牛顿区;随着CF质量分数的增加,CF/PA66复合材料适宜成型温度提高。实验中PA66、CF质量分数为10wt%和20wt%的CF/PA66三种颗粒的适宜成型温度分别为278~285℃、280~287℃、290~298℃,通过对熔体进行Bagley压力校正,三种颗粒适宜成型的最小注塑压力分别为24.3MPa、29.4MPa、35.1MPa;将流变仪模拟所得参数应用于注塑成型工艺,所得样品的拉伸强度与流变仪制备的试样非常接近,进一步说明了毛细管流变仪模拟CF/PA66注塑成型过程的可行性和有效性,为其注塑成型工艺条件提供了理论依据。     

The effect of alkaline and silane treatments on mechanical properties and breakage of sisal fibers and poly(lactic acid)/sisal fiber composites

The main goals of this work were to study the effect of different chemical treatments on sisal fiber bundles tensile properties as well as on tensile properties of composites based on poly(lactic acid) (PLA) matrix and sisal fibers. For this purpose, sisal fibers were treated with different chemical treatments. After treating sisal fibers the tensile strength values decreased respect to untreated fiber ones, especially when the combination of NaOH + silane treatment was used. Taking into account fiber tensile properties and fiber/PLA adhesion values, composites based on silane treated fibers would show the highest tensile strength value. However, composites based on alkali treated and NaOH + silane treated fibers showed the highest tensile strength values. Finally, experimental tensile strength values of composites were compared with those values obtained using micromechanical models.     

短切碳纤维/乙烯基酯树脂片状模塑料拉伸性能的有限元模拟

采用Python语言对ABAQUS软件进行二次开发,生成了短切碳纤维在乙烯基酯树脂中随机分布的二维平面应变模型,建立代表性体积单元（RVE）,通过Hypermesh对模型进行网格划分,为保证RVE应力场的均匀协调性,在周期性边界条件下,对短切碳纤维/乙烯基树脂进行拉伸性能数值模拟计算分析,并结合实验研究了短切碳纤维长度对片状模塑料拉伸性能的影响。结果验证了对短切碳纤维/乙烯基树脂片状模塑料拉伸模量随纤维长度的增大出现先增大后变缓的趋势,表明利用Python-ABAQUS建立二维平面应变RVE模型的合理性。本研究为短切碳纤维/乙烯基树脂片状模塑料在汽车轻量化行业的应用提供了理论及实验依据。      

Studies on the structure and properties of thermoplastic starch/luffa fiber composites

Thermoplastic starch (TPS)/luffa fiber composites were prepared using compression molding. The luffa fiber contents ranged from 0 wt.% to 20 wt.%. The tensile strength of the TPS/luffa fiber composite with 10 wt.% of luffa fiber had a twofold increase compared to TPS. The temperature values of maximum weight loss of the TPS/luffa fiber composites were higher than for TPS. The water absorption of the TPS/luffa fiber composites decreased significantly when the luffa fiber contents increased. The strength of adhesion between the luffa fiber and the TPS matrix was clearly demonstrated by their compatibility presumably due to their similar chemical structures as shown by scanning electron microscope (SEM) micrographs and Fourier transform infrared (FTIR) spectra.     

Hybrid carbon fiber composite lattice truss structures

Carbon fiber reinforced polymer (CFRP) composite sandwich panels with hybrid foam filled CFRP pyramidal lattice cores have been assembled from linear carbon fiber braids and Divinycell H250 polymer foam trapezoids. These have been stitched to 3D woven carbon fiber face sheets and infused with an epoxy resin using a vacuum assisted resin transfer molding process. Sandwich panels with carbon fiber composite truss volumes of 1.5–17.5% of the core volume have been fabricated, and the through-thickness compressive strength and modulus measured, and compared with micromechanical models that establish the relationships between the mechanical properties of the core, its topology and the mechanical properties of the truss and foam. The through thickness modulus and strength of the hybrid cores is found to increase with increasing truss core volume fraction. However, the lattice strength saturates at high CFRP truss volume fraction as the proportion of the truss material contained in the nodes increases. The use of linear carbon fiber braids is shown to facilitate the simpler fabrication of hybrid CFRP structures compared to previously described approaches. Their specific strength, moduli and energy absorption is found to be comparable to those made by alternative approaches.