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.     

新型颗粒增强金属玻璃复合材料的拉伸增韧机制

利用有限元方法探究了颗粒体积分数、颗粒的应变硬化指数、颗粒的间距以及网状结构对新型非晶合金复合材料即金属玻璃基复合材料（Metallic Glass Composites,MGCs）强度和韧性的影响。结果表明：随着颗粒应变硬化指数的增大,复合材料的强度和韧性都有很大提高,颗粒体积分数的增大、颗粒间距的变小和网状结构排布也将提高复合材料的韧性。这些都有利于设计出有较好韧性的复合材料。     

Influence of fillers on abrasive wear of short glass fibre reinforced polyamide composites

Various composites of polyamide 6 filled with short glass fibre, polytetrafluoroethylene and metal powders viz. copper and bronze were formulated in the laboratory and characterised for their various mechanical properties such as tensile strength, tensile elongation, flexural strength, hardness and impact strength. Compositional analysis was done with gravimetry, solvent extraction and differential scanning calorimetry (DSC) techniques followed by tribo-performance evaluation in abrasive wear mode by abrading a sample against silicon carbide (SiC) abrasive paper in a single pass condition under various loads. It was observed that the fibre reinforcement deteriorated the abrasive wear resistance of virgin polymer. Combination of fibre and particulate filler was more detrimental in this respect. Efforts were made to correlate the wear performance with the appropriate mechanical properties. Under selected loading condition, wear as a function of product of hardness, elongation to break (e) and ultimate tensile strength (S) showed better correlation than Ranter-Lancaster plot. Scanning electron microscopy (SEM) was used to analyse the worn surfaces of the samples.     

An experimental analysis of fracture mechanisms of short glass fibre reinforced polyamide 6,6 (SGFR-PA66)

In the present work, toughness of unfilled polyamide 6,6 (PA66) and short glass fibre reinforced polyamide 6,6 (SGFR-PA66) was investigated. Digital image correlation (DIC) was used with a single camera for in-plane displacement field measurement and then strain computation. The results allowed to extract the resistance curve for the PA66 and critical stress intensity factors, K_Ic, for the SGFR-PA66 with three glass fibre contents (15%, 30% and 50% (wt)) and under room temperature (20 °C). The tests were carried out on single edge notched tension (SENT) specimens. The DIC technique allowed to precise the spatial distribution of the local strains in a defined region including the crack tip at different steps of the loading. Scanning electron microscopy observations illustrated different damage mechanisms occurring in the studied composites: matrix crack, fibre–matrix interface failure and fibres pull out.     

Prediction of failure properties of injection-molded short glass fiber-reinforced polyamide 6,6

This study simulates the tensile failure of injection-molded short glass fiber-reinforced polyamide 6,6 (GF/PA66). Tensile tests of unreinforced PA66 are first conducted and the material properties are obtained by fitting a simulated stress–strain curve to the experiment result. Using the obtained material properties, failure simulations of GF/PA66 composites are performed for four types of specimens with various fiber lengths and fiber orientation distributions. In the simulations, multiscale mechanistic model, which can simulate micromechanical damage, and Micromechanics Model (MM), which has very low computational cost, are adapted and the results are compared with experiments. Both models reproduce the experiment results well. Considering the computational cost, MM is the better model for predicting the failure properties of GF/PA66 composites.     

Analysis of the effect of mechanical recycling upon tensile strength of a short glass fibre reinforced polyamide 6,6

The effect of mechanical recycling upon tensile strength of an injection moulded polyamide 6,6 reinforced with 35% by weight of glass fibres has been experimentally investigated. Tensile tests have been conducted on specimens made of virgin material and containing different percentages of mechanically recycled material. Mechanical recycling consisted of regrinding of specimens and further injection moulding the granules into specimens of the same type. The main effect of this type of recycling is fibre breakage with consequent decrement of fibres contribution to composite strength. The results from the experimental tests have been compared with predictions obtained by applying a micro-mechanical model, which allowed taking into account the fibre length distribution and the properties of the phases of the composite. The model appeared to be a useful tool in the eco-design methodology, where the knowledge of property change of recycled material against those of the virgin one is necessary in the assessment of the environmental impacts of different recovery options.     

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.     

Mixing of glass fibers with nylon 6,6

Nylon 6,6 is one of the toughest of the engineering thermoplastic resins. It is resistant to corrosion and chemicals, but has a limited capability due to low rigidity, strength and moisture adsorption. Glass fibers are very strong and rigid but susceptible to environmental attack. Proper mixing of these two materials would form a fiber composite with high strength, toughness, rigidity and stability at elevated temperatures. The main purpose of this work was to study the effect of properties of a fiber composite containing 20% loading of glass fibers in Nylon 6,6. Two different types of twin screw extruders, one a co-rotating and the other a counter-rotating, were used. Two different screw designs, a high-shear and a low-shear design, were used on each of these extruders. A statistical process study was developed using ECHIP. RPM of the screw and the output rate of the extruder were the identified variables in the process. Molded samples were evaluated for tensile, flexural, impact and heat deflection characteristics. Scanning Electron Microscopy study was also performed to evaluate the fiber distribution, length and wetting characteristics. The results were analyzed for all of the above properties and it was concluded that there was a great improvement in the properties of the reinforced material. Also, it was found that low RPM and output rates on the co-rotating twin-screw extruder would result in the best properties.     

Tensile and impact properties of fully green composites reinforced with mercerized ramie fibers

The purpose of this study is to create a natural fiber-reinforced fully green composite with excellent toughness. By treating ramie plied yarns in a high concentration alkali solution, the reinforcements were mercerized. Results of tensile tests showed that unidirectional composites using mercerized ramie yarns exhibited two to three times larger fracture strain, without a marked decrease in strength, than composites using untreated yarns. In addition, mercerization for the ramie yarns brings a better interfacial strength to the composites. Laminated composites using mercerized ramie yarns also showed approximately twice larger impact energy than composites using untreated yarns. Thus, mercerization for natural fibers is expected for application to mechanical materials requiring a high toughness.     

Processing of hybrid wood plastic composite reinforced with short PET fibers

Poly(ethylene terephthalate) (PET) fibers (virgin, waste, and mixed) were incorporated in the composite poly(methyl methacrylate) (PMMA)–wood. Hybrid composite panels were prepared by pressure molding. Toluene-2,4-diisocyanate (TDI) and (3-mercaptopropyl)trimethoxysilane (MPTMS) were used as cross-linking bonding agents for modification of wood fibers. Influence of cross-linking bonding agents, structure, and composition of PET fibers was examined by studying thermomechanical properties as well as moisture absorption. Moisture absorption was lower for composites with bonding agents. Mechanical testing revealed that the addition of PET fibers drastically enhances properties of the composites. Covalent and hydrogen bonds formed with the addition of bonding agents have also improved mechanical properties compared to the untreated composites.     

短纤维增强聚丙烯泡沫复合材料的研究新进展

详细介绍了天然纤维、短玻璃纤维、碳纳米纤维及晶须等在增强PP泡沫复合材料中的应用;重点阐述了短纤维的种类和含量对发泡行为、微观结构及力学性能等的影响规律,并总结了相关增强机理;展望了短纤维/PP泡沫复合材料的发展趋势。     

Enhanced thermomechanical properties of long and short glass fiber-reinforced polyamide 6,6/polypropylene mixtures by tuning the processing procedures

Long and short glass fibers (GF) were incorporated into the polyamide 6,6 (PA66)/polypropylene (PP) mixtures in order to enhance the thermomechanical properties. The effect of fiber length and processing procedures on tensile strength, flexural modulus, impact strength, and heat deflection temperature has been investigated. Miscibility behavior of the PA66/PP mixtures has been examined by performing differential scanning calorimetry analysis and theoretical calculation. The mixtures exhibiting broad coexistent regions such as crystal + crystal (Cr₁ + Cr₂), crystal + liquid (Cr₁ + L₂), and liquid + crystal (L₁ + Cr₂) revealed a significant improvement in thermal and mechanical properties by the addition of GF. Especially, long fiber-reinforced thermoplastics showed better performances compared to short fiber-reinforced thermoplastics at the same filler loading. From the morphological observation of the fractured surface, it was realized that the incorporation of long GF after the melt blending of PA66 and PP was very effective to attain high thermomechanical properties due to the better homogeneity and compatibility.     

Tribological properties of solid lubricants filled glass fiber reinforced polyamide 6 composites

The main purpose of this paper is to further optimize the tribological properties of the glass fiber reinforced PA6 (GF/PA6,15/85 by weight) for high performance friction materials using single or combinative solid lubricants such as Polytetrafluroethylene (PTFE), ultra-high molecular weight polyethylene (UHMWPE) and the combination of both of them. Various polymer blends, where GF/PA6 acts as the polymer matrix and solid lubricants as the dispersed phase were prepared by injection molding. The tribological properties of these materials and the synergism as a result of the incorporation of both PTFE and UHMWPE were investigated. The results showed that, at a load of 40 N and a velocity of 200 rpm, PTFE was effective in improving the tribological capabilities of matrix material. On the contrary, UHMWPE was not conductive to maintain the structure integrity of GF/PA6 composite and harmful to the friction and wear properties. The combination of PTFE and UHMWPE showed synergism on further reducing the friction coefficient of the composites filled with either PTFE or UHMWPE only. Effects of load and velocity on tribological behavior were also discussed. To further understand the wear mechanism, the worn surfaces were examined by scanning electron microscopy.     

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.     

含拼接铺层碳纤维增强树脂复合材料拉伸破坏机制

对于尺寸较大或形状复杂的结构,通常需要在纤维增强树脂（FRP）复合材料内部对铺层进行拼接处理。铺层拼接会在材料内部引起复杂的应力分布,具有突出的安全隐患。以同一位置处出现不同层数铺层拼接的单向碳纤维增强树脂（CFRP）复合材料为研究对象,重点分析了铺层拼接对材料拉伸力学性能的影响机制。通过拉伸实验,测试了拼接对其力学强度的影响;用相机记录了破坏过程,并结合数字图像相关技术（DIC）对拼接位置附近的应变场进行了监测。利用有限元模型（FEM）模拟和分析结构的破坏机制,采用3D-Hashin准则和渐进损伤模型对CFRP复合材料铺层进行模拟;采用内聚力模型对胶层失效行为进行描述。实验结果表明,拼接结构的引入大幅降低了材料的抗拉强度。FEM模拟与实验测试结果吻合度高,说明了模型的有效性。综合实验结果和模拟分析得到,铺层拼接处产生应力集中,造成被拼接的两部分分离并伴随拼接铺层和连续铺层的层间剪切破坏;层间破坏发生后,拉伸载荷完全由连续铺层承载。因此,材料的最终承载能力由材料中连续铺层数决定。      

短玻纤增强丙烯腈-丁二烯-苯乙烯共聚物的制备及性能

以丙烯腈-丁二烯-苯乙烯共聚物(ABS)及短玻璃纤维(SGF)为原料, 以苯乙烯-马来酸酐共聚物(SMA)和环氧树脂(EP)为界面相容剂, 制备了SGF/SMA-EP-ABS复合材料。用扫描电镜(SEM)、 动态力学热分析(DMTA)等研究了界面相容剂对SGF增强ABS复合材料力学性能及界面粘结性能的影响。结果表明:加入SMA或EP, SGF增强ABS复合材料的力学性能明显提高; SMA与EP同时加入具有明显的协同效果, 使复合材料的性能更为优越。当SGF加入质量分数为30%时, SGF/SMA-EP-ABS复合材料的拉伸强度、 弯曲强度、 冲击强度较未添加界面相容剂时分别提高了56%、 42%、 79%。SEM和DMTA测试表明, 加入SMA和环氧树脂后, SGF与ABS基体之间的界面粘结性能得到很大改善。      

Mechanical and electrical performance of Roystonea regia/glass fibre reinforced epoxy hybrid composites

The present paper investigates mechanical and electrical properties of Roystonea regia/glass fibre reinforced epoxy hybrid composites. Five varieties of hybrid composites have been prepared by varying the glass fibre loading. Roystonea regia (royal palm), a natural fibre was collected from the foliage of locally available royal palm tree through the process of water retting and mechanical extraction. Roystonea regia, E-glass short fibres were used together as reinforcement in epoxy matrix to form hybrid composites. It has been observed that tensile, flexural, impact and hardness properties of hybrid composites considerably increased with increase in glass fibre loading. But electrical conductivity and dielectric constant values decreased with increase in glass fibre content in the hybrid composites at all frequencies. Scanning electron microscopy of fractured hybrid composites has been carried out to study the fibre matrix adhesion.     

铁基非晶条带-玻璃纤维混杂复合材料力学特性

针对铁基非晶条带-玻璃纤维混杂增强树脂基复合材料,研究了表面处理、热处理对非晶条带力学性能的影响,在此基础上选取了适宜的树脂基体,制备了混杂复合材料,测试了基本力学性能并分析了破坏模式。结果表明：酸蚀表面处理对条带的拉伸性能影响很小,但改变了条带的表面形貌和表面能,从而提高了条带与树脂的粘结性能;混杂复合材料纵向拉伸弹性模量符合混合定律,横向拉伸弹性模量主要由非晶条带贡献,并且非晶条带的承载对混杂复合材料的横向拉伸强度起到了一定的作用;弯曲破坏和剪切破坏均产生受压侧纤维层与非晶条带的分层以及纤维断裂。     

Polystyrene reinforced by self-welded glass fibers: Kinetics of polyamide 6 preferential segregation

The encapsulation kinetics of short glass fibers (GFs) by polyamide 6 (PA6) during their melt compounding with polystyrene (PS) was studied. The encapsulation correlates to the mechanical strength of the ternary PS/PA6/GF (50/21/29) composites at temperatures higher than the T_g of the PS matrix. It was observed that many fibers are “welded” together by the minor PA6 phase, and a continuous GF-PA6 network is formed throughout the PS matrix. As a result, the elastic modulus is enhanced remarkably over a wide temperature region from the T_g of PS to the T_m of PA6, and the heat distortion temperature of the composites increases significantly up to 201 °C. We verified that the bulk strength of the GF-PA6 network depends on the encapsulation ratio, N_PA6, a parameter denoting the percentage of the PA6 phase encapsulating the fibers. As mixing time increases, N_PA6 increases gradually and then remains constant. The PA6 with a lower viscosity shows a rapid increase in N_PA6, but a larger difference in viscosity between PA6 and PS results in a higher saturating value. A remarkable increase in N_PA6 was observed for samples after isothermal post-treatments. It was concluded that the encapsulation of the GF by polymers and the strength of the GF-PA6 networks are kinetically determined by the migration of the dispersed PA6 domains to the GF surface and the preferential segregation of these PA6 domains to the junction point of fibers under the driving force of capillarity.