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.     

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.     

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.     

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.     

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.     

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.     

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.     

Mechanical behaviour of carbon and glass hybrid fibre reinforced polyester composites

Mechanical behaviour of carbon fibre/glass mat/polyester resin hybrid composites of sandwich construction is studied through tension, flexure, impact and post-impact tension tests. Tensile and flexural strength, modulus and failure strain values are compared to the calculated values. Total impact fracture energy and residual (after impact) tensile strength values of hybrid composites are analysed with regard to corresponding values of carbon/polyester composites. Failure of tested coupons was analysed by visual inspection and observation by scanning electron microscopy.     

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.     

玻璃纤维增强环氧复合材料上超疏水表面层的制备

先采用真空袋压法制备含CaCO3/环氧树脂表面功能层的玻璃纤维增强环氧树脂复合材料,再通过化学刻蚀与表面修饰,在玻璃纤维增强环氧树脂复合材料上制备出超疏水表面。采用扫描电镜和动/静态接触角分析仪,表征表面的形貌和疏水性,结果表明,在复合材料表面构建了具有微-纳米尺度二元粗糙结构;采用1%（质量分数）的硬脂酸修饰后,其表面与水的接触角最高达160.03°;制备的超疏水表面结构在室温环境下具有长期的稳定性。     

Tensile,impact and dielectric properties of three dimensional orthogonal aramid/glass fiber hybrid composites

Aramid/glass hybrid composites with three different stacking sequences and their corresponding single fiber type composites have been fabricated and their tensile, impact and dielectric properties were investigated. The trend of tensile strength and modulus of the composites followed the rule of mixture (ROM) closely and a small but positive hybrid effect for tensile strength of the hybrid composites was observed. The hybrid composites in general had a higher impact resistance than the single fiber type composites and the hybrid composite in which fiber volume fractions for glass and aramid fiber were the most balanced showed the highest impact ductility. The aramid fiber composite showed a lower dielectric constant and a higher dielectric loss than the glass fiber composites. However, the dielectric constant of the hybrid composites decreased first and then increased as the volume fraction of aramid fiber increased, which did not follow the mixing rule for dielectric constants of compounds. The dielectric loss of the composites increased monotonically as the volume fraction of aramid fiber increased which agreed well with the mixing rule.     

Interface enhancement of glass fiber reinforced vinyl ester composites with flame-synthesized carbon nanotubes and its enhancing mechanism

Interface enhancement with carbon nanotubes (CNTs) provides a promising approach for improving shock strength and toughness of glass fiber reinforced plastic (GFRP) composites. The effects of incorporating flame-synthesized CNTs (F-CNTs) into GFRP were studied, including on hand lay-up preparation, microstructural characterization, mechanical properties, fracture morphologies, and theoretical calculation. The experimental results showed that: (1) the impact strength of the GFRP modified by F-CNTs increased by more than 15% over that of the GFRP modified by CNTs from chemical vapor deposition; and (2) with the F-CNT enhancement, no interfacial debonding was observed at the interface between the fiber and resin matrix on the GFRP fracture surface, which indicated strong adhesive strength between them. The theoretical calculation revealed that the intrinsic characteristics of the F-CNTs, including lower crystallinity with a large number of defects and chemical functional groups on the surface, promoted their surface activity and dispersibility at the interface, which improved the interfacial bond strength of GFRP.     

Compressive deformation behaviors of tungsten fiber reinforced Zr-based metallic glass composites

Subjected to a wide range of strain rates, the compressive deformation and fracture behavior at different temperatures of tungsten fiber reinforced Zr-based metallic glass composites (BMGC) were investigated. Upon increasing temperature, the compressive strength decreases, accompanied with reduced elasticity and enhanced plasticity. In combination with fracture analysis, the effects of temperature, applied strain rate, and the reinforcement of tungsten fiber were explicitly described.     

Polyamide 6 composites reinforced with glass fibers modified with electrostatically assembled multiwall carbon nanotubes

Glass fiber-multiwall carbon nanotubes (GF-MWCNTs) hybrid preforms were prepared by electrostatic assembly method. Negatively charged MWCNTs by oxidization treatment were directly adsorbed onto the surfaces of positively charged GF to form tunable structure. The thickness and morphology of GF-MWCNTs preforms can be controlled by the assembly pH value and the concentration of oxidized-MWCNTs solution. We demonstrate that GF-MWCNTs preforms have uniform and porous interconnected network structure of MWCNTs on the surfaces of GF using FESEM. The multi-scale composites with the hybrid preforms were prepared by melt compounding. The presence of MWCNTs with porous nanostructure helps in the formation of interpenetrating network with polyamide 6 (PA 6) at the interface layer. As a result, the tensile tests of these multi-scale composites exhibit higher tensile properties in comparison with composites with GF, showing a promising structural composite to replace the traditional GF-reinforced composites with limited improvement of the performance.     

Fracture behavior of injection-molded short and long glass fiber—polyamide 6.6 composites

Relationships between the fracture toughness, K_Q, and microstructure of chopped short (SGF) and long glass fiber (LGF) reinforced injection-molded polyamide 6.6 composites have been studied. K_Q and elastic modulus, E, of the composites were determined on compact tension specimens as a function of temperature, T, and crosshead speed, v. The microstructure of the composites was characterized by the dimensionless reinforcing effectiveness parameter, R, which was extended in this work for LGF reinforcement. R takes into account not only the processing-induced fiber layer structure, the fiber alignment and the fiber volume fraction but also the aspect ratio and aspect ratio distribution of the reinforcement. The semi-empirical linear relationship between fracture toughness of the composite, K_Q,C, and that of the matrix, K_Q,C, established for SGF-reinforced plastics, i.e. K_Q,C = MK_Q,M = (a + nR)K_Q,M still exists if the newly defined modified R is used. Both the matrix stress condition factor, a, and the energy absorption coefficient, n, have been determined under different testing conditions and tabulated together with K_Q,M. This allows an estimate of K_Q,C for any given R. Normalized fracture maps in form K_Q vs (E,T) have been constructed. Failure mechanisms of both the matrix and the composites which have been revealed by scanning electron microscopy are discussed and summarized in failure maps indicating changes of breakdown processes as a function of T and v.     

Fatigue strength of a clutch pedal made of reprocessed short glass fibre reinforced polyamide

The fatigue behaviour of a clutch pedal made of reprocessed short glass fibre reinforced polyamide 6,6 was experimentally investigated and results were compared with tests on the same part made of virgin material. The study concentrated on the differences between the fatigue behaviour of injection moulded parts and standard specimens made of the same reprocessed reinforced polyamide. The different types of loading than in standard specimens resulted into a different fatigue mechanism. Moreover the presence of sharp notches transformed the diffused damage observed in plain specimens into the formation of cracks at few critical locations. This investigation also allowed to evidence that in real parts the role of fibre shortening due to reprocessing is more pronounced because of the more complex shape of the mould cavity, causing a higher degree of fibre breakage during injection moulding, due to the longer and more tortuous path followed by the melt polymer filling the mould cavity. The use of reground material also caused the appearance of defects in pedals, i.e. voids, which diminished the fatigue strength. Nevertheless, the use of a 100% reprocessed material still ensured a high degree of safety and allowed for obtaining parts fully complying with safety specifications.     

Mechanical properties of single- and double-gated injection moulded short glass fibre reinforced PBT/PC composites

Tensile and flexural properties of single-gated (SG) and double-gated (DG) injection moulded blend of polybutylene terephthalate (PBT) and polycarbonate (PC) and its composites containing 15, 20 and 30 wt.% short glass fibres were investigated. In the DG mouldings, a weldline was formed by direct impingement of two opposing melt fronts (i.e. cold weld). It was found that tensile modulus was not affected by the weldline but flexural modulus decreased in the presence of weldline. For both specimen types, modulus increased linearly with volume fraction of fibres (ϕ _f), according to the rule-of-mixtures for moduli. The weldline integrity (WIF) factor for flexural modulus decreased linearly with increasing ϕ _f. Results showed that tensile and flexural strengths for SG mouldings increase with increasing ϕ _f in a linear manner according to the “rule-of-mixtures” for strengths. The presence of weldline affected both strengths in a significant way; WIF factor decreased linearly with increasing ϕ _f and was independent of loading mode. It was noted also, that the overall fibre efficiency parameter for tensile modulus was independent of specimen type but for flexural modulus it was lower in the case of DG mouldings. In all cases, efficiency parameter for strength was considerably lower than for the modulus. Impact strength and fracture toughness of SG mouldings were significantly greater than for DG mouldings. Although these properties for SG mouldings increased with increasing ϕ _f, they decreased significantly for DG mouldings. Results showed that WIF factor for impact strength and fracture toughness decreased linearly with increasing ϕ _f.