混杂增强聚氨酯复合硬泡塑料的物理及力学性能

研究纤维与颗粒混杂增强聚氨酯复合硬泡塑料的物理及力学性能,着重分析增强剂SiO₂颗粒和玻璃纤维含量以及纤维长度对其性能的影响。结果表明,SiO₂含量为20 wt％,玻璃纤维含量为7.8 wt％时,试样的拉伸强度达到最佳值。此外,还比较了玻璃纤维、尼龙66纤维和PAN基碳纤维的增强效果。结果表明,3 wt%~5 wt％含量碳纤维增强的聚氨酯复合硬泡塑料拉伸强度最佳。     

Structure and properties of coir fibres

In this paper, early research on the structure and properties of coir fibres has been critically reviewed. Gaps in the scientific information on the structure and properties of coir fibre have been identified. Attempts made to fill some of these gaps include the evaluation of mechanical properties (as functions of the retting process, fibre diameter and gauge lengths of fibre, as well as of the strain rates) and fracture mechanisms using optical and scanning electron microscopy. The deformation mechanism of coir fibre resulting in certain observed properties has been discussed with the existing knowledge of the structure of plant fibres as a basis. It is concluded that more refined models need to be developed for explaining the observed mechanical properties of coir fibres. Some of the suggestions for further work include relating properties of fibres to factors like the chemical composition of the fibre and the size and number of cells, size of lumen, variation in micro-fibril angle within each cell and between different cells of the same fibre, and understanding the deformation of the whole fibre in terms of deformation of individual micro-components. Further work is required on the effects of mechanical, thermal and thermomechanical, chemical treatments to modify the structure and mechanical properties of these fibres in such a way as to make them more suitable as reinforcements in polymer, clay and cement matrices.     

Interfacial bonding and degumming effects on silk fibre/polymer biocomposites

Silk fibre has been popularly used for bio-medical engineering and surgically-operational applications for centuries because of its biocompatible and bioresorbable properties. Using silk fibre as reinforcement for bio-polymers could enhance the stiffness of scaffoldings and bone implants. However, raw silk fibre consists of silk fibroin that is bound together by a hydrophilic glued-liked protein layer called “sericin”. Degumming is a surface modification process for sericin removal which allows a wide control of the silk fibre’s properties, making the silk fibre possible to be properly used for the development and production of novel bio-composites with specific mechanical and biodegradable properties. Some critical issues such as wettability, bonding efficiency and biodegradability at the fibre/matrix interface are of interesting topics in the study of the degumming process. Therefore, it is a need to detailedly study the effect on different degumming processes to the properties of the silk fibre for real-life applications.     

The influence of fibre properties of the performance of glass-fibre-reinforced polyamide 6,6

We discuss the effect of fibre strength and diameter on the balance of mechanical properties of glass-reinforced polyamide 6,6. The results show that the elastic properties of injection-moulded short-glass-fibre-reinforced polyamide 6,6 are not strongly influenced by fibre diameter in the 10–17 micron range. The ultimate properties of these composites (strength and Izod impact behaviour) showed a clear dependence on fibre diameter and were increased by the presence of high-strength S-2 glass fibres. The relationship between the observed mechanical properties and the length, diameter and orientation of the fibres is explored. We have measured fibre length as a function of diameter in composites containing a single glass-reinforcement product and blends of two glass products. The reduction in glass-fibre length from glass-fibre production to final composite moulding has been followed step by step. The final composite mechanical properties, the fibre length, strength, diameter and orientation are all inter-related.     

The effect of interfacial imperfections on the micromechanical stress and strain distribution in fibre reinforced composites

A mathematical model for the determination of micromechanical stress and strain distribution in a unidirectional fibre reinforced composite is developed. The model consists of three phases represented as concentric cylinders, including the existence of an interphase. Both fibre and matrix have well defined elastic properties, while the interphase properties follow an exponential law of variation. The effect of an abrupt variation of elastic properties at the fibre—interphase boundary on the micromechanical state of stress is also presented. The degree of adhesion between fibre and matrix is described by means of adhesion parameters introduced, and a parametric study is performed wherein the stress and strain distribution around the fibre are determined as a function of adhesion efficiency and fibre volume fraction. Analytical results were confirmed by means of a finite element technique introduced and applied to the model.     

Ductile creep rupture of fibre bundles

The time dependent rupture of linearly viscous ideal fibre bundles is analysed, considering the influence of locally varying fibre properties. Immediate and delayed rupture modes, which may be of instantaneous or gradual nature, are identified to occur depending upon the distribution of fibre properties. The existence of an incubation time is revealed as a consequence of the assumed fibre properties.     

Failure strain as the key design criterion for fracture of natural fibre composites

Natural fibre composites are often considered to be problematic because of the high variability in their mechanical properties. This short communication considers the statistical variation in the two key fracture properties (strain and strength) for data obtained from tests on 785 jute technical fibres. The fibre strength does have high variability, which arises from the difficulty of determining an accurate fibre cross-sectional area (CSA). Failure strain is more consistent as this property is independent of the fibre cross-section. The authors therefore recommend that the use of failure strain as the key design criterion for natural fibre composites would expedite the adoption of these materials in the market.     

A novel microbond bundle pullout technique to evaluate the interfacial properties of fibre-reinforced plastic composites

The interfacial properties of the fibre composite systems decide the overall usability of a composite in simple and complex shapes, as they are the deciding factors in determination of the mechanical properties, structural properties and above all a complete understanding of the reliability of composite systems. In the present investigation, the interfacial properties of carbon fibre/epoxy composites viz., matrix shrinkage pressure, interfacial frictional stress, interfacial shear stress and coefficient of friction were evaluated through a novel microbond bundle pullout test. This test is different from the single fibre pull out, fibre fragmentation or the fibre push in test. Based on some of the physical principles involving the single fibre microbond pullout test, like the contact angle of the microbond matrix drop with the fibre surface, the surface tension/energy of the two surfaces before and after adhesion and the interfacial fibre/matrix chemistry, this is simple to perform and statistically averaged mesomechanical test is also easy to evaluate and is shown to be a test method that enables a conservative prediction of the laminate level or macromechanical shear properties of fibre composite systems. This test demonstrates the validity of the mesomechanical tests that are more relevant to the macromechanical tests than the micromechanical tests. Fractography carried out to corroborate the observed mechanical properties with the fracture features is also reported. The general advantages of the mesomechanical interfacial tests over those based on micromechanical assumptions is also discussed along with some common limitations.     

Effects of Gear-Shape Fibre on the Transverse Mechanical Properties of Unidirectional Composites: Virtual Material Design by Computational Micromechanics

This paper aims to study the effect of fibre cross-section shape on the mechanical properties of unidirectional fibre reinforced composites. First, the specific surface area of different cross-section shape is compared, and the gear-shape fibre is selected for further study, which has the largest specific surface area. The effect of gear-shape fibre with various tooth number on the transverse mechanical properties of unidirectional composites is investigated by computational micromechanics, comparing with the traditional round fibre. It is found that all the gear-shape fibre reinforced composites have higher transverse stiffness and strength than the round fibre reinforced composite, and the gear-shape fibre with fewer tooth number has greater reinforcing effect on the mechanical properties of the composite. The mechanism of this phenomenon is revealed by examine the damage initiation and evolution process of the composite, and suggestion is made on the optimal cross-section shape of the reinforcing fibre for the composites.     

Evaluation of interfacial properties between carbon fibres and semicrystalline thermoplastic matrices in single-fibre composites

The interfacial properties between pitch-based carbon fibre and semicrystalline thermoplastic matrices have been investigated by using the fragmentation test on single-fibre composites. For this purpose, fibres with seven different degrees of surface oxidation were prepared. From the fragmentation test, it was found that oxidization of carbon fibre reduces the fibre fragment length. Further, the length is also influenced by the nature of resin used as matrix. The morphology of crystallites formed on the fibres has been studied. Based on these results, the interfacial properties of carbon fibre and thermoplastic resins are discussed.     

Quantitative study on the statistical properties of fibre architecture of genuine and numerical composite microstructures

A quantitative study is carried out regarding the statistical properties of the fibre architecture found in composite laminates and that generated numerically using Statistical Representative Volume Elements (SRVE’s). The aim is to determine the reliability and consistency of SRVE’s for representation of the composite microstructure as well as investigate the effect of a varying fibre radii distribution on the fibre architecture. Based on digital image analysis, the fibre architecture of unidirectional glass fibre composites with varying fibre content is recognised. The fibre architecture found is compared to a numerical microstructure generator using Monte Carlo simulations. It is shown that the numerical microstructure generator produces fibre arrangements that are statistically similar to the observed, which indicates a reliable and consistent SRVE. The microstructural effects of a parametric variation of the parameters for fibre radii distribution are simulated, and the influence on the fibre architecture is investigated.     

金属纤维／聚合物导电复合材料的性能研究

以铜纤维和不锈钢纤维为导电填料，分别填充了ＡＢＳ、ＨＩＰＳ和ＰＰＳ对脂基体，制得导电复合材料。研究了金属纤维含量及工艺条件对复合材料的导电性能和力学性能的影响。结果表明，选择合适的工艺条件以保证金属纤维有较大的长径比并在树脂中有良好的分散状态，是制造性能优良的导电复合材料的关键。     

Characteristics of Hermès flax fibres as a function of their location in the stem and properties of the derived unidirectional composites

The tensile mechanical properties of flax fibres from the Hermès variety are estimated according to their diameter and their location in the stems. The large scattering of these properties is ascribed to the variation of the fibre size along its longitudinal axis, as revealed by SEM observations. The higher values of the mechanical properties for the fibres issued from the middle of the stems are associated with the chemical composition of their cell walls. The mechanical properties of unidirectional flax fibre/epoxy matrix composites are studied as a function of their fibre content. The properties of the composites are lower than those expected from single fibre characteristics.     

Flax fibre and its composites – A review

In recent years, the use of flax fibres as reinforcement in composites has gained popularity due to an increasing requirement for developing sustainable materials. Flax fibres are cost-effective and offer specific mechanical properties comparable to those of glass fibres. Composites made of flax fibres with thermoplastic, thermoset, and biodegradable matrices have exhibited good mechanical properties. This review presents a summary of recent developments of flax fibre and its composites. Firstly, the fibre structure, mechanical properties, cost, the effect of various parameters (i.e. relative humidity, various physical/chemical treatments, gauge length, fibre diameter, fibre location in a stem, oleaginous, mechanical defects such as kink bands) on tensile properties of flax fibre have been reviewed. Secondly, the effect of fibre configuration (i.e. in forms of fabric, mat, yarn, roving and monofilament), manufacturing processes, fibre volume, and fibre/matrix interface parameters on the mechanical properties of flax fibre reinforced composites have been reviewed. Next, the studies of life cycle assessment and durability investigation of flax fibre reinforced composites have been reviewed.     

High-modulus-high-strength poly-(p-phenylene benzobisthiazole) fibres

Heat-treatment processing of dry-jet wet-spun poly-(p-phenylene benzobisthiazole) fibres was undertaken to enhance fibre tensile mechanical properties. The effects of fibre tension and temperature and time of heat treatment in a nitrogen atmosphere on fibre mechanical properties were systematically investigated. Fibres possessing a tensile modulus as high as 300 GPa along with a tensile strength of 3 GPa have been produced. To attain this level of tensile properties, heat-treatment temperatures of 630 to 680° C for residence times of under one minute were required while applying tensions approaching fibre breaking stress at the elevated temperatures; conditions bordered on fibre degradation. Fibre structural changes associated with heat treatment and enchancement of mechanical properties are discussed in Part 2 of this work.     

Effects of fibre/matrix adhesion on carbon-fibre-reinforced metal laminates—I.: Residual strength

The role of interfacial adhesion between fibre and matrix on the residual strength behaviour of carbon-fibre-reinforced metal laminates (FRMLs) has been investigated. Differences in fibre/matrix adhesion were achieved by using treated and untreated carbon fibres in an epoxy resin system. Mechanical characterisation tests were conducted on bulk composite specimens to determine various properties such as interlaminar shear strength (ILSS) and transverse tension strength which clearly illustrate the difference in fibre/matrix interfacial adhesion. Scanning electron microscopy confirmed the difference in fracture surfaces, the untreated fibre composites showing interfacial failure while the treated fibre composites showed matrix failure. No clear differences were found for the mechanical properties such as tensile strength and Young's modulus of the FRMLs despite the differences in the bulk composite properties. A reduction of 7·5% in the apparent value of the ILSS was identified for the untreated fibre laminates by both three-point and five-point bend tests. Residual strength and blunt notch tests showed remarkable increases in strength for the untreated fibre specimens over the treated ones. Increases of up to 20% and 14% were found for specimens with a circular hole and saw cut, respectively. The increase in strength is attributed to the promotion of fibre/matrix splitting and large delamination zones in the untreated fibre specimens owing to the weak fibre/matrix interface.     

A study on the characteristics of glass fibre reinforced thermoplastics by transfer moulding

Lately, the use of fibre reinforced thermoplastics (FRTP) has increased due to its increased mouldability compared to thermosetting FRP material.

FRTP includes stampable sheet, short and long fibre reinforced thermoplastic pellets, continuous fibre reinforced thermoplastics sheets, etc. The long fibre reinforced thermoplastic (LFRTP) pellet has better mechanical properties than short fibre reinforced pellets and better mouldability than stampable sheet. At present, injection moulding method is mainly used for moulding LFRTP pellets because of its high productivity.

However, the long fibre of LFRTP pellets, whose length is the same as pellet length, is degraded during processing if conventional injection moulding machines are used, and as a result, the mechanical properties are not improved as expected in many cases. Therefore, a new moulding process is required to make good use of LFRTP pellets.

For this study, a transfer moulding apparatus was designed and built to minimize fibre degradation of the moulded parts.

Firstly, the LFRTP pellets with fibre lengths of 3, 6, 9, 12.7 and 17 mm were prepared in order to clarify the difference of mechanical properties due to fibre length. The fibre ratio was 30% in weight for all cases and the same polypropylene was used. They were moulded to the shape of the test specimens. Tensile, bending and Izod impact strengths were measured by using these test specimens. Secondly, LFRTP pellets were moulded to the shape of test specimens by the transfer moulding apparatus and conventional injection moulding machine, and then mechanical properties were measured. At the same time, short fibre pellets were moulded to the smae shape of test specimens by the injection moulding machine, and mechanical properties were compared with those of LFRTP pellets.

With the long glass fibre reinforced polypropylene, good results of fibre preservation and mechanical properties were obtained by the transfer moulding apparatus which was built for this study. The impact strength was increased remarkably as the fibre length increased, and consequently the preservation of fibre length in the moulded parts was especially effective in improving the impact strength.     

Microstructural characterisation of 3D printed and injection-moulded glass fibre-reinforced polypropylene by image analysis,simulation and experimental methods

The mechanical properties of fibre-reinforced thermoplastics and their dependencies on the manufacturing process, fibre properties, fibre concentration and strain rate have been researched intensively for years in order to predict their macroscopic behaviour by numerical simulations as precisely as possible. Including the microstructure in both real and virtual experiments has improved prediction precision for injection-moulded glass fibre-reinforced thermoplastics significantly. In this work, we apply three established methods for characterisation and modelling to an injection-moulded and to a 3D printed material. The geometric properties of the fibre component as fibre orientation, fibre length and fibre diameter distributions are identified by analysing reconstructed tomographic images. For comparing the fibre lengths, a recently suggested new method is applied. Based on segmentations of the tomographic images, we calculate the elastic stiffness of both composites numerically on the microscale. Finally, the mechanical behaviour of both materials is experimentally characterised by micro tensile tests. The simulation results agree well with the measured stiffness in case of the injection-moulded material. However, for the 3D printed material, measurement and simulation differ strongly. The prediction from the simulation agrees with the values expected from the image analytic findings on the microstructure. Therefore, the differences in the measured behaviour have to be contributed to the matrix material. This proves demand for further research for 3D printed materials for predictable prototypes, preproduction series and possible serial application.     

The size effects on the mechanical behaviour of fibres

The size of a fibre affects its mechanical properties and thus is of theoretical and practical importance for studies of the rupturing process during loading of a fibrous structure. This paper investigates the overall effects of length on the mechanical behaviour of single fibres. Four types of fibres, ranging from brittle to highly extensible, were tested for their tensile properties at several different gauge lengths. Different from most previous studies where the focus has been on the gauge length effects on a single property such as fibre strength or breaking strain, this paper look comprehensively into the effects of length on all three of the most commonly studied mechanical properties, namely strength, breaking strain and initial modulus. Particular emphasis is placed on initial modulus and on the interactions between all three parameters. Influences of strain rate and fibre type on the size effects are also investigated. The effect of potential fibre slippage on experimental error is examined. An image analysis method is used to measure the real fibre elongation in comparison to the same fibre elongation obtained directly from an Instron tester. Finally, a statistical analysis is carried out using the experimental data to test the fitness of the Weibull theory to polymeric fibres. This was done as the Weibull model has been extensively utilized in examining fibre strength and breaking strain, although it is supposed to be valid only for the so-called classic fibres to which more extensible polymeric fibres do not belong. This revised version was published online in November 2006 with corrections to the Cover Date.     

Mechanical properties of flax fibre/polypropylene composites. Influence of fibre/matrix modification and glass fibre hybridization

The effect of fibre treatments and matrix modification on mechanical properties of flax fibre bundle/polypropylene composites was investigated. Treatments using chemicals such as maleic anhydride, vinyltrimethoxy silane, maleic anhydride-polypropylene copolymer and also fibre alkalization were carried out in order to modify the interfacial bonding between fibre bundles and polymeric matrix. Composites were produced by employing two compounding ways: internal mixing and extrusion. Mechanical behaviour of both flax fibre bundle and hybrid glass/flax fibre bundle composites was studied. Fracture surfaces were investigated by scanning electron microscopy. Results suggest that matrix modification led to better mechanical performance than fibre surface modification. A relevant fact is that silanes or MA grafted onto PP matrix lead to mechanical properties of composites even better than those for MAPP modification, and close to those for glass fibre/PP.