A chemical method to graft carbon nanotubes onto a carbon fiber

A simple method is developed for grafting carbon nanotubes (CNTs) onto a carbon fiber surface. CNT and carbon fiber undergo an oxidation treatment. Oxidation generates oxygen, like carboxyl, carbonyl or hydroxyl groups, or amine groups on nanotubes and carbon fiber surface. Functionalized CNTs are dispersed in a solvent and deposited on carbon fibers. The bonds between CNT and carbon fiber are operated by esterification, anhydridation or amidization of the chemical surface groups. The resulting materials are characterized by scanning electron microscopy (SEM). CNTs form a 3D network around the carbon fibers. Likewise, CNT bonding between two fibers is observed.     

Critical fibre length and tensile strength for carbon fibre-epoxy composites

The tensile strength of epoxy resin reinforced with a random-planar orientation of short carbon fibres decreases with increasing temperature. This decrease may be estimated by the strain rate and temperature dependence of both the yield shear strength at the fibre-matrix interphase and the critical fibre length obtained by taking the distribution of fibre strength into consideration. The experimental value at room temperature is smaller than the calculated value. It is inferred that this result is attributed to the stress concentration caused by ineffective fibres produced during preparation which were shorter than the critical fibre length.     

Modification of single-walled carbon nanotubes and its influence on the interfacial strength in polymeric composites

Single-walled carbon nanotubes was purified and modified with dichlorocarbene, HNO₃ or octadecylamine and incorporated in polymeric matrices of polycarbonate and epoxy. Exposing the composite material to a tensile strain and measuring the shift of the G′-band revealed that higher loads could be transferred to the HNO₃-modified carbon nanotubes. Exfoliation was regarded as the main reason for the increased interfacial strength resulting in larger specific surface area and higher hydrostatic compressive stresses on the nanotube bundles.     

The strength of hybrid glass/carbon fibre composites

The tensile mechanical properties of hybrid composites fabricated from glass and carbon fibres in an epoxy matrix have been evaluated over a range of glass: carbon ratios and states of dispersion of the two phases. The failure strain of the carbon phase increased as the relative proportion of carbon fibre was decreased, and as the carbon fibre was more finely dispersed. This behaviour is commonly termed the hybrid effect, and failure strain enhancement of up to 50% has been measured. Only part of the effect may be attributed to internal compressive strains induced in the carbon phase by differential thermal contraction as the composite is cooled from its cure temperature. The laminae or ligaments of carbon fibre dispersed in the glass fibre phase show a multiple failure mode, and when the constitution is favourable catastrophic failure does not occur until a considerable number of ligament fractures have accumulated. Failure is thus progressive, and the material is effectively tougher than equivalent all-carbon fibre composites.     

Multiwalled carbon nanotubes and sepiolite nanoclays as flame retardants for polylactide and its natural fibre reinforced composites

This work aims to develop a fully bio-based polylactic acid (PLA) composite with improved flame retardancy, utilising the unique properties of sepiolite nanoclay (Sep) and multiwalled nanotubes (MWNT). The pyrolysis combustion flow calorimeter (PCFC) also known as the microcalorimeter was used to screen the various PLA nanocomposites with respect to their potential flammability performance. The heat release capacity (HRC) which is an indicator of a materials fire hazard, reduced by 58% for the PLA ternary system based on sepiolite and MWNTs. Thermal gravimetric analysis (TGA) showed significant improvements to the residual char towards the later stages of the thermal ramp. The PLA ternary nanocomposite showed a 45% reduction in peak heat release (PHRR) when tested in the cone calorimeter. A further noteworthy observation was the 25% reduction in PHRR upon the introduction of hemp fibre into the PLA nanocomposite system.     

Effects of fibre length on tensile strength of carbon/glass fibre hybrid composites

The tensile strength of epoxy resin reinforced with random-planar orientation of short carbon and glass fibres increased as the length of the reinforcing fibres increased, and the increase in tensile strength remained almost unchanged after the fibre length reached a certain level. The tensile strength of composites at any fibre length could be estimated by taking the strain rate and temperature dependence of both the yield shear strength at the fibre-matrix interphase and the mean critical fibre length into consideration. The tensile strength of the hybrid composite could be estimated by the additive rule of hybrid mixtures, using the tensile strength of both composites.     

A probabilistic theory for the strength of discontinuous fibre composites

The strength of discontinuous fibre-reinforced composites is often reduced due to local stress concentrations at large fibre-end-gaps. A theoretical prediction of the strength of unidirectional fibre composites is performed based upon a probabilistic model of the fibre configuration. This work further develops the concepts of Bader, Chou and Quigley, and Fukuda and Chou. A limiting case of the present analysis shows good agreement with the results of Smith. Emphases are placed on the effect of matrix stress transfer properties including matrix plasticity. For a matrix deforming elastically, the strength is reduced as the composite size (N) increases. As compared with the rule-of-mixtures prediction for continuous fibre composites with identical fibre volume fraction, the reduction is shown to be proportional to (In N)^–P , with the exponent P being between 0.5 and 1 for two-dimensional composites and between 0.25 and 0.5 for three-dimensional composites. For a matrix deforming plastically, the local stress concentrations are reduced. Based upon the analytical expression of the local load sharing rule for a plastically deformed matrix, the composite strength is shown to approach the modified rule-of-mixtures of Kelly and Tyson as the matrix yield stress decreases.This work was done on leave from Applied Mechanics Section, Central Research Laboratories, Sumitomo Metal Industries, Ltd., Nishinagasuhumdori, Amagasaki, Japan.     

Impact and after-impact properties of carbon fibre reinforced composites enhanced with multi-wall carbon nanotubes

The goal of the present study was to investigate the influence of multi-wall carbon nanotubes (MWCNTs) on the impact and after impact behaviour of carbon fiber reinforced polymer (CFRP) laminates. About 0.5% per weight MWCNTs were dispersed via a high shear device in the epoxy matrix (Bisphenol A) of carbon reinforced quasi-isotropic laminates. Subsequently, the modified CFRPs were subjected to low-energy impact and directly compared with unmodified laminates. In previous studies, the beneficial effect of the MWCNT inclusion to the fracture properties of CFRPs has been demonstrated. In terms of the CFRP impact performance, enhanced performance for the CNT doped specimens was observed for higher energy levels. However, the after-impact properties and more specifically compression after impact were improved for both the effective compression modulus and the compression strength. In addition, compression–compression fatigue after impact performance of the CNT modified laminates was also improved, by extending the fatigue life.     

A probabilistic theory for the strength of short fibre composites

This paper presents a probabilistic theory for predicting the strength of unidirectional short fibre composites. It is assumed that the failure of the composite occurs due to the inability of the short fibres bridging a critical zone to carry the load. The stress concentrations on the fibres bridging a fibre end gap are evaluated as a function of the number of fibre ends forming the gap. The sizes of the gaps are predicted from a probabilistic approach. The short fibre composite strength is then estimated from the gap size and the corresponding stress concentration factor. Comparisons of the present work with existing theories and experiments have been made.On leave from the Institute of Space and Aeronautical Science, University of Tokyo, Japan.     

Compressive strength of unidirectional and crossply carbon fibre/PEEK composites

The commonly accepted production methods of composite systems generally result in departure of the plies properties from transverse isotropy due to stresses acting during fibre—matrix bond formation. This anisotropy coupled with the composite structure affects compressive loading; the ultimate stresses as well as the direction, in- or out-of-plane, of kink propagation. A unidirectional and a crossply carbon fibre/PEEK composites were compression tested at ambient and elevated temperature as well as exposed to various chemical environments. Significant disruptions in fibre—matrix interface in the crossply composite were indicated. The compression tests showed that failure occurred through in-plane and out-of-plane fibre bucking and kinking in the unidirectional and crossply composites, respectively. Failure of the longitudinal plies in the crossply laminate occurred at significantly higher compression stress than for the unidirectional composite. Compressive failure mechanisms in unidirectional and multi-directional laminates are considered.     

The effect of fibre sizing on fibres and bundle strength in hybrid glass carbon fibre composites

Tests have been carried out on single carbon fibres supplied in the sized and unsized conditions, as well as impregnated tows and tows in a glass–carbon fibre hybrid composite of the same fibre. The results were analysed using a Weibull distribution for the strengths of the reinforcing fibres and composites. The tensile strength of the single fibres appeared to be unaffected by the sizing of the filaments. In the case of the impregnated tows, an increase in characteristic strength of 7% was observed for the unsized fibres. The strength of the impregnated tows in hybrid composites was seen to be 15% higher than those tested in air. This can be attributed to the “hybrid effect”. This revised version was published online in November 2006 with corrections to the Cover Date.     

Artificial damage techniques for low velocity impact in carbon fibre composites

Materials and techniques used in artificially induced damage are evaluated and compared. The damage induced by low velocity impacts is characterised using penetrant enhanced radiography and deply techniques. This information is used to construct specimens with simulated damage that will facilitate the study of damage growth. Specimens manufactured match quite closely the properties of specimens which contain actual damage.     

Influence of titanium carbide on the interlaminar shear strength of carbon fibre laminate composites

The potential use of carbon fibre laminate composites is limited by the weak out-of-plane properties, especially delamination resistance. The effect of incorporating titanium carbide to the mesophase pitch matrix precursor of carbon fibre laminate composites on interlaminar shear strength is studied both on carbonised and graphitised composites. The presence of titanium carbide modifies the optical texture of the matrix from domains to mosaics in those parts with higher concentrations and it contributes to an increase of fibre/matrix bonding. This fact produces an increase of the interlaminar shear strength of the material and changes the fracture mode.     

A review on basalt fibre and its composites

In recent years, both industrial and academic world are focussing their attention toward the development of sustainable composites, reinforced with natural fibres. In particular, among the natural fibres (i.e. animal, vegetable or mineral) that can be used as reinforcement, the basalt ones represent the most interesting for their properties. The aim of this review is to illustrate the results of research on this topical subject. In the introduction, mechanical, thermal and chemical properties of basalt fibre have been reviewed. Moreover, its main manufacturing technologies have been described. Then, the effect of using this mineral fibre as reinforcement of different matrices as polymer (both thermoplastic and thermoset), metal and concrete has been presented. Furthermore, an overview on the application of this fibre in biodegradable matrix composites and in hybrid composites has been provided. Finally, the studies on the industrial applications of basalt fibre reinforced composites have been reviewed.     

环己烷浮游催化法在碳纤维表面生长碳纳米管

以环己烷为碳源、二茂铁为催化剂前躯,采用浮游催化法成功的在碳纤维表面生长了碳纳米管(CNT),制备了多尺度杂化材料CNTs/CF。实验重点考察了反应温度、二茂铁浓度、载气等参数对CNT在纤维表面生长的影响,通过扫描电镜(SEM)、投射电镜(TEM)研究了CNTs/CF的形貌及产物CNT的微观结构。当固定反应温度为820℃、二茂铁-环己烷浓度为2g/100mL时,随着氢气在载气中含量在0～100%范围内变化,产物CNT直径亦有86nm降低至39nm。通过单丝拉伸测试发现,相比初始碳纤维,不同长度的CNTs/CF单纤维强度下降幅度均在10%以内。     

Strain rate and temperature dependence of tensile strength for carbon/glass fibre hybrid composites

The tensile strength of epoxy resin reinforced with a random planar orientation of short carbon and glass fibres increased as the strain rate increased, and the increase in tensile strength became slightly remarkable with increasing temperature. The strain rate-temperature superposition was held for each composite. The strain rate and temperature dependence of tensile strength of composites could be estimated based on the dependence of the mechanical properties of the matrix resin, the interfacial yield shear strength and the critical fibre length. The strain rate and temperature dependence of the tensile strength of the hybrid composite could be estimated by the additive rule of hybrid mixtures, using the strain rate and temperature dependence of the tensile strength of both composites. The experimental values at a higher rate were lower than the calculated values. It was hypothesized that this may have been caused by the ineffective fibres formed during preparation of the specimen.     

Dispersion of multi-walled carbon nanotubes and its effects on the properties of cement composites

In this study, two types of multi-walled carbon nanotubes (pristine, p-CNT and functionalized, f-CNT) were dispersed in water by sonication and then added to cement mortar. The purpose of this study was to characterize the dispersion degree of the CNTs in aqueous suspension and to investigate whether achieving dispersion in water would also result in dispersion inside mortar. Dispersion of the CNTs in water was investigated by means of UV–vis spectroscopy, using different CNT concentrations and sonication durations. Dispersion of the CNTs in cement mortar was investigated by measuring the compressive and flexural strength and fracture toughness as well as the microstructural characterizations of scanning electron microscopy and mercury intrusion porosimetry. The effects of the CNT addition on drying shrinkage and cement hydration were also investigated for cement pastes. The results of UV–vis spectroscopy showed that by increasing the sonication time to 120 min, the dispersion degree of the f-CNT suspension increased progressively, while for p-CNT, a maximum was reached with 60 min of sonication. The compressive and flexural strength and fracture toughness of mortars containing f- and p-CNTs were not significantly improved either by increasing the amount of CNT or imposing sonication in mixing water. High CNT dispersion in cement matrix was not equally obtained by utilizing highly dispersed CNT suspension. Sonication of f- and p-CNT led to a remarkable deceleration of cement hydration in the first hour of hydration and drying shrinkage of the cement composites was found to be reduced by f- and p-CNT addition.