Fibre-reinforced composites are rapidly gaining market share in structural applications, but further growth is limited by their lack of toughness. Fibre hybridisation is a promising strategy to toughen composite materials. By combining two or more fibre types, these hybrid composites offer a better balance in mechanical properties than non-hybrid composites. Predicting their mechanical properties is challenging due to the synergistic effects between both fibres. This review aims to explain basic mechanisms of these hybrid effects and describes the state-of-the-art models to predict them. An overview of the tensile, flexural, impact and fatigue properties of hybrid composites is presented to aid in optimal design of hybrid composites. Finally, some current trends in fibre hybridisation, such as pseudo-ductility, are described.

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Fibre hybridisation in polymer composites: a review

Carbon fiber is increasingly being utilized as a reinforcing material due to its high strength and high modulus, which is imparted into the properties of the final composite. A comprehensive review of the carbon fiber production process, from polymerization to fiber spinning and stabilization and carbonization, is provided. Relationships between carbon fiber microstructure and material performance is undertaken in order to assess the current status of the mechanical, thermal, and electrical properties of commercially available PAN and pitch based carbon fibers, as well as recently developed experimental carbon fibers. A discussion of next generation carbon fibers is also provided, with a discussion on carbon fiber derived from alternative precursor materials, as well as hierarchical carbon fiber composites.

Processing, structure, and properties of carbon fibers

For the first time, using aqueous solution calorimetry, we clearly identify the chemisorption of an unusually strong iodine charge-transfer (CT) complex within the cages of a metal–organic framework. Specifically, we studied the sorption of iodine gas in zeolitic imidazolate framework-8 (ZIF-8, Zn(2-methylimidazolate)2). Two iodine-loaded ZIF-8 samples were examined. The first, before thermal treatment, contained 0.17 I2/Zn on the surface and 0.59 I2/Zn inside the cage. The second sample was thermally treated, leaving only cage-confined iodine, 0.59 I2/Zn. The energetics of iodine confinement per I2 (relative to solid I2) in ZIF-8 are ΔHads = −41.47 ± 2.03 kJ/(mol I2) within the cage and ΔHads = −18.06 ± 0.62 kJ/(mol I2) for surface-bound iodine. The cage-confined iodine exhibits a 3-fold increase in binding energy over CT complexes on various organic adsorbents, which show only moderate exothermic heats of binding, from −5 to −15 kJ/(mol I2). The ZIF-8 cage geometry allows each iodine atom to form two CT...

Thermochemical evidence for strong iodine chemisorption by ZIF-8

Towards high-efficiency sorptive capture of radionuclides in solution and gas

Synchrotron radiation computed tomography has been used to analyse fibre break accumulation in unidirectional composites loaded in tension. The data are compared to model predictions. The model only slightly overestimated the composite failure strain, but predictions of fibre break density were too high, which can be mainly attributed to errors in the Weibull distribution. Both the number and percentage of interacting fibre break clusters were under-predicted by the model. This was attributed to an underestimation of stress concentrations in the model. While the experimental observations revealed mainly co-planar clusters, the model predicted mainly diffuse clusters. The experiments showed that the clusters did grow any further after their formation, while the model predicted a gradual development. Both local and dynamic stress concentrations were hypothesised to be key features for further exploration. The discrepancies identified, inform suggestions for directions advancing the state-of-the-art strength models of UD composites.

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Synchrotron radiation computed tomography for experimental validation of a tensile strength model for unidirectional fibre-reinforced composites

https://purehost.bath.ac.uk/ws/files/200176201/Paper_Raman_Okuda_r5.pdf

Investigating nanostructures in carbon fibres using Raman spectroscopy

We have investigated the fracture mechanisms of different types of carbon fibres, in terms of skin-core differences in single fibres, flaw size and fracture toughness. The fibre strength distribution was measured precisely using the fragmentation test for single-fibre composites. The failure probability for intermediate/high modulus types fibres was found to be constant with fibre strength in the range 2-4 GPa, but in contrast the strength scatter for high modulus type fibres was reduced. The fracture toughness of the carbon fibres, determined by introducing notches with lengths in range 60-200 nm, was found to be about 1.1 MPa m(1/2). The average flaw size of the carbon fibres increased with increasing fibre modulus, suggesting that the crack growth of surface flaws on the tens-of-nm scale occurred. This appears to be the main reason for the reduction in tensile strength during the carbonisation treatment. (C) 2013 Elsevier Ltd. All rights reserved.

Factors controlling the strength of carbon fibres in tension

In this study, we determined the strength distribution of high-strength polyacrylonitrile-based carbon fibers of different short gauge lengths (~1 mm) using both the single-fiber-composite four-poi...

Fumihiko Tanaka

Papers

Investigating nanostructures in carbon fibres using Raman spectroscopy

Factors controlling the strength of carbon fibres in tension

Tensile strength distribution of carbon fibers at short gauge lengths

The effect of nanostructure upon the deformation micromechanics of carbon fibres

Tensile failure phenomena in carbon fibres