Search

Fiber-reinforced polymer composite laminate is weak in the Z-direction, which limits its application. Herein, short carbon fiber (SCF) was decorated with graphene oxide (GO) to form GO@SCF, which was used to improve epoxy matrix and thereby the interlaminar shear strength (ILSS) of carbon fiber fabric (CFF)-reinforced epoxy composites. The effect of GO@SCF on the ILSS of the composite has been examined. It showed that the optimal content of GO@SCF was 0.1 wt%, and the maximum value of ILSS reached 59.4 MPa, which was 14.7% higher than the pure CFF/epoxy composite. The neat SCF was also employed to enhance the ILSS for the purpose of comparison. The results indicate that GO@SCF has better effect on reinforcing the ILSS than the neat SCF. This study provides an effective approach for the reinforcement of the ILSS of CFF-reinforced epoxy composites.

This study is concerned with structure–property relationships in different types of carbon nanotubes (CNTs), in particular investigating both interfacial and internal stress transfer for CNTs in nanocomposites. The shift of position and width of the G′-Raman band for single-walled CNTs (SWNTs) and multi-walled CNTs (MWNTs) in an epoxy matrix were used to monitor stress transfer between the nanotubes and an epoxy matrix in nanocomposites. It was found that the rate of band shift per unit strain was higher for the SWNTs than the MWNTs and that the G′ band tended to undergo broadening with strain for the SWNTs and narrowing with strain for the MWNTs. A theory has been developed to simulate this behaviour in terms of stress transfer between the different layers within the MWNTs. It has also enabled the determination of the stress transfer efficiency parameter, (k i) for the MWNTs. It is demonstrated that MWNTs give inferior reinforcement to SWNTs as a result of slippage between the walls giving rise to poor internal stress transfer in the MWNTs. This phenomenon will lead to the MWNTs having a lower effective Young’s modulus in nanocomposites than SWNTs.

The negative and positive piezoresistivity in continuous carbon fiber epoxy-matrix composite has been clarified. The negative piezoresistivity associated with the increase of the through-thickness resistivity upon longitudinal tension and decrease in the through-thickness resistivity upon longitudinal compression is practically attractive for strain sensing and is attributed to the decrease in the degree of contact between fibers of adjacent laminae upon longitudinal tension. This effect is stronger, more reversible and less prone to causing minor damage for the tension case than the compression case. The positive piezoresistivity associated with the longitudinal resistivity increasing upon longitudinal tension is negligibly weak, if any, independent of the number of laminae. The previously reported negative piezoresistivity associated with the longitudinal resistivity decreasing upon longitudinal tension does not occur for a commercially manufactured composite in which the fibers are well aligned.

The interlaminar interface of a crossply carbon fiber epoxy-matrix composite was found to be an impact sensor, with sensitivity to impact from 0.8 mJ to 5 J (though no indentation was observed) and to multiple (up to 35) impacts at the same energy. However, the sensing of a small impact after a large one was not effective if the small impact was much lower in energy than the large one. The higher the impact energy, the lower was the contact electrical resistivity of the interlaminar interface after impact. Above 1 J, the resistance tended to increase with partial or complete reversibility upon impact, though this effect was minor compared to the irreversible resistance decrease mentioned above.

Finite element analysis has been used to model a single unsized carbon fibre embedded in an epoxy matrix subjected to tensile loading. The predicted fibre strain distribution is compared with experimental data, obtained using the technique of laser Raman spectroscopy, for a number of incremental applied strain levels. Good correlation is obtained on the assumption that the prevailing mode of interfacial failure in the composite involves a conical matrix crack initiating at the fibre end. The geometry of the matrix crack is estimated on the assumption that the crack propagates in a self-similar manner.

The non-equilibrium statistical fracture theory has been used to study the statistical aspects of fatigue fracture of fibre-reinforced epoxy composites. An equation for the evolution of microcracks has been established and the general behaviour of nucleation and growth of microcracks discussed. Subsequently, the distribution function of crack density, the fracture probability, the reliability and theS-N relation for the composites have been derived. The theoretical results obtained coincide qualitatively with experiments.