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 pseudoductility, are described.

No abstract

No abstract

No abstract

Three issues are investigated that may influence the accuracy of strength models for unidirectional composites. Firstly, most authors limit themselves to 25-100 single fibre tests to determine the Weibull distribution. This is insufficient to accurately determine this crucial input parameter, leading to significant errors in the predicted composite failure strains. Secondly, random, square and hexagonal fibre packings are shown to lead to a similar predicted failure strain and cluster development. This is the first strong indication that the type of fibre packing has little influence on modelling predictions. Finally, boundary fibres introduced at the model perimeter were shown to prevent preferential cluster formation near the model perimeter. This makes the models less sensitive to the number of fibres. Boundary fibres do not influence the early cluster development, but do increase the critical cluster size. The results provide guidelines for when such boundary fibres should be included.

Despite the crucial significance of failure prediction in composites, such an objective remains challenging, even in unidirectional (UD) systems. A strength model for UD composites was used that has great versatility in handling various matrix and fibre behaviours. This model includes a simplified superposition principle that was found to be reliable in predicting stress concentration factors irrespective of the presence of matrix cracks. The model revealed the negligible influence of matrix cracks on stress concentrations, ineffective length, cluster development and failure strain. The presence of matrix cracks can therefore be safely neglected in models for UD composites. This information is important for experimental validations and for advancing the state of the art in strength models for UD composites.

Fibre-reinforced composites are rapidly increasing their market share in structural applications. Nevertheless, this increase would be much stronger if reliable failure predictions were available. These predictions are not only insufficiently reliable for complex loading of multidirectional composites, but even for longitudinal tensile failure of unidirectional (UD) composites. Since composite failure usually coincides with longitudinal failure of a 0° ply, the reliability often hinges on longitudinal failure predictions of UD composites. Despite great progress in the state-of-the-art models, significant obstacles remain in collecting the necessary input data and understanding the influence of the modelling assumptions. This review therefore surveys the mechanics, chemistry and physics involved in tensile failure of UD composites and highlights potential areas for improvement. Specific proposals are made to advance the state-of-the-art strength models, which could catalyse the use of composites in structural applications.

Please cite this article as: Swolfs, Y., McMeeking, R.M., Verpoest, I., Gorbatikh, L., The effect of fibre dispersion on initial failure strain and cluster development in unidirectional carbon/glass hybrid composites, Composites: Part A (2014), doi: http://dx. AbstractBy adding glass fibres to carbon fibre composites, the apparent failure strain of the carbon fibres can be increased. A strength model for unidirectional hybrid composites was developed under very local load sharing assumptions to study this hybrid effect.Firstly, it was shown that adding more glass fibres leads to higher hybrid effects. The hybrid effect was up to 32% for a hybrid composite with a 10/90 ratio of carbon/glass fibres. The development of clusters of broken fibres helped to explain differences in the performance of these hybrid composites. For 50/50 carbon/glass hybrids, a fine bundleby-bundle dispersion led to a slightly smaller hybrid effect than for randomly dispersed hybrids. The highest hybrid effect for a 50/50 ratio, however, was 16% and was achieved in a composite with alternating single fibre layers. The results demonstrate that thin ply hybrids may have more potential for improved mechanical properties than comingled hybrids. 2