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In this study, a novel shear-lag model based on impregnated fiber bundle (IFB) element is developed to predict the tensile behavior of unidirectional fiber-reinforced polymer (FRP) composites. Rather than using a fiber element, the new model enables a full-field failure simulation due to its finite number of elements. Based on the micromechanical difference equation, we validated the effectiveness of the model and identified the damage evolution pattern by applying it to a basic model of 6 mm FRP tendon. Then, the effect of varied constituent properties, hybrid fibers and initial defects were investigated using the Monte Carlo (MC) method. Several interesting results were found and compared with the findings of earlier studies. For instance, it was found that a more stable IFB strength and higher matrix shear strength reduced variations in composite strength. A moderate hybrid ratio and careful packing of high- and low-elongation fibers helped to achieve optimum composite properties. In the thin-ply composite, transverse initial defects were more detrimental to composite strength than longitudinal defects. These findings prove the value of the bundle-based model, which can be used in future studies as an effective tool for evaluating the strength of various composites.

The failure strain of fibre-reinforced composites can be increased by fibre hybridisation. A recently developed model for unidirectional composites was extended to hybrid composites to analyse this synergetic effect, called the hybrid effect. The model predicts individual fibre breaks and interactions among clusters of fibre breaks. Three key parameters were studied to understand how they can maximise the hybrid effect, namely low elongation fibre strength scatter and hybridisation fibre stiffness and failure strain. Larger strength scatter of the low elongation fibres leads to larger hybrid effects, as the scatter spreads out the cluster development over a larger strain interval. The failure strain ratio of the two fibre types should be above 2 for the properties used here, but a higher ratio did not yield any additional benefits. Increasing the stiffness of the hybridisation fibre reduces the stress concentrations on the low elongation fibre and may also enlarge the hybrid effect. These conclusions provide guidelines for designing optimal hybrid composites. [ABSTRACT FROM AUTHOR]