Fiber morphology has a significant effect on the mechanical properties of fiber/polymer composites. The performance of nine types of long wood fibers (initial aspect ratio of >40), two long agricultural fibers (initial aspect ratio of >40), and one short fiber wood flour (initial aspect ratio of ¼ 5-10) are compared. The fibers were compounded in polypropylene in a Brabender mixer and subsequently injection molded. The longer natural fibers (both wood fibers and agricultural fibers) did not provide significant additional reinforcement when compared to the wood flour. The fibers were extracted from the final specimens and measured using a Fiber Quality Analyzer. They were found to be severely degraded by processing, while the wood flour morphology was only slightly modified. The degree of length degradation was found to be dependent on fiber strength.

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The friction coefficients of unidirectional carbon fibre/epoxy composites (with the fibres parallel and antiparallel to the sliding direction) were measured under severe abrasive conditions. Aluminium oxide sandpapers with three different grits (36, 80, and 120) were used as the counter surfaces. Three different applied loads (5, 10, 22N) and two different sliding speeds (2 m/s, 4 m/s) were selected as the testing parameters. Under these conditions, composites with fibres parallel to the sliding direction had a significantly lower friction coefficient. Using the measured friction coefficients of unidirectional composites, a modified rule of mixtures equation was developed to predict the friction coefficients of woven carbon fibre/epoxy composites under the conditions. The model is based on the hypothesis that the more wear resistant regions of the weave (fibres that are parallel to the sliding direction in this case) would protect the less wear resistant regions (fibres that are antiparallel to the sliding direction), and that the load is redistributed to yield equal wear rates for the two zones. It was found that the model was able to accurately predict the friction coefficients of the woven composites for the abrasive conditions tested in this study.

The wear resistance of unidirectional carbon fiber reinforced epoxy under severe abrasive sliding conditions was studied. It was found that unidirectional laminates tested with the fibers parallel to the sliding direction (UDp) were more wear resistant than the same laminates tested with fibers transverse to the sliding direction (UDap) under the same set of test conditions. A novel energy-based model was developed to explain the difference in the wear rates. It was found that the difference in wear rates between the two orientations was due to differences in the average volume to surface area ratio of the debris, the energy required to generate new surfaces, and a new k factor that represents the fraction of the total friction energy used for creating wear particles. Furthermore, wear volume per sliding distance was found to be linearly proportional the total frictional energy dissipation for both orientations. These findings can be used to simplify wear predictions for industrial applications.

Heterogeneous surface wear (HSW) models have been derived to predict the specific wear rates of woven carbon fibre reinforced epoxy composite materials. The specific wear rates of unidirectional carbon fibre/epoxy composites, with fibres orientated both parallel and antiparallel to the direction of sliding, are used as input variables. The first model (EW mode) is based on an assumption of uniform thickness reduction during wear, but uneven surface pressure. The second model (EP mode) is based on an assumption of even surface pressure throughout the test. The specific wear rates of plain and 5HS woven composite panels were measured to validate the accuracy of the models. It was found that the EW model was able to accurately predict the specific wear rates of the two types of woven composites under mild abrasive conditions (120 grit sandpaper). However, under more severe abrasive conditions (36 grit sandpaper), the woven panels exhibited a new wear mechanism caused by tearing of the out-of-plane fibres at the crossover points of warp and weft fibres. This mechanism caused both models to under-predict the specific wear rates of the woven composites in severe abrasive conditions. However, the EW model can be used with confidence under less abrasive conditions, where the asperities do not have significant interactions with the out of plane fibres.