Tribological behaviour of graphite/date palm fibres reinforced epoxy composites

Tribological behaviour of graphite/date palm fibres reinforced epoxy composites

Natural fibres are becoming alternative candidates to synthetic fibres because of their environmental and economic advantages. In this study, the mechanical and the tribological performance of epoxy composites (ECs) based on date palm fibres (DPFs) was evaluated and compared with neat epoxy (NE). The work is divided into three stages: fibre optimisation, graphite optimisation and final composite selection.

Different fibre diameters (0.3–0.7 mm) and concentration of sodium hydroxide (NaOH) (zero to nine per cent) were used in preparing the fibre. For optimisation purposes, the interfacial adhesion between the DPFs and the epoxy matrix was studied using a new fragmentation technique that considers the influence of the NaOH treatment and the fibre diameter. At this stage, the results revealed that NaOH treatment significantly influences both the fibre strength and the fibre interfacial adhesion. Six per cent NaOH exhibited the optimum concentration to gain good mechanical properties for the EC, since it can maintain good interfacial adhesion, while maintaining good fibre strength.

In the second stage, the influence of the graphite weight presentation on ECs was evaluated from a mechanical and tribological perspective. Different weight percentages were used in the sample preparation (zero to seven per cent) for tensile, hardness and adhesive wear experiments. In the first part of this study, ultimate tensile strength and modulus of elasticity values and fracture morphology are determined. In the second part, specific wear rate, friction coefficient, interface temperature and surface morphology of the composites are determined. The results are discussed to gain the optimum mixing ratio of graphite with epoxy. The results revealed that there is a significant influence of the weight fraction of the graphite on both mechanical and tribological performance of the composites. Intermediate weight percentage of three weight per cent graphite in the EC was considered the optimum from both mechanical and tribological performance, since there is a slight reduction in the tensile properties and significant improvement to the hardness, wear and frictional characteristics. The modification on the wear track roughness significantly controlled the wear and frictional behaviour of the composites. Micrographs of the worn surface showed different wear mechanisms, depending on the content of the graphite in the composites. Softening and fragmentation appeared with low content of graphite presence in the composite, since there was no sign of aggregation or detachments of fillers.

From the second stage on the graphite percentage in the composite, it was concluded that three weight per cent of graphite in the ECs represents the optimum content from mechanical and tribological perspectives. In the third stage, the mechanical and tribological performance of the ECs based on three weight per cent graphite, DPF and three weight per cent graphite plus DPF are discussed and compared with NE. Further, the tribological performance of the composites is discussed, considering two different adhesive wear techniques: block on ring (BOR) and block on disk (BOD). This stage revealed that DPF is able to improve the mechanical properties of the ECs with no signs of pull out or debonding of the fibres. The main fracture mechanism was breakage in the fibre, fracture in the resinous regions and micro-cracks with graphite presence in the composites. Further, the addition of the three weight per cent of the graphite into the date fibre/ECs contributed to the improvement of the ECs; the fibres assisted in strengthening the surface, while the graphite generated the lubricant film transfer. Tribological experimental configuration significantly controlled the wear behaviour of the composite; the wear performance worsened under BOD compared to BOR because of the high thermo-mechanical loading in the case of BOD compared to BOR.