Investigation into the modes of damage and failure in natural fibre reinforced epoxy composite materials

The aim of the research is to develop new high performance composite materials that would potentially compete with existing man made materials and to investigate the physical,
mechanical and thermal properties of crushed (powdered) olive stones (pits) reinforced epoxy composites. This research focuses on development of a new range of sustainable reinforced polymer composite materials using powdered olive pits as a novel filler material to be used
with synthetic resins. A full review has been made of the previous work on different types of natural fibres and fillers used as reinforcement for synthetic polymers. This project attempts to clarify the advantages and limitations resulted from using these fibres/ fillers and endeavours to provide explanation on the mechanical behaviour of these materials.
Prior to investigating the mechanical properties of the powdered olive pits-epoxy composites the density and the mechanical properties of the olive pits were fully characterised. The influence of the untreated and treated powder loading (weight fraction) on the void content and the mechanical properties of the composites was examined using different tests, including flexural, tensile, microhardness and impact testing.
The composites showed significant improvements in mechanical properties including flexural strength (139%) and flexural modulus (149%), tensile strength (121%) and tensile modulus (46%), microhardness (170%), and impact strength (167%) following treatment of the olive pits powder with 2% Al 100 coupling agent. Composites consisting of epoxy resin reinforced with untreated powder exhibited weaker powder to matrix interfacial bonding compared to
those with treated powder composites. The improvements in properties have been attributed to the treatment of the powder with coupling agent, which has resulted in enhanced powdermatrix interaction. Hence it was possible to develop an experimental model of the behaviour of these materials subjected to the above mentioned testing conditions.
Furthermore different thermal analysis techniques including dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) have been used to investigate the influence of the coupling agent on the olive pits powder composites properties by carefully analysing the changes in the thermal properties of the composites; glass transition temperature increased by 38%, tan delta peak decreased by 50%, and room temperature storage modulus improved by 17% and loss modulus peak decreased by 60%. The corroborated mechanical and thermal analysis results support the formation of a strong and efficient interfacial bond between the filler and epoxy matrix.
The influence of powder content and interfacial bond strength on the damage and failure mechanisms operating in the different samples subjected to the destructive testing regime have been examined using optical and scanning electron microscopy (SEM).

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