An investigation into the mechanical properties of composite materials reinforced with the locally obtained natural fibres

Abstract

This abstract summarizes the results of a research work done by Cyrus Concellor Muthuri Kirima, for a master of science degree thesis entitled "AN INVESTIGATION INTO THE MECHANICAL PROPERTIES OF COMPOSITE MATERIALS REINFORCED WITH THE LOCALLY OBTAINED NATURAL FIBRES". A thesis submitted in partial fulfilment for the award of a master of science degree of the University of Nairobi, in December, 1993. The physical and mechanical properties of coconut fibre were investigated. The results obtained for the physical properties were; cross-sectional area, 8.0 x 10-8 m", and density, 5.3 X 10-8 kgm-2• The cross-sectional area of the fibre varied between individual fibres and along its length. The following mechanical properties were obtained; tensile strength 159.30 MNm-2 , Yield stress 70.53 MNm-2 , Modulus of Elasticity 4.02 GNm-2 •.. and an elongation at failure of 24.20% Sisal fibre was used to reinforce the cement mortar matrix in two forms; parallel aligned and chopped randomly aligned. The coconut fibre reinforced the matrix only in chopped form, randomly distributed in the matrix. The resulting composite was tested In flexure, (4-point bending) and direct tensi6n to establish' the effect of fibre reinforcement on the physical and mechanical properties. viii Fibre reinforcement improved some mechanical properties of the composite. A linear increase in flexural and tensile strength with fibre volume fraction was obtained for parallel aligned sisal fibres. The increase in strength attained maximum values of 9.46 MNm-2 for flexure at 7.5% fibre reinforcement volume fraction and 3.98 MNm-2 in tension at 7% fibre volume fraction. Chopped sisal and coconut fibres generally increased the flexural and tensile strengths of the composite, but the maximum values obtained were low compared to the parallel aligned sisal fibre reinforcement. The maximum flexural strength occurred at 6% fibre volume fraction of 4.74 MNm-2 for sisal fibre reinforced composite and 4.24 MNm-2 at 8% volume fraction for coconut fibre reinforcement respectively. The maximum tensile strength values obtained were 2.94 MNm-2 for sisal fibre reinforcement and 2.09 MNm-2 for coconut fibre reinforcement. These occurred at 7% and 6% fibre volume fraction for sisal and coconut respectively. On the other hand, fibre reinforcement resulted into a linear decrease in the composite Modulus of Elasticity. Based on the above, the results obtained were therfore valid for the range of study. Fibre addition into the cement mortar matrix gave a decrease in the composite density, while the amount of voids present increased. The interfacial bond strength , between sisal fibre and the cement mortar matrix decreased with increase .in fibre volume fraction. The calculated value tends to a mean value above a fibre volume fraction of 4%.