Analysis of stiff fibres in low modulus resin

Abstract

The aim of this project is to experimentally investigate the physical properties of flexible fibre reinforced composites fabricated in house using stiff fibres and low modulus resin. A literature review was done to review past research done in this area, such that relevant experimental results and theoretical predictions could be extracted and used for comparison. In this project, steel wires were used as the reinforcing fibres. For the matrix, three resins (polyester, polypropylene, elvax 3185) were experimented on. Polyester and polypropylene were found to be too brittle and not suitable to be used as the low modulus resin and so elvax 3185 was used as the matrix material. Samples were fabricated with the fibres placed at various fibre orientations (0o, 30o, 45o, and 60o). Tensile tests were then carried out on these samples to study their physical properties as well as observe any fibre reorientation. Based on previous research done in this area, it was predicted that the physical properties such as Young's modulus, maximum tensile strength, and tensile toughness worsened as fibre orientation increased. Also, significant fibre reorientation was predicted and the change in fibre orientation increased at an increasing rate. The experimental results from this study agreed closely with the predictions made in previous research. It was found that as fibre orientation increased, physical properties worsened. Significant fibre reorientation was also observed during the experiments, with the sample with the largest fibre orientation experiencing the largest reorientation of fibres. Besides placing the fibres at several orientations, fibres were placed closer together to investigate the effect of increased fibre volume ratio on the physical properties of the flexible composite. It was expected that the physical properties would improve as the steel fibres at high load carrying capacity and high stiffness. However, it was the opposite as the physical properties worsened instead and the samples with higher volume ratio had a lower Young's modulus, tensile strength, and tensile toughness. This is because the additional fibres were intrusions in the composite and were defects instead of reinforcements. Further research can be done in this area such as doing finite element analysis to better analyze the stresses and strains at each material point. Other recommendations and suggestions for future research are provided at the end of this report.