The low velocity impact, tension-tension fatigue and stress relaxation behaviour of glass fibre and natural fibre composites were investigated. For glass fibre composites, two fibre architectures ([±45<sup>o</sup>]<sub>4</sub> and [0/90<sup>o</sup>]<sub>2s</sub>) and two matrix resins (polyvinyl-ester and polyester) were used. Non-woven randomly oriented hemp fibre mat was used as reinforcement of natural fibre composites. The effects of low velocity impact on residual tensile properties, fatigue life and modulus degradation behaviour during cyclic loading were investigated. Damage mechanisms of the composites during impact and fatigue loading were discussed. It was found that modulus degradation behaviour of composites was strongly dependent on the reinforcing fibres and their architecture. Multistage modulus degradation behaviour with gradual reduction in modulus was observed during fatigue loading of [±45<sup>o</sup>]<sub>4</sub> glass fibre composites. For hemp fibre composites, however, no decrease in modulus was observed before final fatigue failure. Low velocity impact did not significantly change the modulus degradation behaviour of composites during fatigue loading. Since the normalized S-N curves for undamaged and impacted samples superimposed, the fatigue life of impact damaged composites could be predicted from knowledge of the S-N curve of non-impacted composites and the static residual strength of impact damaged composites. Stress relaxation curves of [±45<sup>o</sup>]<sub>4</sub> and [0/90<sup>o</sup>]<sub>2s</sub> glass fibre composites were compared, and the effects of initial stress, impact damage, fatigue loading and the combination of impact and fatigue were investigated. Mechanisms of stress relaxation of composites were discussed. Stress relaxation curves of the glass fibre composites could be modelled by a simple logarithmic equation. Stress relaxation tests were found useful to characterise the loading history of composites.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:639251 |
| Date | January 2004 |
| Creators | Tong, Y. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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