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The Effects of Thermal Spiking on a High Temperature Carbon Fibre Reinforced Polyimide.

Bellara, Sumeet Amar. (2003) The Effects of Thermal Spiking on a High Temperature Carbon Fibre Reinforced Polyimide. Doctoral thesis, University of Surrey (United Kingdom)..

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Abstract

The response of a range of T650-35/Avimid® laminates to various environmental conditioning regimes incorporating thermal spikes has been investigated. Materials based on non-woven and woven reinforcements of different thicknesses were studied; the (minor) differences between the materials seemed to be a consequence of slight differences in resin chemistry as a result of different processing routes, rather than any effect of the reinforcement type. The base-line (standard) conditioning regime used was an isothermal hot-wet condition. One variant on this incorporated a low temperature spike at 220°C, while another incorporated a high temperature spike at 275°C. The final regime, which was intended to be representative of service condition comprised isothermal ageing (hot-wet), a low temperature spike and a period of prolonged drying. The sets of samples exposed to low temperature or high temperature spiking conditions showed enhanced moisture absorption compared to the standard regime. Blistering was seen in some samples after exposure to a significant number of spikes. The effect of varying the spike frequency was investigated and the blistering behaviour was not apparently influenced significantly by the spike frequency. On the other hand, by subjecting wet samples to a single spike at different temperatures, a link between moisture content and spike temperature required to cause blistering was established. The enhanced moisture absorption observed in spiked samples was permanent in that when (undamaged) samples were dried and then reconditioned using the standard regime, the enhanced moisture absorption was still apparent. Enhanced moisture absorption was also shown by the samples subjected to the service cycle, subsequently dried and reconditioned. The moisture distribution across the thickness of samples has been modelled using a commercially available finite difference model. This model enables the moisture uptake during the first few spikes to be simulated reasonably well, but the enhanced moisture saturation level can only be incorporated in an empirical manner. Potential chemical changes in the polymer matrix during conditioning have been investigated using mechanical testing, dynamic mechanical thermal analysis and diamond ATR infra-red spectroscopy of unidirectional material. Not surprisingly there were some changes in the matrix-dominated mechanical properties of wet samples. Interestingly there were changes in the glass transition of samples which had been exposed and then dried out. However, there was no significant chemical change or degradation apparent, even in blistered material.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors : Bellara, Sumeet Amar.
Date : 2003
Additional Information : Thesis (Ph.D.)--University of Surrey (United Kingdom), 2003.
Depositing User : EPrints Services
Date Deposited : 24 Apr 2020 15:27
Last Modified : 24 Apr 2020 15:27
URI: http://epubs.surrey.ac.uk/id/eprint/854877

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