The compressive behaviour of unidirectional carbon fibre reinforced plastic

This thesis reports the results of an investigation into the compressive strength of unidirectionally reinforced carbon fibre composites when loaded parallel to the fibres. A comprehensive review of previous research is presented and from this it is clear that no overall theory e,d.sts for predicting the unidirectional compressive strength of high volume fraction carbon composites. A study of the points raised in the survey led to the postulation of a three dimensional analytical model based on energy considerations, which provides substantial insights into the behaviour of unidirectional composite under compressive load. Strength predictions were made using the results of this three dimensional model and .the finite element analysis of the composite micro-structure, the latter providing infoxmation about the stress state at the fibre matrix interface, Different techniques used for measuring the unidirectional compressive strength of carbon fibre reinforced plastic are compared, since the published data shows a considerable variability between methods. This comparison was carried out at an analytical level, using MSC-Nastran finite element analysis software and at an experimental level by comparative testing. Using the optimum test technique selected from these results, measurements were made on XAS/91 1+, T300/914 and HMS/914 composite with and without absorbed moisture. These were then compared to the strength predictions made from the model a good fit being shown for dry composite strength predictions