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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: The impact properties of advanced carbon fibre thermoplastic composites

Author: LEICY, Daryoush

Year: 1991

Supervisor(s): Paul Hogg

The impact properties of carbon fibre reinforced thermoplastic composites (CFRTP) produced with PEEK and PPS matrices have been studied extensively. The force and energy absorbed data from these tests suggests that within this class of material, the matrix does not have any particular influence on impact behaviour, although the PEEK based composites are shown to be superior to PPS based composites and amorphous systems superior or competitive to crystalline equivalents under impact. Similar observations were made from material property test for both systems. However, scanning electron microscopy study has indicated that the superiority of the CFPEEK to CFPPS may be attributed to the greater interfacial bond characteristics of the CFPEEK fibre-matrix interface.
In addition, the lower fibre volume fraction percentage of the CFPPS laminates compared to CFPEEK is thought to have contributed to its relatively poorer impact response. Processing modifications that lead to the suppression of crystallinity in the thermoplastics does influence the nature of crack development during low energy impacts. This may have long term consequences for the durability of different thermoplastic laminates.

The results from the CFRTP systems as a class of materials do however show significant differences to toughened epoxy laminates from comparable experiments. Under low energy impacts, the thermoplastic composites absorb less energy than epoxies with this difference being attributed to a reduction in the amount of microcracking. The assessment of damage using optical microscopy and ultrasonic C-scanning indicated that the onset of damage and its subsequent propagation occur at higher incident energy levels for CFRTP compared to toughened epoxy laminates.