Life prediction for carbon fibre filament wound composite structures

Abstract

The processes governing the failure of filament wound composite structures have been examined. It is shown that the fibres controlling the failure of such a structure, when it is internally pressurised, can be considered to be subjected only to tensile loads. A multi-scale model has been developed which considers the effects on the scale of the elastic fibres and includes the effects of the viscoelastic matrix as well as debonding around fibre failures. The intact fibres neighbouring fibre-breaks are subjected to an increase in stress and a higher probability of failure than elsewhere in the composite. During a monotonic failure test, the initially random fibre failures are seen to begin to coalesce in a way governed by the stochastic nature of the fibre-breaks and this eventually leads to failure. Under prolonged loading, relaxation of the matrix around fibre-breaks causes overloads in the neighbouring fibres to evolve and induce delayed fibre-breaks, which eventually lead to instability in the structure. The model allows these processes to be considered in calculating the behaviour of the whole composite structure.

Keywords:

• life prediction
• composite filament wound structures
• fibre failures
• viscoelasticity
• debonding
• pressure vessels

Acknowledgements

The authors wish to thank Dr D.H. Allen, Dean of Engineering at the University of Nebraska, Lincoln, USA for his support and valuable suggestions and S. Camara, of the same university, for help with the study and for supplying some of the figures.