Temperature dependent torsional properties of high performance fibres and their relevance to compressive strength

Abstract

A simple arrangement for the measurement of torsional moduli of high performance fibres as a function of temperature has been reported. Torsional moduli and damping factors have been measured on a number of polymeric [Kevlar™, poly(p-phenylene benzobisoxazole) (PBO), poly(p-phenylene benzobisthiazole) (PBZT) and Vectran™] and carbon fibres [pitch and PAN based, and one bromine intercalated pitch based carbon fibre] as a function of temperature (room temperature to 150 °C, range) and as a function of vacuum level (1.1–80 ×103 Pa). At these vacuum levels damping in the fine fibres is mainly due to aerodynamic effects. In general PAN based carbon fibres have higher torsional moduli than pitch based carbon fibres. Kelvar™ 149, PBO and PBZT fibres have comparable room temperature torsional moduli, while the torsional modulus of Vectran™ fibre is very low, probably due to the torsional flexibility of the -COO- group. In the above temperature range, torsional moduli of both pitch and PAN based carbon fibres do not change significantly, while for polymeric fibres they decrease; a small decrease is observed for PBO and PBZT, and a significantly higher decrease is observed for Vectran™. Relationships between compressive strength and torsional moduli have been discussed