Mechanical properties of the glass fibre-polyester interphase

Abstract

Single-fibre pull-out experiments were carried out on samples which had been immersed in water at 22°C, 60°C and 75°C for periods of up to 13 000 h. A curve-fitting technique was used to estimate the pressure and coefficient of friction during sliding, as the fibre was pulled out of the polymer. The immersion reduced the pressure from about 16 M Pa to about 6 M Pa for immersion at 75°C. The effect was much smaller at 60°C and still less at 22°C. The results indicated that, except at 75°C, the pressures were governed by the thermal and chemical shrinkages, water dilation of the polymer, and the change in Young's modulus of the polymer caused by the water. At 75°C the apparent thermal shrinkage stress was anomalously low, taking into account the dilatation and plasticization of the resin. This could have been due to some slight dissolution of the glass by the water. The coefficient of friction was reduced, possibly by softening of the interphasial material when silanes were present. When the silane coating was removed the friction did not appear to obey Amontons law and it was concluded that a water film was probably present at the interface.