Abstract
Composites based on isotactic polypropylene matrix and short glass fibres were tested for creep, creep damage and creep rupture at different temperatures and stress levels. Four composites of 5–30 wt% of glass fibre content having standard fibre/matrix adhesion were used, while two materials with 20 and 30 wt% of fibres were prepared as elevated adhesion composites. Unreinforced polypropylene was tested as a reference material. The rate of steady-state creep (which was determined by an arbitrary method) was used as a criterion for the examination of glass fibre content and fibre/matrix adhesion effects on creep. Secondary criteria, type and extent of damage and time to rupture were applied. Up to 40°C the steady-state creep and creep damage of all tested polypropylene composites are retarded by glass fibres according to the fibre content. At 60°C and above, there is a distinct difference between composites of standard and elevated fibre/matrix adhesion. At higher temperatures the creep and creep damage are more or less accelerated by higher content of standard adhesion fibres; these fibres induce crazing (as a typical creep damage) at relatively low stress. Fibres of elevated adhesion shift the processes of non-recoverable creep and crazing to the higher stress range, even if their craze inducing activity remains. It was found that the creep, creep damage and creep rupture are controlled by the steady-state creep mechanism of polypropylene, a conclusion which was deduced from the stress and temperature dependence of the creep rate, as well as from the morphological analysis of damaged and ruptured specimens.
Published Version
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