RATE SENSITIVITY OF MODE-II INTERLAMINAR FRACTURE-TOUGHNESS IN GRAPHITE EPOXY AND GRAPHITE PEEK COMPOSITE-MATERIALS

This paper presents results from an experimental study of the effect of rate on the Mode II interlaminar fracture toughness, GIIC, in graphite/PEEK (APC-2) and graphite/epoxy (AS4/3501-6) laminates. The end notched flexure test geometry was employed for Mode II experiments which were performed at room temperature over a range of crosshead speeds from 4·2 × 10-6 to 9¢2 × 10-2 mc-1. The APC-2 material exhibited ductile crack growth at low rates and brittle crack growth at high rates. The change in fracture mechanism resulted in a decrease in GIIC from 1·0 to 0·40 kJ m-2 at the upper range of test rates. The AS4/3501-6 material exhibited brittle crack growth at all rates. The GIIC values also decreased at higher test rates from 0·46 to 0·06 kJ m-2. © 1987.