Effect of temperature on fracture toughness of an amorphous poly(ether-ether ketone) film using essential work of fracture analysis

Abstract

The effect of temperature on plane-stress ductile fracture of an amorphous poly(ether-ether ketone) (PEEK) film of thickness 0.125 mm was studied between 23 and 140 °C using double edge notched tension (DENT) specimens. Within this temperature range, DENT specimens underwent full-ligament yielding prior to final fracture, producing load–displacement curves at various ligament lengths that were geometrically similar to one another at a given temperature. The ‘essential work of fracture’ methodology was used to determine the temperature dependence of the fracture toughness of PEEK film. Results showed that specific total work of fracture ( w f) is a linear function of ligament length ( L) over the entire temperature range under consideration. The value of w f at L=0 which is referred to as the ‘specific essential work of fracture’, w e decreased with increasing temperature. However, below the glass transition temperature, T g (≈140 °C), the decrease in w e was not more than 10%. The slope of the line w f versus L, which is referred to as the ‘specific non-essential work of fracture’, βw p increased with increasing temperature and showed a significant drop in value at T g. It is shown that w e and βw p are both composite terms, each consisting of yielding ( w ey, β y w py) and necking/tearing ( w ent, β nt w pnt) components. It is found that w ent⪢ w ey and β nt w pnt⪢ β y w py, at all temperatures, thus indicating that plastic deformation zone is linked mostly to the necking/tearing component of the fracture process. Finally, it is shown that temperature dependence of the specific essential work of fracture parameters ( w e, w ey, w ent) can be predicted via crack opening displacement values.