Effect of temperature on work of fracture parameters in poly(ether-ether ketone) (PEEK) film

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. On the basis of these, “essential work of fracture (EWF)” methodology was used to determine the temperature dependence of the fracture toughness of PEEK film. Results showed that specific total work of fracture (wf) is a linear function of ligament length (L) over the entire temperature range under consideration. The value of wf at L=0 which is referred to as the “specific essential work of fracture, we” decreased with increasing temperature. However, below the glass transition temperature, Tg (≈140 °C), the amount we decreased but was less than 10%. The slope of the line wf versus L which is referred to as the “specific non-essential work of fracture, βwp” increased with increasing temperature and showed a significant drop in value at Tg. It is shown that we and βwp are both composite terms, each consisting of a yielding (wey, βywpy) and necking/tearing (went, βntwpnt) components. It is found that went≫wey and βntwpnt≫βywpy, at all temperatures thus indicating that plastic deformation zone is linked mostly to necking/tearing component of the fracture process. Finally, it is shown that temperature dependence of the specific essential work of fracture parameters (we, wey, went) can be predicted via crack opening displacement values.