Effect of thermal and hygrothermal aging on the plane stress fracture toughness of poly(ethylene terephthalate) sheets

The in-plane (plane stress) fracture toughness of two polyester (PET, PETG) sheets were assessed using the essential work of fracture (EWF) method after thermal and hygrothermal aging performed just below glass temperature. This ensured that physical aging takes place. On the aged sheets the yield stress (σy), enthalpy relaxation (ΔH) and EWF parameters were determined. It was observed that the essential work of fracture component related to the...