Effects of molecular structure on the essential work of fracture of amorphous copolyester at various deformation rates

The fracture behavior of amorphous copolyesters with different molecular structure was studied with double edge notched tensile loaded specimens (DENT) using the essential work of fracture (EWF) approach. Various deformation rates ranging from 1 rnm/min to 1000 mm/min were employed. Amorphous poly (ethylene terephthalate) (aPET) exhibited considerably higher specific essential and nonessential work of fracture than the copolyesters containing either cyc10hexylenedimethylene (aPET-C) or neopentyl glycols (aPET-N). At high deformation rates, ductilelbrittle fracture transition was observed with aPET-C and aPET-N, while aPET always fractured in ductile mode within the entire deformation rate range. These phenomena were ascribed to the different molecular flexibility and entanglement density of the copolyesters. The specific essential work of fracture of the aPET as a function of deformation rate went through a minimum. The initial decrease in toughness was caused by the hampered segmental mobility due to the increased deformation rate. The subsequent increase in toughness was attributed to the adiabatic heating induced temperature rise in the process and plastic zones.