On the plane-strain essential work of fracture of polymer sheets

The essential work of fracture (EWF) is the most straightforward method to assess the toughness of ductile polymer films and sheets in which per se pl ane-stress conditions prevail. The interest is focused, however, on the det ermination of the plane-strain fracture toughness being a material paramete r. It was demonstrated that the plane-strain essential work of fracture (de termined in dynamic tensile impact tests) agreed well with that of the yiel ding-related specific essential work of fracture concluded from static mech anical tests for an amorphous copolyester sheet. This agreement still held when the plane-strain essential work of fracture derived by considering the experimental data in the plane-stress/plane-strain transition range (layin g below the lower threshold ligament for which a linear regression was adop ted) for a thicker sheet of the same polymer has been considered.