On the use of the material plastic deformation function in fracture testing of ductile polymers

The plastic deformation behaviour of a material in a fracture process can be described by a plastic deformation function (H function), which is established by the load separation criterion. H function is the basis of single-specimen methodologies for the construction of the material crack growth resistance (JR) curve, but it can be given further significant roles in the study of the fracture behaviour of materials. This work describes further applications of H function in fracture characterization of ductile polymers. By referring to results obtained from single edge notched in bending, SE(B), specimen tests on different polymeric materials, H function is shown as an effective tool for: i. guiding specimen preparation for fracture testing, through its character of local property and the capability to reflect directly the geometry constraint degree; ii. studying the effects of the testing conditions on the plastic deformational mechanisms involved in the fracture process. Industrial grades of both amorphous and semi-crystalline polymers were examined [acrylonitrile-butadiene- styrene resin, high-impact polystyrene, polycarbonate, rubber toughened poly(methylmethacrylate), rubber toughened poly(lactic acid); linear low-density polyethylene, rubber toughened polyamide 66, rubber toughened poly(butylene terephtalate)]. It is worth noting, with reference to point ii., that the approach here employed for the evaluation of the H function, which is based on the execution of stationary crack experiments on blunt notched specimens, does not require the measurement of the crack extension produced in the test. This makes the approach suitable to be used at different testing conditions (temperature and loading rate) and, in particular, in impact tests.