Fracture toughness of rubber in quasi-static conditions: How to experimentally obtain results intrinsic to the material?

Fracture toughness, defined as the energy dissipated to advance a crack by a unit area, is an intrinsic material property, which should not depend on the geometry and dimensions of the specimen used to obtain it. One of the most frequently used test configurations to determine rubber fracture toughness at crack initiation in quasi-static conditions is the single edge notched in tension specimen (SENT). The aim of this work is to quantitatively define the limitations of specimen dimensions needed to obtain an intrinsic value of fracture toughness for a nitrile-butadiene rubber (NBR), and to investigate the possible effects of the test procedure on the results. These show that a minimum width of 10 mm and a minimum height/width ratio of 4.6 are necessary to obtain a fracture toughness independent of specimen dimensions.