Hard Problems with Soft Materials: Fracture Toughness by the cutting method

RUEDA, FEDERICO; FASCE, LAURA; FRONTINI, PATRICIA

Encuentro; 3er Encuentro Nacional de Materia Blanda; 2010

The basis of fracture mechanics relies on the fact that bodies contain flaws or cracks and that failure occurs at the largest of these cracks. When the crack grows in size, the potential energy in the body is released to form new surfaces of the growing crack. The minimum energy per unit area necessary to produce the crack is called the fracture toughness, Gc. The term Gc includes the intrinsic surface-separation work as well as other local dissipative work at the crack tip. When materials exhibit a high degree of non-linearity, visco-elastic effects and low stiffness, conventional fracture mechanics tests such as SENB (single-edge notched bend) and SENT (single edge notched tension), that are widely used to determine Gc of engineering materials are very difficult to apply. This is the case of soft polymers, wood, hydrogels, food and some biological materials. Instead, alternative tests in the form of wire and blade cutting tests have been proposed. Since the cutting process is accompanied by material deformation and surface friction effects, it is, in principle possible to quantify these material parameters from the cutting test. However, the separation of total cutting energy into individual components is still an open question.