INTEMA   05428
INSTITUTO DE INVESTIGACIONES EN CIENCIA Y TECNOLOGIA DE MATERIALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Influence of actual crack propagation rate on fracture toughness characterization of hydrogels by the Wire Cutting Technique
Autor/es:
M. CZERNER; L.A. FASCE; P.M. FRONTINI
Lugar:
Santa Fe
Reunión:
Congreso; 14er Congreso Internacional de Metalurgia y Materiales-IBEROMAT XIII (SAM-CONAMET / IBEROMAT 2014); 2014
Resumen:
Fracture of hydrogels has been little investigated in comparison with other materials such as metals, ceramics or polymers. The Wire Cutting method was recently proposed and used to determine fracture toughness of different soft solids. The test involves pressing wires of different diameters (d) on the specimen while force and displacement are continuously recorded. The process can be divided into two phases: an initial indentation phase, in which the force increases with wire displacement, and a steady state cutting phase, where the force remains constant (Fc). The method states that the cutting force is proportional to the wire diameter and the fracture toughness is a constant contribution to be obtained from the y-intercept of the linear fit of Fc vs. d data. However, we have recently demonstrated that the validity of the method is limited by the development of a single fracture surface morphology for all wire diameters used. In this work, we deeply explore the influence of the actual crack propagation rate on the developed fracture surface morphology and on Wire Cutting plots. To this end, cutting tests are performed using bovine gelatin hydrogels of different stiffness at different testing conditions (cutting rate, wire diameter, pre-notching). Fracture surface morphology (and so crack propagation mode) of gelatin hydrogels changes from a rhombus-like like pattern to a striated or smooth pattern at a critical velocity, which depends on gel stiffness. It is observed that the actual crack propagation rate differs from the imposed cutting rate and it is largely influenced by the initial indentation phase. The use of pre-notched samples arises as a good strategy to control the initial crack propagation rate. The results of this research contribute to establish the experimental conditions under which the Wire Cutting test becomes valid to evaluate fracture toughness of engineering soft solids.