CHARACTERIZATION of the CRACK PROPAGATION in A MICROSTRUCTURALLY RANDOM MATERIAL

In the study of mechanical properties of materials the microstructure of a material is usually subjected to some kind of homogenization; however, there are materials in which the microstructural disorder must be considered. This disorder manifests itself in the fracture resistance of materials. Some empirical experimental studies and various types of models (based on variations in mass per unit area) have been made to relate the effect of the disorder during crack propagation with the macroscopic resistance of the material, but the absolute-density/mass projections have not been a good descriptor to extrapolate the behavior of the material between its microstructure and the macroscale since it is difficult to determine the porosity and the net trajectory of the fibers. The physical phenomenon of the instability of the crack propagation of interest in the present work occurs on a meso-scale, where the microstructure of the materials can be characterized only statistically and has been established as the range in which the bridge can exist between the micro and macro behavior of this kind of materials. By the Digital Image Correlation Technique the crack propagation is followed based on the displacements produced locally by the arrangement of the fibers in front of the crack tip of paper, as a material model. At the beginning of the load process is observed a smooth trace in the peak local deformation corresponding with the elastic part of the stress-curve; after, when the stress-curve starts to deflect, the peak local-deformation trace change in its slope and it becomes intermittent, this behavior is attributed to the local conditions of material. Finally, it observed that the local deformation is a good descriptor for the crack extension.