Determination of Cohesive Laws for Materials Exhibiting Large Scale Damage Zones

Large cohesive zones have been experimentally observed in the crack wakes of various non-homogeneous materials, such as continuous-fibre composites, shortfibre composites, paper materials and adhesively joined structures. Traditionally, fracture resistance curves (R-curves) have been used to characterize this class of materials. Since the cohesive zones are comparable in size with test specimen dimensions, the R-curve behaviour can not be used as a material property (Suo et al., 1992). Instead, a cohesive law may be deduced as a material property. This law relates the crack surface traction to the opening displacement. Since a lot of experimental data exist in the form of R-curves, it would be useful to develop an approach, where this data could be used to extract cohesive laws. In the present study, means to acquire the cohesive law from conventional R-curve data are presented.