A simple deformation criterion based on Dugdale's cohesive zone model is presented. The criterion can be used for both the experimental determination of the critical stress intensity factor, KIc, and the critical tip opening displacement, CTODc. It can also be applied for the evaluation of the load capacity of structural elements. The criterion is presented in explicit and compact form, which allows straightforward calculations to be performed for the estimation of KIc and CTODc values from the experimental data obtained from samples with a U-shaped notch, rounded with an arbitrary radius. Thanks to the simple form of the approximate relationship between the maximal load level and the dimensionless notch tip opening displacement, the reverse procedure was obtained, i.e., the estimation of the value of the maximal force loading the structural element as a function of the known critical stress intensity factor.
Keywords: cement composite; deformation criterion; notch; stress intensity factor.