STRUCTURAL MECHANICS IN REACTOR TECHNOLOGY

The paper deals with the effect of crack gro1lJth rate and creep in static fracture of concretc. The available experimental data and various modeling approaches, including a rate-dependent generalization of the cohesive crack model based on the activation energy concept are reviewed. Attention is then focused on the description of these effects by means of a generalization of the equivalent linear elastic fracture model based on the R-curve concept, and a new model of this type is presented in detail. The crack propagation velocity is assumed to depend on the ratio of the stress intensity factor to its critical value from the R-curve. This dependence can be assumed as a power function 1IJith an exponent much larger than 1. The shape of the R-curve is determined as the envelope of the fracture equilibrium c:., u;,s con-esponding to the maximum load values for geometrically similar specimens of different sizes. The creep in the bulk of a concrete specimen must be taken into account in the case of static loading, which is done by replacing the elastic constants with a linear viscoelastic operator in time. The model fits the existing data on concrete (as well as rock) reasonably well. It exhibits not only the effects of size and rate, but for concrete it also exhibits an increase of brittleness with a decrease of loading rate, manifested a.' a shifl of the maximum load points in the size effect plot toward linear elastic fracture mechanics (LEFM).