A cohesive model for the rupture of concrete by low-cycle fatigue

In this work, a finite element cohesive fatigue model for concrete is proposed. A procedure to simulate monotonic rupture is included. Damage is calculated as a function of accumulated crack openings and the current traction on the cohesive zone. Only mode I fracture is considered. Concretes with different strengths and specimens with different sizes are considered. Size dependency was introduced in the model through the cohesive strength and the corresponding cohesive length. Other monotonic and cyclic properties are considered constant or dependent on the material strength. An excellent fit with experiments is obtained. Methodology is able to capture an embrittlement of the fatigue process with increase in size. In this case, crack (or process zone) becomes unstable for shorter sizes and a more abrupt change to unstable growth is observed. Predictive capabilities of the model are observed considering S-N curves. A good match was observed in the low-cycle fatigue range. Size dependency is introduced in the model by the cohesive strength Exponent parameter used to estimate damage depends primarily on concrete strength Relative endurance limit magnitude is related to the process zone size Model is able to capture a size embrittlement in the fatigue propagation