Numerieke modellering van cyclisch gedrag in quasi-brosse materialen

This thesis develops a comprehensive modeling framework for the cyclic behavior of quasi-brittle materials, such as concrete, masonry, and rock, by integrating a micromechanics-based variational phase-field approach. The model represents distributed microcracks within a solid matrix and links damage to microcrack opening and plasticity to frictional sliding, naturally capturing both tensile and shear failure mechanisms. Calibrated using Brazilian splitting tests and validated against various specimen geometries, it reproduces monotonic fracture behavior while maintaining physical interpretability. The cyclic response of the framework is modified by distinguishing reversible strains associated with the opening of microcracks from irreversible plastic strains caused by frictional sliding of closed microcracks, enabling realistic load-unload behavior. The model is further extended to capture fatigue fracture through an energy-based degradation approach. In addition, ratcheting is incorporated to represent the accumulation of inelastic strain under low-cycle fatigue in a thermodynamically consistent manner, providing independent control over volumetric and deviatoric components. Numerical simulations demonstrate the model's ability to predict complex fracture, fatigue and cyclic plasticity behaviors.