STUDIES ON FRACTURE PROCESSES IN CEMENTITIOUS COMPOSITE UNDER FATIGUE LOADING

Abstract

Fracture behaviour of concrete is complex and sensitive to nature of loading. In concrete like material, upon loading a significant inelastic nonlinear zone called fracture process zone (FPZ) is formed ahead of the crack tip. It is the fracture process zone which is responsible for the exhibition of size effect in concrete and governing the overall fracture behaviour. Understanding of the evolution and properties of fracture process zone is essential for the prediction of fracture behaviour in concrete. The characterization of FPZ in concrete has been a challenging task due to application of various type of loading and existence of heterogeneity. Concrete structural member often encounters repetitive nature of loading during their service life. Under such scenario, even though the applied load level is significantly lower than the static peak load, gradual stiffness degradation of the material takes place leading to fracture of the member. The characteristics of the process zone have been observed to be different in the case of fatigue loading than that of static. In fact it has been established that fundamentals associated with the fracturing mechanism in concrete under the action of cyclic loading is highly complex and multiscale phenomenon. Therefore, analytical study focusing on multiple scales in concrete would provide improved understanding on the cyclic fracture process zone. Further energy based parameters are considered to be better than the stress parameter for characterizing the process zone and overall fracture behaviour. There have been difference in opinion regarding critical energy dissipation in concrete under monotonic and fatigue loading cases. It has been claimed that the critical energy dissipation under fatigue loading often called as fatigue fracture energy is different than that of static case. Therefore, in this thesis, an attempt has been made to develop a mathematical model, for the prediction of critical energy dissipation under fatigue loading adopting multiscale fracture approach. Such a study will contribute towards realistic prediction of fracture behaviour and the service life of the structure under fatigue loading. Additionally, an analytical expression has also been derived for the fully developed fracture process zone length to counter the material heterogeneity and size effect.