Application Of J-Integral In Concrete Subcritical Crack Growth Modelling

In engineering practice,where designing a structure is strictly following the codes,engineers often focus on the bearing capacity of that structure.However,the service lifespan is an equally important issue for ensuring its safety,which is significantly affected by the durability of the construction materials.Concrete,as one of the most widely used construction materials,due to its special nature,always suffers from unavoidable initial defects formed at the early stage of hardening,such as microcrack,pores.The existence of the initial defects and the creep of concrete may lead to the slow development of crack growth with stress level under the tensile strength or fracture energy.This will eventually lead to macroscale damage after a certain period of time when the crack has been fully developed.The slow development of cracks is the critical process that controls the durability of concrete structures and materials-the subcritical crack growth of concrete.A deep and clear understanding of subcritical crack growth of concrete is fundamentally important for an accurate estimation of the durability of concrete materials.This research investigated the subcritical crack growth and related properties of concrete via a numerical model representing concrete fracture mechanics,which is based on theory of fracture mechanics and the finite element method.For concrete,a cohesive model is built,featuring “compound softening equation”which can be applied to concrete fracture.The subcritical crack growth is described by the stress intensity factor and the power law formula,and the stress intensity factor is calculated according to the relation of the J integral and the energy release rate.The numerical model is developed in the general finite element platform ABAQUS.A special plane stress quadrilateral user-defined element(UEL)is developed to perfectly participate in the elastic analysis,and calculate the J-integral at the same time.For subcritical crack growth,a user-defined cohesive material model(UMAT)is coded to represent the cohesive properties of concrete and be capable of deleting the element when enters the subcritical crack growth zone.Using the numerical model,this research provides a new idea to study the mechanism of subcritical crack growth of concrete using J-integral,which is critical in predicting the service lifespan of concrete structures.