A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1990

Microcracking and bridging are major mechanisms in fracture of quasi-brittle materials such as concrete, rock and ceramics. An analytical model of fracture process zone which includes both microcracking and bridging is developed to estimate the effects of microcracking and bridging. While the material property on bridging is represented by the tension-softening curve, which is the inelastic component of post-peak behavior in tension test, that on microcracking is related to the pre-peak nonlinear behavior. Relationship between microcrack density and the stress level is determined from pre-peak stress-strain curve in uniaxial tension test. The material parameters on microcracking are identified through a microcracking law which relates the orientation and the density of microcracks to the state of stress at the point in question. The dominant microcracking parameter is found through the model. With the given material properties on bridging and microcracking, the model predicts the shape and size of the microcracking zone, the distribution of microcrack density and the length of bridging zone at each load level. Results of the present model are compared with those of the model which includes only bridging. It is shown that the increase in toughness due to microcracking varies for different materials but remain_s small portion of the total toughness for real materials. For the case that bridging is dominant, Dugdale-Barenblatt-type model, which includes bridging zone only, serves as a good model of fracture phenomena and provides reasonable estimate of, for example, the maximum load of structures.