Computer simulation of linear and nonlinear crack propagation in cementitious materials.

摘要

This thesis deals with the computer simulation of crack propagation in cementitious materials. Both linear and nonlinear aspects of crack propagation are addressed. The problems addressed gradually increase in complexity, starting from LEFM (Linear Elastic Fracture Mechanics) for two dimensional models, and going up to NLFM (NonLinear Fracture Mechanics) for three dimensional problems. The goal is not only to model the physics involved, but also to provide tools for visualizing the crack propagation process. Size effects are also investigated and related to the crack propagation process.;First, the use of LEFM concepts for two dimensional models is considered, and a strategy to model crack propagation with minimum user interaction is presented. In a following step, the application of the fictitious cohesive crack model for two-dimensional problems is explored. A new, integrated, arbitrary, cohesive crack propagation strategy is proposed. This strategy is based on: interactive, effective total crack (true crack plus fracture process zone) length control, a criterion for propagation based on fictitious crack tip parameters (opening profile, tip stress, or tip singularity), a local principal-stress-based criterion for direction of propagation, a dynamic relaxation solver for determining propagation length, and automatic remeshing to accommodate arbitrary growth. Finally, a new method to solve the cohesive crack problem in three dimensions is proposed. This method is capable of modeling the propagation of both the true crack and process zone on a pre-defined crack path for different specimen geometries and absolute sizes. The influence of specimen size on the determination of fracture toughness is investigated by simulating the short-rod specimen response for concrete.;The use of computer graphics is stressed not only to control the crack propagation process, but also to allow fast and comprehensive interpretation of the results.