This doctoral thesis by Per-Erik Pettersson, published in 1981, focuses on the crack growth and development of fracture zones in plain concrete and similar materials. The study is conducted at the Division of Building Materials at Lund University, Sweden, and is financially supported by grants from the Swedish Board for Technical Development. The thesis begins with an introduction to fracture mechanics, covering linear elastic fracture mechanics, elastic-plastic fracture mechanics, and models that consider the influence of the fracture zone. It then introduces the Fictitious Crack Model, which models the fracture zone as a stress-transferable crack, and discusses its applicability. The finite element method is applied to the Fictitious Crack Model, and various calculation methods are presented, including substructure and superposition principles. The thesis also explores the width and development of the fracture zone, comparing the Fictitious Crack Model with other approaches such as linear elastic fracture mechanics, J-integral, Crack Opening Displacement, and R-curve analysis. It finds that these methods are limited in their applicability to cementitious materials. Additionally, the thesis details the determination of material parameters such as tensile strength, Young's modulus, and fracture energy, and presents experimental results for different qualities of concrete. It introduces a new type of testing machine for stable tensile tests on concrete and discusses the σ-w curves for various concrete qualities. The thesis concludes by summarizing the findings and emphasizing the importance of the Fictitious Crack Model for analyzing crack propagation in concrete and similar materials. It highlights the model's ability to describe the development of fracture zones and its applicability to both notched and unnotched structures.This doctoral thesis by Per-Erik Pettersson, published in 1981, focuses on the crack growth and development of fracture zones in plain concrete and similar materials. The study is conducted at the Division of Building Materials at Lund University, Sweden, and is financially supported by grants from the Swedish Board for Technical Development. The thesis begins with an introduction to fracture mechanics, covering linear elastic fracture mechanics, elastic-plastic fracture mechanics, and models that consider the influence of the fracture zone. It then introduces the Fictitious Crack Model, which models the fracture zone as a stress-transferable crack, and discusses its applicability. The finite element method is applied to the Fictitious Crack Model, and various calculation methods are presented, including substructure and superposition principles. The thesis also explores the width and development of the fracture zone, comparing the Fictitious Crack Model with other approaches such as linear elastic fracture mechanics, J-integral, Crack Opening Displacement, and R-curve analysis. It finds that these methods are limited in their applicability to cementitious materials. Additionally, the thesis details the determination of material parameters such as tensile strength, Young's modulus, and fracture energy, and presents experimental results for different qualities of concrete. It introduces a new type of testing machine for stable tensile tests on concrete and discusses the σ-w curves for various concrete qualities. The thesis concludes by summarizing the findings and emphasizing the importance of the Fictitious Crack Model for analyzing crack propagation in concrete and similar materials. It highlights the model's ability to describe the development of fracture zones and its applicability to both notched and unnotched structures.