TY - BOOK

T1 - Optimization of toughness in materials with propagating and reinitiating cracks

AU - Rettl, Matthias

N1 - no embargo

PY - 1800

Y1 - 1800

N2 - In many technical applications, materials need to absorb energy or be tolerant towards flaws that may already be generated in the manufacturing process. This behavior is known as toughness, and the fracture toughness is a widely known measure that allows to compare various materials to each other. Solid materials can be tough if they form a plastic zone, but in nature one can also observe hierarchical structures of very brittle base materials, where the overall mechanical response is much tougher than the brittle base material. This work aims to create such structures with a high toughness. To obtain such a structure, homogeneous 2D plates with arbitrarily shaped holes are considered. The goal is to optimize the shape of the holes, but first the fracture process must be predicted. During the fracture process, new cracks can initiate from surfaces and existing cracks may propagate. Crack initiation from a surface can be predicted using Leguillon's Coupled Criterion or the Theory of Critical Distances of Taylor. For the crack propagation, two parameters need to be predicted: the critical load at which a crack will propagate and the direction of the crack propagation. According to Griffith, a load becomes critical when the energy release rate exceeds the critical energy release rate which is a material parameter. A common criterion for the direction of the crack propagation is the Maximum Energy Release Rate (MERR) criterion. In this work, Configurational Forces are implemented as an Abaqus plugin. This implementation can be used to predict both, the critical load and the direction of the crack initiation. This allows to simulate the fracture process and the tensile toughness of the overall structure can be computed. Furthermore, an optimization algorithm is developed to maximize the tensile toughness. For an example problem, a hole structure is found with a tensile toughness more than 4.5 times higher compared to a solid material.

AB - In many technical applications, materials need to absorb energy or be tolerant towards flaws that may already be generated in the manufacturing process. This behavior is known as toughness, and the fracture toughness is a widely known measure that allows to compare various materials to each other. Solid materials can be tough if they form a plastic zone, but in nature one can also observe hierarchical structures of very brittle base materials, where the overall mechanical response is much tougher than the brittle base material. This work aims to create such structures with a high toughness. To obtain such a structure, homogeneous 2D plates with arbitrarily shaped holes are considered. The goal is to optimize the shape of the holes, but first the fracture process must be predicted. During the fracture process, new cracks can initiate from surfaces and existing cracks may propagate. Crack initiation from a surface can be predicted using Leguillon's Coupled Criterion or the Theory of Critical Distances of Taylor. For the crack propagation, two parameters need to be predicted: the critical load at which a crack will propagate and the direction of the crack propagation. According to Griffith, a load becomes critical when the energy release rate exceeds the critical energy release rate which is a material parameter. A common criterion for the direction of the crack propagation is the Maximum Energy Release Rate (MERR) criterion. In this work, Configurational Forces are implemented as an Abaqus plugin. This implementation can be used to predict both, the critical load and the direction of the crack initiation. This allows to simulate the fracture process and the tensile toughness of the overall structure can be computed. Furthermore, an optimization algorithm is developed to maximize the tensile toughness. For an example problem, a hole structure is found with a tensile toughness more than 4.5 times higher compared to a solid material.

KW - Bruchmechanik

KW - Optimierung

KW - Fracture Mechanics

KW - Finite Fracture Mechanics

KW - Coupled Criterion

KW - Optimization

M3 - Doctoral Thesis

ER -