Phase-field modeling of fracture: regularization length insensitivity and mixed mode ductile fracture

Predicting crack nucleation and propagation in materials is of critical importance in designing structural components. Due to the cost, time, and occasional impossibility of performing fracture experiments, computational approaches have become instrumental to understand and assess fracture and failure processes in materials and optimize the design of structures. The development of quantitative computational models for predicting crack initiation and propagation has remained an important area of research because of the complexities that arise from topologically complex crack growth and interactions with other inelastic phenomena. Among computational fracture models, the phase-field modeling approach has emerged as a superior model to overcome the discontinuities associated with cracking. However, we identified a number of shortcomings with existing models, namely in the sensitivity of phase-field model predictions to the regularization length and in the prediction of accurate crack paths and load-displacement curves for ductile materials. In this Ph.D. research, in contrast to previous phase-field fracture models, we proposed a novel approach to attain a length-scale insensitive mechanical response, which considers a continuous approximation of a crack boundary with a function of infinite support. The predicted mechanical response and crack paths were validated against experimental results from a three-point bending test on concrete and an in-plane shear test on steel. These models are capable of predicting crack propagation in a wide range of materials and structures. Additionally, for the first time, we developed a mixed-mode phase-field model for ductile fracture which combines two phase-fields for shear (mode II) and tensile (mode I) fractures. Unlike many previous phase-field models, the proposed model implicitly includes the important effects of lode angle (via the maximum shear stress) and triaxiality (via the first principal stress and pressure) on the initiation and propagation of ductile fracture. Model predictions of slant and cup cone crack paths as well as load-displacement responses were comparable to the results of plane-strain tension, round bar tension and notched round bar tension experiments in Al 2024-T351. The proposed model is a practical tool for ductile fracture prediction in a wide range of stress states. Finally, the developed phase-field models were applied to the study of mode II crack propagation in a heterogeneous domain consisting of intermetallic particles inside an aluminum alloy matrix (Al 2024). Attention was given to the effects of particle size and area fraction on predicted crack growth resistance curves. In this Ph.D. research, we introduced advanced phase-field models for the accurate prediction of complex crack paths and mechanical responses in engineering materials under a variety of loading configurations. These models are practical tools to predict, understand and assess fracture and failure processes in a variety of materials.

Name thesis:degree_name

Doctor of Philosophy (Ph.D.)

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor dc:publisher

Colorado School of Mines. Arthur Lakes Library

Year dc:date.issued

2024

Author dc:creator

• Huber, William

Advisor dc:contributor.advisor

• Asle Zaeem, Mohsen

Committee members dc:contributor.committeemember

• Hedayat, Ahmadreza
• Thomas, Brian G.
• Tucker, Garritt J.

Statement dc:rights

• Copyright of the original work is retained by the author.

Language dc:language.iso

eng, English

Dc Identifier Other

T 9714

OAI identifier oai:identifier

oai:repository.mines.edu:11124/179353