Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
Peridynamic Models for the Influence of Microstructure and of Temperature in Dynamic and Quasi-Static Brittle Fracture
Extensive efforts have been devoted to understanding brittle failure using numerical simulation, as a complement to theory and experiments. In this thesis, peridynamic models are used to study dynamic and quasi-static brittle fracture. Failure in materials starts from the microscale and can affect, sometimes catastrophically, the structure scale. The goal of computational modeling of fracture is to predict the initiation, growth, and coalescence of cracks/damage. Achieving this goal would allow one to change material design at the microstructure to increase toughness and reliability. We first introduce a microstructure-level peridynamic model of solder joints to understand fracture evolution under dynamic (drop-test) loading conditions. Loads are transferred from the larger scale, for which we create a board-level finite element analysis. We find that samples with larger inclusions show significantly more cracks than those with smaller inclusions, which correlates well with experimental observations. The approach mentioned above (explicit representation of material microscale) becomes computationally prohibitive for problems in which the damage zone is relatively large, as is the case of fiber-reinforced composites (FRC). Homogenization methods have been well established for modeling the linear elastic behavior of FRCs, but not for fracture, a nonlinear and dissipative phenomenon. Here we develop a fully-homogenized peridynamic (FH-PD) model (using the Halpin-Tsai homogenization method) to simulate transverse fracture of unidirectional FRCs. We show some limitations of this model and introduce a new intermediately-homogenized peridynamic (IH-PD) model for transverse loading of unidirectional FRCs. We show that the IH-PD model leads to crack path tortuosity similar to that observed experimentally and without the need for an explicit representation of the FRC microstructure. For many decades, computational models have been over predicting the measured crack speed in dynamic crack propagation in PMMA materials. Experiments show that for PMMA, high temperatures are generated in the fracture process zone, which then soften the material around the crack tip. We consider this effect by introducing a new constitutive model: peridynamic bonds near the crack tip are significantly softer than in the rest of the material. With the new model, the computed crack speed and crack length evolution match very closely those found experimentally.
Mehrmashhadi, Javad, "Peridynamic Models for the Influence of Microstructure and of Temperature in Dynamic and Quasi-Static Brittle Fracture" (2020). ETD collection for University of Nebraska - Lincoln. AAI27956343.