Design of lightweight fracture-resilient structures

Dabbara, Raghavendra Rohit

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https://hdl.handle.net/2142/124468 Copy

Description

Title

Design of lightweight fracture-resilient structures

Author(s)

Dabbara, Raghavendra Rohit

Issue Date

2024-05-03

Director of Research (if dissertation) or Advisor (if thesis)

Geubelle, Philippe H

Department of Study

Aerospace Engineering

Discipline

Aerospace Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

Fracture, Topological Derivative, Ansys Mechanical, Optimization

Abstract

This thesis discusses the applications of the Topological Derivative (TD) method in the design of lightweight fracture-resilient structures and as a tool to identify the crack initiation parameters. The topological derivative describes the variation of a response functional to infinitesimal changes in topology, such as the introduction of an infinitesimal crack or hole. In previous work, Alidoost et al. developed an approximation of the energy release rate field in a three-dimensional domain associated with a small surface crack of any boundary location, direction, and orientation combination using the topological derivative which requires only one analysis of the non-cracked domain. The current work integrates the TD formulation into Ansys Mechanical to identify the crack initiation parameters of a half-penny-shaped crack on the surface of a three-dimensional body. First, comparisons have been made between the values calculated using the TD method, those available in the literature, and those computed using Ansys to demonstrate the accuracy of TD-based calculations. Later, a gradient-based optimization scheme is developed, which takes the stress state of a crack-free domain to calculate the energy release rate of a surface crack of any arbitrary rotation and creates an energy contour to locate the crack initiation coordinates and crack orientation. In the second part of this thesis, we developed a gradient-based shape optimization scheme built upon the topological derivative method. This work is a continuation to where a similar scheme to design fracture-resilient structures is developed. However, a fundamental limitation of formulation in was that it employed super ellipses to define the hole boundaries, which restricts the optimizer regarding the shapes it can produce. The current work utilizes a boundary generated by the zero level-set of a B-surface controlled by a grid of design points that are free to create any arbitrary shape to optimize the objective function. Another advantage of B-surfaces is that they can move the hole boundary to the optimal location in the domain irrespective of the starting point. Novel concavity and curvature constraints have also been developed to keep the domain smooth and void-free. Multiple examples have been provided to demonstrate the effectiveness of this method in finding the optimum.

Graduation Semester

2024-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2024 Raghavendra Dabbara

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