Brittle fracture simulation with boundary elements for computer graphics Dissertation Thesis

Author(s): Hahn, David
Advisor(s): Wojtan, Chris
Committee Chair(s): Hof, Björn
Committee Member(s): Edelsbrunner, Herbert; Schrefl, Thomas
Title: Brittle fracture simulation with boundary elements for computer graphics
Affiliation IST Austria
Abstract: This thesis describes a brittle fracture simulation method for visual effects applications. Building upon a symmetric Galerkin boundary element method, we first compute stress intensity factors following the theory of linear elastic fracture mechanics. We then use these stress intensities to simulate the motion of a propagating crack front at a significantly higher resolution than the overall deformation of the breaking object. Allowing for spatial variations of the material's toughness during crack propagation produces visually realistic, highly-detailed fracture surfaces. Furthermore, we introduce approximations for stress intensities and crack opening displacements, resulting in both practical speed-up and theoretically superior runtime complexity compared to previous methods. While we choose a quasi-static approach to fracture mechanics, ignoring dynamic deformations, we also couple our fracture simulation framework to a standard rigid-body dynamics solver, enabling visual effects artists to simulate both large scale motion, as well as fracturing due to collision forces in a combined system. As fractures inside of an object grow, their geometry must be represented both in the coarse boundary element mesh, as well as at the desired fine output resolution. Using a boundary element method, we avoid complicated volumetric meshing operations. Instead we describe a simple set of surface meshing operations that allow us to progressively add cracks to the mesh of an object and still re-use all previously computed entries of the linear boundary element system matrix. On the high resolution level, we opt for an implicit surface representation. We then describe how to capture fracture surfaces during crack propagation, as well as separate the individual fragments resulting from the fracture process, based on this implicit representation. We show results obtained with our method, either solving the full boundary element system in every time step, or alternatively using our fast approximations. These results demonstrate that both of these methods perform well in basic test cases and produce realistic fracture surfaces. Furthermore we show that our fast approximations substantially out-perform the standard approach in more demanding scenarios. Finally, these two methods naturally combine, using the full solution while the problem size is manageably small and switching to the fast approximations later on. The resulting hybrid method gives the user a direct way to choose between speed and accuracy of the simulation.
Publication Title: IST Dissertation
Degree Granting Institution: IST Austria  
Degree Date: 2017-08-14
Copyright Statement: CC BY-SA
Sponsor: ERC H2020 programme (grant agreement no. 638176)
DOI: 10.15479/AT:ISTA:th_855
Notes: First of all, let me thank my committee members, especially my supervisor, Chris Wojtan, for supporting me throughout my PhD. Obviously, none of this work would have been possible without you. Furthermore, Thank You to all the people who have contributed to this work in various ways, in particular Martin Schanz and his group for providing and supporting the HyENA boundary element library, as well as Eder Miguel and Morten Bojsen-Hansen for (repeatedly) proof reading and providing valuable suggestions during the writing of this thesis. I would also like to thank Bernd Bickel, and all the members – past and present – of his and Chris’ research groups at IST Austria for always providing honest and insightful feedback throughout many joint group meetings, as well as Christopher Batty, Eitan Grinspun, and Fang Da for many insights into boundary element methods during our collaboration. As only virtual objects have been harmed in the process of creating this work, I would like to acknowledge the Stanford scanning repository for providing the “Bunny” and “Armadillo” models, the AIM@SHAPE repository for “Pierre’s hand, watertight”, and S. Gainsbourg for the “Column” via Sorry for breaking these models in many different ways.
Open access: yes (repository)
IST Austria Authors
  1. Chris Wojtan
    33 Wojtan
  2. David Hahn
    4 Hahn
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