University of Illinois Urbana-Champaign

Ruga mechanics of composite media with soft inclusions

Abdelmeguid, Mohamed Ezzeldin Elsayed Ahmed

Content Files
ABDELMEGUID-THESIS-2017.pdf

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https://hdl.handle.net/2142/99523

Description

Title
Ruga mechanics of composite media with soft inclusions
Author(s)
Abdelmeguid, Mohamed Ezzeldin Elsayed Ahmed
Issue Date
2017-12-11
Director of Research (if dissertation) or Advisor (if thesis)
Elbanna, Ahmed
Department of Study
Civil & Environmental Eng
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Date of Ingest
2018-03-13T17:35:52Z
Keyword(s)
  • Negative stiffness
  • Ruga mechanics
  • Band-gaps
Abstract
This thesis presents an investigation for the elastic deformation of two-phase fibril composites with soft inclusions, specifically, the influence of soft inclusions on the behavior of fibrils under compressive loading. It is demonstrated that the inclusion of soft material in the fibril matrix substantially alters the post-bifurcation response of elastic fibrils. First, nonlinear finite element analysis is used to demonstrate that due to localized instabilities, fibrils with soft inclusions exhibit negative post-buckling stiffness. The local instability is postulated to follow the same post- buckling behavior as a beam on an elastic foundation, through a semi-analytical approach, it is shown that an unstable post-bifurcation response emerges. Additionally, using numerical analysis, careful patterning of the inclusions is shown to induce complex surface topography attributed to the local buckling modes, such as wrinkles and folds. Furthermore, through natural frequency eigenvalue analysis, it is demonstrated that fibrils with soft inclusions in the post-buckling region have local modes with negative ω2. Negative ω2 is only observed in negative stiffness systems and associated with local modes of instability. Through Bloch wave analysis it is observed that due to the complex deformation modes of buckled fibrils with soft inclusions widening band-gaps that are proportional to the prescribed load emerge. The findings presented in this thesis provide alternatives to the manufacturing of negative stiffness systems that relies on curved beam elements. It also serves to introduce the possibility of utilizing soft inclusions in achieving controllable surface morphologies. Finally, demonstrates the possibility of modulating acoustic bandgaps and optimizing damping properties of composites through end-shortening.
Graduation Semester
2017-12
Type of Resource
text
Permalink
http://hdl.handle.net/2142/99523
Copyright and License Information
Copyright 2017 Mohamed Abdelmeguid

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Graduate Theses and Dissertations at Illinois
Dissertations and Theses - Civil and Environmental Engineering