2026-09-21T01:32:14Z https://www.ideals.illinois.edu/oai-pmh

oai:www.ideals.illinois.edu:2142/99523 2023-07-11 col_2142_5131 col_2142_14770 com_2142_5130 com_2142_3518 com_2142_234

Elbanna, Ahmed Abdelmeguid, Mohamed Ezzeldin Elsayed Ahmed 2018-03-13T17:35:52Z 2018-03-13T17:35:52Z 2020-03-14T09:15:12Z 2017-12-11 2017-12 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. Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2019-12-01 The student, Mohamed Abdelmeguid, accepted the attached license on 2017-12-08 at 14:10. The student, Mohamed Abdelmeguid, submitted this Thesis for approval on 2017-12-08 at 14:18. This Thesis was approved for publication on 2017-12-11 at 14:08. DSpace SAF Submission Ingestion Package generated from Vireo submission #11927 on 2018-03-13 at 10:38:01 Made available in DSpace on 2018-03-13T17:35:52Z (GMT). No. of bitstreams: 2 ABDELMEGUID-THESIS-2017.pdf: 20541237 bytes, checksum: 6e230eff5d98089a081babfe5902789c (MD5) LICENSE.txt: 4216 bytes, checksum: 25c4ab74630a4a5e3de6517d8a62bdbd (MD5) Previous issue date: 2017-12-11 Embargo set by: Seth Robbins for item 105492 Lift date: 2020-03-13T17:36:05Z Reason: Author requested closed access (OA after 2yrs) in Vireo ETD system Limited Restriction Lifted for Item 105492 on 2020-03-14T09:15:12Z. application/pdf http://hdl.handle.net/2142/99523 en Copyright 2017 Mohamed Abdelmeguid Negative stiffness Ruga mechanics Band-gaps Ruga mechanics of composite media with soft inclusions text text Civil & Environmental Eng Civil Engineering University of Illinois at Urbana-Champaign Thesis M.S.