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There is now a CONTENT FREEZE for Mercury while we switch to a new platform. It began on Friday, March 10 at 6pm and will end on Wednesday, March 15 at noon. No new content can be created during this time, but all material in the system as of the beginning of the freeze will be migrated to the new platform, including users and groups. Functionally the new site is identical to the old one. webteam@gatech.edu
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MSE PhD Defense - Prateek Verma
Monday, June 1 at 2:00 p.m.
MRDC Room 3515
Committee:
Dr. Anselm Griffin (co-adviser), MSE
Dr. Meisha Shofner (co-adviser), MSE
Dr. Naresh Thadhani, MSE
Dr. David Bucknall, MSE
Dr. Preet Singh, MSE
Dr. Angus Wilkinson, CHEM
Title: Auxetic Behavior in Some Fiber Network Structures
Abstract:
Auxetic materials are a rare class of materials that exhibit negative Poisson’s ratio. While most substances (like a rubber band) become thinner in lateral direction when stretched, auxetic materials grow thicker. The broad objective of this research is to study the origins of auxetic behavior in fibrous networks and to develop predictive processing-structure-property relations for these materials systems. We start by examining out-of-plane Poisson's ratio in paper by investigating a range of carefully chosen commercial paper samples. Laboratory handsheets were also produced and examined for their out-of-plane auxetic response. A geometrical model was devised and a finite element analysis on the model was performed to understand the origin of and underlying mechanism responsible for this auxetic response. Additionally, we were able to create a similar auxetic response in needle-punched nonwoven fiber networks by a heat-compression treatment. Thickness direction strain with respect to uniaxial in-plane strain was measured for these materials and a series of microscopic and tomographic characterization was performed. From results on paper and nonwovens, it is evident that the fiber network structure itself plays an important role in defining the Poisson’s ratio behavior. The type of network stabilization (hydrogen bonding in paper and needle-punching in nonwovens) and the choice of subsequent processing conditions have a significant influence on the out-of-plane Poisson’s ratio in these materials. Ultimately, a fundamental understanding of the origins of deformation behavior in these fiber networks should lead to the prospect of rational design of new auxetics and, in turn, to new product development opportunities for fiber-network materials.
