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Visualization of Particle-Toughening Mechanism in Transparent Polyurethanes

[+] Author Affiliations
Mohammad H. Malakooti, Henry A. Sodano

University of Florida, Gainesville, FL

Patrick L. Anderson

Calvin College, Grand Rapids, MI

Paper No. SMASIS2014-7450, pp. V001T01A006; 8 pages
doi:10.1115/SMASIS2014-7450
From:
  • ASME 2014 Conference on Smart Materials, Adaptive Structures and Intelligent Systems
  • Volume 1: Development and Characterization of Multifunctional Materials; Modeling, Simulation and Control of Adaptive Systems; Structural Health Monitoring; Keynote Presentation
  • Newport, Rhode Island, USA, September 8–10, 2014
  • Conference Sponsors: Aerospace Division
  • ISBN: 978-0-7918-4614-8
  • Copyright © 2014 by ASME

abstract

Highly cross-linked polyurethanes have a high elastic modulus and creep resistance, but they undergo a brittle fracture below the glass transition temperature. Unfortunately, a large number of glassy polyurethanes are prone to brittle fracture without undergoing large elastic deformations; in particular, brittle failure is common under conditions such as low temperature and high strain rates. While the rigidity in polymers is required for practical applications, the lack of resistance against crack propagation is essential to avoid catastrophic failures. The toughening of polymers is a crucial aspect of improving the strength and ductility at specific temperatures and deformation rates. One method that has shown promise in recent years is the creation of local regions of reduced modulus that absorb strain energy and toughen the polymer. For instance, rubbers are typically added to epoxy which phase separate upon polymerization and create local elastic regions that significantly toughen the polymer.

In this study, a variety of two-phase transparent polyurethanes in the form of single inclusions is designed to study the toughening mechanism of the local regions of reduced modulus with an embedded crack. Synthesized heterogeneous polyurethanes show a transition from brittle to ductile behavior in addition to a drastic increase in the maximum load that the polymer can withstand. Compact tension experiments demonstrate that a small reduction in the inclusion’s Young’s modulus (∼10%) leads to an increase in the toughness by factor of 7 (∼700%). Moreover, digital image correlation is performed to map the strain distribution around the crack in order to visualize possible toughening mechanism. Comparison between the induced strain field in samples with inclusion and samples without inclusion reveals an efficient toughening mechanism of the polymers.

Copyright © 2014 by ASME

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