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Journal of Polymers and the Environment

, Volume 26, Issue 1, pp 183–190 | Cite as

The Effect of Ultraviolet Radiation on the Hyperelastic Behavior of Polyurea

  • George YoussefEmail author
  • Joseph Brinson
  • Ian Whitten
Original Paper

Abstract

Polyurea is widely used in military and civilian applications, where long durations of exposure to the sun is common. Extended ultraviolet exposure can deteriorate the mechanical performance of the material to suboptimal levels. This study reports on the hyperelastic behavior of polyurea as a function of exposure duration to ultraviolet radiation. Initially, five sets of samples were continuously exposed to ultraviolet radiation for different durations up to 15 weeks. An additional set of samples were kept unexposed to report on the properties of an as-cast polyurea control. The samples were then loaded uniaxially in tension under a quasi-static loading rate (\(\dot{\epsilon }=0.0127{s}^{-1}\)) using a standard load frame. All exposed samples exhibited incremental color changes, which ranged from transparent yellow in virgin samples to opaque tan after 15 weeks of exposure. Changes in color were observed as early as 3 weeks of ultraviolet exposure. In addition to discoloration, crazing developed in all samples for exposure durations of 3 weeks and beyond. The size of the cracks increased as the duration of exposure continued. Postmortem examination indicated the initial microcracks grew due to loading and were visible to the naked eye. Discoloration and crazing were attributed to the formation of a thin ultraviolet-degraded layer due to the interaction of oxygen and ultraviolet light with the chromophoric groups in the polyurea macromolecule. The hyperelastic behavior was studied by fitting the stress–strain data into a four-term Ogden model. The overall hyperelastic behavior of polyurea remained unchanged even after 15 weeks of continuous ultraviolet exposure, where no permanent failure (except the ultraviolet-induced cracks) was recorded at the gauge length up to 250% strain. The values of the fitting parameters were nearly identical, supporting the conclusion of the insensitivity of polyurea hyperelastic behavior to ultraviolet radiation.

Keywords

Polyurea Artificial weathering Ultraviolet radiation Hyperelasticity Mechanical properties 

Notes

Acknowledgements

The research leading to these results was supported in part by the United States Department of Defense under Grant Agreement No. W911NF-14-1-0039. The authors also acknowledge the assistance of Dr. Steve Barlow, and use of equipment at the San Diego State University Electron Microscopy Facility acquired by NSF instrumentation grant DBI-0959908.

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Copyright information

© Springer Science+Business Media New York 2017

Authors and Affiliations

  1. 1.Mechanical Engineering DepartmentSan Diego State UniversitySan DiegoUSA
  2. 2.Mechanical Engineering DepartmentCalifornia State University NorthridgeNorthridgeUSA

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