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Broadband nanoindentation of glassy polymers: Part II. Viscoplasticity

Published online by Cambridge University Press:  18 November 2011

Joseph E. Jakes*
Affiliation:
Performance Enhanced Biopolymers, USDA Forest Service, Forest Products Laboratory, Madison, Wisconsin 53726; and Materials Science Program, University of Wisconsin–Madison, Madison, Wisconsin 53706
Rod S. Lakes
Affiliation:
Department of Engineering Physics, University of Wisconsin–Madison, Madison, Wisconsin 53706
Don S. Stone
Affiliation:
Materials Science Program, University of Wisconsin–Madison, Madison, Wisconsin 53706; and Department of Materials Science and Engineering, University of Wisconsin–Madison, Madison, Wisconsin 53706
*
a)Address all correspondence to this author. e-mail: jjakes@fs.fed.us
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Abstract

The relationship between hardness and flow stress in glassy polymers is examined. Materials studied include poly(methylmethacrylate), polystyrene, and polycarbonate. Properties are strongly rate dependent, so broadband nanoindentation creep (BNC) is used to measure hardness across a broad range of indentation strain rates (10−4 to 10 s−1). Molybdenum (Mo) is also studied to serve as a “control” whose rate-dependent hardness properties have been measured previously and whose flow stress, unlike the polymers, is pressure insensitive. The BNC hardness data are converted to uniaxial flow stress using two methods based on the usual Tabor–Marsh–Johnson correlation. With both methods the resulting BNC-derived uniaxial flow stress data agree closely with literature compression uniaxial flow stress data for all materials. For the polymers, the BNC hardness data depend on initial rate of loading, indicating that the measured properties are path dependent. Path dependence is not detected in Mo.

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Articles
Copyright
Copyright © Materials Research Society 2011

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References

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