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Spherical Indentation Creep Following Ramp Loading

Published online by Cambridge University Press:  01 February 2011

Michelle L. Oyen*
Affiliation:
Department of Biophysical Sciences and Medical Physics, University of Minnesota Minneapolis, MN 55455
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Abstract

Depth-sensing indentation testing is a common way to characterize the mechanical behavior of stiff, time-independent materials but presents both experimental and analytical challenges for compliant, time-dependent materials. Many of these experimental challenges can be overcome by using a spherical indenter tip with a radius substantially larger than the indentation depth, thus restricting deformation to viscoelastic (and not plastic) modes in glassy polymers and permitting large loads and contact stiffness to be generated in compliant elastomers. Elastic-viscoelastic correspondence was used to generate spherical indenter solutions for a number of indentation testing protocols including creep following loading at a constant rate and a multiple ramp-and-hold protocol to measure creep response at several loads (and depths) within the same test. The ramp-creep solution was recast as a modification to a step-load creep solution with a finite loading rate correction factor that is a dimensionless function of the ratio of experimental ramp time to the material time constant. Creep tests were performed with different loading rates and different peak load levels on glassy and rubbery polymeric materials. Experimental data are fit to the spherical indentation solutions to obtain elastic modulus and time-constants, and good agreement is found between the results and known modulus values. Emphasis is given to the use of multiple experiments (or multiple levels within a single experiment) to test the a priori assumption of linear viscoelastic material behavior used in the modeling.

Type
Research Article
Copyright
Copyright © Materials Research Society 2005

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References

REFERENCES

1. Oliver, W.C. and Pharr, G.M., J Mater Res 7, 1564 (1992).Google Scholar
2. Oyen, M.L. and Cook, R.F.. J Mater Res, 18, 139 (2003).Google Scholar
3. Oyen, M.L., Cook, R.F., Moody, N.R., and Emerson, J.A.. J Mater Res, 19(8):2487 (2004).Google Scholar
4. Briscoe, B.J., Fiori, L., and Pelillo, E., J Phys D: Appl. Phys. 31, 2395 (1998).Google Scholar
5. Johnson, K.L., Contact Mechanics. (Cambridge University Press, Cambridge, UK, 1985).Google Scholar
6. Lee, E.H. and Radok, J.R.M., Journal of Applied Mechanics 27, 438 (1960).Google Scholar
7. Cook, R.F., personal communication.Google Scholar