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Nanoindentation behavior of muscovite subjected to repeated loading

TitleNanoindentation behavior of muscovite subjected to repeated loading
Publication TypeJournal Article
Year of Publication2011
AuthorsYin H, Zhang G
JournalJournal of Nanomechanics and Micromechanics
Start Page72
Date Published06/2011
ISSN 2153-5434
KeywordsHardness, Incipient kink band, Muscovite, Nanoindentation, Repeated loading, Shakedown, Young’s modulus

A series of repeated loading nanoindentation experiments were performed on muscovite with a sharp indenter tip and loading direction normal to the basal plane, and the maximum load (FmaxFmax⁡) was varied between 0.05 and 2.0 mN to examine the influences of load level on the modes of nanoscale deformation and the resulting estimation of hardness and elastic modulus. A critical maximum load, (Fmax)crit(Fmax⁡)crit, of about 0.25–0.5 mN marks the material’s completely different responses to repeated loading. If Fmax<(Fmax)critFmax⁡<(Fmax⁡)crit, fully closed, completely reversible loading-unloading (L/UL/U) hysteresis loops were observed with characteristic smooth, nonlinear curves, which can be attributed to the formation and annihilation of incipient kink bands. If Fmax>(Fmax)critFmax⁡>(Fmax⁡)crit, dispersed L/UL/U loops characterized by nonrecoverable deformation and randomly occurring pop-ins in the loading section of the loops were observed; moreover, it appears that pop-ins are the major cause for the dispersion of the L/UL/U loops. For the latter case, after a few L/UL/U cycles, pop-ins tend to disappear, and the L/UL/U loops start to merge together, resulting in the shakedown of the repeated loading. A comparison of the unloading section of the loops indicates that the contact stiffness increases with the number of L/UL/U cycles, or the mineral exhibits cyclic hardening behavior. The resulting influences on the hardness and elastic modulus are evaluated against those obtained by monotonic loading and further discussed in accordance with indentation size effects and underlying nanoscale deformation mechanisms at different load levels.