Abstract:
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This work concerns analysis of spherical indentation experiments through
extensive finite element simulations involving the J2 flow and the J2 deformation
plasticity theories both under finite and infinite deformations
to gain a fundamental comprehension into the mechanics of the transition
between elasto-plastic and fully-plastic contacts. A decrease in hardness
with increasing penetration is found to be a manifestation of the differences
in material pileup responses between the two plasticity theories, so that in
contrast to prior investigations, a peak in hardness cannot be taken to mark
onset of a so-called finite deformation fully-plastic regime. The accuracy of
Tabor’s hardness relation is examined in detail in light of the simulations
and a general relation is proposed through dimensional analysis to correlate
hardness with the uniaxial mechanical properties for any arbitrary
elasto-plastic or fully-plastic contact. Experiments are also performed in
different groups of metallic materials and a methodology is proposed to extract
yield strength ys and power-law strain hardening parameter n from
a minimum of two hardness measurements performed at different penetration
depths. Influence of pressure sensitivity in the extracted properties is
then examined through the experimental results. The issue of the uniqueness
in the extracted properties and of frictional effects between indenter
and material are briefly covered. The investigation ends with a discussion
on the robustness of mechanical property extractions through single
crystal spherical indentation experiments. Along these lines, consistency is
found between simulations with the flow theory of plasticity and the crystal
plasticity model for fcc metals. Finally, the potential of spherical indentation
to distinguish between single crystal elastic and plastic anisotropy is
considered. |