Biomedical Engineering Reference
In-Depth Information
“Plateau”
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Figure 6-6. The schematic of the possible existence of the mystical materials and relevant
indenter angle ranges - they correspond to the “plateaus” on the multi-dimensional
“surface” of the shape factors of the indentation curves.
“surface”, the “slope” may not be large and distinct everywhere, and
The mystical materials and the relevant indenter angle ranges would
correspond to such “plateaus” (with zero or almost zero “slope”) of the
multi-dimensional “surface” - although these plateaus are small compare
with the entire parameter space, they still exist and thus have important
theoretical value for probing the uniqueness of indentation analysis.
The mystical materials have many interesting properties.
65
When the
difference between the dual indenter angle (
) is small, more mystical
pairs can be found with larger differences of their elastoplastic properties.
A gold mine of mystical materials can be identified when
n
is about 0 to
0.2, and when
Δ
E
σ is about 0.01. These mystical materials are difficult
to be identified by a wide range of indenter angle, and they correspond to
technically important high-strength metals and alloys.
Figure 6-7a
gives an example: this pair of mystical material leads to
almost the same indentation loading-unloading behaviors when the
indenter angle changes from 60° to 80°, which has reached the limit of
the indenter angles used in most studies. Consequently, most existing
dual (or plural) indentation methods in the literature would fail to
distinguish them and more extreme indenters are needed. However this is
often not practical because without advanced knowledge, one could not
/
y
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