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Figure 5.3
Rheological model and strain components of rock salt (Kiehl et al. 1998, Wittke 2000b)
The primary, secondary and tertiary creep rates
,
and
, respectively, as
well as the viscoplastic strain rates after failure
in this model are determined with
the aid of fl ow rules according to (3.34).
Primary creep is described by the following fl ow rule:
(5.8)
where
In (5.8), the yield function F
p
and the plastic potential Q
p
are defi ned as
(5.9)
(5.10)
where
(5.11)
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