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Considerably simplified models of macroscopic material behavior,
such as the idealization for metals of elastic-time independent
plastic response with a yield (onset) criterion, have served the
engineering profession well for many years. They are still basic to
the design and analysis of most structural applications. In the
need to use materials more effectively, there are circumstances
where those traditional models are not adequate, and constitutive
laws that are more physically realistic have to be employed. This
is especially relevant to conditions where the inherent time
dependence of inelastic deformations, referred to as
"viscoplasticity," is pronounced such as at elevated temperatures
and for high strain rates. Unified theories of elastic-viscoplastic
material behavior, which are primarily applicable for metals and
metallic alloys, combine all aspects of inelastic response into a
set of time dependent equations with a single inelastic strain rate
variable. For such theories, creep under constant stress, stress
relaxation under constant strain, and stress-strain relations at
constant rates are each special cases of a general formulation.
Those equations mayor may not include a yield criterion, but models
which do not separate a fully elastic region from the overall
response could be considered "unified" in a more general sense. The
theories have reached a level of development and maturity where
they are being used in a number of sophisticated engineering
applications. However, they have not yet become a standard method
of material representation for general engineering practice.
Considerably simplified models of macroscopic material behavior,
such as the idealization for metals of elastic-time independent
plastic response with a yield (onset) criterion, have served the
engineering profession well for many years. They are still basic to
the design and analysis of most structural applications. In the
need to use materials more effectively, there are circumstances
where those traditional models are not adequate, and constitutive
laws that are more physically realistic have to be employed. This
is especially relevant to conditions where the inherent time
dependence of inelastic deformations, referred to as
"viscoplasticity," is pronounced such as at elevated temperatures
and for high strain rates. Unified theories of elastic-viscoplastic
material behavior, which are primarily applicable for metals and
metallic alloys, combine all aspects of inelastic response into a
set of time dependent equations with a single inelastic strain rate
variable. For such theories, creep under constant stress, stress
relaxation under constant strain, and stress-strain relations at
constant rates are each special cases of a general formulation.
Those equations mayor may not include a yield criterion, but models
which do not separate a fully elastic region from the overall
response could be considered "unified" in a more general sense. The
theories have reached a level of development and maturity where
they are being used in a number of sophisticated engineering
applications. However, they have not yet become a standard method
of material representation for general engineering practice.
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