Download Abaqus Analysis User's Manual, vol3

CRUSHABLE FOAM
You provide the value of
Input File Usage:
Abaqus/CAE Usage:
.
*CRUSHABLE FOAM, HARDENING=ISOTROPIC
Property module: material editor: Mechanical→Plasticity→Crushable
Foam: Hardening: Isotropic
Hardening
A simple uniaxial compression test is sufficient to define the evolution of the yield surface. The hardening
law defines the value of the yield stress in uniaxial compression as a function of the absolute value of
the axial plastic strain. The piecewise linear relationship is entered in tabular form. The table must start
with a zero plastic strain (corresponding to the virgin state of the materials), and the tabular entries must
be given in ascending magnitude of
. For values of plastic strain greater than the last user-specified
value, the stress-strain relationship is extrapolated based on the last slope computed from the data. If
desired, the yield stress can also be a function of temperature and other predefined field variables.
Input File Usage:
Abaqus/CAE Usage:
*CRUSHABLE FOAM HARDENING
Property module: material editor: Mechanical→Plasticity→Crushable
Foam: Suboptions→Foam Hardening
Rate dependence
As strain rates increase, many materials show an increase in the yield stress. For many crushable foam
materials this increase in yield stress becomes important when the strain rates are in the range of 0.1–1 per
second and can be very important if the strain rates are in the range of 10–100 per second, as commonly
occurs in high-energy dynamic events.
Two methods for specifying strain-rate-dependent material behavior are available in Abaqus as
discussed below. Both methods assume that the shapes of the hardening curves at different strain rates
are similar, and either can be used in static or dynamic procedures. When rate dependence is included,
the static stress-strain hardening behavior must be specified for the crushable foam as described above.
Overstress power law
You can specify a Cowper-Symonds overstress power law that defines strain rate dependence. This law
has the form
with
where , specified as part of the crushable foam hardening definition, is the static uniaxial compression
yield stress at a given value of
for the experiment with the lowest strain rate, and
is the yield
22.3.5–10
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