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ʵ
.
/s
compressed polypropylene structures with constant strain rate ˙
=0
04681
.
Thevaluesofidentifiedparametersforthisparticularcaseare:
s
−
1
;
E
=40
MPa
;
D
0
=10000
n
=0
.
23;
D
1
=0
.
732
MPa
;
MPa
−
1
;
MPa
−
1
;
m
1
=35
m
2
=449
R
0
=1
.
8
MPa
;
R
1
=3
.
8
MPa
Theidentificationresultswereverifiedbynumericalsimulationofthelabora-
torytests usingthecalculatedmaterialparameters.Aspecialnumericalappli-
cationdescribedin[19]wasinvolvedinthesesimulations.
TheresultsoftheverificationcalculationsfortheBodner-Partommodelcom-
paredwithlaboratorytestswiththesamestrainratearepresentedinFig.3.
Fig. 3.
Verificationofnumericalandexperimentaldata
Thebestaccuracyofthenumericalandexperimentaldatahasbeennoticed
for the case b depicted in Fig. 3. Taking into account the fact that for this
specificcasetheidentificationprocesswascarriedout,sucharesultisobviously
expected.DatadepictedinFig.2aand2crevealsomeinaccuraciesbetweenthe
realandsimulatedbehaviourofspecialgranularstructures.
IntroducedinSec.4,methodologyfortheBodner-Partomparameter-iden-
tification was primarilyproposed for strain rate dependent steels. Although it
could be successfully adopted for other classical materials as various types of
metalalloys,polymersorevensolidpropellants[23],itmaynotnecessarilybe
suitablefor”innovative”materialsofwhichvacuumpackedparticlesaretypical
examples.
5 Conclusions
TheidentificationoftheBodner-Partomviscoplasticmodelhasbeenperformedon
thebasisofuniaxialcompressiontestscarriedoutoncylindricalspecimenscom-
posedofspecialgranularstructures.Manymoreviscoplasticmodelscanbefound
intheliterature,buttheirapplicationislimitedduetothelargenumberofmaterial
parameterswhichneedtobedeterminedbefore.Therefore,theauthorsdecidedto
applyinthepresentworkoneofthebestknownanduniversalmodelsforpopular
structuralmaterials.Also,thenumberofparametershasbeenreducedtothemost
importantones(omittingtemperatureandrecoveryeffects).
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