modeling plastics in ansys [compatibility mode].pdf

8/14/2019 Modeling plastics in ANSYS [Compatibility Mode].pdf

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2011 ANSYS, Inc. November 14, 20131 Release 14.0

14. 0 Release

ANSYS Mechanical

Experimental Elatomer

Mo!elin" #latic in ANSYS


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2011 ANSYS, Inc. November 14, 20132 Release 14.0

Intro!$ction

The large strain nonlinear stress-strain behavior of thermoplastic exhibitsthe following:

Strong hysteresis

Rate dependence

Softening after yielding

rittle fail!re at low temperat!res and d!ctile behavior at higher

temperat!re

Thermoplastics !s!ally show different material behavior !nder differentloading and environmental conditions. Th!s !s!ally one single materialmodel co!ld not be !sed to predict plastic nat!re. "ollowing slides will

disc!ss the thermoplastic behavior !nder different conditions and #$S%Smaterial models which co!ld be !sed to model s!ch behavior.


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2011 ANSYS, Inc. November 14,

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%niaxial behavior o& thermoplatic

&nder monotonically increasing !niaxial testing conditions' generallythermoplastics exhibits following behavior:

Stress increases monotonically witho!t any softening after yield (sample 1).

Stress softening after yield and then res!mes hardening (sample *).

This is typical behavior of

thermoplastics !nder !niaxial tensile

loading.


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'ehavior $n!er (oa!in")$nloa!in" con!ition

&nder loading-!nloading !niaxial testing conditions' generally thermoplasticsexhibits strong hysteresis effect which is followed by permanent (plastic)deformations. +hile considering plastic components' it is very important todetermine if there is any possibility of that component experiencing loading-

!nloading conditions.

,enerally the reverseloading slope is not same asthe loading c!rve slope.


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*reep an! relaxation

reep is the tendency of a solid material to move slowly or deform permanently!nder the infl!ence of stresses. t occ!rs as a res!lt of long term expos!re to highlevels of stress that are below the yield strength of the material.

t is more severe in materials that are s!b/ected to heat for long periods' and nearmelting point and always increases with temperat!re.

Thermoplastic also shows creep andrelaxation behavior. f the material isnown to show creep behavior at

operating conditions' it is alwaysadvisable to consider creep d!ringn!merical modeling of thatcomponent.


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Available ANSYS Material Mo!el

#$S%S offers range of material models which co!ld be !sed to model differentthermoplastic behavior !nder different conditions. hoice of material modeldependents on:

1) xperimental data available

*) 2perating conditions

3ifferent models which co!ld be !sed are: Small deformation plasticity (lasto-plastic) ress!re dependent plasticity models (3r!cer rager5 xtendend 3r!cer

rager) 6arge deformation elasticity models (7yperelastic) ergstrom oyce 8odel Rate dependent plasticity models (9iscoplastic) 9iscoelastic reep


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*011 #$S%S' nc. $ovember 14'

*01;

orrect? model@

Aey is to first narrow down all the material behavior !ser wish to incl!de for thematerial.

List all the material behavior

Brittle/Ductile/high strain elasticDifferent loading unloading behavior

Permanent deformation

Stress relaxation/Creep


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*011 #$S%S' nc. $ovember 14'

*01;

B

*hooin" ri"ht mo!el..

#$S%S offers vario!s models which co!ld help to describes the material behavior of

thermoplastics.

7owever iss!e remains on how to choose the >orrect? model@

Second step is to list all the loading conditions for which the str!ct!ral component needs

to be designed.

Cyclic/non-cyclic loadingLoading rate

emperature loading

List all the loading condition


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*011 #$S%S' nc. $ovember 14'

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#$S%S offers vario!s models which co!ld help to describes the material behavior of

thermoplastics.

7owever iss!e remains on how to choose the >orrect? model@

"inal step is to list down the sim!lation ob/ective. This is very important steps since it

also determine the material model.

Stress !nalysis

Life prediction

Design "ptimi#ationList all the simulation ob$ective


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#s mentioned earlier there is no single >8aterial 8odel? which co!ld model all thebehavior described in the last slides. Th!s it is advisable to gather all experimentaldata and list all the operating conditions and choose material model. 6et considerfew scenarios:

.


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*ae 1

Str!ct!re is s!b/ected to monotonically increasing load where Stress increasesmonotonically witho!t any softening after yield. There is no reverse loading andtemperat!re variation is not m!ch ie. Stress-strain behavior is similar in the vicinityof the operating temperat!re.

Mo!el +ecommen!ation (in increasing order ofcomplexity):

1) Small strain metal plasticity (elasto-plastic):

#ro: asiest to !se.

*on: $ot advisable for large strains and may not be

easy to define yield point.

*) 6arge Strain hyperelastic:

#ro: ncl!de large strain effect in the eC!ation

*on: $eed more experimental data to properly definethe model.

;) ergstrom-oyce:

#ro: ncl!de large strain effects

*on: $eed more experimental data to properly definethe model and c!rrently no c!rve fitting in #$S%S


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*ae 2

Str!ct!re is s!b/ected to monotonically increasing load where Stress softening isocc!ring after yield and then res!mes hardening . There is no reverse loading andtemperat!re variation is not m!ch ie. Stress-strain behavior is similar in the vicinityof the operating temperat!re.

Mo!el +ecommen!ation (in increasing order ofcomplexity):

1) 6arge Strain hyperelastic:

#ro: ncl!de large strain effect in the eC!ation

*on: $eed more experimental data to properly define

the model.*) ergstrom-oyce:


*on: $eed more experimental data to properly definethe model and c!rrently no c!rve fitting in #$S%S.

8etal lasticity cannot be !sed since DSofteningE reC!iresdecrease in stress-strain slope which is not allowed in thismodel.


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*ae 3

Str!ct!re is s!b/ected to loading F!nloading load' !nloading slope is not same asthe loading slope and permanent deformation is present. t is ass!med thattemperat!re variation is not m!ch ie. Stress-strain behavior is similar in the vicinityof the operating temperat!re.

Mo!el +ecommen!ation1) ergstrom-oyce:


*on: $eed more experimental data to properlydefine the model and c!rrently no c!rve fitting in

#$S%S.

8etal lasticity cannot be !sed since DSofteningE reC!iresdecrease in stress-strain slope which is not allowed in thismodel and also !nloading slope is same as the loading

slope.7yperelastic models do not show any hysteresis and th!scannot be !sed here.

modeling plastics in ansys [compatibility mode].pdf

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