abaqus users - johnson cook vumat

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Johnson Cook VUMAT

11 posts

Hi all,

I am trying to write a VUMAT for Johnson cook criteria.With the same

Johnson cook coefficients the model works fine in Explicit but

through VUMAT the analysis terminates in the very begining due toexcessive distrotions of some elements. I am unable to find, where I

have done the mistake in the coding. I am pasting here my VUMAT

subroutine.I shall be thankful If anybody can help

Regards

umer

C

C User subroutine VUMAT

subroutine vumat (C Read only -

* nblock, ndir, nshr, nstatev, nfieldv, nprops, lanneal,

* stepTime, totalTime, dt, cmname, coordMp, charLength, * props, density, strainInc, relSpinInc,

* tempOld, stretchOld, defgradOld, fieldOld, * stressOld, stateOld, enerInternOld, enerInelasOld,

* tempNew, stretchNew, defgradNew, fieldNew,

C Write only - * stressNew, stateNew, enerInternNew, enerInelasNew )

C

include 'vaba_param.inc'C

dimension coordMp(nblock,*), charLength(nblock), props(nprops),

1 density(nblock), strainInc(nblock,ndir+nshr), 2 relSpinInc(nblock,nshr), tempOld(nblock),

3 stretchOld(nblock,ndir+nshr),

4 defgradOld(nblock,ndir+nshr+nshr), 5 fieldOld(nblock,nfieldv), stressOld(nblock,ndir+nshr),

6 stateOld(nblock,nstatev), enerInternOld(nblock), 7 enerInelasOld(nblock), tempNew(nblock),

8 stretchNew(nblock,ndir+nshr),

9 defgradNew(nblock,ndir+nshr+nshr), 1 fieldNew(nblock,nfieldv),

2 stressNew(nblock,ndir+nshr), stateNew(nblock,nstatev),

3 enerInternNew(nblock), enerInelasNew(nblock)C

character*80 cmname

parameter ( zero = 0.d0, one = 1.d0, two = 2.d0, * third = 1.d0 / 3.d0, half = 0.5d0, op5 = 1.5d0 )

CC For plane strain, axisymmetric, and 3D cases using

C the J2 Mises Plasticity with linear hardening.

C The state variable is stored as:C STATE(*,1) = equivalent plastic strain

C STATE(*,2) = plastic strain rate

C C

C User needs to input

Mar 01, 2007; 8:45pm Johnson Cook VUMAT

Abaqus Users - Johnson Cook VUMAT http://abaqus-users.1086179.n5.nabble.com/Johnson-Cook-VUMAT-td106...

1 of 7 1/16/2014 11:17 AM

C props(1) Young's modulus

C props(2) Poisson's ratioC

C e = props(1)

xnu = props(2)

twomu = e / ( one + xnu ) alamda = xnu * twomu / ( one - two * xnu )

thremu = op5 * twomu

* if ( stepTime .eq. zero ) then

do k = 1, nblock

trace = strainInc(k,1) + strainInc(k,2) + strainInc(k,3) stressNew(k,1) = stressOld(k,1)

* + twomu * strainInc(k,1) + alamda * trace stressNew(k,2) = stressOld(k,2)

* + twomu * strainInc(k,2) + alamda * trace

stressNew(k,3) = stressOld(k,3) * + twomu * strainInc(k,3) + alamda * trace

stressNew(k,4)=stressOld(k,4) + twomu * strainInc(k,4)

if ( nshr .gt. 1 ) then stressNew(k,5)=stressOld(k,5) + twomu * strainInc(k,5)

stressNew(k,6)=stressOld(k,6) + twomu * strainInc(k,6)

end if end do

else

do k = 1, nblock

* Finding yield value

* Johnson cook parameters..A=674.8,B=239.2, C=0.027,

n=0.28, m=2.7, Tmelt=1480,Troom=20

if (stateOld(k,2).eq.zero) then yield=674.8

else

A=1+0.027*log(stateOld(k,2)) B=1-((tempOld(k)-20)*0.0006849)**2.7

yield=(674.8+239.2* stateOld(k,1)**0.28)* A*B end if

trace = strainInc(k,1) + strainInc(k,2) + strainInc(k,3)

s11 = stressOld(k,1) + twomu * strainInc(k,1) + alamda *trace

s22 = stressOld(k,2) + twomu * strainInc(k,2) + alamda *

trace s33 = stressOld(k,3) + twomu * strainInc(k,3) + alamda *

trace s12 = stressOld(k,4) + twomu * strainInc(k,4)

if ( nshr .gt. 1 ) then

s13 = stressOld(k,5) + twomu * strainInc(k,5) s23 = stressOld(k,6) + twomu * strainInc(k,6)

end if

* smean = third * ( s11 + s22 + s33 )

s11 = s11 - smean

s22 = s22 - smean s33 = s33 - smean

if ( nshr .eq. 1 ) then vmises = sqrt( op5*


2 of 7 1/16/2014 11:17 AM

(s11*s11+s22*s22+s33*s33+two*s12*s12) )

else vmises = sqrt( op5 * ( s11 * s11 + s22 * s22 + s33 * s33

+ * two * s12 * s12 + two * s13 * s13 + two * s23 *

s23 ) )

end if*

sigdif = vmises - yield

facyld = zero if ( sigdif .gt. zero ) facyld = one

deqps = facyld * sigdif / thremu

** Update the state variable

stateNew(k,1) = stateOld(k,1) + deqps stateNew(k,2) = deqps/dt

stateNew(k,3)=yield

*

* Update the stress

factor = yield / ( yield + thremu * deqps ) stressNew(k,1) = s11 * factor + smean

stressNew(k,2) = s22 * factor + smean

stressNew(k,3) = s33 * factor + smean stressNew(k,4) = s12 * factor

if ( nshr .gt. 1 ) then stressNew(k,5) = s13 * factor

stressNew(k,6) = s23 * factor

end if*

* Update the specific internal energy -

if ( nshr .eq. 1 ) then stressPower = half * (

* ( stressOld(k,1) + stressNew(k,1) ) * strainInc(k,1) +

* ( stressOld(k,2) + stressNew(k,2) ) * strainInc(k,2) + * ( stressOld(k,3) + stressNew(k,3) ) * strainInc(k,3) )

+ * ( stressOld(k,4) + stressNew(k,4) ) * strainInc

(k,4)

else stressPower = half * (

* ( stressOld(k,1) + stressNew(k,1) ) * strainInc(k,1) +

* ( stressOld(k,2) + stressNew(k,2) ) * strainInc(k,2) + * ( stressOld(k,3) + stressNew(k,3) ) * strainInc(k,3) )

+

* ( stressOld(k,4) + stressNew(k,4) ) * strainInc(k,4)+

* ( stressOld(k,5) + stressNew(k,5) ) * strainInc(k,5)

+ * ( stressOld(k,6) + stressNew(k,6) ) * strainInc

(k,6) end if

enerInternNew(k) = enerInternOld(k) + stressPower / density

(k)*

* Update the dissipated inelastic specific energy -

plasticWorkInc = yield * deqps enerInelasNew(k) =

enerInelasOld(k)

* + plasticWorkInc / density(k) end do

end if*


3 of 7 1/16/2014 11:17 AM

Dean Bonorchis-2 Reply | Threaded | More

usamaumer Reply | Threaded | More

return

end

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3 posts

When you calculate:A=1+0.027*log(stateOld(k,2))

you must not use stateOld(k,2) inside the log, you must use

stateOld(k,2)/ref_StrainRate so that the value inside the log is neverless than one.

Also when you do this:

if (stateOld(k,2).eq.zero) then

yield=674.8rather have

if (stateOld(k,2).eq.zero) then

yield=stateOld(k,3)because you may have had plastic straining previously and your yield

surface would have changed.

Further: it is difficult to get this simple explicit method of plastic

strain calculation (deqps = facyld * sigdif / thremu) to work becauseof strain rate effects. Rather use one of the iteration (like ABAQUS)

or linearisation methods (like AUTODYN).

Dean

usamaumer wrote:

>> Hi all,

>

> I am trying to write a VUMAT for Johnson cook criteria.With the same> Johnson cook coefficients the model works fine in Explicit but

> through VUMAT the analysis terminates in the very begining due to> excessive distrotions of some elements. I am unable to find, where I

> have done the mistake in the coding. I am pasting here my VUMAT

> subroutine.I shall be thankful If anybody can help... [show rest of quote]

11 posts

Hi dean

Thanks for reply.

I have ref_strainrate=1...so it will not effect the equation. I have

also tried... yield=stateOld(k,3)...but still the problem persists.

Could you please more elaborate on how to calculate the incremental

plastic strain (deqps) for this problem

Regards

umer

Mar 02, 2007; 12:03pm Re: Johnson Cook VUMAT

Mar 02, 2007; 10:44pm Re: Johnson Cook VUMAT


4 of 7 1/16/2014 11:17 AM

Dean Bonorchis-2 Reply | Threaded | More

--- In [hidden email], Dean Bonorchis <bnrdea001@...> wrote:

>> When you calculate:

> A=1+0.027*log(stateOld(k,2))

> you must not use stateOld(k,2) inside the log, you must use> stateOld(k,2)/ref_StrainRate so that the value inside the log is

never

> less than one.>

> Also when you do this:

> if (stateOld(k,2).eq.zero) then> yield=674.8

> rather have> if (stateOld(k,2).eq.zero) then

> yield=stateOld(k,3)

> because you may have had plastic straining previously and youryield

> surface would have changed.

>> Further: it is difficult to get this simple explicit method of

plastic

> strain calculation (deqps = facyld * sigdif / thremu) to workbecause

> of strain rate effects. Rather use one of the iteration (like

ABAQUS)

> or linearisation methods (like AUTODYN).>

> Dean

>>

> usamaumer wrote:

> >> > Hi all,

> >... [show rest of quote]

same> > Johnson cook coefficients the model works fine in Explicit but

> > through VUMAT the analysis terminates in the very begining due to

> > excessive distrotions of some elements. I am unable to find,where I

> > have done the mistake in the coding. I am pasting here my VUMAT> > subroutine.I shall be thankful If anybody can help

> >> > Regards

> >

> > umer> >

> > C

> > C User subroutine VUMAT... [show rest of quote]

3 posts

Hi Umer,

Even if you have reference strain rate = 1/s you must still have a an IF

statement to prevent the value inside the log from being less than one.It will be less than one whenever the strain rate somewhere in your

model is less than one. If it is less than one then set the log term tozero. There are modified JC models if you want to avoid this eg.

Mar 05, 2007; 10:35am Re: Re: Johnson Cook VUMAT


5 of 7 1/16/2014 11:17 AM

munozcim Reply | Threaded | More

amzir Reply | Threaded | More

(1+ep_rate/ep_rate_ref)^C. You can search the technical reports on the

AUTODYN website to see how they do the linearised form which requires noiteration but includes strain rate effects when calculating deqps.

Search the technical library (www.autodyn.com) for Johnson-Cook and from

the papers select:

"Improved numerical integration of elastic-viscoplastic models withhardening and rate-dependence in AUTODYN"

Dean

usamaumer wrote:

>

> Hi dean

>> Thanks for reply.

>

> I have ref_strainrate=1...so it will not effect the equation. I have> also tried... yield=stateOld(k,3)...but still the problem persists.

>

> Could you please more elaborate on how to calculate the incremental... [show rest of quote]

1 post

In reply to this post by usamaumer

Dear usamaumer,

There is an article describing how to implement Johnson-cook hardening law into Abaqus. If youwant, I could send it to you.

Regards,

Raul

usamaumer wrote

Hi all,

I am trying to write a VUMAT for Johnson cook criteria.With the sameJohnson cook coefficients the model works fine in Explicit butthrough VUMAT the analysis terminates in the very begining due toexcessive distrotions of some elements. I am unable to find, where Ihave done the mistake in the coding. I am pasting here my VUMATsubroutine.I shall be thankful If anybody can help

... [show rest of quote]

This post has NOT been accepted by the mailing list yet.

Hi dears

Would you please help me to find a vumat code for johnson cook and j2 plasticity?thanks a lot

Aug 28, 2008; 4:20pm Re: Johnson Cook VUMAT

Nov 09, 2013; 11:33am Re: Johnson Cook VUMAT


6 of 7 1/16/2014 11:17 AM

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