I am comparing solutions of linear elastic response of a material in Abaqus explicit with inbuilt model and with VUMAT (Linear Elastic) code on single element.
I am getting almost same results for stress and deformation for both models but Kinetic Energy is high compare to Internal Energy in the case of VUMAT. Can you suggest why this is happening?
Hi Piyush, what kind of linear elastic material model do you use? isotropic? what element do you use? If you are using shell, you should expect differences, but if you are using solid 3D you should get matching result with the abaqus (assuming your code is right).
Romik Khajehtourian Dear sir, thanks for your reply. I am using linear elastic isotropic material with C3D8 element. I am getting matching results for stress and strains but Kinetic and Internal energies significantly different in both cases. here is code which I am using:
VUMAT elastic
subroutine vumat(
C Read only -
1 nblock, ndir, nshr, nstatev, nfieldv, nprops, lanneal,
2 stepTime, totalTime, dt, cmname, coordMp, charlength,
3 props, density, strainInc, relSpinInc,
4 tempOld, stretchOld, defgradOld, fieldOld,
5 stressOld, stateOld, enerInternOld, enerInelasOld,
6 tempNew, stretchNew, defgradNew, fieldNew,
C Write only -
7 stressNew, stateNew, enerInternNew, enerInelasNew )
C
C implicit none
INCLUDE 'VABA_PARAM.INC'
C
C Shim viscoelastic model with nonlinear strain rate
C dependency for bovine cortical bone
C
C All arrays dimensioned by (*) are not used in this algorithm
dimension props(nprops), density(nblock),
1 coordMp(nblock,*),
2 charLength(*), strainInc(nblock,ndir+nshr),
3 relSpinInc(*), tempOld(*),
4 stretchOld(*), defgradOld(*),
5 fieldOld(*), stressOld(nblock,ndir+nshr),
6 stateOld(nblock,nstatev), enerInternOld(nblock),
7 enerInelasOld(nblock), tempNew(*),
8 stretchNew(*), defgradNew(*), fieldNew(*),
9 stressNew(nblock,ndir+nshr), stateNew(nblock,nstatev),
1 enerInternNew(*), enerInelasNew(*)
C
character*80 cmname
C
dimension intv(2)
parameter ( zero = 0.d0, one = 1.d0, two = 2.d0, three = 3.d0,
1 third = one / three, half = 0.5d0, twothds = two / three)
e = props(1)
xnu = props(2)
twomu = e / ( one + xnu )
alamda = twomu * xnu / ( one - two * xnu )
do k = 1, nblock
C Trial stress
trace = strainInc(k,1) + strainInc(k,2) + strainInc(k,3)
stressNew(k,1) = stressOld(k,1)
1 + twomu * strainInc(k,1) + alamda * trace
stressNew(k,2) = stressOld(k,2)
2 + twomu * strainInc(k,2) + alamda * trace
stressNew(k,3) = stressOld(k,3)
3 + twomu * strainInc(k,3) + alamda * trace
stressNew(k,4)=stressOld(k,4) + twomu * strainInc(k,4)
stressNew(k,5)=stressOld(k,5) + twomu * strainInc(k,5)
stressNew(k,6)=stressOld(k,6) + twomu * strainInc(k,6)
end do
return
end
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