Actually, I am wondering if I can request the (∆σ)change of stressfor all integration points in Abaqus analysis through Umat ? As I can request stresses and strains and change in strains as well.
Many thanks
Yes, you can do that. Just calculate the stress using your constitutive law and the strain increment but you need to set your stress variable equal to zero every time. See the code below (for composite material)
do 10 i=1,3
do 20 j=1,3
ddsdde(i,j) = 0.0;
20 continue
stress(i) = 0.0;
10 continue
ddsdde(1,1) = E11 / (1.0-(nu12*nu21))
ddsdde(2,2) = E22 / (1.0-(nu12*nu21))
ddsdde(2,1) = (nu21*E11 / (1.0-(nu12*nu21))
ddsdde(1,2) = ddsdde(2,1)
ddsdde(3,3) = G12
stress(1) = ddsdde(1,1) * dstran(1) +ddsdde(1,2) * dstran(2) +ddsdde(1,3) * dstran(3))
stress(2) = ddsdde(2,1) * dstran(1) +ddsdde(2,2) *dstran(2) +ddsdde(2,3) * dstran(3))
stress(3) = ddsdde(3,1) * dstran(1)) +ddsdde(3,2) * dstran(2) +ddsdde(3,3) * dstran(3))
You will only calculate the stress increment. Off course, if you need to calculate the total stress, you will need to use other variable for the stress increment, for example, call stressinc.
Thanks Marcelo for your kind answer.
Basically, I am looking to get dstress (dS11) and I can get stresses and strains at each increment. I do not know with the attached Umat (for linear elastic) I can not request DSTRESS (dS11) !!
Also, when I request (dstrain) , I have got values at strains = 0 ?
Thank you for your help.
Hi,
I did not see any problems with your umat (IF YOUR NTENS =1).
Try to write only DSTRESS(1).
open(105,file='C:\Temp\aA.txt',position='append')
WRITE(105,*) NOEL,KINC, S11,dS11, DSTRESS(1).
Regarding your question about zero values, you will always obtained zero values for the first increment (zero load or displacement), unless you define some pre-load.
regards
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