Error in VUMAT

[chindan]

Hi all,

I am running a VUMAT and i found this error. The problem is that when i ran a similar VUMAT earlier i have not encountered this error. Could anyone please shed some light on this.

The error message is the following:
***Error: Bad Material definition: zero or negative initial dilatational modulus caused by bad material data. Please check your material input and any initial conditions if necessary.

Now the error message i understand and i checked my definition of the modulus and it is definately not zero (112 GPa). This is input in the input file as one of the properties. So in my VUMAT, E=PROPS(1).

Thanks for any advice

[Jorgen]

Does the error occur right away during the first increment, or later in the simulation?

That is a curious error message that I have never seen before. I would print out the stress calculated by the VUMAT to make sure it is what you expect.

- Jorgen

[chindan]

Right the error occurs right away before any time increment. I printed out the stress values and they are negative due to the strainInc which shows a value of -2.0e-3, so this is quite strange as i checked my VUMAT and i could not find a place where i am setting the strainInc to be that particular value.

Maybe i need to add another step wherein for stepTime = 0, strainInc = 0. Possibly this might make it work. Can you think of any other reason.

Thanks,

[chindan]

Nice after doing the aforementioned wherein i set the strainInc to be 0.0 at stepTime=0.0 i get an ABAQUS error code 696.

[Jorgen]

strainInc is an input vector that should not be modified from within the VUMAT.

Before starting the simulation, Abaqus/Explicit calls the VUMAT with a fictitious strain increment to check that the VUMAT gives a reasonable response. I recommend that you print the input strains and the calculates stress response in order to verify that the predictions make sense.

- Jorgen