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Hello everyone.

I am trying to do something with the deformation gradient in UMAT. I used F=DFGRD0 as the gradient. but i found that it always comes to be a identity tensor not only for the case of a 3d isotropic elastic material but also for the ramberg osgood model. it was very surprising for me so i also tried to print DFGRD1 it was also identity tensor.

I have used a C3D8 single element and was doing the uniaxial test. Please help me out with this.

In Classical Continuum Mechanics, the entropy(s) and temperature(T) are considered to be dual in the second thermodynamics principle,

by define a relation between internal energy(e) and Helmhotz free energy(ψ): ψ = e - s * T .  As you can find it in many CM books, such as [2008][J.N.Reddy]Introduction to Continuum Mechanics.

Here is my questions:

1. Is the transformation between internal energy and Helmhotz free energy a Legendre Transform?

I am trying to model a simple compression test (50% reduction in height) using Abaqus.

So for this, I have a lower die, Specimen and an upper die.

The dies are modeled as deformable, and I've also added reference points to both the dies so that I can add a rigid body constraint to both of the dies.

For the boundary condition, I've fixed the top die and for the lower die I've applied a velocity of 10. 

I'm unable to get a 50% reduction in height. Can someone please help me with this?

I am using cohesive elements coupled with USDFLD subroutine. I have a damage variable in my subroutine, which according to the calculations is updating in a correct way. But my problem is that SDEG is not updating, hence the elements are not being deleted. I have called the STATUS variable and that is also not updating. Can anybody provide some help?

Hello everyone,

In mixed-mode CZM in Abaqus, it seems that the fracture load in not sensitive to mode II fracture energy as the cohesive elements undergo mostly opening deformation. However, when I model elastic properties for the material, it undergoes both opening and shear displacements. It means CZM elments don't model the deformation properly. Even change in relative stiffness couldn't solve the issue. Has anybody faced this problem? If CZM elements cannot represent the deformation well, what have people done in the literature to find the failure load for mixed-mode loading?

Dear all,

I have a dummy question, but it seems there is no universally accepted answer. For a general structure subject to a cyclic loading with constant ampitude, we use FEA program to run stress analysis under peak and valley load point respectively. Now, we need to post process the FEA result to come up with the stress range that will be plugged into S-N curve to come up with a "N" value.