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Type: Posts; User: matsgd

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1. ## Thread: Visco-elastic model in ABAQUS

by matsgd
Replies
2
Views
941

### I haven't used this... but, there's a Prony...

I haven't used this... but, there's a Prony series viscoelastic model in ABAQUS, if I am not mistaken. You should be able to specify the shear relaxation modulus in ABAQUS so that it follows your...
2. ## Thread: Error with one simple UMAT code for isotropic material

by matsgd
Replies
2
Views
896

### Print DSTRAN and DSTRES and make sure your...

Print DSTRAN and DSTRES and make sure your routine does the right thing.
3. ## Thread: Periodic boundary conditions in ABAQUS

by matsgd
Replies
21
Views
12,308

### You'd have to use multi-point constraints. But...

You'd have to use multi-point constraints. But the easiest way to do what you need to do is to write a piece of Matlab code in which you construct a regular, nice, mesh on the surface of the cube,...
4. ## Thread: Periodic Boundary Conditions

by matsgd
Replies
2
Views
1,151

### Sounds like a sign error in the constratint...

Sounds like a sign error in the constratint equation. If you're using *EQUATION to accomplish this, be advised that all terms are on the lefthand side of the equation, meaning that a constraint A=B...
5. ## Thread: problems in vumat for beam element

by matsgd
Replies
8
Views
1,499

### Ziguo, The strain increment is used by ABAQUS...

Ziguo,

The strain increment is used by ABAQUS to estimate a globally stable time step. Without going into detail (mostly because I really don't know these things well enough!), the stable time...
6. ## Thread: questions about computing strain in VUMAT (plane stress condition)

by matsgd
Replies
4
Views
953

### I *think* that F is also, in fact, in the local...

I *think* that F is also, in fact, in the local coordinates of the element. You should not use the 33 component of F, I think (not sure what it contains when passed to the VUMAT). Instead, F(3,3)...

by matsgd
Replies
4
Views
569

Mats
8. ## Thread: questions about computing strain in VUMAT (plane stress condition)

by matsgd
Replies
4
Views
953

### Is this a a case of plane stress then? What...

Is this a a case of plane stress then?

What strain measure are you trying to calculate? If you are trying to calculate the Green-Lagrange strain, then do it this way:

E=0.5*(U*U - I)=0.5*(F^t*F...
9. ## Thread: RHS in VUEL

by matsgd
Replies
1
Views
601

### The internal force vector of a solid element is...

The internal force vector of a solid element is given by
F=integral(BL^T*sigma)dV

where BL is the linear strain displacement matrix, and sigma is the stress tensor. In a UL formulation, BL is...
10. ## Thread: problems in vumat for beam element

by matsgd
Replies
8
Views
1,499

### 1) Not an expert on beams, but in general,...

1) Not an expert on beams, but in general, stresses are given by the elastic strains and the elastic moduli. Take a look at Hooke's law for the 3-D case, and impose sig22=sig33=0. Then you should get...
11. ## Thread: problems in vumat for beam element

by matsgd
Replies
8
Views
1,499

### No, they are the transverse normal strains, i.e....

No, they are the transverse normal strains, i.e. affecting the thickness of your beam. And, no, ABAQUS does not do this by itself, because it cannot. The transverse normal STRESSES are, by...
12. ## Thread: UMAT - problems with memory allocation?

by matsgd
Replies
4
Views
569

### It must be that your argument list in the UMAT is...

It must be that your argument list in the UMAT is incorrect, or something along those lines. I notice that there are spaces that separate certain variable names. Is that ok? I don't know. By the way,...
13. ## Thread: Hyperelastic PMMA - convergence issues

by matsgd
Replies
3
Views
1,001

### I agree! Consider the case of imposing a...

I agree! Consider the case of imposing a deformation such that I2=0. Does it seem alright to produce a negative strain energy..?
Mats

by matsgd
Replies
2
Views
451

### Be more specific. Give us a piece of your code so...

Be more specific. Give us a piece of your code so that we can take a look at it...

M
15. ## Thread: Polycrystal Shape Memory Alloys

by matsgd
Replies
4
Views
909

### Here's a suggestion: Print, to a text file,...

Here's a suggestion:

Print, to a text file, the stress at some time t+dt, and the six stress vectors corresponding to the perturbed states. Then post them here. Let's take a look at it all.
Also,...
16. ## Thread: UMAT anisotropic elasto-plastic material

by matsgd
Replies
20
Views
4,998

### Yes, that won't work. Here's why: The *PLASTIC...

Yes, that won't work. Here's why: The *PLASTIC assumes that plastic flow is incompressible, i.e. plastic volumetric strains remain zero, and the plastic behavior only depends on the deviatoric part...

by matsgd
Replies
2
Views
551

### No it is not possible. In a VUMAT, however, it is...

No it is not possible. In a VUMAT, however, it is possible to deactivate elements (integration points).
Mats
18. ## Thread: UMAT anisotropic elasto-plastic material

by matsgd
Replies
20
Views
4,998

### This is steel? With a factor of 35 between...

This is steel? With a factor of 35 between tensile and compressive yield stresses? Do you have some more info on it?

Mats
19. ## Thread: UMAT anisotropic elasto-plastic material

by matsgd
Replies
20
Views
4,998

### You need to use one of the material models with...

You need to use one of the material models with pressure dependent yield surfaces / flow rules. Examples are the Mohr-Coulomb and Crushable foam models.

Mats

by matsgd
Replies
1
Views
284

### *depvar 1 ... allocates memory for one state...

*depvar
1

... allocates memory for one state variable that your UMAT can use. The length of STATEV is 1, since NSTATV = 1 in this case (in the UMAT).
21. ## Thread: subroutine of URDFIL

by matsgd
Replies
4
Views
635

### The code uses the utility routine DBFILE to read...

The code uses the utility routine DBFILE to read from the .fil-file. Each time the DBFILE is called, it reads one record, which is an array. This array contains values, both integers and double...
22. ## Thread: subroutine of URDFIL

by matsgd
Replies
4
Views
635

### The dimensions of ARRAY and JRRAY are given so...

The dimensions of ARRAY and JRRAY are given so that they'll match the sizes that the various utility routines require. See the examples in the URDFIL documentation. The equivalence statement is used...
23. ## Thread: ABAQUS UEL post processing..

by matsgd
Replies
1
Views
916

### And one more thing before I start anything. The...

And one more thing before I start anything. The UEL documentation states, regarding the force vector RHS, that

"For most nonlinear analysis procedures, NRHS=1 and RHS should contain the residual...
24. ## Thread: ABAQUS UEL post processing..

by matsgd
Replies
1
Views
916

### ABAQUS UEL post processing..

... is it possible?

I realize that nodal dofs can be tied to dummy elements, provided that there IS a standard element with the same topology. But what about integration point values? Is there a...
25. ## Thread: Use URDFIL subroutine to extract data

by matsgd
Replies
2
Views
986

### I don't have time to run your problem, but I...

I don't have time to run your problem, but I notice that you're assigning elements of ARRAY to integers (KD1, KD2, KD3). Instead, use names for the output starting with (A-H,O-Z), or simply replace
...
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