Learning Forum

[lavansy]

Hi everybody,

I have to study a transversely isotropic material in ansys apdl. My material is a (unidirectional) composite, but I only know the mechanical properties of composite, and I don't know the fiber and matrix properties. In the direction of fibers I have an elastic modulus that it's the same in compression and tension (about 10GPa). Instead, in the other two directions the behavior is the same, but the elastic modulus is different in tension(5GPa) and compression (2GPa).

I didn't find any solution in the range of elasticity. 

I have tried with TB,ANISO which permits a different behavior in plastic zone in compression and tension and it's anisotropic. Setting a low yield strength I thought it could works. (with SOLID95)

But there is a problem, because it always appears errore: "TB,ANISO table has anisotropic yield stresses that not longer satisfy the consistency equation. Make the slopes more equal or possibly use a smaller time step". I have changed yield strength and elastic moduli, tangent moduli and time step but it doesn't work. Anyway the solution doesn't stop immediately. After some iterations (depending on the moduli and yield strength) it's stop and the error is "Errore in element formulation". Model goes over elastic behavior, so it makes some iteration in plastic zone, but then it stops.

Is there a model models more suitable? I have seen anisotropic elasticity in the linear material properties, but it doesn't have different behavior in tension and compression.

Or is it possible to fix the ANISO model?

Thanks.

 

[Sandeep Medikonda]

What version are you using?

TB, ANISO is no longer supported. Are you referring to TB, ANEL? 

Also, please use the newer elements types such as SOLID 185/186 which are more robust.

How to access the ANSYS Online Help

[lavansy]

I'm using 17.2 and 18.2. 

I'm using TB,ANISO (anisotropic plasticity), and it appears to work for small loads. I have used SOLID 95 because SOLID 185/186 can't be used with TB,ANISO I think. 

TB,ANEL is anisotropic elasticity which doesn't differs from tension and compression, am I right?

 

[jj77]

TB,ANISO defines only the stress strain curve thus the plastic response, not the elastic modulus in different directions (and tens/comp.), like you want.

TB,ANEL, there is no distinction of tension compression a far as I can see.

 

In ABAQUS to do what you need one uses subroutines (USDFLD) and field variables to show say how Young's modulus varies with stress state. Something like that might be possible using user defined field variables in Ansys - see help manual on user defined material and subroutines. Not sure though never used this in Ansys, but I think one can use userfld subroutine and some calls like ensget to get stresses, and then relate the stress state (say some measure, perhaps a signed VM stresses so you know if it is in comp. or tens.) and then use that to define the Young's Modulus.