Learning Forum

[dada taka]

Hello, I am going to analyze a part using Static Structural and the properties of the material of the part change depending on the orientation. For example yield stress L: 530 MPa, LT: 510 MPa.
When I select the Tensile Yield Strengt section I can only enter one data.
How do I define the properties of this material?

[Armin]

Hi Dada,

If you'd like to consider anisotropy in yielding and subsequent plastic deformation of your material, please check the material options available under "Plasticity" menu in the Engineering Data application. 
For example, the Hill yield criterion should be able to resolve the orientation-dependency you're looking for.  

[dada taka]

 

Hi Armin,
As you said, I chose Hill yield Criterion and i see “Yield stress ratio”. What does it mean about ratio ? Also i just have 2 yield stress values depend on rotation ( Longitudinal and Long-Transverse) but here there are x,y,z,xy,yz and xz directions. If I leave it blank, it will continue to look yellow.
And the other case I want to learn how “anisotrophic elasticity” matrix works ? Is it related with my problem ?

 

[Armin]

Hi Dada,
These are the normalized yield stresses with respect to a reference direction. For example, when the yield stress ratio of your material in the x-direction is 1 (530/530), the yield stress ratio in the y direction will be 0.96 (510/530). If you don't know your materials response in some directions, as an initial guess, you can set their behavior to that of an isotropic von Mises material (i.e. tensile stress ratios will be 1 and shear stress ratios will be 0.58). Please check the documentation to learn more about the Hill criterion: 4.4. Rate-Independent Plasticity (ansys.com)

Anisotropic elasticity can also be considered in Ansys Mechanical but for large deformation application, like in metal forming, the anisotropic elasticity is typically neglected since the elastic deformation is a very small portion compared to plastic deformation. Check also more details in the documentation for anisotropic elasticity.

[dada taka]

Hi Armin,

As you said, I fill the blanks as you menitioned. X direction 1, y=0,96 and other paramaters are 1. But as you see in the following picture, there is a question mark near the "Hill Yield Criterion" so I can't define these datas. What is the problem?
Secondly I wonder that for the shear stress ratio, how did you get 0,58 ?
Thanks

[Armin]

The question mark appears because you haven't defined a hardening (stress-strain) curve for your model. You can add the hardening curve using the bilinear or multilinear isotropic hardening models under the Plasticity tab.

The value of (1/sqrt(3) ≈ 0.58) is from the ratio of shear yield stress to tensile yield stress using isotropic von Mises criterion and is just an estimate. If you have experimental data for your specific material, you can use those corresponding values for the shear yield stress ratios.