Learning Forum

[Kariuki Karanja]

Hello,

I am using the Hertz contact to define the contact between the indenter and the sample. I have follwed this video https://youtube.com/playlist?list=PLtt6-ZgUFmMKfcjKvN4Uoc7Z6CP4q8OAU&si=wEcjyGVTDq13Esbc . After running the simulation the indentation caused by the spherical ball is not taking the shape of the sphere. I have used a stiffnes factor of 1, formulation is augmented langrage and the contact friction is zero. The CONTACT element is the specimen and the TARGET is the indenter.

My queries are, why is the indentation not speherical, the indentatio appears to be too small and the hardness number calculated is not corresponding to the theoretical value. 

Finally how do i calculate the tagent modulus for bilinear isotropic hardening.

 

[Ashish Khemka]

Hi,

Can you try refining the mesh and then rerun the model? Also, please the snapshots of the contact results. The tangent modulus is material input and needs to be provided by the user.

 

Regards,

Ashish Kumar

[David Mercier]

Hi, Hertz model is to define pure elastic contact. In your case, you want to extract hardness value from the indentation test and expect to have a residual imprint (corresponding to a plastic deformation). By curiosity, have you define plastic properties for the indented material  for example (at least simple bilinear work hardening law)? Then, is the applied load big enough to deform plastically the tested material? Is the indenter well defined as a rigid body?

[Kariuki Karanja]

Yes I used bilinear isotropic plasticity for the material sample. The Force applied is 500kgf which is 4905N. The force is applied for 10seconds.

[David Mercier]

OK and what is the scale of your indenter. If the indenter size is not well defined, maybe you don't apply enough pressure on the specimen, and thus no deformation observed... 

[Kariuki Karanja]

The size of indenter is 10mm diameter and a force of 500kgf is applied from the top

[David Mercier]

OK, you can easily check here if the stress will be high enough to deform plastically the material. https://amesweb.info/HertzianContact/HertzianContact.aspx

Following what you give in terms of numbers, you achieve a shear stress higher than 1GPa in the specimen at 10% of indentation. Make sure you have the right units (GPa and not MPa for example), to be consistent with the applied load in N and the indenter in m or mm...