When the pore part elements were not removed (A model), the results were very close to the analytical formulas.
However, when the pore part elements were removed (B model), the mechanical properties results were almost same as those of solid (C model).
To verify this, I created a geometry in ANSYS APDL (D model) and applied the same boundary conditions.
However, the mechanical properties results of the D model were also same as those of solid (C model).
I wonder that is it possible to recognize pore (air) in ANSYS APDL or do I have to assign pore parts as air?
If the boundary condition is not the cause, I think that for my project, it is appropriate to keep the pore part elements and assign mechanical properties close to zero.
Please refer to the below figure:
So, how to
I didn't look at the pictures, but in general in ANSYS APDL, you can assign different mechanical properties to different parts of your model, including the pore space. If you want to keep the pore part elements and assign mechanical properties close to zero, you can assign a low Young's modulus and Poisson's ratio to the pore space.
To assign the pore space as air, you can use the DEFINE MATERIAL command in ANSYS APDL. This command allows you to define a material with specific mechanical properties, including Young's modulus, Poisson's ratio, and density. You can assign a low Young's modulus and Poisson's ratio to the air material to represent the pore space. Then, you can assign this air material to the pore part elements in your model.
Alternatively, you can also use the DEFINE PROPERTY command to assign specific mechanical properties to individual elements or element groups in your model. This allows you to assign different mechanical properties to the solid and pore parts of your model.
If you have already assigned mechanical properties to the pore space in your model, but the results are still similar to those of the solid model, it is possible that the boundary conditions are the cause. It is important to ensure that the boundary conditions are appropriate for the specific problem being analyzed.
Rather than removing elements you should try to introduce the pores in the original CAD model and then remesh. Removing elements from a meshed model is a bit more tricky, because essentially you have to 'deactivate' them rather than delete them which means that they don't impart a stiffness when loaded yet can still be subjected to forces.
This method has always worked for me with APDL. Also, be sure to check that the measurement of the Young's modulus is done correctly - even if the pore is introduced, the cross-sectional area of the system remains the same as that of the solid system.
I am curious about the boundary conditions. If there was something like pressure on area, the results could look as if the material had no pores (decreased area -> decreased load).
Another important factor is how do you calculate equivalent moduli of the porous material. Do you use full areo or the reduced (porous)?
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