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[Jana Rittelmann]

I defined a body-to-ground revolute joint for one of my components. In the details window, the torsional stiffness of the joint can be defined which, by default, is set to 0 Nmm/°. From my understanding, the torsional stiffness refers to the ability of an object to withstand a torsional load and can be calculated by using the shear modulus of the material, the length of the object and its torsional moment of inertia which is calculated from the cross-sectional geometry.

Now, in Ansys, the geometry is already given and I wondered why Ansys does not calculate the torsional stiffness itself and instead assigns a default value of zero? In which cases does it make sense to actually use the default value and when do I need to change the torsional stiffness value to one I calculated myself beforehand? I hope somebody can clarify this for me. Thanks in advance! 

[Aniket]

In Ansys, the torsional stiffness of a joint is indeed a measure of the resistance of a shaft to a twisting or torsional force. This property can be added only for cylindrical and revolute joints: https://ansyshelp.ansys.com/Views/Secured/corp/v232/en/wb_sim/ds_Joints_manual.html

The default value of zero for torsional stiffness implies that the joint is perfectly flexible, which is a common assumption in many engineering analyses when the stiffness of the joint is not the primary concern.

However, if the torsional stiffness of the joint is significant to your analysis, you should input the value you calculated. This could be the case if you are studying the dynamic behavior of the system, or if the joint stiffness could influence the stress distribution or deformation in your component.

In other words, whether you should use the default value or input your own depends on the specifics of your analysis and the importance of the joint stiffness to your results.

-Aniket

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[Jana Rittelmann]

 

Thank you for your explanation. I do think I need to take into account the torsional stiffness in my case.

One more question: I am trying to calculate it for my component. For that I want to use the following formula for the torsional stiffness k: k=GJ/L, G being the shear modulus, L being the beam length and J being the torsional moment of inertia.

Is it correct that I can find the torsional moment of inertia of my component by the following process: 

 

• conducting a static structural analysis of said component with a fixed support on one end and applying a moment on the other end
• going into the solution information and searching for the total inertia about center of mass (which represents the inertia tensor)
• taking the I_zz entry of the tensor (lower right corner) as the torsional moment of inertia around the z axis?