Torsional Stress Calculation for a Rotating Actuator Bracket Design

[Jungyong Ko]

I am designing a rotating actuator bracket similar to the one shown in the diagram below.
To ensure the bracket has sufficient thickness, I need to calculate the torsional stress acting on it. Specifically, I am focused on calculating the stress in the area indicated in the diagram.

Would it be a reasonable approach to use the formula for a "Twin channel with flanges inward" from 'Table 10.2, Roark's Formulas for Stress and Strain 8th edition' to calculate the stress in this case?
If I assume the value of 𝑏1 in the formula to be zero, would this match the cross-sectional shape of the bracket as shown in my design?
I would appreciate any insights or alternative suggestions.

 

[Doug Hunter]

I don't think that your proposed approach will yield what you want. Be careful that your Roark's reference isn't for shear and bending stresses in beams instead of torsional stress. You can analyze the torque capability of your bracket concept at your section surface of concern by calculating the moment of the shear stress around the rotation axis. The 'b'-distances will influence total angular deflection but not the stress levels.

Best regards,
Doug Hunter
Altarium Technical Consulting

https://www.altarium.us/

 

[btrueblood]

What Doug said. Usually the displacement and spring-back of the bracket dominates its design more than the stresses.