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Rotational Stiffness

Rotational Stiffness

(OP)
Dear All,

I am trying to calculate the rotational stiffness of a front knuckle.  I applied three seperate 1Nm torques at the wheel center in X,Y,Z.  I constrained the UBJ and LBJ in 1,2,3 and the OTR in 2.

The analysis runs fine, but I am having a hard time determining what the true rotation is to use to calculate the rotational stiffness.  My post process gives me rotational vector and magnitude but I am not sure that is the right value to divide into the torque.

Should I use the maximum values of rotation or the rotation only in the plane normal to the induced moment?

Should I use some node that is linked to the wheel center and project it back to a common plane and measure the angle.

Also, the rotation is not about the wheel center because the part is not symmetrical.

The rotational values I am getting are extremely low like  4.5e-5 rad for a 1Nm torison input.  It seems very stiff to me for cast iron.

Any help would be appreciated.

Thanks

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