CBUSH Rotational stiffness calculation

[sych]

Does anyone have any reference(s) to calculate the rotational stiffness for CBUSH in FEM to account for the moments due to the heel-to-toe effect for a L-angle?

 

[Aerodesign]

Sych, we have been doing some work on this recently. Our customer (large aircraft firm beginning with letter A but they dont make buses), has a methodology requirement that simulates the heel/toe or prying effect of L flanges and angles. We did some work from first principles to derive the appropriate in-line rotational stiffness of the CBUSH element. Trouble is that the number you get out varies hugely depending up the assumptions. I did a quick check of the suppliers we know well and the values of Rx stiffness varied by a factor of 10000 or more.

So the approach we took was to use a more conventional CBUSH plus CGAP FEM approach and then match the shear and pull-thru forces along the flange using variable in Rx. We found a value that matched pretty good, although it differed from other siuppliers assumptions.

I suggest you use a test FEM to make a comparison analysis and then use the value of Rx that gives best correlation.