Sizing Fuselage Frames using FEA Results
Sizing Fuselage Frames using FEA Results
(OP)
I've run acoss a number of engineers questioning how to use results from FEA models to Size Fuselage frames for bending moment. I've always thought one typically takes Shear loading in the frame between longerons (q lbs/inch) X distance between longerons (inch)==> this gives total shear force (V lbs). Then multiply this total shear X frame depth (dx)to give total Moment (M in-lbs) i.e. M = V x dx. But when shear loads come out of a FEA model that idealizes the frame with outer & inner caps as Rods and the frame web as a membrane (or shear panel), Then the question arises how one relates these Rod loads (lbs) & panel shear (lbs/in) to estimate total moment in the Frame.
What would be nice is a sample problem that illustrates how one can use the FEA results of Rod axial loads and panel shear loads to compute bending moment in the Frame. Any comments out there?
What would be nice is a sample problem that illustrates how one can use the FEA results of Rod axial loads and panel shear loads to compute bending moment in the Frame. Any comments out there?
David R. Dearth, P.E.
Applied Analysis & Technology





RE: Sizing Fuselage Frames using FEA Results
corus
RE: Sizing Fuselage Frames using FEA Results
But regardless, if you have all the internal forces at a particular cross section, it's not hard to find the resulting moment- perhaps tedious if there's a lot of elements.
RE: Sizing Fuselage Frames using FEA Results
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Sizing Fuselage Frames using FEA Results
David R. Dearth, P.E.
Applied Analysis & Technology
RE: Sizing Fuselage Frames using FEA Results
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Sizing Fuselage Frames using FEA Results
David R. Dearth, P.E.
Applied Analysis & Technology
RE: Sizing Fuselage Frames using FEA Results
What I did is to use like what David mentioned to obtain the moment. Now this is the FEM's moment. Besides moment, you'll also have axial loads, which is the summation of the outer and inner chord (idealized as rods) loading.
Depending on the actual sectional properties, you'll have additional moments when you shift the axial loads from the FEM centriod to the actual section's centriod.
As for the shear stress in the web element, I'll use it to check the web for panel buckling.
Using the sectional properties of the frame, Mc/I + P/A will give you the chord's tension and compressive stress. Tension stress is checked against material tensile properties while compression is checked for lateral instability using Johnson-Euler's column buckling check, ref. Bruhn's.
Besides the frame's primary loading, I'll check if the skin has gone into intermediate diagonal tension, as this will dump secondary loads to the frame chords. See Bruhn's Section C11 on curve skins for more insight to the problem.
If I missed out anything, feel free to add.
Gordon