I need to sharpen the pencil regarding a spar to skin joint analysis.
I have a global fem with CQUAD elms for the spar webs and skins and rod elms for the spar caps and stringers. There is one skin element between stringers.
I already have a freebody force extraction in Patran for the spar elms and one skin elm that gives me P,V,M for the spar and skin (i.e. half of the skin to the first stringer is included in this section cut).
Currently the spar cap to skin joint is stress based on q=V/h (h, section height) - easy and conservative.
I am considering using q=VQ/I to get the running load at the spar cap to skin interface, my questions are:
1. What skin area to put in the Q and I calculations, (a) half the distance to the first stringer (b) half the distance to the rear spar.
2. As the box is loaded in bending and torsion is the VQ/I unconservative for the portion of the vertical shear V due to torsion.
3. If so how could I calculate V_bending and V_torsion from the global FEM.
There are other ways I could stress this joint, i.e. using freebody forces from the skin but I'd like to understand if I have options to use the P,V,M section forces already extracted as this will cut down on the rework.