Average shear stress

[shearlag]

Dear all,
I do have a general model of nose box. The spar web has a cutout. But FE model does not have it. The web has around 18 CSHELL elements between two stiffeners. The shear flow values vary from 30 N/mm to 150 N/mm. My doubt: Should I take max shear flow or average shear flow or…(no idea) to check the cut hole doubler ring thickness and width (Michael Niu equation in Ch.CUTOUTS has been used ). Initially I took max shear flow for being on safer side and the bending stresses +tensile stresses in the ring was twice the material UTS.(aluminium). If I take average I am getting net stress moderately . Is it ok if I consider avg of all the vertical elements on either side of stiffener. Or if I take avg shear stress * thickness … Then how to plot avg shear stress……Kindly clarify…
Thanks in advance

 

[rb1957]

i'd take the average of the elements cut. else use bruhn (webs with lightening holes) to calculate the reduced allowable for the hole. this could reasonably (IMHO) be applied at the average of the panel shear stresses.

and you might do a local principal stress (or vM) to clear the shear stress hot spot.

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[shearlag]

Yes I tried bruhn, but got low net stress. Moreover in my problem its 2mm thick machined rib web with 5 mm thick doubler. I think the graphs are valid for lightly loaded shear webs, ( ribs formed from sheet metal). I shall try with averaging the element shear flows across the web section. Thank you rb

 

[rb1957]

Favbel has a good write up on webs reinforced with doublers

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