I am sizing a hypersonic wing structure, with multiple ribs and spars.
The skin is modeled as stiffened panels, ribs and spars are represented by open beams for their caps, and small panels for their webs (like the AP1 tutorial).
If I only optimise this structure for the pressure load case, I get a wing of 50 tonnes (30 for the skin, 20 for the ribs+spars). However, by turning off the buckling failure mode for beams and panels, my weight is reduced to only 17 tons (15 for the skin and 2 for the ribs+spars !).
Since the weight of this wing has been estimated at 15 tonnes (almost the same weight than the case without buckling), I was wondering how I could reduce considerably the weight (in order to get something close to the estimated value of 15 tons) by allowing the buckling failure mode ?
I tried to change a lot of different parameters, but the buckling mode always imposes a very high weight. Did you have any similar behaviour ? If yes, how did you solve it? How could I get rid of this big weight increase due to the buckling failure ?
P.S: Uniaxial and grid stiffened panel families for my wing skin, with T-shape beams for the spars/ribs caps, have been all tested, but the results give the same order of magnatiude. Note that the number of ribs and spars has also been varied (between 3 and 8 ). The X-span and Y-span buckling lengths have also been verified and modified when not correct. The beam orientation seems also right (the same than AP1 when compared graphically).
Thanks a lot.
Regards