Figure 4-3. Geometry and loads for laminates

The design problem was formulated as (Thickness are in inches)

 minimize h= 4(tz + t2
 such that



 7Y12 I 12
 0.005 <; t,, t2
 0.040 <; h


elastic modulus transverse to fiber direction, E2, and the shear modulus, G12, are reduced

by 20 percent and the transverse strain allowable, 82u, iS increased. The rest of the

laminate must not have matrix cracking and must provide at least 8 contiguous intact

plies (0.04 inch) in order to prevent hydrogen leakage.

Optimization Formulation

 Laminates with two ply angles, [f Bi/f 62 S, See Figure 4-3, were optimized. The x

direction here corresponds to the hoop direction on a cryogenic propellant tank, while the

y direction corresponds to the axial direction. The laminates are made of IM600/133

graphite-epoxy material with ply thickness of 0.005 inch and subjected to mechanical

load and an operating temperature of -4230F. Nx is 4,800 lb./inch and N, is 2,400

lb ./inch.



 N\


X I


(4-9)