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)