where b, h, tl and tz are the design variables; W is the weight of the panel; P"=10-4 is the
limit on the probability of failure, P. The four design variables are b, h, tl and tz.
Geometric imperfections such as global, local, inter-ring, and general ovalization
of cylindrical panels are taken into account in PANDA2 software directly by specifying
the geometric imperfection amplitudes as shown in Table 8-1.
Table 8-1. Amplitudes of geometric imperfection handled by PANDA2 software
.Buckling modal general
Out of roundness (in) Initial local amplitude (in)
amplitude (in)
0.8 0.8 0.008
Uncertainties
The material used in the study is Al 2219-T87, which has a density of 0.1 lb/in3
Two for elastic properties (Young's modulus E and Poisson's Ratio pu) and the strength
allowable o are assumed to be normally distributed and uncorrelated random variables
with mean values and coefficients of variation shown in Table 8-2.
Table 8-2. Uncertainties in material properties (Al 2219-T87) modeled as normal random
variables
Young's Modulus (E) Poisson Ratio (pu) Stress Allowable (4,)
Mean value 0.107x10s psi 0.34 0.58x105 psi
Coefficient of
0.03 0.03 0.05
variation
Table 8-3. Uncertainties in manufacturing process modeled as uniformly distributed
random design variables around design (mean) value
b h tl tz
Percentage
il % +2% +4% +4%
variation
The four design variables (b, h, tl and tt) are also random around design (mean)
value due to manufacturing uncertainties. They are assumed to be uniformly distributed
with percent variation shown in Table 8-3. These data are intended only for illustration.