Table 5-15. Sensitivity of failure probability to mean value of 82u (CV=0.09) for 0. 12
inch-thick 1(f6)s aminates
Probability of failure from MCS 10,000,000 samples
E(82u)=0.0154 E(82u)=0.01694 E(82u)=0.013 86
24.00 60.5e-6 2.5e-6 1082.3e-6
25.00 56.5e-6 3.4e-6 996.7e-6
26.00 60.7e-6 3.4e-6 1115.7e-6
The failure probability also depends on the coefficient of variation (CV) of 82u. The
CV can be improved if the manufacturing could be more consistent. Table 5-16 shows
that the failure probabilities are not as sensitive to changes of coefficient of variation as
to changes in the mean value of E2u, but 10 percent reduction in the coefficient of
variation can still reduce the failure probability by about a factor of five.
Table 5-16. Sensitivity of failure probability to CV of 82u ( E(82u)=0.0154 ) for 0. 12 inch-
thick (16)s laminates
Probability of failure from MCS 10,000,000 samples
CV=0.09 CV=0.099 CV=0.081
24.00 60.5e-6 209.5e-6 9.8e-6
25.00 56.5e-6 208.2e-6 10.8e-6
26.00 60.7e-6 224.2e-6 11.1e-6
Figure 5-1 combines several effects discussed earlier to show a tradeoff plot of
probability of failure, cost (truncating and changing the distribution of 82u), and weight
(thickness) for a laminate of [ f25]s. For probability of failure less than le-3, quality
control at the -20 level is more effective for reducing the probability of failure than
increasing the mean value by 10 percent or decreasing the coefficients of variation by 10
percent. The reason is that small failure probability is heavily affected by the tails of the