PSI - Issue 79

Luciano Smith et al. / Procedia Structural Integrity 79 (2026) 275–282

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Figure 6 Importance Factors for the Initial Case at the 5% Probability Level.

3.2. SOLR Analysis From the importance factors, it can be seen that the SOLR variable is an important variable due to the large amount of scatter assumed for the blind prediction. After the blind prediction, the mean test life of 132,626 cycles to failure was provided for the nominal coupon geometry. This allowed us to tune the SOLR variable so that the nominal deterministic analysis matched the test data. This resulted in a mean SOLR value of 2.6 with a much smaller standard deviation from the test data of 0.05. Testing to determine the amount of retardation in a crack growth analysis is widely performed as part of the initial aircraft development process. The analysis was performed again with the new inputs for SOLR. The cumulative probability of failure for the updated SOLR value is added to the graph (Figure 7). As can be seen this reduces the scatter slightly and the nominal life has increased.

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

Probability

0

100,000

200,000

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Cycles to Failure Initial SOLR

Figure 7. Comparing the Cumulative Probability of Failure Between the Initial Case and the Reduced Variability in SOLR Case.