Effects of Structural Tests on Aircraft Safety

摘要

This paper presents amethodology to investigate the effects of structural tests on aircraft safety. In particular, thenpaper focuses on the effect of the number of coupon tests and structural element tests on the final distribution ofnfailure stress. Themean failure stress is assumed to be predicted by a failure criterion (e.g., Tsai-Wu), and the initialndistribution of thismean failure stress reflects the uncertainty in the analysis procedure that uses coupon test data tonpredict structural failure. In addition to the uncertainty in the mean failure stress, there is also uncertainty in itsnvariability due to the finite number of coupon tests. Bayesian updating is used to update the failure stress distributionnbased on results of the element tests.AMonteCarlo simulation of a large number of uncertainties and the possible testnresults are used to obtain the probability of structural failure in a certification test or in actual flight. Incorporatingnthe Bayesian updating into the Monte Carlo simulation loop is computationally prohibitive; therefore, a surrogatenprocedure is devised to overcome the computational challenge. A structural design following the Federal AviationnAdministration regulations is considered, and the tradeoffs between the number of tests and the weight andnprobability of failure in the certification test and in service are explored. To make this tradeoff analysisncomputationally affordable, response surface approximations are used to relate the knockdown factor to thenprobability of failure in service and in the certification test. It is found that it is possible to do a simultaneouslynprobabilistic design and satisfy the Federal Aviation Administration regulations for deterministic design.