Simultaneous optimization of an unstiffened aircraft panel and the number of structural tests by using probabilistic methods

The safety of aircraft structures can be achieved by designing the structure against uncertainty and by taking steps to reduce the uncertainties. Safety factors and allowable material properties are the measures for compensating uncertainties, while coupon tests, structural element tests, quality control, inspection, health monitoring and maintenance are uncertainty reduction measures. In this paper, only structural tests are considered among these uncertainty reduction measures. A represantative unstiffened aircraft panel is considered and the effects of the structural tests on aircraft panel?s structural reliability are investigated and aircraft panel?s thickness and the number of structural tests are simultaneously optimized. Structural uncertainties and future tests are modelled, probability of failure in certification testing and probability of failure during service life are computed through Monte Carlo simulations. Then, aircraft panel thickness and the number of structural tests are simultaneously optimized for minimum life time cost by using probabilistic methods. The effect of weight penalty factor on the obtained results are investigated. The value of the weight penalty factor is varied in the reasonable range based on other works in literature. The results show that optimization results depend heavily on the weight penalty factor. Optimal number of coupon tests is determined 80 (upper limit in the work) and found to be independent of the weight penalty factor. The reason for this is argued to be the very low cost of the coupon tests. Optimal element test changes from four to five and depending on the weight penalty factor. Finally, probabilistic design optimization problem is solved for minimum probability of failure besides minimum operational life time and similar results are obtained.