1 Modeling the Effect of Structural Tests on Uncertainty in Estimated Failure Stress

This paper investigates the effects of the number of coupon and element tests on uncertainty in element failure stress. In aircraft structural design, failure stress is first obtained from coupon tests, which is then used in predicting failure stress of structural element under combined loads. The mean and standard deviation of failure stress are expressed as a distribution due to errors in failure theory and variability due to finite number of coupon tests. This paper focuses on identifying the effect of the number of coupon and element tests on the distribution of failure stress of structural element. This paper assumes isotropic properties and the failure stress of structural element is assumed to be predicted by a failure theory (e.g. Von Mises), and initial distribution of this failure stress reflects uncertainties. Bayesian updating is used to reduce the uncertainties in the initial failure stress distribution by using element tests. The relation between the number of tests and the level of uncertainties is presented for a simple test case. I