Statistical analysis of multistress aging studies of polyetherimide

Multistress accelerated aging experiments on polyetherimide (PEI) film were conducted by applying a combination of accelerated thermal and electrical (400 Hz) stresses in a full factorial experiment. Weibull and lognormal distributions are used along with general goodness-of-fit measures, the Shapiro-Wilk, W test, and the Shapiro-Brain, W´test, to assess the statistical distribution of the lifetimes for all stress combinations. To detect significant interaction between the individual stresses and quantify the effect of each stress on the life of the film, an analysis of variance is conducted. The obtained mean life data are then fitted to various existing empirical multistress aging models to suggest the most statistically significant among the tested models. It is shown that either the Weibull or the lognormal distribution can estimate statistical mean within a range of acceptable linearity. The goodness of fit measures, W test and W´ test, also consistently support the hypothesis and provide no evidence of rejecting either as an adequate statistical distribution