ACCELERATED LIFE TESTS FOR PRODUCTS OF UNEQUAL SIZE

This paper considers 'estimation of the lifetime distribution' and 'op timal design of constant-stress accelerated life test plans' for produ cts of unequal size. The distribution is Weibull with a scale paramete r that is a 'log-linear function of stress' and a 'power function of p roduct size with a size-effect parameter'. Maximum likelihood estimato rs (MLE) of model parameters are obtained, and their properties are st udied. Two stress-level optimal test plans are obtained for products t hat come in two sizes, and a table useful for finding optimal test pla ns is given. The sum of asymptotic variances of MLE of a specified qua ntile of the distributions for products of both sizes is used as the o ptimality criterion. Optimum plans can be used when the ratio of two s izes is not too large. When the ratio is very large, the pre-estimate of size effect parameter should be carefully chosen.