A BSTRA C T
In industrial development it is essential to improve product reliabilio: In this paper some new methods to model reliability improvement and reliability growth process are suggested. Stress-strength modelling is used in considering some interesting issues of an hnprovement process resulting in reliability growth. The reliability is the probability that the strength of the product is greater than the working as well as environmental stress. An)" improvement of product reliability at the production stage may be considered as the increase of the strength distribution using artificial heredity, as Dr van Otterloo suggested in a recent editorial. The increase in strength may usually be modelled by some changes to the parameters of the strength distribution. Generally the mean strength may be increased to get greater reliability. Also in man)" practical situations an improvement may be achieved by reducing the strength t'ariation; this is in line with Taguchi's ideas for quality improvement. Some explicit expressions are derived for calculating these effects, assuming normally distributed stress and strength.