Reliability analysis using an additive Weibull model with bathtub-shaped failure rate function

Lifetime distributions for many components usually have a bathtub-shaped failure rate in practice. However, there are very few practical models to model this type of failure rate function. In this paper we study a simple model based on adding two Weibull survival functions. Some simplifications of the model are also presented. The graphical estimation technique based on the conventional Weibull plot is demonstrated to be useful in this case.