Shock Models and Wear Processes

The life distribution H (t) of a device subject to shocks governed by a Poisson process is considered as a function of the probabilities Pₖ of not surviving the first k shocks. Various properties of the discrete failure distribution Pₖ are shown to be reflected in corresponding properties of the continuous life distribution H (t). As an example, if Pₖ has discrete increasing hazard rate, then H (t) has continuous increasing hazard rate. Properties of Pₖ are obtained from various physically motivated models, including that in which damage resulting from shocks accumulates until exceedance of a threshold results in failure. We extend our results to continuous wear processes. Applications of interest in renewal theory are obtained. Total positivity theory is used in deriving many of the results.