Discussion on the paper <>

The Discussers illustrate an analytical solution to the general form of a “Stress-Strength Model”, by which the reliability function of an insulation device, for a given mission time t. The Authors find that the solution of the Discussers is correct, but point out that the primary purpose of discussed paper was not solving a general Stress-Strength Model, but finding reasonable physical-probabilistic motivations for explaining the phenomenon of decreasing hazard rate functions, a property which has been sometimes observed also for insulating materials. This led the Authors to use a Log-logistic RF based upon a Stress-Strength Model, “resorting to strong simplifying hypotheses that, strictly speaking, could hold only in a few cases”, as clearly written in the discussed paper. In conclusion, the Authors are interested in an engineering – not mathematical – approach, which must be based on few parameters, while the expression derived by the Discussers is rather cumbersome and contains too many parameters to be useful in practice.