Parameter compatibility relations for accelerated testing

It is pointed out that the use of acceleration studies implies that stress does not change the mechanisms of failure but only contracts the time to reach failure level. This implication is translated into a requirement that the parameter set for the failure distribution does not change, but values of the parameters may. The generality of the relationship between parameter values at various stress levels and the time transformation that connects the respective distributions is emphasized. These are termed compatibility relations. An example of compatibility relations for acceleration studies described by a Weibull distribution is given in detail. The compatibility relations between the coefficients in the time transformation in acceleration studies based on exponential, gamma, log-normal, and Weibull distributions and respective parameter values are discussed generally. Compatibility relations can be used to improve estimation procedures, check the consistency of parameter estimation during analysis of acceleration test data, and check the validity of the use of acceleration studies in the first place