Cost models in reliability testing and evaluation

Abstract

This research is concerned with the development of cost models for use in reliability testing and evaluation. Individual models are derived for deferred state life test plans, group/system life test plans, and fixed time life test plans. The objective of this research is to enable selection of a re liability life test plan, through use of the cost models, which will reduce, if not minimize, the overall cost of testing. Two separate and distinct cost models are derived for the deferred state and fixed time life test plans. The first model is developed on the hypothesis that failed items in the test sample are replaced while the second model is derived on the assumption that failed items in the test sample are not replaced. In addition, a cost model is developed for the group/system deferred life plan for the case in which the test system is not replaced when failed. The deferred state life test plan is an addition to the conventional re liability life plans currently in use. Its operating procedure is such that each tested lot is (a) unconditionally accepted, (b) placed in a deferred category pending results of subsequent tests, or (c) unconditionally rejected. Cost comparisons using the aforementioned cost models indicate that this testing concept may reduce overall test costs approximately 30% over conventional fixed time tests. The group/system deferred life test is conducted on one system at a time. The operating procedure of this plan is characterized by the same deferral philosophy as for the deferred state plan. This plan is predicated on the assumption that it is possible for the system to experience multiple failures and yet be acceptable to the consumer.