The simplest models of repairable systems reliability are based on either the maximal or perfect repair assumption (good-as-new) or the minimal repair assumption (bad-as-old). In practice these assumptions are not always fulfilled. However, the models may be adequate for some purposes. SOmetimes the degree of repair has to be considered. The term repair should be interpreted in a wide sense. It can refer to a concerete repair action, a restoration, or a thorough modification. THe state of the system after the repaire will often be intermediate between good-as-new and bad-as-old, but may also be outside these limits. The purpose of this paper is to describe somm imperfect repair models. The various types of models are compared with respect to the shape of intensity, or rate of occurrence of failures, and with respoect to the possibility of field data collection and analysis.
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