en قابلیت اطمینان Reliability and Maintenance پژوهشي Research <pre style="margin: 0px; text-indent: 0px; text-align: justify;"> <span style="font-size:12pt"><span style="text-justify:inter-ideograph"><span style="line-height:115%"><span style="tab-stops:center 240.0pt right 475.0pt"><span style="font-family:Calibri,sans-serif"><i><span new="" roman="" style="font-family:" times="">A periodic maintenance policy through either an imperfect repair or replacement is proposed for a repairable system. It is assumed that the system is subject to an inverse Gaussian degradation process. The effect of imperfect repair is modelled through both arithmetic reduction of degradation and arithmetic reduction of age approaches. The degradation level of the system is measured after each imperfect repair in periodic time intervals. The system is replaced if its deterioration level exceeds a pre-determined technical threshold or at the </span></i><m:omath><i><span cambria="" math="" style="font-family:"><m:r>n</m:r></span></i></m:omath><i><span new="" roman="" style="font-family:" times="">th inspection time, whichever occurs first. The main goal of the paper is to find the optimal value of </span></i><m:omath><i><span cambria="" math="" style="font-family:"><m:r>n</m:r></span></i></m:omath><i><span new="" roman="" style="font-family:" times="">&nbsp;based on expected cost rate function. Some theoretical results are derived and then the optimal policy is obtained numerically. The effect of imperfect repair, the inspection time interval, the value of technical degradation threshold, and the costs of interest are all studied on the optimal policy. </span></i></span></span></span></span></span> </pre> Cost function,Inverse Gaussian process,Maintenance,Reduction of degradation (age) model 29 38 http://ijiepr.iust.ac.ir/browse.php?a_code=A-10-3053-1&slc_lang=en&sid=1 Khatereh Rajinia kh.rajinia@mail.um.ac.ir 1800319475328460013412 1800319475328460013412 No Department of Statistics, Faculty of Mathematical Sciences, Ferdowsi University of Mashhad, P. O. Box 1159, Mashhad 91775, Iran Mostafa Razmkhah razmkhah_m@um.ac.ir 1800319475328460013413 1800319475328460013413 Yes Department of Statistics, Faculty of Mathematical Sciences, Ferdowsi University of Mashhad, P. O. Box 1159, Mashhad 91775, Iran