life extension for a coherent system through cold standby and minimal repair policies for their independent components

We consider life extension for a class of coherent system consisting of independent components with an increasing failure rate functions. the maintenance action is applied in a fixed component called the target component. to this end, the minimal repair and cold standby actions are provided. we also consider two alternative policies for the target component. a component following a new random variable, and another following the same distributions of the target component. these policies obviously increase the reliability and life of the target component and consequently, the life and reliability of a coherent system are also increased. in this regard, the life of the system is also extended. some numerical results considering these life extensions are presented.