on possibility of extending the optimal replacement time of series and parallel systems

Among all systems, the series system has the lowest optimal replacement time, while the parallel system has the highest optimal replacement time. this paper is comparing the standard age replacement strategy (sars) with some proposed replacement strategies (strategy a and strategy b) for two multi-unit systems. two numerical examples are provided for a simple illustration of the proposed replacement cost models under sars, strategies a and b. the results obtained showed that strategy b can extend the optimal replacement time of a series system.