Importance-based system cost management and failure risk analysis for different phases in life cycle

System life cycle can be divided into four phases: the production phase, the operation phase, maintenance phase and the end-of-life phase. Component failure leads to the different variable costs in different phases. Existing studies have investigated systems from a cost-effectiveness perspective of the operation and maintenance stage, which may not be holistic. Furthermore, the expected failure cost can be used to evaluate the failure risk. In this paper, a generalized system cost for different phases is analyzed in life cycle, then a risk optimization is studied based on an improvement importance. Firstly, a comprehensive life cycle cost model is proposed. Specifically, the operation and maintenance costs due to the different types of component failures are discussed, respectively. Besides, a specific selection method for performing end-of-life in case of component failure is given using the recovery importance. Secondly, an improvement importance is proposed to optimize system reliability under invariant resources. Thirdly, the specific process of the failure risk under limited resource using improvement importance is analyzed. Finally, the proposed methods are verified using two applications, and a discussion on unlimited resources for risk optimization is given.