Applicability and Limitations of Reliability Allocation Methods

The process of assigning reliability requirements to individual subsystems and components to attain the desired system reliability goal is known as reliability allocation. The purpose of this paper is to review the literature on reliability allocation and to propose a guideline to choose the most suitable allocation method, in respect to desired goals and available resources. The proposed review systematically analyzes allocation methods in literature, determining main features and the area of application. The choice of a reliability allocation method depends on several factors and moreover, the considered design stage. However, in literature there is a lack of comprehensive methods’ summarization, making it difficult to choose the most suitable strategy. New criteria for the classifications are also highlighted. Furthermore, reliability allocation methods become even more complex and accurate, in particular through the employment of advanced mathematical tools.The review of existing literature shows that there is a continuous improvement of conventional methods and several new ones have been developed in recent years. In general, each method requires its own level of system information and can be appropriate only for some phases of the product development. Each analyzed reliability allocation method shows different characteristics and own strengths and limitations. Some methods can be used when very few data are available about the system, as the number of components and their connections, at the same time more accurate methods have been proposed for an advanced phase of the product development process. Optimal reliability allocation methods require applying mathematical programming methods to obtain the optimum system allocation. The cost minimization problem formulation requires defining components reliability cost models, system reliability model, and upper and lower bounds of component reliability. Optimal reliability allocation techniques can be applied to series, parallel, and complex configurations such as bridge and series parallel.