A method for reliability allocation with confidence level

One of the important reliability activities in Design for Reliability (DFR) is system reliability allocation at the early product design stage. Usually system reliability is given as a product performance requirement under the normal use condition (e.g., the probability of failure for a 2-year operation should be less than 0.05 with a confidence level of 90%). Complex systems consist of many subsystems, which are developed concurrently and sometimes independently. It would be too late to validate the system reliability until the final system prototype is ready after months or years of development. From a project management point of view, the reliability for each subsystem or sub-function should be examined as early as possible. Therefore, allocating a reasonable reliability requirement to each subsystem and sub-function based on the system reliability requirement is very important. Many reliability allocation approaches can be used, such as the AGREE, weighted, equal reliability, and cost-based methods. Traditional system reliability allocation is conducted on the reliability requirement alone. None of the above existing methods considers allocating the reliability requirement together with a confidence level. In this paper, we will propose a new approach for allocating system reliability together with confidence level to the subsystems. The proposed method can be used for complex systems with serial, parallel, and k-out-of-n configurations.