Implementing the Failure Free Operating Period Process

Objectives

Background

Approach

Objectives

To provide the mathematical background for failure free operating period (FFOP) implementation, including how to calculate the FFOP, how to obtain confidence limits, and how to prepare qualification testing (sample size, time to first failure etc.). FFOP and associated confidence limit prediction for systems subject to multiple failure mechanisms as well as both series and parallel systems will be addressed.

Background

A broad-based process for implementing FFOPs in electronic systems was overviewed in the project C99-02. With the basis laid in the C99-02 project and supplementary work performed in the USAF PASES program we can now develop a mathematical approach to implement FFOP using a 3-parameter Weibull distribution. This approach enables calculating the system FFOP and confidence intervals using probabilistic virtual qualification and developing probability distributions for the 3-parameter Weibull location parameter (gamma).

Approach

Analysis Outline:

1. FFOP requirements
   1. Environmental requirements
   2. Functional requirements
   3. Reliability requirements
2. Variabilities in assembly and manufacture
3. Sub-system design using virtual qualification
   1. Automated probabilistic analysis [C01-17]
   2. FFOP and confidence interval determination using the 3-parameter Weibull distribution
   3. System FFOP calculation from sub-system characteristics
4. FFOP verification
   1. Acceleration factor determination [previous CALCE projects]
   2. Sample size determination for a given test time, number of failures and FFOP
   3. Test time determination for a given sample size, number of failures and FFOP
   4. Goodness of fit test
5. FFOP prediction for multiple failure mechanism systems and series and parallel systems
   1. FFOP prediction
   2. Confidence limit prediction