Research on Modeling Method of Testability Design Based on Static Automatic Fault Tree

Ensuring user safety has become increasingly essential, especially for safety-critical systems (SCSs) that are vital to human life or significant property. However, the prevailing design-for-testability (DFT) model, which relies on dependencies, overlooks safety-related faults and lacks adequate metrics for evaluating system safety. Consequently, the current dependency model is insufficient in effectively assessing system safety. To address this issue, this study has developed a comprehensive DFT model that integrates system safety considerations, known as the safety-related fault model (SRFM). SRFM uses internal block diagrams (IBDs) as a means, employs a nine-tuple model to create a static automatic fault tree, and establishes mapping relationships. Sensitivity analysis is utilized to quantify system safety factors, resulting in a safety-related dependency matrix. Two crucial concepts, design safety sensitivity (DSS) and theoretical safety sensitivity (TSS), are introduced to quantify system safety loss after a fault occurs. Additionally, two new safety-related testability metrics—test advantage of safety assessment on probability (TASAP) and test advantage of safety assessment on number (TASAN)—are developed for a robust evaluation of system safety. To validate the effectiveness of SRFM, it is applied to an electronic safety and arming device (ESA), demonstrating superior performance in TASAP and TASAN compared to existing models, with a negligible impact on expected test cost (ETC).