Application of hardware reliability calculation procedures according to ISO 26262 standard

Abstract

The second edition of standard ISO 26262 (ed. 2018) for functional safety assessment in the automotive industry requires a hardware evaluation using the probabilistic metric for random hardware failures (P MHF). The standard for mentioned purpose highly recommends the fault tree analysis (FTA) utilization but does not give any specific calculation example. Therefore, this article describes computational procedures with derivation and explanation of mathematical formulas for various hardware architectures of electronic systems. Described formulas consider impact of multiple failures and impact of elf-tests, but formulas are relatively simple. This simplicity allows them to be used in the early stages of hardware development when frequent hardware design changes can be expected. Thus, the article with attached case study is intended not only for scientists but also for developers of critical safety-related electronic systems in the automotive industry. K E Y W O R D S car functional safety, fault tree analysis (FTA), hardware assessment, hardware development, ISO 26262, P MHF 1 | INTRODUCTION As in all other areas of industry, the number of electronic systems in car design is constantly growing. This is closely related to the implementation of industry standards in the field of functional safety, based on the principles described in the basic safety standard EN 61508. In the automotive industry, standard ISO 26262:2018 is already established for vehicles up to 3.5 tons. One of the objectives of this standard is to adjust the procedures for Automotive Safety Integrity Level (ASIL) assessment. Generally, standard ISO 26262 assumes for electrical/electronic systems possibility of occurrence of two types of failures, the systematic failures and the random failures, and standard also sets the procedures for failures elimination. However, random failures cannot be completely eliminated, because of their stochastic nature, but it is possible to assess their expected frequency, respectively probability of occurrence, by applying appropriate computational methods. The standard requirement for validation of hardware of assessed system according to ISO 26262 is to perform a quantitative analysis to demonstrate compliance with specific target values depending on the desired ASIL level in two areas. The first area is the diagnostic coverage, thus the ability to detect dangerous system failures robustly and timely. Diagnostic coverage procedures are well described in ISO 26262 and are complemented by a sample example to help developers. Therefore, in the article, this issue will only be mentioned to the extent necessary to understand other texts.

Stochastic Strength Analyses of Screws for Femoral Neck Fractures

“…Its application allows desired transitioning from the deterministic to the probabilistic concept of reliability assessment of the natural phenomena, i.e., transitioning from deterministic reliability assessment to probabilistic assessment of structures or sys-tems. With the SBRA method, the calculated probability of failure is estimated according to the theory of limit states [21,[23][24][25][26][27]30,31].…”