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Integration with eXpress Models

eXpress integrates the root failure causes, object effects, design effects and failure rates into a unified hierarchical system model. The effects defined for the failure modes and effects analysis (FMEA) can be reused for the fault tree analysis (FTA) or developed exclusively for each type of analysis. Failure rates defined on the root failures are defined once and reused in eXpress for all different types of analysis performed by eXpress.

Traditionally, a FMEA examines failures by listing the effects at each hierarchical level of the system for all root failures of the system regardless of their severity or critically. The critically calculation used to change a FMEA into a failure mode and effects criticality analysis (FMECA) is derived from the failure rate of the root failures in the system and the severity assigned to each effect.

A FTA analysis is generated by examining all the most severe or most critical events in the system and then using the failure rates to define the likelihood of occurrence within a given period of performance which is usually a standard mission length. A FTA also takes into account redundancies within the system and external events to correctly calculate the likelihood of occurrence for the event.

In eXpress, a FTA can be defined by reusing the FMEA data to generate a top down or inverted FMEA which shows all the root causes of the critical failures as a list of events that are related to each other through a series of “OR” gates. Adding redundancy relationships using “AND” or polling “OR” gates and external events changes the inverted FMEA into a true FTA. The events used to define the redundancy relationships may be developed for both the FMEA and the FTA or may be unique events developed just the FTA.


Design Failure Effects showing the Usage settings

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