ADS-79D-HDBK Downloaded from https://www.everyspec.com An essential diagnostic purpose of laboratory SFT is the ability to accurately correlate an indication level from a CI to a known damage condition. When the specific goal of SFT is to develop or verify a prognostic model, it is necessary to measure the rate of failure progression (i.e. crack growth) and the corresponding rate of change in measured indicators. Note, laboratory testing may confirm some failure modes and fault conditions are not reliably detectable by measured indicators and should not be transitioned to a CBM system.
Laboratory testing may also reveal an impending fault may not exhibit any measurable indication prior to complete failure, and, therefore, it also may not be a good CBM candidate. SFT involves most steps normally associated with aircraft component qualification testing. Figure J-1 and reference J.2(c) outline example SFT and qualification processes used by the US Army. As shown in the Figure, the process is organized into four general steps. J.4.1 Step 1: Foundation. Initial test planning begins with determination of goals and objectives for the experiment and should be clearly defined in a Statement of Work (SoW) for the effort.
These goals and objectives should be coordinated through the respective aircraft platform‘s Project Manager‘s Office and all stakeholders. The primary paths SFT can take are to create or develop CI‘s, refine or mature the CI‘s, or to validate CI‘s for on condition maintenance progression (ref. para. 5.9). During the initial planning step, it is customary that the test articles be procured by the appropriate agency. a. Failure mode review – The failure mode review should include all available resources of information pertaining to the component‘s known or anticipated fault mechanisms leading to failure modes.
As a minimum, this should include the OEM‘s initial and updated Failure Mode Effects and Criticality Analysis (FMECA), applicable DA Form 2410 reported failures, and any reported failures from both the Joint Deficiency Reporting System and the U.S. Army Combat Readiness/Safety Center. b. Seeding the part with a fault – Once the failure mode review has defined the applicable failure modes of interest, representative fault mechanisms should be selected for SFT that will accurately manifest themselves into the failure mode(s) to provide the anticipated result(s) during testing.
For example, if the failure mode is bearing thermal runaway (or plastic flow) typical fault mechanisms leading to this failure mode are usually grease degradation/depletion or excessive loading. If the failure mode is Fatigue/Spalling, typical fault mechanisms leading to this failure are corrosion or excessive loading. These fault mechanisms are the subject of focus for the test in question.
Depending on the goals and objectives of testing, the test should be provided a specimen that will either operate at an initially measured level of fault damage/degradation to enable fault diagnosis or allow a progression to failure in such a way to permit accurate prognosis of the rate of degradation during the course of the experiment. Introduction of a specimen which is degraded or deformed in a specified or controlled manner will help to ensure the desired fault condition will occur during the test or, if desired, failure will 177