ADS-79D-HDBK Downloaded from https://www.everyspec.com occur within a reasonable test timeframe. The component may be seeded by manually faulting the part in the laboratory, for example, notching the part to initiate a crack at a desired location. Alternatively, an SFT may employ a used, worn, or deformed part from the field which may ultimately result in the anticipated failure when under the induced stress of the laboratory test setup. Additional effort should be considered to ensure initiation of artificially induced faults (i.e. EDM notches, acid etched pitting) that aid in predicting results are representative of expected outcomes.
This can be accomplished through pre-testing on material coupons or actual components. i) Component Failure can be classified as a complete failure if the article under test can no longer perform its intended function. This can happen in a slow progression or quickly. The point at which it is possible to detect the fault that leads to failure will also determine how much time is remaining before progressing to a complete failure. If faults are not observed early enough prior to failure, the component under test may not be an appropriate CBM candidate. ii) A second classification of Component Failure can be referred to as a near failure or when a failure is imminent.
This occurs when the component under test reaches a point when it is no longer safe to operate in the test fixture or on the platform during a test cycle. Safe operating limits and inspections are imposed on the test to ensure test progression does not cause harm to equipment or personnel. Note, component failure can involve considerations of the method of aircraft component lifing: safe life or damage tolerance. If a safe life approach was applied to an aircraft component design then a component with a flaw in it under this design approach is considered to be unacceptable for further aircraft usage due to failing inspection for safety.
As a result, prior to introducing a faulted, safe-lifed component on an aircraft for limited on-aircraft SFT, the safe-life of the component (time to failure) should be accurately measured in the laboratory. This will provide some assurance the test article will not progress to a state where component failure during on-aircraft SFT. Also note the statistical significance while analyzing the margin of indication (e.g. delta in CI magnitude differentiating Green to Yellow to Red) of a faulted component for transitioning to on condition monitoring. Analysis may illustrate it may not be beneficial to take the component to failure under the definitions noted in paragraphs 1(i) and (ii), above.
For instance, it may prove to be more beneficial to take the component to a known condition that meets the Red criteria (as defined in D.4.2, Appendix D). J.4.2 Step 2: Pre-Testing. Test planning continues with evaluation of vendors and final vendor selection. The vendor should clarify all test objectives before initiating test fixture development. a. Test fixture development – The laboratory test jig should be configured to induce enough stress to produce the desired fault condition in the seeded (deformed or worn) test part. The laboratory nature of seeded fault testing should allow for the careful isolation of a specific failure condition without interference from other fault conditions.
Typically, the test stand 179