Slides · 1.2
Figure 1.4. The five purposes, and the blended cases, by article, level relative to service, what a pass proves, whether damage is allowed, what happens to the article afterward, and where each sits on the sequence.
Qualification, Acceptance, Development, Screening, Margin
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Qualification, Acceptance, Development, Screening, Margin
- Say which of the five purposes a test serves
- Say what a pass proves
- Say whether the article on the shaker is allowed to be damaged
Qualification and Acceptance
- Qualification: the design survives the sequence with margin; harder and longer than service
- A qualification pass says the design is good, and nothing about next month's unit
- Acceptance: this unit was built right; every unit or a sample, at or near service level
- An acceptance pass says this unit is fit to ship, and nothing about the design
Development and Screening
- Development: learn something; levels chosen to find the weak point
- No pass or fail; the deliverable is knowledge
- Screening: make hidden workmanship defects fail on the bench, not in the field
- Screening levels must fail the bad unit and not the good one
Margin
- Find out how much is left: step above qualification until something fails or a stated margin is shown
- The deliverable is a number: fails at so many dB above the requirement
- The article is expected to be damaged or destroyed
- The lab sets the step size, the dwell, the inspection between steps, and when to stop
The Blurred Cases
- Qualification with mass mockups is still qualification, if mass, center of gravity and interface stiffness are right
- An instrumented unit driven with flight data looks like qualification and is development in purpose
- A qualification test that keeps going past its pass/fail test level is a margin test
- The lab records which parts are real and which are mockups, and which channels learn unknown responses and which qualify
Where Each Sits on the Sequence
- Qualification, development and margin answer for the whole sequence
- Acceptance and screening answer for the factory step: the question is the unit, not the environment
- Margin is usually the last thing done to a qual unit
The Two Traps
- Running the qualification profile on flight or production units because it was the profile on file
- The unit passes and has used up life it still needed in service
- The reverse: running acceptance levels and calling the design qualified
The Five Purposes Side by Side
| Purpose | Article | Level vs service | A pass proves | Damage allowed | Afterward | On the sequence |
|---|---|---|---|---|---|---|
| Qualification | design proof, one or a few | above, with margin | the design is good | none for a pass; life is used up | usually not fielded | whole sequence |
| Acceptance | every production unit | at or near | this unit was built right | none intended | ships | factory step |
| Development | breadboard, partial, or qual unit | chosen to find the weak point | nothing; it teaches | yes; finding the weak point is the aim | as needed | whole sequence |
| Screening | production units | tuned to fail the bad unit only | no hidden defect showed up | the bad unit only; the good unit must not be | ships | factory step |
| Margin | qual unit after the pass | stepped above the requirement | a number, not a pass | expected, up to destruction | used up | whole sequence |
| Blended: qual with mockups, development on flight data | mixed real and mockup, extra channels | as the plan says | depends on which channels | as the plan says | as the plan says | whole sequence |
Decide
- Know which of the five you are running before the article is on the table
- It sets what pass means, the margin in the levels, whether damage is allowed, and the disposition
- Write it in the log header, with which parts are real and what the extra channels are for
- If the plan does not say, ask before the low-level run