Engineering Design and Analysis
What this domain tests
Engineering Design and Analysis tests the path from requirement to verified design: how inputs are written, how failure modes are identified, how margins are chosen, and how reviews and verification close the loop.
Core rules
- Design inputs must be measurable. "Robust" is not a requirement; "withstands 5 g sine sweep 10–500 Hz for 2 h per axis" is.
- Factor of safety = failure strength / working stress. It never substitutes for identifying the governing failure mode first: yield, fatigue, buckling, deflection or wear.
- Verification asks "does it meet the specification?"; validation asks "does it meet the user need?" They are different activities with different evidence.
- Preliminary design review confirms the concept can meet requirements; critical design review confirms the detail design can be built, tested and maintained.
- Worst-case tolerance stack-up sums nominal dimensions and sums all tolerances arithmetically.
Worked example
Three stacked dimensions: 20 ± 0.10, 15 ± 0.05 and 10 ± 0.08 mm. Nominal total = 45 mm; worst-case tolerance = 0.10 + 0.05 + 0.08 = 0.23 mm, so the assembly is 44.77 to 45.23 mm. A root-sum-square treatment gives √(0.10² + 0.05² + 0.08²) ≈ 0.14 mm, but RSS assumes independent, centred, in-control processes - it is not a substitute for worst case on a safety-critical clearance unless justified and agreed.
Traps
Applying a general safety factor to a buckling case that needs a higher one; constraining an FEA model more stiffly than the real boundary; quoting RSS where the drawing or contract mandates worst case; and answering a validation question with verification evidence.