Design, Analysis, and Technical Problem Solving
This domain tests structured design under constraints: requirements, load cases, failure modes, tolerances, verification, and root-cause reasoning. Items often ask you to select the governing case or interpret a calculation, not just recall a formula.
Core rules and concepts
- Convert needs into measurable requirements and constraints; define function, interfaces, environment, and acceptance criteria.
- Check strength, stiffness, fatigue, buckling, wear, and thermal effects as applicable; the lowest safety factor governs.
- Use worst-case tolerance stacks for assembly fit; use statistical root-sum-square only when independence and process capability support it.
- DFMEA links failure mode, effect, severity, occurrence, detection, and action priority.
- Verification confirms the item meets specified requirements; validation confirms the user need is met in the intended use.
Worked example
Gap = housing A − (B+C+D). A=25.0±0.1, B=8.0±0.05, C=7.0±0.05, D=6.0±0.05 mm. Nominal gap =25.0−21.0=4.0 mm. Minimum gap =24.9−(8.05+7.05+6.05)=24.9−21.15=3.75 mm. Maximum =25.1−(7.95+6.95+5.95)=25.1−20.85=4.25 mm. The assembly remains positive, so the nominal design is acceptable for this fit check; confirm the minimum clearance requirement.
Traps that cost marks
- Reversing tolerance direction or adding tolerances without considering stack sign.
- Treating validation as a final inspection.
- Choosing an average load when the code requires an ultimate or abnormal load.
- Fixing a symptom before confirming root cause.