Discipline-Specific Engineering Knowledge
This section checks whether you can apply your discipline's first principles under time pressure: statics and mechanics, materials behaviour, fluid flow and thermodynamics, electrical circuits and machines, or process balances - depending on your registered discipline. Questions are numerical or judgment-based, in SI units, and often reference allowable stresses, load factors or efficiency.
Method that earns marks
- Write the governing equation before substituting numbers; examiners award method marks.
- Convert everything to base SI at the start - mm to m, kPa to Pa, kN to N.
- State assumptions explicitly: linear elastic, steady state, negligible losses, thin-walled.
- Use the factor-of-safety definition the question gives; FoS = failure stress / working stress is not the same as working stress / failure stress.
- Sanity-check the magnitude: steel stresses in tens to hundreds of MPa, not thousands.
Worked example
A thin-walled cylindrical air receiver has 1.0 m internal diameter, 10 mm wall and 1.5 MPa gauge pressure. Hoop stress: radius r = 0.5 m, thickness t = 0.010 m, so sigma = pr/t = (1.5 x 10^6 x 0.5) / 0.010 = 75 MPa. If the plate yields at 240 MPa, the factor of safety on yield is 240/75 = 3.2. Note that gauge pressure is correct because atmospheric pressure acts on both faces; using diameter instead of radius would double the answer to 150 MPa.
Traps that cost marks
Diameter substituted for radius; mm/m slips of 10^3; gauge versus absolute pressure; rounding intermediate values and carrying the error; ignoring temperature derating or corrosion allowance; answers with no units.