21-Mat-A5 Phase Transformations and Thermal Treatment, May 2017: worked solutions

Paper format. National Exams, May 2017 — 10-Met-A5, Mechanical Behaviour and Fracture of Materials. Three hours, closed book, any non-communicating calculator permitted. Eight questions of 20 marks each; the rubric states that five questions constitute a complete paper and that only the first five appearing in the answer book are marked. All eight are answered here, because this set is a study resource rather than an exam script. Several questions ask explicitly for essay-format answers, and the marking scheme rewards clarity and organisation, so the discursive answers below are written as structured prose rather than as note form.

Note on the paper's subject

The printed exam header reads 10-Met-A5, Mechanical Behaviour and Fracture of Materials. The paper has no phase-transformation or heat-treatment question in the classical (TTT/CCT diagram, hardenability, tempering-curve) sense; the syllabus actually examined is fracture mechanics and fatigue-crack-growth life, strengthening and toughening of engineering materials, creep and fatigue testing, deformation processing, and elastic–plastic forming behaviour.

Reference texts. The answers below are keyed to the works normally recommended for this syllabus code:

G. E. Dieter, Mechanical Metallurgy, 3rd ed. — strengthening and plastic instability (Ch. 3, 4, 6), fracture (Ch. 7), fatigue (Ch. 12), creep and stress rupture (Ch. 13), forming processes (Ch. 15–19).
W. D. Callister and D. G. Rethwisch, Materials Science and Engineering: An Introduction, 10th ed. — strengthening (Ch. 7), failure: fracture, fatigue and creep (Ch. 8), composites (Ch. 16), corrosion and degradation (Ch. 17).
M. F. Ashby and D. R. H. Jones, Engineering Materials 1 & 2 — fast fracture, the transition flaw size, toughening mechanisms, and creep-mechanism maps.
ASM Handbook, Vol. 11 (Failure Analysis and Prevention), Vol. 14A (Metalworking: Bulk Forming) and Vol. 19 (Fatigue and Fracture) — process selection, fractography, single-crystal casting and fatigue design.
Test standards cited where relevant: ASTM E8/E8M (tension), E139 (creep and stress rupture), E466 (constant-amplitude axial fatigue), E647 (fatigue crack growth rate), E399/E1820 (fracture toughness).

21-Mat-A5 Phase Transformations and Thermal Treatment: May 2017