HKIE Professional Assessment - Materials Discipline cheat sheet

Ashby material property charts plot Young's modulus (E) vs density (ρ) on log-log axes; performance index M = E^(1/2)/ρ for a light stiff beam, M = E^(1/3)/ρ for a light stiff panel, and M = σ_y^(2/3)/ρ for a light strong beam.

Crystal structures: BCC (α-Fe, W, Mo) has 2 atoms/cell, APF 0.68, 8 nearest neighbours; FCC (γ-Fe, Al, Cu, Ni) has 4 atoms/cell, APF 0.74, 12 nearest neighbours; HCP (Mg, Zn, Ti) has 6 atoms/cell, APF 0.74, c/a ideal = 1.633.

Theoretical shear strength τ_th ≈ G/2π (≈ G/10 to G/30 in practice); yield occurs by dislocation glide, described by Schmid's law τ_RSS = σ cosφ cosλ, with maximum at φ = λ = 45°.

Hall–Petch relation: σ_y = σ_0 + k_y d^(−1/2), where d is grain diameter; strengthening arises from dislocation pile-up at grain boundaries.

Rule of mixtures for composites: E_c = f E_f + (1−f) E_m (isostrain, loading parallel to fibres); E_c = E_f E_m / [f E_m + (1−f) E_f] (isostress, loading perpendicular).

Material selection steps: (1) translate design requirements into function, constraints, objective and free variables; (2) screen using constraints; (3) rank using performance index; (4) investigate top candidates for detailed trade-offs.

Griffith fracture criterion: σ_f = (2Eγ_s / πa)^(1/2) for plane stress; for plane strain replace E with E/(1−ν²); crack-tip stress intensity K_I = Y σ (πa)^(1/2), fracture when K_I ≥ K_IC.

Diffusion: Fick's first law J = −D dC/dx; Arrhenius temperature dependence D = D_0 exp(−Q/RT); vacancy diffusion is slower than interstitial diffusion (e.g., C in α-Fe vs Fe self-diffusion).

Iron–carbon phase diagram: eutectoid at 0.76 wt% C and 727 °C (pearlite = ferrite + cementite); eutectic at 4.3 wt% C and 1147 °C (ledeburite); maximum solubility of C in austenite is 2.14 wt% at 1147 °C, in ferrite only 0.022 wt% at 727 °C.

Martensite forms by diffusionless shear; its hardness increases with carbon content up to about 0.6 wt% C; Ms and Mf temperatures decrease as carbon content rises, so high-carbon steels retain austenite after quenching.

Hardenability is measured by the Jominy end-quench test (ASTM A255 / ISO 642); it is governed by austenite grain size and alloying elements (B, Mo, Cr, Mn, Ni increase hardenability; Co decreases it).

Tempering: low-temperature tempering (150–250 °C) gives high hardness and wear resistance; high-temperature tempering (500–650 °C) gives improved toughness and ductility; temper embrittlement occurs in the 250–400 °C and 450–550 °C ranges for susceptible alloy steels.

Austenitic stainless steels (e.g., 304, 316) are FCC and non-magnetic in the annealed condition; sensitisation occurs by Cr23C6 precipitation at grain boundaries in the 450–850 °C range, causing intergranular corrosion; low-carbon grades (304L, 316L) or stabilised grades (321, 347) mitigate this.

Aluminium alloys: 2xxx (Cu) and 7xxx (Zn) are precipitation-hardenable by solution treatment, quench and artificial ageing; 6xxx (Mg–Si) also age-harden; 5xxx (Mg) and 3xxx (Mn) are strain-hardening grades and not heat-treatable.

Cast irons: grey (flake graphite, good damping), ductile/nodular (spheroidal graphite, higher strength and ductility), white (cementite, hard and brittle), malleable (tempered white iron).

Case hardening processes: carburising (0.7–1.2 mm case, 58–62 HRC), nitriding (0.1–0.6 mm case, no quench required, 65–70 HRC surface), induction and flame hardening (selective surface hardening of medium-carbon steels).

Polymer molecular weight: number-average M_n = Σ N_i M_i / Σ N_i; weight-average M_w = Σ N_i M_i² / Σ N_i M_i; polydispersity index PDI = M_w/M_n ≥ 1; mechanical properties depend strongly on M_w and degree of crystallinity.

Glass transition temperature T_g marks the change from glassy to rubbery behaviour; semi-crystalline polymers show both T_g and a crystalline melting point T_m, with T_m typically 1.3–1.5 times T_g in kelvin.

Ceramics: brittle, high compressive strength, low tensile strength; strength is flaw-controlled and described statistically by the Weibull distribution, P_f = 1 − exp[−(σ/σ_0)^m], where m is the Weibull modulus (higher m = more reliable).

Composite rule of mixtures and load-sharing: fibres carry most load when aligned with the loading axis; continuous fibre composites are anisotropic, and laminate design must consider ply orientation (0°, ±45°, 90°) and stacking sequence.

Concrete mix design: water/cement ratio (w/c) controls strength and durability; Abram's law states strength decreases as w/c increases; typical w/c is 0.40–0.55 for structural concrete; minimum cement content and maximum w/c are specified for exposure classes (e.g., BS 8500 / EN 206).

Concrete curing: moist curing at ≥ 95% RH and ≥ 10 °C for at least 7 days (or longer for blended cements) is needed for adequate hydration; maturity is estimated by the Nurse–Saul function M = Σ (T − T_0) Δt.

Admixtures: plasticisers/superplasticisers (water reduction 5–30%), air-entraining agents (improve freeze–thaw resistance; 4–8% air), retarders, accelerators, and silica fume (pozzolanic, increases strength and reduces permeability).

Fibre-reinforced polymers (FRP) for strengthening: carbon FRP (high strength and stiffness, but galvanic corrosion risk with steel), glass FRP (lower modulus, susceptible to alkali attack), aramid FRP (impact resistant, poor compressive strength).

Electrochemical corrosion requires an anode, cathode, electrolyte and metallic path; the anodic reaction is M → M^(n+) + n e^−, and the cathodic reaction in neutral aerated water is O2 + 2H2O + 4e^− → 4OH^−.

Galvanic series in seawater: more active (anodic) metals include magnesium, zinc, aluminium and mild steel; more noble (cathodic) metals include stainless steel, copper, silver and graphite; the potential difference and area ratio (small anode/large cathode is worse) drive galvanic corrosion.

Pitting resistance equivalent number PREN = %Cr + 3.3 %Mo + 16 %N; a PREN above about 40 is typical for super duplex and 6 % Mo stainless steels used in chloride environments.

Cathodic protection: sacrificial anode systems use metals more active than the structure (e.g., Zn or Al anodes for steel); impressed current systems use an inert anode and a DC power supply; protection criterion for steel in soil/seawater is typically −850 mV vs Cu/CuSO4 or 100 mV polarisation shift.

Coatings: barrier coatings (paints, galvanising) isolate the substrate; galvanising provides both barrier and sacrificial protection; coating adhesion and surface preparation (e.g., Sa 2½ blast cleaning to ISO 8501-1) are critical to performance.

Corrosion rate from mass loss: CR (mm/year) = 87.6 W / (ρ A t), where W is mass loss in mg, ρ is density in g/cm³, A is area in cm² and t is time in hours.

Degradation of polymers: UV exposure causes chain scission (photodegradation), mitigated by UV stabilisers and carbon black; thermal oxidation is mitigated by antioxidants; hydrolysis affects polyesters and polyamides in moist environments.

Concrete deterioration: chloride-induced corrosion of reinforcement (threshold ~0.4% by mass of cement), carbonation reducing pore-water pH below ~10 (depassivation), sulfate attack (ettringite formation), and alkali–silica reaction (ASR) with reactive aggregates.

Tensile test (ISO 6892-1 / ASTM E8): yield strength is determined by the 0.2% offset method for materials without a distinct yield point; engineering stress = F/A_0, engineering strain = ΔL/L_0; true stress = σ(1+ε) and true strain = ln(1+ε) up to necking.

Hardness scales: Brinell (HBW, 10 mm ball, 3000 kgf for steel), Vickers (HV, 136° diamond pyramid, loads 1–100 kgf), Rockwell (HRC, 150 kgf diamond cone; HRB, 100 kgf 1/16 in ball); conversion between scales is approximate and should follow ASTM E140 / ISO 18265.

Charpy V-notch impact test (ISO 148-1 / ASTM E23) measures absorbed energy in joules; the ductile-to-brittle transition temperature (DBTT) is often defined at 27 J absorbed energy or 50% shear fracture appearance.

Fatigue testing: S–N curve (Wöhler curve) gives fatigue life; endurance limit exists for steels (typically ~0.4–0.5 UTS) but not for aluminium alloys; fatigue strength is reduced by stress concentration, surface roughness and corrosive environments.

Non-destructive testing methods: ultrasonic testing (internal flaws, thickness), radiographic testing (internal volumetric flaws), magnetic particle inspection (surface/near-surface flaws in ferromagnetic materials), dye penetrant inspection (surface-breaking flaws in non-porous materials), eddy current testing (surface and conductivity).

Metallography: specimen preparation by grinding and polishing to 1 μm diamond, then etching (e.g., 2% nital for carbon steels) to reveal grain boundaries and phases; grain size is measured by the ASTM E112 intercept or planimetric method.

Quality assurance: calibration traceability to national standards, measurement uncertainty budgets (ISO/IEC 17025), and statistical process control (control charts, C_pk = min[(USL−μ)/3σ, (μ−LSL)/3σ]).

Concrete testing: slump test (EN 12350-2) for workability; cube compressive strength at 28 days (150 mm cubes, EN 12390-3); concrete cover measured by cover meter (BS 1881-204); rebound hammer (Schmidt hammer) and ultrasonic pulse velocity for in-situ strength estimation.

Structural steel grades (EN 10025): S275 and S355 are common; the number denotes minimum yield strength in MPa for thickness ≤ 16 mm; Charpy impact grades (J0, J2, K2) specify test temperature (0 °C, −20 °C, −40 °C).

Reinforcement: high-yield deformed bars to BS 4449 / EN 10080, grades B500A and B500B (500 MPa characteristic yield); ductility class B requires higher elongation and bend performance than class A.

Concrete exposure classes (EN 206): XC (carbonation), XD (chloride, non-marine), XS (chloride, marine), XF (freeze–thaw), XA (chemical attack); each class sets minimum strength class, minimum cement content, maximum w/c and minimum cover.

Prestressing steel: high-strength wires/strands (e.g., 7-wire strand with f_pk = 1770 or 1860 MPa) are susceptible to stress corrosion cracking and hydrogen embrittlement; grouting quality in post-tensioned ducts is critical to durability.

Timber: strength classes C16, C24 and C30 (EN 338); design to EN 1995 (Eurocode 5); moisture content affects strength and dimensional stability; preservative treatment is required where hazard classes 3–5 apply (EN 335).

Masonry: clay bricks (EN 771-1) and concrete blocks (EN 771-3); mortar designation (i, ii, iii, iv) governs compressive strength and durability; movement joints are required to accommodate thermal and moisture movement.

Geotechnical materials: soil classification by particle size (gravel > 2 mm, sand 0.06–2 mm, silt 0.002–0.06 mm, clay < 0.002 mm); compaction to a target dry density and moisture content (Proctor test) controls engineering behaviour.

Bituminous materials: penetration grade and PG (performance grade) systems; Superpave PG grading specifies high and low pavement service temperatures; asphalt stiffness depends on binder grade, temperature and loading rate (viscoelastic).

Bearing materials require low friction, high wear resistance and embeddability; common choices include white metal (babbitt), bronze and polymer composites; the PV limit (pressure × velocity) governs dry-running applications.

Gears and shafts: case-carburised alloy steels (e.g., 16MnCr5, 20MnCr5) for gears; through-hardened or induction-hardened steels for shafts; surface hardness and core toughness must both be specified.

Electrical conductors: copper (100% IACS conductivity) and aluminium (about 61% IACS, lower density); contact materials use silver alloys or silver–tungsten for arc resistance; insulation classes (Y, A, E, B, F, H) define maximum operating temperatures (e.g., class F = 155 °C).

Magnetic materials: soft magnetic materials (silicon steel, ferrites, permalloy) for transformers and motors; hard magnetic materials (NdFeB, SmCo, ferrite) for permanent magnets; NdFeB has the highest energy product but limited temperature capability (max ~200 °C).

Manufacturing processes: casting (sand, die, investment), forging, rolling, extrusion, machining, welding, additive manufacturing; process selection depends on material, tolerance, surface finish, quantity and cost.

Welding metallurgy: heat-affected zone (HAZ) experiences thermal cycles that can cause grain growth, hardening or softening; carbon equivalent CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15; CE > 0.4 indicates need for preheat to avoid cold cracking.

Powder metallurgy: compaction and sintering produce near-net-shape parts; porosity reduces strength and ductility but can be beneficial for self-lubricating bearings and filters.

Failure in electronic materials: solder joint fatigue due to thermal cycling (Coffin–Manson relation Δε_p/2 = ε_f' (2N_f)^c), electromigration in fine interconnects, and tin whisker growth in lead-free solders.

Failure analysis sequence: collect background data, inspect and document the failed component (photographs, fracture surface preservation), select and perform tests, analyse data, formulate and verify hypotheses, and report root cause with recommendations.

Fracture surface features: beach marks (fatigue progression), striations (one per fatigue cycle, visible under SEM), chevron marks (point toward crack origin), and dimples (microvoid coalescence, ductile overload).

Fracture mechanics assessment: K_I = Y σ (πa)^(1/2); failure occurs when K_I ≥ K_IC; for elastic–plastic conditions use CTOD or J-integral; BS 7910 provides fitness-for-service assessment procedures for flaws in metallic structures.

Fatigue life prediction: Basquin's law σ_a = σ_f' (2N_f)^b for high-cycle fatigue; Coffin–Manson for low-cycle fatigue; Miner's rule for cumulative damage: Σ (n_i/N_i) = 1.

Creep: deformation at constant stress and elevated temperature; Norton–Bailey law ε̇ = A σ^n exp(−Q/RT); Larsen–Miller parameter P = T (C + log t_r) with C ≈ 20 for many steels, used to extrapolate rupture life.

Hydrogen embrittlement: high-strength steels (UTS > 1000 MPa), electroplated components and welds are susceptible; mitigation includes baking after plating, low-hydrogen welding consumables and avoiding cathodic overprotection.

Stress corrosion cracking (SCC): requires susceptible material, tensile stress and corrosive environment (e.g., stainless steel in chlorides, brass in ammonia); threshold stress intensity K_ISCC and crack growth rate da/dt characterise the material–environment system.

Forensic engineering and expert evidence: maintain chain of custody for samples; document all observations contemporaneously; distinguish facts from opinions; expert evidence must be independent and comply with the applicable court or tribunal rules.

Life cycle assessment (LCA) follows ISO 14040/14044: goal and scope definition, inventory analysis, impact assessment and interpretation; embodied carbon is reported as kgCO2e per functional unit.

Embodied carbon benchmarks: structural steel (virgin) ~1.5–2.5 kgCO2e/kg; concrete ~0.1–0.15 kgCO2e/kg; timber (softwood) can be net negative when biogenic carbon storage is counted; recycled content and reuse reduce embodied impact.

The circular economy hierarchy: reduce, reuse, recycle, recover, dispose; design for deconstruction and material passports support reuse of structural components.

Standards framework in Hong Kong: Buildings Department Code of Practice for Structural Use of Concrete (2020), Code of Practice for Structural Use of Steel (2011), and the corresponding Eurocodes; materials standards are cited in these codes.

Professional ethics: the HKIE Code of Conduct requires members to act with integrity, competence and objectivity, to avoid conflicts of interest, to maintain confidentiality, and to give priority to public safety and health.

Continuing professional development (CPD): HKIE requires a minimum of 45 CPD hours per year for members, with at least 15 hours in structured activities; records must be retained and declared.

Environmental legislation in Hong Kong: Air Pollution Control Ordinance, Water Pollution Control Ordinance, Waste Disposal Ordinance; construction waste management requires trip-ticket system for disposal at designated facilities.

Green building assessment: BEAM Plus (Hong Kong) covers site aspects, materials, energy use, water use, indoor environmental quality and innovations; materials credits reward sustainable sourcing and reduced embodied carbon.

Project delivery stages: feasibility, concept design, detailed design, tender, construction, commissioning and handover; the RIBA Plan of Work or HKIE project stages provide a common framework.

Procurement routes: traditional (design–bid–build), design–build, management contracting, and engineering, procurement and construction (EPC); risk allocation differs between routes and must be reflected in the contract.

Contract types: lump sum, remeasurement, cost-plus, and target-cost; standard forms include the HKIA/HKIS Standard Form of Building Contract and the NEC4 suite, which uses defined cost and compensation events.

Programme and progress: critical path method (CPM) identifies the longest path through the network; float is the amount by which an activity can be delayed without delaying the project; earned value management uses CPI = EV/AC and SPI = EV/PV.

Quality management: ISO 9001:2015 quality management systems; inspection and test plans (ITPs) define hold points and witness points; non-conformance reports (NCRs) track and close out defects.

Risk management: ISO 31000 process of risk identification, analysis, evaluation and treatment; risk register records likelihood, consequence, owner and mitigation; residual risk must be accepted by the appropriate authority.

Communication: technical reports should state purpose, scope, methodology, results, discussion, conclusions and recommendations; drawings and specifications must be coordinated and version-controlled; BIM (ISO 19650) provides a common data environment.

Professional responsibility: engineers must work within their competence, seek advice when necessary, keep accurate records, and report unsafe practices; whistleblowing protections exist under the Employment Ordinance in Hong Kong.