HKIE Professional Assessment - Materials Discipline flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Hall–Petch equation

Empirical relationship σ_y = σ_0 + k_y d^(−1/2) showing that yield strength increases as grain size d decreases, because grain boundaries impede dislocation motion.

Jominy end-quench test

Standard test (ASTM A255 / ISO 642) that measures steel hardenability by quenching one end of a cylindrical bar and plotting hardness against distance from the quenched end.

Martensite formation

Diffusionless shear transformation of austenite to a supersaturated body-centred tetragonal phase; hardness rises with carbon content, and retained austenite increases as Ms/Mf fall.

Sensitisation of stainless steel

Chromium carbide precipitation at grain boundaries during heating to 450–850 °C, which depletes chromium locally and makes the steel susceptible to intergranular corrosion.

Galvanic corrosion

Accelerated corrosion of a metal when it is electrically coupled to a more noble metal in an electrolyte; the less noble metal becomes the anode and corrodes faster.

PREN

Pitting resistance equivalent number, calculated as %Cr + 3.3 %Mo + 16 %N, used to rank stainless steels for chloride environments; higher values indicate better pitting resistance.

Cathodic protection

Technique that makes a metal structure the cathode of an electrochemical cell by supplying electrons, using either sacrificial anodes or an impressed current system.

Ashby performance index

A material property combination, derived for a specific loading and objective, that allows materials to be ranked; for a light stiff beam it is E^(1/2)/ρ.

Schmid's law

Resolved shear stress τ_RSS = σ cosφ cosλ, where φ and λ are the angles between the loading axis and the slip plane normal and slip direction respectively.

Griffith criterion

Fracture stress for a brittle material containing a crack of length a: σ_f = (2Eγ_s/πa)^(1/2); the criterion explains why brittle materials are flaw-sensitive.

Fick's first law

Diffusion flux J = −D dC/dx, stating that atoms diffuse down a concentration gradient at a rate proportional to the diffusion coefficient and gradient.

Number-average molecular weight

M_n = Σ N_i M_i / Σ N_i, the total mass of polymer molecules divided by the total number of molecules; it is sensitive to low molecular weight species.

Glass transition temperature

Temperature at which an amorphous polymer changes from a hard glassy state to a rubbery state; below T_g the polymer is brittle, above it is flexible.

Weibull modulus

The exponent m in the Weibull strength distribution P_f = 1 − exp[−(σ/σ_0)^m]; a higher m indicates less scatter in strength and greater reliability of ceramics.

Water/cement ratio

Mass ratio of water to cement in a concrete mix; lower w/c increases strength and durability, while higher w/c improves workability but reduces strength.

Superplasticiser

A concrete admixture that significantly reduces water demand (typically 12–30%) by dispersing cement particles, allowing high-slump concrete without adding water.

Alkali–silica reaction

Concrete deterioration in which alkalis from cement react with reactive silica in aggregates to form a hygroscopic gel that swells and cracks the concrete.

0.2% offset yield strength

Stress at which the stress–strain curve deviates by 0.2% plastic strain from the linear elastic line; used for materials without a distinct yield point.

Charpy impact test

Notched-bar impact test (ISO 148-1 / ASTM E23) that measures the energy absorbed during fracture and is used to assess ductile-to-brittle transition behaviour.

Magnetic particle inspection

Non-destructive test in which a magnetic field is applied to a ferromagnetic component and magnetic particles reveal surface or near-surface discontinuities.

ASTM grain size number

A scale (ASTM E112) where the grain size number G is related to the number of grains per square inch at 100× magnification by N = 2^(G−1).

Concrete exposure classes

EN 206 classification (XC, XD, XS, XF, XA) that defines the environmental conditions a concrete element will face and sets limits on mix design and cover.

Prestressing strand

High-strength steel wire strand (commonly 7-wire, f_pk = 1770 or 1860 MPa) used to apply compressive force to concrete; susceptible to stress corrosion and hydrogen embrittlement.

Timber strength class

Designation such as C16 or C24 (EN 338) that specifies characteristic strength and stiffness values for structural timber of a given species group and grade.

Carbon equivalent

Formula CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 used to assess weldability; values above about 0.4 indicate a need for preheat to avoid cold cracking.

Bearing PV limit

Maximum product of contact pressure and sliding velocity that a bearing material can sustain without excessive wear or overheating in dry-running applications.

Insulation class

Classification (Y, A, E, B, F, H) of electrical insulation by maximum allowable operating temperature, ranging from 90 °C for class Y to 180 °C for class H.

Beach marks

Macroscopic progression markings on a fatigue fracture surface that indicate successive positions of the fatigue crack front during cyclic loading.

Miner's rule

Linear cumulative damage rule Σ(n_i/N_i) = 1, used to predict fatigue failure under variable-amplitude loading by summing fractional damage from each stress level.

Larson–Miller parameter

Creep rupture correlation P = T(C + log t_r), with C ≈ 20 for steels, used to extrapolate long-term rupture life from short-term elevated-temperature tests.

Life cycle assessment

ISO 14040/14044 methodology that quantifies environmental impacts of a product or structure over its whole life, including embodied carbon and end-of-life effects.

HKIE Code of Conduct

Professional code requiring members to act with integrity, competence and objectivity, avoid conflicts of interest, and give priority to public safety and health.

Earned value management

Project control technique using cost performance index CPI = EV/AC and schedule performance index SPI = EV/PV to measure cost and schedule efficiency against the baseline.