QCAA Engineering EA cheat sheet

The engineering method cycles: define the problem, research constraints, generate concepts, analyse and select, prototype, test, evaluate, iterate; documentation runs alongside every stage.

A design brief states function, client needs, constraints and success criteria; a specification converts these into measurable, testable requirements with tolerances.

Constraints are fixed limits (budget, standards, materials); criteria are variables traded off in selection, commonly weighted in a decision matrix scored out of a common scale.

Systems thinking separates inputs, processes, outputs and feedback; open systems exchange mass or energy with surroundings, closed systems do not.

Functional decomposition breaks a system into sub-functions mapped to components; a function-means tree links each required function to candidate solutions.

Standard units: SI base units include metre, kilogram, second, ampere, kelvin, mole, candela; derived units combine them (N = kg·m/s², Pa = N/m², J = N·m, W = J/s).

Significant figures and unit consistency: carry units through every calculation; conversion errors and unit mismatch are the most common source of wrong answers.

Iteration is evidence-based: each prototype test should produce measurable data compared against the specification, not opinion.

Mechanical properties: strength (stress at failure or yield), stiffness (modulus), ductility (strain at fracture), toughness (area under stress–strain curve), hardness (scratch/indentation resistance).

Stress σ = F/A; engineering strain ε = ΔL/L₀; Young's modulus E = σ/ε in the linear elastic region; Hooke's law σ = Eε.

Ductile materials show large plastic strain before fracture (mild steel); brittle materials fracture with little plastic deformation (cast iron, glass, ceramics).

Yield strength is the stress at the onset of plastic deformation, often taken by the 0.2% offset method on the stress–strain curve.

Ferrous metals: carbon content raises hardness and strength but lowers ductility and weldability; alloying (Cr, Ni, Mo) improves corrosion resistance or hardenability.

Non-ferrous metals: aluminium has low density and good corrosion resistance but lower stiffness; copper alloys offer high electrical and thermal conductivity.

Polymers: thermoplastics soften on reheating (recyclable), thermosets cross-link permanently; both have low stiffness and creep under sustained load.

Composites combine a stiff, strong fibre with a matrix; properties are directional (anisotropic) and depend on fibre volume fraction and orientation.

Material selection uses Ashby-style charts and indices (e.g. stiffness-to-density E/ρ) matched to the dominant loading and constraint.

Equilibrium of a particle: ΣF = 0, so ΣFx = 0 and ΣFy = 0; for a rigid body add ΣM = 0 about any point.

Moment M = F × d, where d is the perpendicular distance from the pivot to the line of action; units N·m.

A couple is two equal, opposite, parallel forces; its moment equals F × the perpendicular separation and is the same about any point.

Free-body diagrams isolate the body, show all external loads and reactions, and are the required first step before equilibrium equations.

Supports: a roller provides one reaction normal to the surface; a pin provides two reaction components; a fixed support provides two forces plus a moment.

Truss analysis assumes pin joints, loads applied only at joints, and members carrying axial force only (tension or compression).

Method of joints solves two unknowns per joint via ΣFx = 0 and ΣFy = 0; the method of sections cuts three members and uses ΣM = 0.

Centroid of a composite area: x̄ = Σ(Aᵢxᵢ)/ΣAᵢ and ȳ = Σ(Aᵢyᵢ)/ΣAᵢ; for symmetric sections the centroid lies on the axis of symmetry.

Friction limit: Fmax = μN, where μs applies at impending motion and μk during sliding; μk is generally less than μs.

Linear motion: v = u + at; s = ut + ½at²; v² = u² + 2as; these apply only for constant acceleration.

Newton's second law: F = ma; weight W = mg with g ≈ 9.81 m/s² near Earth's surface.

Work W = Fs cosθ (θ between force and displacement); power P = W/t = Fv; efficiency = useful output energy / input energy × 100%.

Kinetic energy KE = ½mv²; gravitational potential energy ΔPE = mgΔh; elastic strain energy in a spring U = ½kx².

Conservation of energy: total mechanical energy is constant when only conservative forces act; friction converts mechanical energy to heat.

Impulse J = FΔt = Δ(mv); momentum p = mv is conserved in collisions when no external net force acts.

Circular motion: v = 2πr/T; centripetal acceleration a = v²/r directed toward the centre; centripetal force F = mv²/r.

Rotational equivalents: torque τ = Fd, angular velocity ω = 2πn/60 for n in rpm, and power P = τω.

Simple machines trade force for distance: mechanical advantage = load/effort; velocity ratio = effort distance/load distance; efficiency = MA/VR × 100%.

Orthographic projection shows an object in multiple views (front, top, side); first-angle and third-angle differ in how views are arranged relative to the front view.

A section view cuts the object to reveal internal features; hatching indicates cut material and section lines follow standard conventions.

Dimensioning rules: dimensions give true size, are placed on the view showing the feature, avoid duplication, and use a single unit convention.

Tolerances define allowable variation; clearance = hole size − shaft size; fits range from clearance through transition to interference.

Geometric tolerancing controls form, orientation and location (flatness, perpendicularity, position) independently of size tolerance.

Scale drawings state the ratio (e.g. 1:10 or 2:1); scale factor conversions must be applied to every dimension and area scales as the square.

CAD modelling: parametric models drive geometry from constraints and dimensions; assemblies use mates to define relative motion; drawings are generated from the 3D model.

Isometric and oblique sketches communicate 3D form; isometric axes are 120° apart, while oblique keeps the front face true shape.

Line conventions: visible outlines solid thick, hidden features dashed, centre lines chain-dashed, and dimension lines thin with arrowheads.

Design phases: needs analysis, concept design, embodiment, detailed design, manufacture, verification; each phase has review gates.

Design for manufacture and assembly (DFMA) reduces part count, standardises fasteners and simplifies handling to cut cost and defects.

Manufacturing processes: casting (complex shapes), forging (strong grain flow), machining (precision), welding (joining), injection moulding (high-volume polymers).

Tolerances and surface finish drive process choice: tighter tolerance and finer finish generally raise cost non-linearly.

Quality tools: control charts distinguish common-cause from special-cause variation; Pareto analysis ranks defect causes by frequency.

Project scheduling: a Gantt chart shows timing of tasks; a critical path network identifies the longest dependent path and the minimum project duration.

Float (slack) = late start − early start; tasks on the critical path have zero float, so any delay there delays the whole project.

Risk management scores risk as likelihood × consequence and assigns mitigation to high-score items before execution.

Cost estimating combines material, labour, machine and overhead costs; a bill of materials supports both costing and procurement.

Sustainable design considers the triple bottom line: environmental, social and economic outcomes across the full life cycle.

Life cycle assessment quantifies impacts from raw material extraction through manufacture, use and end-of-life (cradle to grave).

Design for sustainability strategies include material efficiency, recyclability, energy efficiency in use, and extended product life.

Embodied energy and carbon are the energy and emissions tied to making a product; operational energy is used during service life.

The waste hierarchy ranks prevention, reuse, recycling, recovery and disposal, in that order of preference.

Professional ethics: engineers hold public safety paramount, report honestly, declare conflicts of interest, and act within competence and codes of practice.

Hierarchy of control for safety: eliminate, substitute, engineer controls, administrative controls, then personal protective equipment.

Risk is reduced by designing out hazards (inherently safe design) rather than relying on warnings or training.

Standards and regulation (e.g. Australian Standards, WHS legislation) set minimum compliance; conformity assessment verifies compliance before release.

Problem definition precedes solution: an unclear problem statement leads to solving the wrong problem, so requirements are validated with the client.

Verification confirms the design meets the specification; validation confirms the product meets the user's actual need; both are required.

Brainstorming and morphological analysis generate concept variants by combining sub-solution options for each function.

Weighted decision matrices normalise criteria weights to sum to 1 and score each concept on a consistent scale (e.g. 1–5).

Sensitivity analysis tests whether the chosen concept still wins if criterion weights change, revealing robust versus fragile decisions.

Prototyping types: proof-of-concept (feasibility), form (appearance/ergonomics), and functional/pre-production (performance) models serve different purposes.

Failure analysis tools: root cause analysis (5 Whys, fishbone) trace symptoms to underlying causes rather than blame.

Technical reports follow a structure: aim, background, method, results, discussion, conclusion, references, with data in labelled tables and graphs.

Hardness scales: Brinell (large indenter, coarse materials), Vickers (wide range), Rockwell (rapid production testing); values are not directly interchangeable.

Fatigue failure occurs under repeated cyclic stress below yield strength; fatigue life improves with smooth surfaces and compressive residual stress.

Creep is time-dependent deformation under sustained load, significant at high temperature relative to melting point (polymers, turbine alloys).

Corrosion: galvanic corrosion occurs when dissimilar metals contact in an electrolyte; the more anodic metal corrodes.

Protective methods: coatings, cathodic protection, alloying, and design that avoids trapped water and dissimilar-metal contact.

Thermal properties: thermal expansion coefficient α drives ΔL = αL₀ΔT; mismatched expansion causes thermal stress in joined materials.

Electrical conductivity in metals decreases with rising temperature; insulators (polymers, ceramics) have very low conductivity.

Heat treatment of steel: quenching forms hard, brittle martensite; tempering restores toughness by controlled reheating.

Recycling: metals are highly recyclable without property loss; mixed or thermoset polymers are difficult to separate and reprocess.

Resultant of concurrent forces: resolve into x and y components, sum, then R = √(Rx² + Ry²) and θ = tan⁻¹(Ry/Rx).

Beam reactions: for a simply supported beam with point loads, take moments about one support to find the other reaction, then use ΣFy = 0.

Shear force diagram steps by the load magnitude at point loads; bending moment is the area under the shear diagram and is maximum where shear is zero.

A uniformly distributed load w over length L gives total load wL acting at its centroid, and maximum bending moment wL²/8 for a simply supported beam.

Bending stress σ = My/I, where M is moment, y distance from neutral axis, I second moment of area; maximum stress occurs at maximum y.

Second moment of area for a rectangle about its centroid: I = bh³/12; parallel axis theorem I = I_c + Ad².

Section modulus Z = I/y_max, so σ_max = M/Z; a larger Z reduces bending stress for the same moment.

Buckling of a slender column under axial compression depends on length, end conditions and stiffness, not just material strength.

Static determinacy: a 2D structure needs three independent reactions; more than three creates redundancy requiring compatibility methods.

Projectile motion separates horizontal (constant velocity) and vertical (constant acceleration g) components; time of flight depends only on vertical motion.

Relative velocity adds vectors: v_A relative to B = v_A − v_B, handled component-wise.

Friction on an incline: component of weight along the slope is mg sinθ; the normal reaction is mg cosθ.

Moment of inertia resists angular acceleration: τ = Iα; for a solid disc I = ½mr², for a rod about its centre I = (1/12)mL².

Rotational kinetic energy KE = ½Iω²; a rolling body's total KE combines translation and rotation.

Angular kinematics mirror linear: ω = ω₀ + αt; θ = ω₀t + ½αt²; ω² = ω₀² + 2αθ (constant α).

Conservation of mechanical energy neglects losses; real systems lose energy to friction and air resistance, so output energy is always less than input.

Stress and strain energy: strain energy density in the elastic region = ½σε = σ²/(2E).

Fluid pressure p = F/A and hydrostatic pressure p = ρgh increase with depth; flow rate Q = Av (continuity) for incompressible flow.

Third-angle projection places the top view above the front view and the right-side view to the right; first-angle places the top view below the front view.

Auxiliary views show features that are inclined to all principal planes in true shape, projected perpendicular to the inclined surface.

Detail drawings dimension individual parts; assembly drawings show part relationships, item numbers and a parts list.

A title block records drawing number, scale, projection symbol, units, material, tolerances and revision history.

Datums establish a reference origin for dimensions and geometric tolerances, ensuring consistent inspection.

CAD workflow: sketch, constrain (coincident, parallel, perpendicular, tangent), dimension, then extrude or revolve into a solid feature.

File exchange formats: DXF/DWG for 2D drawings, STEP/IGES for 3D solids, STL for mesh/3D printing; STEP preserves solid geometry best.

Graphs in reports need labelled axes with units, a descriptive caption, and a stated trend or conclusion drawn from the data.

Ergonomic design uses anthropometric data (5th–95th percentile ranges) so products fit most users; adjustable designs extend the range.

Tolerances stack: worst-case tolerance stack sums individual tolerances; statistical (root-sum-square) stacking assumes independent variation.

Process capability Cp = (USL − LSL)/(6σ); Cpk additionally accounts for how centred the process is within the limits.

Lean manufacturing targets the seven wastes (overproduction, waiting, transport, overprocessing, inventory, motion, defects).

Just-in-time production reduces inventory but increases vulnerability to supply disruption; buffer stock trades cost against resilience.

Earned value: schedule variance = EV − PV; cost variance = EV − AC; negative values indicate behind schedule or over budget.

Prototyping and testing stages: alpha (internal), beta (external users), then production release; each stage has defined exit criteria.

A work breakdown structure decomposes deliverables into manageable tasks that can be estimated, scheduled and assigned.

Bill of materials lists components, quantities and specifications; it links design data to purchasing and assembly instructions.

Carbon footprint sums greenhouse gas emissions (often as CO₂-equivalent) across the product life cycle.

Renewable versus non-renewable energy: renewables (solar, wind, hydro) are replenished naturally; fossil fuels are finite and emit CO₂ when burned.

Circular economy keeps materials in use through repair, remanufacture and recycling, replacing the linear take-make-dispose model.

WHS risk assessment: identify hazards, assess likelihood and severity, apply controls, then review and record.

Incident reporting and safety data sheets (SDS) communicate chemical hazards, handling and first-aid requirements.

Whistleblowing and duty to report: engineers who identify a serious public safety risk must escalate through appropriate channels, even against employer pressure.

Intellectual property: patents protect novel, useful inventions for a limited term; copyright protects drawings and documentation automatically.

Equity in design considers accessibility (e.g. universal design principles) and impacts on diverse community groups.

Greenwashing is unsubstantiated sustainability claims; genuine claims are supported by measurable, verifiable data.

Requirements should be SMART: specific, measurable, achievable, relevant and time-bound, so each can be tested.

Trade-off analysis documents why a chosen design sacrifices one criterion (e.g. mass) to gain another (e.g. strength).

Testing plans define the variable measured, the instrument, sample size and acceptance threshold before testing begins.

Measurement uncertainty: every instrument has resolution and accuracy limits; report results with appropriate precision and uncertainty.

Error types: systematic error shifts all readings in one direction (calibration); random error scatters readings and reduces with averaging.

Reverse engineering analyses an existing product's function, materials and manufacturing to inform new designs without copying protected IP.

Design reviews (preliminary and critical) catch errors early; cost of correction rises sharply the later a defect is found.

Traceability matrices link each requirement to the design element and test that verifies it.

Frames and machines contain multi-force members that may carry bending; unlike trusses, their members are not necessarily two-force.

A two-force member has forces applied only at two points, so the resultant force acts along the line joining them.

Cable and pulley systems: an ideal frictionless pulley changes force direction but not magnitude; multiple rope segments share the load.

Centroid versus centre of mass versus centre of gravity: identical for uniform density and gravity fields, otherwise distinct.

Distributed load equivalent: replace with a single resultant at the load's centroid for reaction calculations.

Hydrostatic force on a vertical surface F = ρg × (depth to centroid) × area, acting at the centre of pressure below the centroid.

Stability: an object topples when the line of action of its weight falls outside its base; a lower centre of gravity and wider base increase stability.

Torsion in a circular shaft: τ = Tr/J, where J is the polar second moment of area; maximum shear occurs at the outer surface.

Factor of safety = failure stress / allowable working stress; values above 1 provide margin against uncertainty and overload.

Free fall from rest: v = gt and s = ½gt²; air resistance reduces acceleration as speed rises until terminal velocity.

Graph interpretation: the slope of a displacement–time graph is velocity; the slope of a velocity–time graph is acceleration; area under velocity–time is displacement.

Newton's third law pairs act on different bodies, so they never cancel in a free-body diagram of a single object.

Tension in a lift cable: T = m(g + a) when accelerating upward, T = m(g − a) when accelerating downward.

Springs: Hooke's law F = kx; springs in parallel add stiffness (k₁ + k₂), springs in series combine as 1/k = 1/k₁ + 1/k₂.

Power in linear motion P = Fv; a vehicle climbing a slope must overcome both gravity component and rolling resistance.

Coefficient of restitution e = relative separation speed / relative approach speed; e = 1 elastic, e = 0 perfectly inelastic.

Gear trains: velocity ratio = driven teeth / driving teeth; torque increases proportionally as speed decreases (ideal gears).

Energy audits: energy input = useful output + losses (heat, sound, friction); efficiency is always below 100% in real machines.

Hidden detail is shown dashed only where necessary; overlapping hidden lines are omitted for clarity.

Centre lines mark axes of symmetry and hole centres and extend slightly beyond the feature outline.

A broken-out section reveals part of an internal feature without a full section view; a half section shows one quarter removed.

Thread representation: external threads shown with a thick major diameter and thin minor diameter line; thread callouts give nominal size and pitch.

Surface finish symbols specify roughness (Ra) and machining requirements where tolerance alone is insufficient.

Drawing revision control: each change gets a revision letter or number with date and description, so superseded drawings are traceable.

3D printing (additive manufacturing) builds from sliced layers; layer height and orientation affect strength and surface finish.

Orthographic to isometric conversion: measure along the three isometric axes at 30° from horizontal, keeping true lengths along each axis.

Schematic versus layout drawings: schematics show function and connections, layouts show physical position and routing.

Concurrent engineering runs design, manufacturing and support planning in parallel to shorten time to market.

Standardisation and modularity reduce variety, simplify spares and lower lifecycle cost.

Process selection matrix: match material, batch size, tolerance and surface finish to candidate processes before costing.

Six Sigma DMAIC: define, measure, analyse, improve, control; it targets reduction of process variation and defects.

PERT uses three time estimates (optimistic, most likely, pessimistic) to model schedule uncertainty; critical path method uses single deterministic estimates.

Resource levelling shifts non-critical tasks within their float to smooth peaks without extending the project duration.

Change control: any design or scope change is documented, assessed for cost and schedule impact, approved, then implemented.

Acceptance testing compares finished product against specification criteria; non-conformance triggers rework, concession or rejection.

Stakeholder communication plans define audience, message, channel and frequency for project reporting.

Environmental impact assessment predicts likely effects of a project before approval, including cumulative and indirect impacts.

Energy payback period = embodied energy / annual energy saved; shorter payback indicates a better sustainability return.

Design for disassembly uses reversible fasteners and material labelling so components can be recovered at end of life.

Safety in design (Safe Design) requires hazards to be considered at concept stage, when changes are cheapest.

Codes of ethics typically require competence limits: engineers must not accept work outside their expertise without support.

Conflict of interest must be disclosed and managed, not merely avoided; transparency protects public trust.

Regulatory approval processes (e.g. building, electrical, environmental) verify compliance before operation; operating without approval is unlawful.

Social licence to operate reflects community acceptance; consultation and honest impact communication build it.

Data and privacy ethics: designs collecting user data must minimise collection, secure storage and obtain informed consent.