Tamil Nadu HSE Second Year Basic Mechanical Engineering cheat sheet

Ferrous metals contain iron as the principal element; cast iron has about 2–4% carbon, mild steel about 0.05–0.3% carbon, and high-carbon steel about 0.6–1.5% carbon.

Mechanical properties: elasticity regains shape after unloading; plasticity retains permanent deformation; ductility permits drawing into wire; malleability permits rolling into sheets; toughness absorbs energy before fracture; hardness resists indentation.

Within the proportional limit, Hooke's law gives stress/strain = E; typical Young's modulus is about 200 GPa for steel and about 70 GPa for aluminium.

Heat treatment: annealing softens and relieves stress; normalizing refines grain structure; hardening by quenching increases hardness; tempering after hardening reduces brittleness.

Alloy steels add Cr, Ni, Mo, V, Mn or Si to improve hardenability, strength, wear resistance or corrosion resistance compared with plain carbon steel.

Non-ferrous metals: copper has high electrical and thermal conductivity; aluminium has low density and good corrosion resistance; brass is Cu–Zn; bronze is Cu–Sn; bearing alloys have low friction.

Cast iron types: grey cast iron has graphite flakes and good damping; white cast iron has cementite and is hard but brittle; malleable cast iron is heat-treated; spheroidal graphite iron is ductile.

Material selection considers strength, density, machinability, weldability, corrosion resistance, availability and cost; no single property decides the choice for every component.

Scale representative fraction = drawing length / actual length; 1:2 is a reducing scale, 1:1 is full size, and 2:1 is an enlarging scale.

First-angle projection places the object between observer and plane; the front view is above the top view and the left side view appears on the right. Third-angle projection places the plane between observer and object; top view is above front view and right side view is on the right.

Line conventions: continuous thick lines for visible outlines, dashed lines for hidden edges, chain thin lines for centre lines, continuous thin lines for dimension and extension lines, and wavy lines for break boundaries.

A dimension needs a dimension line, extension lines, arrowheads and a numeral; radius is marked R, diameter Ø, spherical radius SR and spherical diameter SØ.

Sectional views use evenly spaced thin hatching lines usually at 45°; adjacent parts are hatched in opposite directions, and hidden details are omitted when a section clearly shows them.

Isometric axes are drawn at 30° to the horizontal; lengths along the axes are true lengths, while non-isometric lines are not true length; the isometric scale is about 0.816 of true length.

Orthographic projection shows true shape in principal views; an auxiliary view is used to show the true shape of an inclined surface that is foreshortened in the principal views.

Limits and fits: clearance fit has the hole larger than the shaft, interference fit has the shaft larger than the hole, and transition fit may give either clearance or interference; tolerance = upper limit − lower limit.

Equilibrium requires sum of forces = 0 and sum of moments = 0; a free-body diagram isolates the body and replaces supports by reaction forces or moments.

Moment = force × perpendicular distance from the pivot; a couple consists of two equal, opposite and parallel forces; torque = force × radius.

Direct stress σ = P/A and direct strain ε = ΔL/L; Young's modulus E = σ/ε; factor of safety = ultimate stress / allowable working stress.

Shear stress τ = V/A and shear strain γ = deformation/height; modulus of rigidity G = τ/γ.

Bending equation M/I = σ/y = E/R; bending stress is maximum at the fibre farthest from the neutral axis, and I depends on the cross-section shape.

Torsion equation T/J = τ/r = Gθ/L; for a solid circular shaft the polar moment is J = πd⁴/32.

SFD and BMD: a point load causes a shear jump and a moment slope change; a UDL gives linear shear and parabolic bending moment; maximum bending moment occurs where shear is zero.

Thermal stress = EαΔT when expansion is fully restrained; α is the coefficient of linear expansion and ΔT is the temperature change.

Sand casting sequence: pattern making, moulding, core setting, melting, pouring, solidification, shakeout, fettling and inspection.

Pattern allowances: shrinkage allowance compensates contraction, draft allows easy withdrawal, machining allowance provides extra metal, and distortion and rapping allowances correct expected changes.

Green sand mould contains silica sand, clay binder, water and additives; required properties include permeability, refractoriness, cohesiveness and collapsibility.

Welding includes fusion processes such as arc, gas, TIG and MIG, and solid-state processes such as friction and resistance spot welding; electrode coating stabilizes the arc and protects the weld.

Arc welding polarity: DCEN or straight polarity concentrates heat at the workpiece; DCEP or reverse polarity concentrates heat at the electrode; AC alternates direction.

Hot working is above the recrystallization temperature and cold working is below it; cold working causes strain hardening, while hot working permits large deformation.

Forging refines grain and improves strength; closed-die forging gives accurate shape; upsetting decreases height and increases diameter.

Casting defects include blowhole, shrinkage cavity, hot tear, cold shut, misrun and sand inclusion; each has specific cause and remedy.

Lathe operations include turning, facing, chamfering, knurling, threading, boring and drilling; the workpiece rotates and a single-point tool feeds along or across the axis.

Cutting speed V = πDN/1000 in m/min when D is in mm and N is in rpm; feed is in mm/rev; depth of cut = (D − d)/2 for turning.

Drilling uses a rotating twist drill with axial feed; reaming improves hole size and finish; boring enlarges an existing hole and corrects its location.

Milling uses a multi-tooth rotating cutter with work feed; up milling or conventional milling has cutter rotation opposing feed, while down milling or climb milling has cutter rotation in the feed direction.

Shaping uses a reciprocating single-point tool with intermittent feed; planing moves the work past the tool; slotting machines cut vertical internal surfaces.

Grinding uses an abrasive wheel; dressing reshapes the wheel face, truing restores its geometry, and coolant reduces heat and improves surface finish.

Tool materials: high-carbon steel for low speeds, HSS for toughness and red hardness, carbide for high speeds, and ceramic or diamond for very hard materials.

Chip types are continuous, discontinuous and built-up edge; coolant improves finish and tool life, and CNC machines use programmed coordinates for tool motion.

A closed system has fixed mass, an open system allows mass crossing its boundary, and an isolated system exchanges neither mass nor energy with surroundings.

First law for a closed system: Q = ΔU + W; energy is conserved, and work done by the system is usually taken positive.

Second law: heat cannot flow spontaneously from a colder body to a hotter body; entropy of an isolated system increases; no heat engine can be 100% efficient.

Ideal gas: PV = mRT; for air R is about 287 J/kgK; Cp − Cv = R and γ = Cp/Cv.

Processes: isothermal has T constant, adiabatic has Q = 0, isobaric has P constant and isochoric has V constant; a polytropic process follows PV^n = constant.

Work: isobaric W = P(V2 − V1); isothermal W = mRT ln(V2/V1); adiabatic W = (P1V1 − P2V2)/(γ − 1).

Thermal efficiency = W_net/Q_in = 1 − Q_out/Q_in; Carnot efficiency = 1 − T_cold/T_hot using absolute temperatures.

Entropy change ΔS = Q_rev/T; irreversible processes create entropy; enthalpy H = U + PV.

Steam formation: sensible heat raises water to saturation, latent heat of vaporization converts it to dry saturated steam, and further heating produces superheated steam; h = hf + xhfg for wet steam.

Dryness fraction x = mass of dry steam / total mass of wet steam; wet steam enthalpy = hf + xhfg, while superheated steam enthalpy is greater than hg.

Fire-tube boilers have hot gases inside tubes surrounded by water; water-tube boilers have water inside tubes; mountings are boiler fittings for safety and operation, while accessories improve efficiency.

Rankine cycle: pump, boiler, turbine and condenser; reheating and regeneration improve cycle efficiency, which depends on steam pressure and temperature.

Four-stroke SI engine: suction, compression, power and exhaust strokes; a spark plug ignites the petrol–air mixture; the cycle takes two crankshaft revolutions.

Four-stroke CI engine: fuel is injected near the end of compression and self-ignites; compression ratio is higher than in an SI engine because diesel ignites by heat of compression.

Compression ratio r = (Vs + Vc)/Vc; the Otto cycle efficiency is approximately 1 − 1/r^(γ−1), and actual engine efficiency is lower because of losses.

Valve timing: inlet opens before TDC and closes after BDC; exhaust opens before BDC and closes after TDC; valve overlap near TDC improves scavenging.

Fluid properties: density ρ = m/V, specific weight γ = ρg, specific gravity = ρ/ρ_water, and viscosity is resistance to shear deformation.

Pressure p = F/A; gauge pressure = absolute pressure − atmospheric pressure; hydrostatic pressure p = ρgh.

Continuity for steady incompressible flow: A1V1 = A2V2; mass flow rate ρAV remains constant.

Bernoulli equation in head form: P/ρg + V²/2g + z = constant along a streamline for ideal, steady, frictionless flow.

Flow regimes: laminar at Reynolds number below about 2000, transitional between about 2000 and 4000, and turbulent above about 4000; Re = ρVD/μ.

Centrifugal pumps use a rotating impeller to add energy; reciprocating pumps are positive displacement; cavitation occurs when local pressure falls below vapour pressure.

Turbines extract energy: Pelton is an impulse turbine for high head, Francis is a mixed-flow reaction turbine for medium head, and Kaplan is a propeller turbine for low head and high flow.

Pump overall efficiency η = ρgQH/P_shaft; turbine efficiency η = P_shaft/(ρgQH); Q is discharge and H is head.

Accuracy is closeness to the true value; precision is repeatability of readings; systematic errors have a consistent bias, while random errors vary unpredictably.

Vernier caliper least count = 1 main scale division − 1 vernier scale division; a common metric least count is 0.02 mm.

Micrometer least count = pitch / number of circular scale divisions; a common metric least count is 0.01 mm.

A dial gauge measures small linear displacements and is used with a magnetic stand for runout, flatness or alignment checks.

A sine bar sets or measures angles using sin θ = h/L, where h is the slip gauge height and L is the centre distance between rollers.

Limits are upper and lower permissible sizes; tolerance = upper limit − lower limit; the fit type depends on the relative tolerance zones of hole and shaft.

A Go gauge checks the maximum material condition and must pass; a No-Go gauge checks the minimum material condition and must not pass; gauges do not give actual size.

Surface roughness Ra is the average deviation from the mean line; a smaller Ra means a smoother surface; a profilometer measures roughness and waviness.

PPE includes safety helmet, eye goggles, ear plugs, gloves, safety shoes and respiratory mask; the correct type depends on the specific hazard.

Fire classes: A for solids, B for flammable liquids, C for gases, D for metals and E for electrical equipment; water is unsuitable for electrical and oil fires.

Maintenance types: preventive is scheduled servicing, predictive is condition-based, corrective is after a fault, and breakdown maintenance is emergency repair.

5S means sort, set in order, shine, standardize and sustain; it organizes the workplace and reduces time lost searching for tools.

Hand tools: spanner for nuts, screwdriver for screws, chisel for cutting, file for smoothing and hacksaw for metal cutting; use the correct size for the fastener or job.

Workshop safety: guard rotating parts, keep floors clear, clamp work securely, use a brush rather than a hand to remove chips, and wear eye protection.

Lockout/tagout isolates energy sources, applies locks and tags, and verifies zero energy before repair to prevent accidental startup.

Lifting: assess the load, use the correct sling, keep the load close, avoid jerking and never stand under a suspended load.