Lesson 1Mechanical behavior of steels: tensile strength, yield, fatigue limit, toughnessThis lesson looks at tensile strength, yield strength, ductility, and toughness in shaft steels, linking them to fatigue limits and crack growth. It discusses stress-strain curves, strain rates, temperature influences, and design safety factors.
Engineering stress–strain curves and key parametersYield criteria and work hardening in steelsImpact toughness and ductile-to-brittle behaviorFatigue limit, mean stress, and R-ratio effectsTemperature and loading rate influences on behaviorLesson 2Non-ferrous alternatives: bearing bronzes, aluminum alloys, and when to use themThis lesson compares bearing bronzes and aluminium alloys to steels for shafts. It covers strength, stiffness, resistance to galling, machinability, and costs, explaining when non-ferrous materials address corrosion, weight, or lubrication challenges.
Bearing bronzes for bushings and low-speed shaftsAluminum shaft alloys and weight reductionGalling, seizure, and compatibility with bearingsMachinability, cost, and supply considerationsSelection guidelines versus carbon and alloy steelsLesson 3Common shaft materials and grades: AISI 1045, 4140/42CrMo4, stainless options (AISI 304/316)This lesson reviews common shaft steels like AISI 1045, 4140/42CrMo4, and stainless 304/316. It compares compositions, hardenability, machinability, weldability, and corrosion resistance, with advice for typical shaft uses in Botswana industries.
Chemical composition of 1045, 4140, 42CrMo4Strength and hardenability differences by gradeMachinability, weldability, and heat-treat response304 vs 316 stainless: corrosion and cost tradeoffsApplication mapping to torque and environmentLesson 4Failure modes and fatigue life estimation methods (S-N curves, Goodman, Miner’s rule)This lesson explains shaft failure types and fatigue life prediction. It includes high- and low-cycle fatigue, S-N curves, Goodman and Gerber diagrams, Miner’s rule, and handling stress raisers, surface finish, and varying loads.
Typical shaft failure modes and fracture featuresGenerating and interpreting S–N fatigue curvesGoodman and Gerber mean stress correctionsMiner’s rule and cumulative damage assessmentStress concentrations and surface finish factorsLesson 5Surface engineering for shafts: carburizing, nitriding, induction hardening, chrome platingThis lesson reviews surface treatments for shafts like carburizing, nitriding, induction hardening, and chrome plating. It compares case depths, hardness, residual stresses, distortion risks, and fit for various load conditions.
Carburizing cycles, case depth, and distortionGas and plasma nitriding for wear and fatigueInduction hardening of journals and shouldersHard chrome plating and alternative coatingsResidual stresses and grinding burn controlLesson 6Corrosion and wear behaviour in wash-down environmentsThis lesson examines corrosion and wear of shaft materials in wash-down settings. It covers water-based chemicals, stainless steel performance, crevice corrosion, erosion, and tribocorrosion, plus design and upkeep strategies for longer life.
Typical wash-down chemistries and exposure cyclesStainless steel behavior and pitting mechanismsTribocorrosion: combined wear and corrosion effectsSeal design, drainage, and crevice avoidanceCleaning, passivation, and inspection practicesLesson 7Standards and specifications for shafts (dimensional, material, mechanical property limits)This lesson outlines main shaft standards, including size tolerances, material grades, mechanical limits, and checks. It shows how to read standards and record compliance in engineering plans for Botswana manufacturing.
Relevant ISO, DIN, and ANSI shaft standardsMaterial designation and traceability rulesSpecified mechanical property ranges and testsDimensional tolerances and geometric controlsCertification, inspection, and test reportingLesson 8Design allowances and tolerances: keyways, fits, surface finish impact on fatigue lifeThis lesson covers design fits and tolerances for shafts, like keyways, runout, and surface finish. It explains how finish quality, radii, and geometry affect stress points, fitting, and fatigue endurance.
ISO and ANSI fit classes for shaft–hub jointsKeyway geometry, fillets, and stress raisersRunout, straightness, and balance tolerancesSurface roughness and fatigue strength reductionMeasurement methods and drawing specificationLesson 9Microstructure and property relations: ferrite/pearlite, martensite, tempered martensite, bainiteThis lesson connects steel microstructures like ferrite-pearlite, martensite, tempered martensite, and bainite to strength, toughness, and fatigue resistance. It covers heat treatments, hardness patterns, and how microstructure variations impact shaft performance.
Ferrite–pearlite in normalized and hot-rolled barsQuenched martensite and associated brittlenessTempered martensite for strength–toughness balanceBainitic structures and fatigue performanceMicrostructural gradients in large diameter shafts
