Applied Mechanical Design

Ammar Grous, CEGEP de l'Outaouais, Gatineau, Quebec, Canada.

• Preface xiiiIntroduction xvChapter 1 Case Study-based Design Methodology 11.1 Methodology for designing a project product 11.2 Main players involved in the design process 21.3 Conceptualization and creativity 41.4 Functional analysis in design: the FAST method 41.4.1 Decision-support tools in design 51.5 Functional specifications (FS) 71.5.1 Operational functions, using the APTE method or octopus diagram 81.5.2 Linguistic (or syntactical) writing of the functional specifications 101.6 Failure Mode Effects and Criticality Analysis 101.7 PERT method 131.7.1 Logic of construction of the graph per level of operations 141.7.2 Statistical approach to the PERT diagram using the Gamma distribution 161.8 The Gantt method (Henry Gantt’s graph, devised 1910) 171.9 Principal functions of a product 201.10 Functional analysis in mechanical design 211.10.1 Product cost in mechanical design 221.10.2 Creation- and monitoring sheets in mechanical design 221.11 Scientific writing on a project 281.11.1 Project process 281.11.2 Development of the conceptual model 291.11.3 Development (recap) on a spiral model 301.12 Esthetics of materials in mechanical design 301.13 Conclusion 31Chapter 2 Materials and Geometry in Applied Mechanical Design, Followed by Case Studies 332.1 Introduction to materials in design 332.2 Optimization of mass in mechanical design 382.3 Case study of modeling based on the material–geometry couple 392.4 Geometry by standard sections in strength of materials 422.4.1 Choice of materials in design (airplanes and bikes) 462.4.2 Form factors ψ of some usual cross-sections 492.4.3 Form factors in mechanical design 502.5 Case study of design of multi-purpose items 512.6 Case study of superposed bimetallic materials 552.7 Curving and incurvate elements by sweeping of sheet metals 582.7.1 Sensible choice of optimizing materials in Palmer micrometers 592.8 Conclusion 60Chapter 3 Geometrical Specification of GPS and ISO Products: Case Studies of Hertzian Contacts 633.1 Introduction 633.2 Dimensional and geometrical tolerances in design 653.2.1 Case study of a bicycle wheel hub 673.3 Envelopes and cylinders under pressure (for R/e < 20) 723.4 Case study 763.5 Rotating cylinders with a full round cross-section: flywheel 763.5.1 Materials used for flywheels with centrifugal effects 783.6 Press fit and thermal effects through bracing 803.7 Case study applied to bolted tanks 833.8 Case studies applied to contact stresses (Hertz) in design 893.8.1 First case: sphere-to-sphere contact 903.8.2 Second case: contact between two parallel cylinders 933.9 Conclusion 96Chapter 4 Design of Incurvate Geometries by Sweeping 974.1 Introduction 974.2 Case studies 994.2.1 Case study 1: frame sweeping 994.2.2 Case study 2: frame sweeping 1014.2.3 Case study 3: frame sweeping 1044.2.4 Case study 4: frame sweeping 1064.2.5 Case study 5: example of a connecting rod of SAE 8650 1094.2.6 Case study 6: swept double elbow 1114.2.7 Case study 7: frame sweeping 1134.3 Conclusion 115Chapter 5 Principles for Calculations in Mechanical Design: Theory and Problems Strength of Materials in Constructions 1175.1 Essential criteria of constructions in design 1175.1.1 Stress intensification in shafts and beams 1185.1.2 Homogeneous, solid, round sections 1195.1.3 Homogeneous, solid, square sections with recessed section 1195.1.4 Homogeneous, hollow, square sections, with no external variation 1205.1.5 Homogeneous, solid, round sections with a shoulder (shouldered shaft) 1215.1.6 Homogeneous, solid, rectangular or square sections, with a groove 1215.1.7 Homogeneous, hollow, round and flat sections (pierced flat piece with an axle) 1225.1.8 Homogeneous, hollow, round sections (shaft with groove) 1225.2 Principles of calculations for constructions in design 1235.2.1 Example on stress intensifications 1245.2.2 Case study on torsion angles 1265.2.3 Case study: Tresca and von Mises yield criteria 1305.3 Pressurized recipients and/or containers 1335.4 Calculation principles and solution method for compound loading 1355.4.1 Case study: mechanical fit 1385.4.2 Case study of a profiled piece stressed under conditions of elasticity 1435.5 Buckling of elements of machines, beams, bars, shafts and stems 1445.5.1 Case study: buckling of an I-beam according to AISI specifications 1475.5.2 Case study: I-beams and U-beams, homogeneous and isotropic 1495.6 Design of stationary and rotating shafts 1525.6.1 Design (dimensioning) of shafts subjected to rigidity 1545.6.2 Case study 1, solution 1 1565.6.3 Case study 2 with solution: shear, moments, slope, elasticity deflection Applied SOM in mechanics and civil engineering 1565.7 Power transmission elements: gear systems and pulleys 1595.7.1 Case study 1595.7.2 Case study: statement of problem 2 1615.7.3 Case study: statement of problem 3 1635.8 Sizing and design of couplings 1655.8.1 Design of a universal coupling, known as a Hooke coupling 1675.9 Design of beams and columns 1705.9.1 Solved case study: bending and torsion of a shaft 1725.9.2 Case study 3: equivalent bending moment and ideal moment on a shaft 1765.9.3 Case studies: maximum performance of pre-stressed bi-materials 1775.9.4 Case study: deflection and buckling of elements of machines 1785.10 Case studies using the Castigliano method 1805.11 Conclusion 183Chapter 6 Noise and Vibration in Machine Parts 1856.1 Noise and vibration in mechanical systems 1856.1.1 Aerodynamism of moving mechanical bodies 1886.2 Case study 1 1896.2.1 Lightweight vehicles and trucks 1896.2.2 Case study 1 1916.2.3 Case study of the rotor blade of a fire brigade helicopter 1946.3 Vibration of machines in mechanical design 1956.4 Case studies with a numerical solution 2016.4.1 Case study: input parameters: M = 1; k = 1; φ0 = 1 and c = 2.25 2016.4.2 Case study: system with free vibrations 2026.4.3 Case study: problem with solution and discussion 2046.4.4 Case study: problem 3 with solution 2066.4.5 Case study: problem 2 Engine represented on two springs 2076.4.6 Case study based on a concrete problem with solution 2126.5 Critical speeds of shafts in mechanical systems 2156.5.1 Case study with solution and discussion 2186.5.2 Method of approximation using the Dunkerley equations 2226.5.3 Method of approximation using the Rayleigh–Ritz equation 2236.5.4 Method of approximation using the equations of the rotation frequencies 2246.5.5 Method for solving the function F(ωc): roots → (r0 and r1) 2246.6 Conclusion 225Chapter 7 Principles of Calculations for Fatigue and Failure 2277.1 Mechanical elements of failure through fatigue 2277.2 Analysis of materials and sizing in applied design 2297.3 Sizing of pivot joints with bearings 2327.3.1 Basic formulae for calculating lifetime 2337.3.2 Determination of the minimum viscosity necessary 2387.4 Faults of form and position of ranges on the operating clearance fit 2397.5 Friction and speed of bearings 2407.6 Sizing of bearing pivot joints and lifetime 2417.7 Case study: statement of the problem 2437.7.1 Internal clearance fit of bearings 2447.8 Biaxial stresses combined with shear for ductile materials in concrete application 2467.9 Fundaments of sizing in mechanical design Soderberg equations in fatigue of ductile materials 2487.9.1 Application of Soderberg equations 2487.9.2 Stress intensification factors (SIFs) 2497.9.3 Case study 2507.10 Welding and fatigue 2537.10.1 Case study: calculation of resistance of weld joints in design 2547.10.2 Real-world case study: welded cross-shaped structure 2567.10.3 Case study: fracture mechanics and stresses 2617.10.4 Case study in fatigue fracture mechanics 2627.11 Limits of performance and of strength in the elastic domain 2677.12 Proposed project: outboard motor for a small boat 2697.13 Conclusion 270Chapter 8 Friction, Brakes and Gear Systems 2718.1 Friction, materials and design of assembled systems 2718.2 Buttressing of mechanical connections 2748.3 Case study: principles of calculations for brakes 2798.3.1 Design of a double brake block by calculation 2818.3.2 Design of inner double-shoe block brake 2828.3.3 Design of a band brake block 2848.3.4 Examples of principles of calculations for brake design, with solutions 2878.3.5 Case study: hypothesis of the design of a double-shoe brake 2898.3.6 Case study: hypothesis of the band brake whose drum has a radius R (mm and in) 2918.3.7 Case study: differential brake using a roller pressed against a drum 2928.3.8 Symmetrical shoe brake pressed against a drum with radius R 2948.4 Principles of calculations of a gear system or gear disc 2988.4.1 Case study: principles of calculations for gear systems 2998.4.2 Analysis and choice of the dimensions of the cam gear system 3008.4.3 Sizing of a cam gear system and case study 3018.4.4 Case study: principles of calculations for gear systems in design 3048.4.5 Conical gear system 3078.5 Flywheels and rims (discs and rims) 3098.5.1 Flywheel for a solid disc 3118.5.2 Flywheel system with rim and discs (internal and external) made of cast iron 3128.5.3 Flywheel: numerical applications Hypothesis II 3148.6 Conclusion 315Chapter 9 Sizing of Creations 3179.1 Elastic machine elements and bolted assemblies 3179.2 Dimensions (sizing) of bolted assemblies 3219.3 Fatigue, shocks and endurance of bolted assemblies 3249.4 Springs in mechanical design 3259.4.1 Materials and geometry of compression springs 3269.4.2 Case study of helical springs in mechanical design 3389.4.3 Case study of a spring in a rocker switch 3409.4.4 Verification of buckling of compression spring 3449.5 Simple blade and spiral blade springs 3459.6 Main expressions of design calculations for Belleville washers 3469.7 Power transmission Case study: hoist 3479.7.1 Power transmission and simple drum brake 3489.8 Case study on couplings 3509.8.1 Case study: analysis in design of brake elements 3519.9 Case study on power transmission: external spring clutch 3529.9.1 Case studies: power transmission Bolted assembly 3539.9.2 Computer-assisted design of a hub (bolted assembly) 3559.10 Couplings and machine elements subjected to stress at high speeds 3569.10.1 Determination of the error in position of the shaft 3579.10.2 Determination of the output velocity of the shaft 3589.11 Design of spring rings 3599.12 Principle of calculations for a Belleville washer: case study 3619.13 Determination of the pressing moment for a bolted assembly 3629.14 Power transmission by epicyclic gear system 3639.15 Conclusion 365Chapter 10 Design of Plastic Products 36710.1 Calculations for the design of plastic parts 36710.1.1 Mechanical parameters used during traction tests 36810.2 Jointing of a ball bearing in a metal casing 37010.3 Cylindrical clip of PP (e.g blinds): force exerted 37110.3.1 Spherical clip of a PP: force exerted 37410.4 Types of clip fitting: counter-cylindrical cantilever 37610.4.1 Conical cantilever 37810.4.2 Short cantilever 37810.5 Configuration of strips: two-dimensional spline interpolation 38110.5.1 Graphs of the model of the original surface 38310.6 Press assembly 38310.7 Reduction of stress relaxation: bolts and self-tapping screws 38510.8 Case study: piping link 38610.9 Assembly by forced jointing 38810.10 Stress and thermal swelling in assembled materials 39110.10.1 Stress intensifications 39310.11 Capacity and reliability of roller bearings (plastic and otherwise) 39510.12 Safe stress of the appropriate material for a plastic clutch system 39610.13 Case study: plastic ball bearings 39810.13.1 Calculation of the lifetime of roller bearings 40110.14 Limits of performances of polymer design 40110.15 Case study: fan with plastic blades 40210.16 Conclusion 404Chapter 11 Mechanical Design Projects 40511.1 Proposed projects in mechanical design 40511.2 Case studies of hoisting and handling devices 40511.3 Projects design proposal for a lifting winch 40611.3.1 Case study: parameters in sketching a lifting hook 40811.3.2 Principles of calculations of the resistance of a lifting hook 40911.3.3 Calculation and design (choice) of the round-wire coil spring 41211.4 Calculation and design of a bolted assembly 41411.5 Yield of power transmission of a screw mechanism 41711.5.1 Calculations of stresses on the threads of a screw mechanism 41911.5.2 Calculations of stresses at the root of the thread in a screw mechanism 42011.5.3 Case study: numerical applications 42011.6 Project 2: case studies: scooter 42411.6.1 Presentation of the main parts 42611.7 Project 3: dental hygiene dummy 42811.7.1 Support clamped to the lab bench in the dental hygiene department 43511.7.2 Case studies of a complete block and crank link 43811.7.3 Explanatory photographic definition of the final product 439Conclusion 443Appendix 445Bibliography 467Index 471