1. Chapter 1: Introduction

2. WHAT IS A MACHINE MACHINE : A device for transforming or transfering energy MACHINE : A device for transforming or transfering energy An apparatus consisting of interrelated units (machine elements) An apparatus consisting of interrelated units (machine elements) A device that modifies force and motion A device that modifies force and motion

3. A machine receives energy in some available form and uses it to do some particular kind of work A machine receives energy in some available form and uses it to do some particular kind of work A petrol engine is a machine, which may use the heat energy derived from the combustion of the fuel to propel a vehicle along the road A petrol engine is a machine, which may use the heat energy derived from the combustion of the fuel to propel a vehicle along the road

4. A lathe is a machine which receives mechanical energy from the line shaft through the belt or gears and uses that energy to remove metal from a bar or other piece of work A lathe is a machine which receives mechanical energy from the line shaft through the belt or gears and uses that energy to remove metal from a bar or other piece of work LINK OR ELEMENT : Each part of a machine which has motion relative to some other part LINK OR ELEMENT : Each part of a machine which has motion relative to some other part STRUCTURES : Made up of series of members of regular shape that have a particular function for load carrying STRUCTURES : Made up of series of members of regular shape that have a particular function for load carrying

5. SYNTHESIS : Concerned with the problem of selecting the size of the mechanism to perform a given function SYNTHESIS : Concerned with the problem of selecting the size of the mechanism to perform a given function STRESS : Internal reacting force per unit area due to the effects of external applied forces STRESS : Internal reacting force per unit area due to the effects of external applied forces

6. DESIGN Formulate a plan for the satisfaction of a human need Formulate a plan for the satisfaction of a human need The need for the problem has to be identified The need for the problem has to be identified Design problem have no unique answer Design problem have no unique answer

7. A good answer today may well turn out to be a poor answer tomorrow, if there is a growth of knowledge during the period A good answer today may well turn out to be a poor answer tomorrow, if there is a growth of knowledge during the period A design is always subject to certain problem- solving constraints A design is always subject to certain problem- solving constraints A design problem is not a hypothetical problem A design problem is not a hypothetical problem

8. Design has an authentic purpose Design has an authentic purpose the creation of an end result by taking definite action, or the creation of something having physical reality

9. ENGINEERING DESIGN The process in which scientific principles and the tools of engineering mathematics, computers, graphics and English are used to produce a plan which, when carried out, will satisfy a human need The process in which scientific principles and the tools of engineering mathematics, computers, graphics and English are used to produce a plan which, when carried out, will satisfy a human need

10. MECHANICAL ENGINEERING DESIGN Design of things and systems of mechanical nature, machines, products, structures, devices, and instruments Design of things and systems of mechanical nature, machines, products, structures, devices, and instruments For the most part, mechanical design utilizes mathematics, the materials sciences, and the engineering mechanics sciences For the most part, mechanical design utilizes mathematics, the materials sciences, and the engineering mechanics sciences

11. The ultimate goal in machine design is to The ultimate goal in machine design is to size and shape the parts choose appropriate material and choose manufacturing process So that resulting machine can be expected to perform its intended function without failure

12. An engineer should be able to calculate and predict the mode and conditions of failure for each element and then design it to prevent that failure An engineer should be able to calculate and predict the mode and conditions of failure for each element and then design it to prevent that failure This requires stress and deflection analysis for each part This requires stress and deflection analysis for each part

13. Stresses are functions of applied and inertial loads Stresses are functions of applied and inertial loads An analysis of the forces, moments, torques and dynamics of system must be done before stresses and deflections can be completely calculated An analysis of the forces, moments, torques and dynamics of system must be done before stresses and deflections can be completely calculated

14. Design A design must be: A design must be: Functional- fill a need or customer expectation Functional- fill a need or customer expectation Safe- not hazardous to users or bystanders Safe- not hazardous to users or bystanders Reliable- conditional probability that product will perform its intended function without failure to a certain age. Reliable- conditional probability that product will perform its intended function without failure to a certain age. Competitive- contender in the market Competitive- contender in the market Usable- accommodates human size and strength Usable- accommodates human size and strength Manufacturable- minimal number of parts and suitable for production Manufacturable- minimal number of parts and suitable for production Marketable- product can be sold and serviced Marketable- product can be sold and serviced

15. Design Process Actions Conceive alternative solutions Conceive alternative solutions Analyze, test, simulate, or predict performance of alternatives Analyze, test, simulate, or predict performance of alternatives Choose the “best” solution Choose the “best” solution Implement design Implement design

16. Design is… An innovative and iterative process An innovative and iterative process A communication intensive activity A communication intensive activity Subject to constraints Subject to constraints

17. Steps to Design

18. Design Considerations 1. Strength 2. Stiffness 3. Wear 4. Corrosion 5. Safety 6. Reliability 7. Friction 8. Usability 9. Utility 10. Cost 11. Processing 12. Weight 13. Life 14. Noise 15. Styling 16. Shape 17. Size 18. Control 19. Thermal Properties 20. Surface 21. Lubrication 22. Marketability 23. Maintenance 24. Volume 25. Liability 26. Recovery

19. Codes and Standards Code- a set of specifications for the analysis, design, manufacture, and construction of something Code- a set of specifications for the analysis, design, manufacture, and construction of something Standard- a set of specifications for parts, materials, or processes intended to achieve uniformity, efficiency, and a specified quality Standard- a set of specifications for parts, materials, or processes intended to achieve uniformity, efficiency, and a specified quality

20. Organizations Aluminum Association (AA) Aluminum Association (AA) American Gear Manufacturers Association (AGMA) American Gear Manufacturers Association (AGMA) American Institute of Steel Construction (AISC) American Institute of Steel Construction (AISC) American Iron and Steel Institute (AISI) American Iron and Steel Institute (AISI) American National Standards Institute (ANSI) American National Standards Institute (ANSI) American Society for Metals (ASM) American Society for Metals (ASM) American Society of Mechanical Engineers (ASME) American Society of Mechanical Engineers (ASME) American Society of Testing Materials (ASTM) American Society of Testing Materials (ASTM) American Welding Society (AWS) American Welding Society (AWS) American Bearing Manufacturers Association (ABMA) British Standards Institute (BSI) Industrial Fasteners Institute (IFI) Institution of Mechanical Engineers (I. Mech. E.) International Bureau of Weights and Measures (BIPM) International Standards Organization (ISO) National Institute for Standards and Technology (NIST) Society of Automotive Engineers (SAE) American Society of Agricultural and Biological Engineers (ASABE)

21. Economics Cost plays an important role in design decision process Cost plays an important role in design decision process No matter how great the idea may be, if it’s not profitable it may never be seen No matter how great the idea may be, if it’s not profitable it may never be seen The use of standard sizes and large manufacturing tolerances reduce costs The use of standard sizes and large manufacturing tolerances reduce costs Evaluating design alternatives with regard to cost Evaluating design alternatives with regard to cost Breakeven Points Breakeven Points Cost Estimates Cost Estimates

22. Product Liability “Strict liability” concept prevails in the U.S. “Strict liability” concept prevails in the U.S. Manufacturers are liable for any damage or harm that results from a defect. Manufacturers are liable for any damage or harm that results from a defect.

23. Uncertainty Roman Method- repeat designs that are proven Roman Method- repeat designs that are proven Factor of Safety Method of Philon- separate the loss-of- function load and the impressed load using a ratio Factor of Safety Method of Philon- separate the loss-of- function load and the impressed load using a ratio Permissible Stress- fraction of significant material property (i.e., strength) Permissible Stress- fraction of significant material property (i.e., strength)

24. Uncertainty Design Factor Method- factor of safety is increased with rounding error to achieve nominal size (5.3 mm designed bolt size is increased to 6.0 mm) Design Factor Method- factor of safety is increased with rounding error to achieve nominal size (5.3 mm designed bolt size is increased to 6.0 mm) Stochastic Design Factor Method- uncertainty in stress and strength is quantified for linearly proportional loads Stochastic Design Factor Method- uncertainty in stress and strength is quantified for linearly proportional loads

25. Measures of Strength S – Strength S – Strength S s – Shear Strength S s – Shear Strength S y – Yield Strength S y – Yield Strength – Ultimate Strength S u – Ultimate Strength - Mean Strength - Mean Strength

26. Measures of Stress  – Shear Stress  – Shear Stress  –  Normal Stress  –  Normal Stress   –  Principal Stress   –  Principal Stress  y  – Stress in y-direction  y  – Stress in y-direction  r  – Radial Stress  r  – Radial Stress  t  – Tangential Stress  t  – Tangential Stress

27. Stress Allowable (AISC) Tension: 0.45 S y ≤  all ≤ 0.60 S y Tension: 0.45 S y ≤  all ≤ 0.60 S y Shear:  all = 0.40 S y Shear:  all = 0.40 S y Bending: 0.60 S y ≤  all ≤ 0.75 S y Bending: 0.60 S y ≤  all ≤ 0.75 S y Bearing:  all = 0.90 S y Bearing:  all = 0.90 S y

28. Loads Used to Obtain Stresses Where: Where: W d - dead loads W l - live loads k- service factor F w - wind load F misc - locality effects (earthquakes)

29. Service Factors ApplicationsElevators Traveling Crane Supports Light Machinery Supports Reciprocating Machinery Supports Floor and Balcony Supports k 2 1.25 1.20 1.50 1.33

30. Factor of Safety Design factors (n d ) are defined as: Design factors (n d ) are defined as:andwhere n s -accounts for uncertainty of strength n d -accounts for uncertainty of loads

31. Realized Factor of Safety

32. Reliability Probability that a mechanical element will not fail in use Probability that a mechanical element will not fail in use 0 ≤ R ≤ 1 Reliability approach to design: judicious selection of material, processes, and geometry to achieve reliability goal Reliability approach to design: judicious selection of material, processes, and geometry to achieve reliability goal Factor of Safety Method- time proven, widely accepted Factor of Safety Method- time proven, widely accepted Reliability Approach- new, requires data Reliability Approach- new, requires data