Design Fundamentals and Mechanical Properties in Engineering

1. Dr. DYPIEMR, AKURDI Unit 2Design fundamentals Mr. PrafullaNalawade

2. Unit 2.Design fundamentals Syllabus Steps in design process, Mechanical properties (strength, toughness, hardness, ductility, malleability, brittleness, elasticity, plasticity, resilience, fatigue, creep) and selection of engineering materials, applications of following materials in engineering- Aluminium, Plastic, Steel, brass, Cast iron, Copper, Rubber. Mechanism (Descriptive treatment only): Definition and comparison of mechanism and machine, four bar mechanism, slider crank mechanism

3. Introduction • The term design refers to a plan for the construction of an object. • The term machine design or mechanical design concerns with the systems by which energy is converted into useful mechanical forms and of mechanism required to convert output of machines to the required form. • The machine design may lead to an entirely new machine or machine element or improvement of an existing machine.

4. Need of design • Functional requirement • User comfort • Safety • Modification • Appearance • Cost reduction

5. General Considerations in Design • Type of load • Selection of material • Shape and size • Friction and lubrication • Operational safety • Machine availability • Motion of element • Use of standard parts • Production quantity • Maintenance of element • Life of element • Capacity of element • Weight of element • Cost of element

6. Steps in design process General procedure in Design

7. Properties of materials • The knowledge of materials and their properties is of great significance for design engineer. • Property of a material is a factor that influences qualitatively or quantitatively the response of a given material under the action of forces. • Property indicates that, whether a material is suitable or unsuitable for a particular use in industry. • Various material properties are divided into following groups • Mechanical properties • Thermal properties • Electrical properties • Chemical properties

8. Mechanical properties • The knowledge of mechanical properties of materials is very essential in order to construct a mechanically fool-proof structure. • Mechanical properties include those characteristics of a material that describes its behavior under the action of external forces. • Some of the important mechanical properties are 1. Elasticity 2. Plasticity 3. Toughness 4. Resilience 5. Strength 6. Stiffness 7. Ductility 8. Malleability 9. Brittleness 10. Hardness 11. Fatigue 12. Creep

9. Mechanical properties • Elasticity • It is the property of material to regain its original shape after deformation when the external forces are removed. • This property is required for materials used in tools and machines. • It is important to note that steel is more elastic than rubber • Plasticity • The property of a material which retains the deformation produced under the load permanently is called as plasticity. • This property is essential in stamping, press work, forgings, ornamental work, etc. E F stress F F O Tension test specimen Strain A

10. Mechanical properties • Toughness • Toughness is total amount of energy absorbed by the material before its failure. • It is the complete area under the stress-strain curve. • This property is essential in parts subjected to shock and impact loads. • Resilience • It is the total amount of energy absorbed by the material during its elastic deformation. • The are under stress strain curve up to the elastic limit is called as Resilience. • This property is essential for springs, shock absorbers, etc. σ E2 E1 ϱ

11. Mechanical properties • Strength • It is ability of a material to resist the externally applied forces without failure. • It is measured in N/mm2 or kg/mm2 . • Stiffness • It is the ability of a material to resist deformation under stress. • It is defined as the force or load per unit deflection and measured in N/mm. • Ductility • It is ability of material to undergo plastic deformation under tensile loading, before its failure. • It is the property of material by virtue of which it can be drawn into the fine wires.

12. Mechanical properties • Malleability • It is the ability of material to be formed by hammering of rolling. • It is the capacity of material to withstand deformation under compression without failure. • Brittleness • It is the property of breaking of a material with little permanent distortion. • It is opposite to ductility. • Hardness • It is defined as the resistance of a material to plastic deformation usually by indentation. • It is also defined as resistance to scratching, abrasion or cutting.

13. Mechanical properties • Fatigue • The failure of a material subjected to repeated stresses or loading is called as fatigue. • Fatigue failure is caused by means of a progressive crack formation which are generally of microscopic size. • It is considered while designing shafts, gears, springs, etc. • Creep • When a material is subjected to constant stresses at high temperature for a long period of time, it will undergo a slow and permanent deformation which is called as creep. • It is considered while designing of boilers, I.C. engines, pumps, turbines, etc.

14. Engineering materials • Availability of materials • Working environmental conditions • Properties of materials • Performance requirements • Reliability of materials • Disposability and recyclability • Safety factor • Manufacturing considerations • Cost of materials Factors to be considered

15. SELECTION OF ENGINEERING MATERIALS The material should be already available in the market in the abundant quantity. Availability The cost of the material selected for a particular job from several alternatives should be minimum. Cost The properties of the materials selected should meet the functional requirements and the service conditions. Material Properties It has been the most important factor while selecting the material for a particular job. The materials should be selected for particular part based on the process by which it is going to be manufactured. Manufacturing Considerations

16. The effect of environmental conditions [Like temperature, humidity, etc.] should be given more attention during selection of material. Environmental Considerations Machinability is the case with which a given metal can be machined. Machinabilityof the material depends upon hardness, strength and chemical Composition of materials. Machinability It is an indication of suitability of the metal for a machine part that requires forming. Forming depends upon ductility and tensile Strength. Formability

17. Classification of engineering materials

18. Applications of Engineering materials

19. Applications of Engineering materials

20. Applications of Engineering materials

21. Applications of Engineering materials

22. Applications of Engineering materials

23. Applications of Engineering materials

24. Mechanism • Mechanism (Descriptive treatment only): Definition and comparison of mechanism and machine, four bar mechanism, slider crank mechanism

25. Introduction • Machine is a device consists of fixed and moving parts that modifies energy and transmits it in the useful form. e. g. Lathe machine, heat engine • Mechanism is a part of machine which has moving parts that performs some function. e. g. threading mechanism in a lathe machine, steering gear mechanism • The study of mechanism involves its analysis as well as synthesis. • Analysis includes the study of motions and forces concerning different parts of an existing mechanism, whereas synthesis includes the design of different parts of mechanism.

26. Kinematic link (Element) • Kinematic link or element is a resistant body or an assembly of resistant bodies which become a part or parts of a machine connecting other parts which have motion relative to it. • Resistant body is the body which do not suffer appreciable distortion or change in the physical form by the forces acting on them. • Kinematic link should be completely rigid. • In slider crank mechanism, input link 2 is connecting rod, link 3 is coupler rod, link 1 is frame (fixed link) and link 4 is slider Slider-crank mechanism

27. Machine and structure • Machine • Machine is a device consists of fixed and moving parts that modifies energy and transmits it in useful form. • Machine is an assemblage of links (fixed and moving) or mechanisms which are used to transmit required motion and forces. • For example, milling, drilling, shaper, etc. • Structure • It is an assemblage of resistant bodies (members) which have no relative motion between them. • It is made for carrying loads which have straining action. • For example, roof trusses used in bridges, buildings, transmission towers, machine frames, railway platforms, etc.

28. Kinematic pair and kinematic chain • Kinematic pair • When two kinematic links of a machine are connected together in such a way that their motion is completely or successfully constrained then these two links are said to form a kinematic pair. • For example, piston and cylinder of an engine forms a kinematic pair. • Kinematic chain • When the kinematic pairs are connected in such a manner that the last link is joined to the first link to transmit completely or successfully constrained motion then it is called as kinematic chain. C B Kinematic chain (four bar chain) D A

29. Mechanism • When one of the links of a kinematic chain is fixed then the chain is called as mechanism. • The mechanism may be used for transmitting or transforming the motion. • A mechanism with four links or elements is known as simple mechanism, whereas mechanism with more than four links or elements is known as compound mechanism.

30. Difference between Machine and Mechanism

31. Four bar mechanism C Link 3(coupler) B Link 4(lever or rocker) • It consists of 4 links which forms 4 turning pairs at A, B, C and D. • The lengths of four links may be different. • The shortest link will make a complete revolution relative to the other three links. This link is called as driver or crank (link AB). • The link which makes a partial rotation or oscillates is called as lever or rocker (link CD). • The link which connects the crank and lever is called as coupler (link BC). • The fixed link of the mechanism is called as frame (link AD). Link 2(crank) Coupled wheels of locomotives D A Four bar chain Link 1(frame)

32. Inversions of four bar mechanism • method of obtaining different mechanisms by fixing different links in a kinematic chain, is known as inversion of the mechanism. Coupling rod of a locomotive (Double crank mechanism) Beam engine (crank and lever mechanism) Watt’s indicator mechanism (Double lever mechanism)

33. Slider crank mechanism Slider crank mechanism • It widely used in mechanical engineering field. • It consists of four links which forms three turning pairs and one sliding pair. • Shortest link will make complete revolution called as crank. • The link which makes a partial rotation or oscillates is called as connecting rod. • The link which is connected to connecting rod is called as slider or piston.The sliding path of piston is called as line of stroke.

34. Inversions of slider crank mechanism Oscillating cylinder engine Pendulum pump or Bull engine Rotary internal combustion engine or Gnome engine Crank and slotted lever quick return motion mechanism

35. TYPES OF KINEMATIC PAIR On the basis of relative motion: Turning pair Rolling Sliding Screw Spherical On the basis of types of contact: Lower pair: Surface contact Higher pair: Point and line contact