Presented By, K.V.L Bhuvaneswary Asst. Prof. Mechanical Engineering DYPIMR,AKURDI Pune

1. Chapter 2Design fundamentals Presented By, K.V.L Bhuvaneswary Asst. Prof. Mechanical Engineering DYPIMR,AKURDI Pune

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

4. Design process • Design: Design is essentially a decision-making process. If we have a problem, we need to design a solution. In other words, to design is to formulate a plan to satisfy a particular need and to create something with a physical reality. • Consider for an example, design of a chair. A number of factors need be considered first: • The purpose for which the chair is to be designed such as whether it is to be used as an easy chair, an office chair or to accompany a dining table. • Whether the chair is to be designed for a grown up person or a child. • Material for the chair, its strength and cost need to be determined. • Finally, the aesthetics (Look) of the designed chair.

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 designprocess

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 • 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 • 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.

11. 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.

12. Stress-Strain Diagram ultimate tensile strength 3 necking Strain Hardening Slope=E yield strength Fracture 5 2 Elastic region slope =Young’s (elastic) modulus yield strength Plastic region ultimate tensile strength strain hardening fracture Plastic Region Stress (F/A) Elastic Region 4 1 Strain ( ) (DL/Lo)

13. Classification of engineering materials

15. Applications of Engineering materials

16. Applications of Engineering materials

17. Applications of Engineering materials

18. Mechanism Definition and comparison of mechanism and machine four bar mechanism slider crank mechanism

19. Kinematic Link or Element Each part of a machine, which moves relative to some other part, is known as a kinematic link (or simply link) or element. A link may consist of several parts, which are rigidly fastened together, so that they do not move relative to one another. For example, in a reciprocating steam engine, as shown in Fig. 1, piston, piston rod and crosshead constitute one link ; connecting rod with big and small end bearings constitute a second link ; crank, crank shaft and flywheel a third link and the cylinder, engine frame and main bearings a fourth link.

20. 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

21. 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.

22. Difference between Machine and Mechanism

23. 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)

24. 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.