11ME503 Design of machine elements

Design

• Design is essentially a decision making process

• For every problem we need to design a solution

• Formulation of a plane for the satisfaction of human need

• To create something new or arrange existing things in a new order to satisfy a recognized need of society

Mechanical Engineering Design

• The design of parts, Products and systems of mechanical nature– Machine design– Thermal engineering– Fluid power engineering– Refrigeration and AC, etc

Machine

• Machine is a device consists of one or more fixed and moving parts that modifies energy in to more useful form.

• Mechanism is to transmit or modify motion where as a machine is to obtain mechanical advantage.

Machine Design

• The process of selection of materials, shapes, sizes and arrangements of mechanical elements so that the resultant machine will perform the prescribed task.

Machine element

• Each part of a machine which has motion with respect to some other part is called a machine element– Each machine element may consists of several

parts which are manufactured separately » Example: rolling contact bearing

• Inner race, outer race, ball and cage

Classification of machine element

• General purpose machine elements» Shaft» Coupling» Bearing» Spring» Gears

•Special purpose machine elements» Pistons» Valves» spindle

Design of Machine elements

• Defined as the selection of material and the values for the Independent geometrical parameters so that the element satisfies its functional requirements and undesirable effects .

Prerequisites

• Knowledge of

–Engineering Mechanics–Strength of Material

UNIT I STEADY AND VARIABLE STRESSES IN MACHINE MEMBERS

9

Introduction to the design process - factor influencing machine design, selection of materials based on mechanical properties, Preferred numbers – Direct, Bending and torsional stress equations – Impact and shock loading – calculation of principal stresses for various load combinations, eccentric loading – Design of curved beams – crane hook and ‘C’frame - Factor of safety - theories of failure – stress concentration – design for variable Loading– Soderberg, Goodman and Gerber relations.

UNIT II DESIGN OF SHAFTS AND COUPLINGS 9

Design of solid and hollow shafts based on strength, rigidity and critical speed – Design of Keys and key ways - Design of rigid and flexible couplings.

UNIT III DESIGN OF TEMPORARY AND PERMANENT JOINTS

9

Threaded fasteners - Design of bolted joints including eccentric loading – design of knuckle joints-Design of welded joints, riveted joints for structures - theory of bonded joints.

11ME503 DESIGN OF MACHINE ELEMENTS (Use of P S G Design Data Book is permitted in the University examination)

L T P C M 3 1 0 4 100

UNIT IV DESIGN OF SPRINGS AND LEVERS

9

Design of helical, leaf, disc and torsional springs under constant loads and varying loads – Concentric torsion springs - Belleville springs – Design of Levers.

UNIT V DESIGN OF BEARINGS AND FLYWHEELS 9

Design of bearings – sliding contact and rolling contact types – Cubic mean load – Selection of ball and roller bearings - Design of journal bearings – Mckees equation – Lubrication in journal bearings – calculation of bearing dimensions – Design of flywheels involving stresses in rim and arm.

Text and Reference Books

The Question Paper Pattern

CCE Test 1/ CCE Test 2/ CCE Retest/ Model Examination/ End Semester Examination

Duration – 3 hours, Maximum Marks – 75

Section A: one word/simple phrase/few words – Objective Type – Answer all questions – 15 questions – 1 mark each – 15 marks (TEN questions will be multiple choice type)

Section B: <50 words – Short Answer Type – Answer all questions – 5 questions – 2 marks each – 10 marks

Section C: 500 to 600 words – from any one of the FIVE units – CompulsoryQuestion Descriptive Type – ONE question – 10 marks – 10 marks

Section D: 500 to 600 words – from the remaining FOUR units – DescriptiveType (either or) – FOUR questions – 10 marks each – 40 marks.

Evaluation

• End semester examination :75 Marks• Internal Assessment :25 Marks

• Distribution of marks for Internal Assessment:– CCE1 - 10– CCE2 - 10– Model - 15– Tutorial/Assignment/Quiz(Minimum 2) -

15

Total - 50

Selection of materialsSelection of

shapes

Selection of sizes

Sele

ction

of

Arra

ngem

ents

Machine design

Concept of Machine Design

Classification of machine design

• Adaptive design: • Adaptation of existing design• Need no special knowledge or skill

• Development design• Modifying existing design in to new one • Started with existing design but the final product may

differ quite markedly from the original product

• New design • This type of design is entirely new one• Creative thinking is necessary

Types of Machine Design

Machine Design

System Design

Product Design

Element Design

Empirical Design

Optimum Design

Computer Aided Design

RationalDesign

• Gordon E. Moore Award winner• Ionut Alexandru Budisteanu, 19, of Romania, won the Gordon E.

Moore Award for using artificial intelligence to create a viable model for a low-cost, self-driving car.

• Ionut’s research addresses a major global issue. Annually, car accidents cause 1.24 million deaths worldwide1, 90 percent of which result from driver error2.

• With 3-D radar and mounted cameras, Ionut created a feasible design for an autonomously controlled car that could detect traffic lanes and curbs, along with the real-time position of the car. And the cost: only $4,000.

• The Gordon E. Moore Award, named in honor of the Intel co-founder and retired chairman/CEO, includes USD 75,000 in scholarship funds.

Eesha Khare, 18, recently won the $50,000 Intel Foundation Young Scientist Award for her fast-charging device.

The device uses an improved supercapacitor that can store a lot of energy into a small space using a nano rod electrode. It is capable of 10,000 charge-recharge cycles and can fully charge a cell phone in 20-30 seconds.

Design process-Phases of DesignRecognition of

need

Definition of Problem

Synthesis

Analysis and optimization

Evaluation

Presentation

1. Strength2. Rigidity3. Reliability4. Safety5. Cost6. Weight7. Ergonomics8. Aesthetics9. Manufacturing10. Conformance to standard 11. Assembly12. Friction and wear

13. Life14. Vibration15. Thermal consideration 16. Lubrication17. Maintenance18. Flexibility19. Size and shape20. Stiffness21. Corrosion22. Noise

Factors Influencing Machine Design

Factors influencing selection of material

1. Availability of material2. Cost of material3. Manufacturing consideration4. Material properties

Mechanical properties of materialMECHANICAL

PROPERTIES

Static strength-ability to resists stress without failure under static loading

Fatigue strength-ability to resists stress without failure under fatigue loading

Elasticity-ability to regain permanent deformation after load removal

Plasticity-ability to retain permanent deformation after load removal

Stiffness /rigidity- ability to resist deformation under load

Ductility-ability to drawn in to wire or elongated

Brittleness-ability to rupture with negligible deformation

Malleability-ability to undergo change in size and shape

Resilience-Capacity to absorb energy when deformed within elastic range

Toughness-Capacity to absorb energy without fracture

Hardness-Resistance to penetration, abrasion or plastic deformation

Creep-Progressive deformation under load at high temperature

Static strength

A gradually applied load which does not change in magnitude, direction or point of application with respect to time is known as static load.

Static strength is the ability of that material to resist stress without failure, when subjected to static loading

The yield strength and ultimate strength are measure of static strengths of the material.

The static strength of the materials can be determined by a tensile test.

Stress strain diagram

Proportionality limit is the point up to which the stress remains directly proportional to strain whereas elastic limit is the point up to which the material remains elastic ie. if the stress is removed within elastic limit, then the material will regain its original shape and size.

Fatigue strength A load which varies in magnitude and/or direction with respect

to time is known as fatigue or fluctuating or alternating load.

Normally a fatigue or fluctuating loads are cyclic in nature.

The term load includes: a force, a bending moment or torque.

A fatigue strength is the ability of a material to resist stress without failure, when subjected to a fatigue load

• Endurance limit:• Is the measure of fatigue strength • Maximum value of the a completely reversed stress

(Stress amplitude) that the standard test specimen of the material can withstand without failure for an infinite number of cycle (usually 106 cycles)

Elasticity

• The property of a material which enables it to regain its original shape after the external load is removed is called elasticity

• This property is very important, especially , for the components subjected to fatigue loading

Plasticity

• The property of a material which enables it to retain the permanent deformation after external load is removed is called plasticity

• This property is essential in forging , stamping, press working

Stiffness

• The ability of material to resist deformation under the load is called stiffness.

• It is also known as rigidity• It is measured by modulus of elasticity and

modulus rigidity

Ductility

• The property of a material that enables it to be drawn out or elongated is called is called ductility

• It is usually measured in terms of percentage of elongation or percentage of reduction in area

• If the percentage of elongation of a standard test specimen is more than 15%, it is rated as ductile material

• Example: mild steel, aluminium and copper

brittleness

• Brittleness is the property opposite to ductility• The brittle material show lack of deformation

before rupturing• Normally, the material with less than 5%

elongation are considered brittle.• Example: Cast iron

Malleability

• The property of a material which enables it to undergo change in space and size without rupture under external load is called malleability.

• A malleable material should possess a good plasticity. This property is important in press work

Ductility Vs Malleability

• Ductility is the ability of material to deform under tensile force, while malleability is the ability of the material to deform under compressive force.

• Ductility is an important property when the component is drawn, whereas malleability is an important property when the component is forged, rolled or extruded.

• Ductility decreases with temperature, while malleability increases with temperature.

• Gold or copper for example, are both highly ductile and malleable, whilst lead is only malleable.

Resilience• The capacity of a material to absorb energy

(Elastic strain energy) within the elastic range is called resilience.

• The modulus of resilience is the energy absorbed per unit volume of material when loaded to its elastic limit.

•

Toughness• The capacity of the material to absorb energy

with out fracture is called toughness• Modulus of toughness is the total energy

absorbed per unit volume of material when loaded till its fracture.

• The components subjected to impact loads are normally designed for toughness

• This can be tested using charpy or izod impact test

Hardness

• The property of a material which enables it to resist penetration, abrasion, indentation or plastic deformation is called Hardness.

• It is normally measured by Brinell hardness number and Rockwell hardness number

• This property is very important for the components subjected to surface stresses.

Creep• When a machine component is subjected to a constant

stress at high temperature, it deforms slowly but progressively over a long period of time.

• This progressive deformation under the load at high temperature is called creep.

• The creep depends upon the stress, the temperature, and material .

• At high temperatures the creep exists even at a stresses much below the yield strength of the material