machine elements w2-w3

8/10/2019 Machine Elements w2-w3

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Ubaidillah, ST.,M.Sc

[email protected]


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Machine design is the creation of new and better machinesand improving the existing one especially in terms ofeconomical and overall cost product and operation.

In designing a machine component, it is necessary to have

a good knowledge of many subject such as Mathematics,Engineering Mechanics, Strength of Material, WorkshopProcess and Technical Drawing


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PRODUCT POINT OFVIEW

Adaptive DesignConcern with

adaptation of existingdesign

Development Design

Need scientific trainingand design ability to

modify existing designinto a new idea

New Design Needs lot of researches,creative thinking andtechnical ability


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METHOD POINTOF VIEW

Rational Design Mathematical formulae of principle mechanics

Empirical Design Empirical formulae based on the practice and past experience

Industrial Design The production aspect to manufacture any machine component inindustry

Optimum designThe best design for the given objective function under specific

constrain

System Design Complex mechanical system

Element Design Design of any machine elements

Computer AidedDesign

The use of computer system to assist in creation, modification,analysis and design optimisation


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Type of load and stresses caused by the load Motion of the parts or kinematics of the machine Selection of materials

Form and size of the parts Frictional resistance and lubrication Convenient and economical feature Use of standard part Safety operation

Workshop facilities Number of machines to be manufactured Cost of construction Assembling


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Bricks and glass do not deform and break easily.

Rubber bands deform a lot but return to their originalshape

A paper clip easily deforms but does not easily returnto its original shape

The thicker something is, the more force we have toexert to get it to break


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The knowledge of materials and their properties is of greatsignificance for design engineer.

The machine elements should be made of such a materialwhich has properties suitable for the conditions of

operation A design engineer must be familiar the effects which the

material processes and heat treatment have on theproperties of the materials


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ENGINEERINGMATERIALS

Metals and their

alloys

Ferrous material(Iron, steel)

Non-ferrous

material (copper,aluminum, and

etc.)

Non-metals

Glass, rubber,

plastic and etc


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Selection Factors

Availability of the materials

Sustainability of the materials for theworking condition

The cost of the materials


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Strength. The ability of a material to resist the externally appliedforce without yielding

Stiffness. The ability of material to resist deformation understress. The modulus of elasticity is the measure of stiffness

Elasticity. The property of material to regain its original shapeafter deformation when the external forces are removed

Plasticity. Property of material which retains the deformationproduces under load permanently.

Ductility. The property of material enabling it to be drawn intowire with the application of a tensile force. It must be bothstrong and plastic. It is measured by the terms percentageelongation and percentage reduction area in a tensile test


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Brittleness. Opposite to ductility, breaking of a materialwith little permanent distortion

Malleability. A special case of ductility which permitsmaterials to be rolled or hammered into thin sheets

Toughness. The property of material to resist fracture dueto high shock or impact loads like hammer blows.

Machinability. Property of material which refers to arelative case with which a material can be cut.

Resilience. The property of material to absorb energy andto resist shock and impact loads


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Creep. When a part is subjected to a constant stress at hightemperature for a long period of time, it will undergo aslow and permanent deformation

Fatigue. When a material is subjected to repeated stresses,

it fails at stresses below the yield point stresses Hardness. It is a very important property of the metals and

has a wide variety of meanings such as resistance to wear,scratching, deformation and machinability.


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Engineering Materials


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Materials

Nanomaterials, shape-memory alloys, superconductors,

Ferrous metals: carbon-, alloy-, stainless-, tool-and-die steels

Non-ferrous metals: aluminum, magnesium, copper, nickel,titanium, superalloys, refractory metals,beryllium, zirconium, low-melting alloys,gold, silver, platinum,

Plastics: thermoplastics (acrylic, nylon, polyethylene, ABS,)thermosets (epoxies, Polymides, Phenolics, )elastomers (rubbers, silicones, polyurethanes, )

Ceramics, Glasses, Graphite, Diamond, Cubic Boron Nitride

Composites: reinforced plastics, metal-, ceramic matrix composites


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Properties of materials

Mechanical properties of materialsStrength, Toughness, Hardness, Ductility,Elasticity, Fatigue and Creep

Chemical propertiesOxidation, Corrosion, Flammability, Toxicity,

Physical propertiesDensity, Specific heat, Melting and boiling point,Thermal expansion and conductivity,Electrical and magnetic properties


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Chemical composition

Mechanical properties Strength, hardness (undervarious conditions: temperature, humidity, pressure)

Physical properties density, optical, electrical,magnetic

Environmental green, recycling


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Ferrous Metals Cast irons

Steels

Super alloys Iron-based

Nickel-based

Cobalt-based

Non-ferrous metalsAluminum and its alloys

Copper and its alloys

Magnesium and its alloys

Nickel and its alloys

Titanium and its alloys

Zinc and its alloys

Lead & Tin Refractory metals

Precious metals


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Ferrous alloys are useful metals in termsof mechanical, physical and chemicalproperties.

Alloys contain iron as their base metal.

Carbon steels are least expensive of allmetals while stainless steels is costly.


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Carbon steels Classified as low, medium and high:

1. Low-carbon steel or mild steel, 0.60% C, springs,

cutlery, cable.


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Alloy steels Steels containing significant amounts of

alloying elements.

Structural-grade alloy steels used forconstruction industries due to high strength.

Other alloy steels are used for its strength,hardness, resistance to creep and fatigue, and

toughness.

It may heat treated to obtain the desiredproperties.


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High-strength low-alloy steels Improved strength-to-weight ratio.

Used in automobile bodies to reduce

weight and in agricultural equipment.

Some examples are:

1. Dual-phase steels

2. Micro alloyed steels

3. Nano-alloyed steels


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Characterized by their corrosion resistance,high strength and ductility, and highchromium content.

Stainless as a film of chromium oxide protects

the metal from corrosion.


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Five types of stainless steels:

1. Austenitic steels

2. Ferritic steels3. Martensitic steels

4. Precipitation-hardening (PH) steels

5. Duplex-structure steels


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TABLE 5.1

Product Steel Product Steel

Aircraft forgings,

tubing, fittings

Automobile bodies

Axles

Ball bearings and races

Bolts

Camshafts

Chains (transmission)Coil springs

Connecting rods

Crankshafts (forged)

4140, 8740

1010

1040, 4140

52100

1035, 4042, 4815

1020, 1040

3135, 31404063

1040, 3141, 4340

1045, 1145, 3135, 3140

Differential gears

Gears (car and truck)

Landing gear

Lock washers

Nuts

Railroad rails and wheels

Springs (coil)

Springs (leaf)Tubing

Wire

Wire (music)

4023

4027, 4032

4140, 4340, 8740

1060

3130

1080

1095, 4063, 6150

1085, 4063, 9260, 61501040

1045, 1055

1085


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TABLE 5.2 Typical Mechanical Properties of Selected Carbon and Alloy Steels in the Hot-Rolled,Normalized, and Annealed Condition

AISI Condition Ultimate

tensile

strength

(MPa)

Yield

Strength

(MPa)

Elongation in

50 mm (%)

Reduction of

area (%)

Hardness

(HB)

1020

1080

3140

4340

8620

As-rolled

Normalized

AnnealedAs-rolled

Normalized

Annealed

Normalized

Annealed

Normalized

Annealed

Normalized

Annealed

448

441

3931010

965

615

891

689

1279

744

632

536

346

330

294586

524

375

599

422

861

472

385

357

36

35

3612

11

24

19

24

12

22

26

31

59

67

6617

20

45

57

50

36

49

59

62

143

131

111293

293

174

262

197

363

217

183

149


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TABLE 5.3

Yield Strength Chemical

Composition

Deoxidation

Practice

psi x 103

MPa

35

40

45

50

60

70

80

100

120

140

240

275

310

350

415

485

550

690

830

970

S = structural alloy

X = low alloy

W = weathering

D = dual phase

F = killed plus sulfide inclusion control

K = killed

O = nonkilled


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TABLE 5.4Room-Temperature Mechanical Properties and Typical Applications of Selected AnnealedStainless Steels

AISI(UNS)

Ultimatetensile

strength(MPa)

Yieldstrength(MPa)

Elongationin 50 mm

(%) Characteristics and typical applications

303(S30300)

550620 240260 5350 Screw machine products, shafts, valves, bolts,bushings, and nuts; aircraft fittings; bolts; nuts;rivets; screws; studs.

304(S30400)

565620 240290 6055 Chemical and food processing equipment,brewing equipment, cryogenic vessels, gutters,downspouts, and flashings.

316(S31600)

550590 210290 6055 High corrosion resistance and high creep strength.Chemical and pulp handling equipment,photographic equipment, brandy vats, fertilizerparts, ketchup cooking kettles, and yeast tubs.

410(S41000)

480520 240310 3525 Machine parts, pump shafts, bolts, bushings, coalchutes, cutlery, tackle, hardware, jet engine parts,mining machinery, rifle barrels, screws, andvalves.

416(S41600)

480520 275 3020 Aircraft fittings, bolts, nuts, fire extinguisherinserts, rivets, and screws.


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TABLE 5.6Processing and Service Characteristics of Common Tool and Die Steels

AISI

designation

Resistance to

decarburization

Resistance to

cracking

Approximate

hardness

(HRC) Machinability Toughness

Resistance to

softening

Resistance to

wear

M2 Medium Medium 6065 Medium Low Very high Very high

T1 High High 6065 Medium Low Very high Very high

T5 Low Medium 6065 Medium Low Highest Very high

H11, 12, 13 Medium Highest 3855 Medium to high Very high High Medium

A2 Medium Highest 5762 Medium Medium High High

A9 Medium Highest 3556 Medium High High Medium tohigh

D2 Medium Highest 5461 Low Low High High to very

high

D3 Medium High 5461 Low Low High Very high

H21 Medium High 3654 Medium High High Medium to

high

H26 Medium High 4358 Medium Medium Very high High

P20 High High 2837 Medium to high High Low Low to

medium

P21 High Highest 3040 Medium Medium Medium Medium

W1, W2 Highest Medium 5064 Highest High Low Low to

medium

Source: Adapted from Tool Steels, American Iron and Steel Institute, 1978.


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Factors for selecting are:

1. High strength to weight ratio

2. Resistance to corrosion

3. High thermal and electrical conductivity

4. Ease of Machinability

5. Non-magnetic


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Magnesium (Mg) is the lightest metal. Alloys are used in structural and non-

structural applications.

Typical uses of magnesium alloys are aircraftand missile components.

Also has good vibration-dampingcharacteristics.


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Copper alloys have electrical andmechanical properties, corrosionresistance, thermal conductivity and wear

resistance. Applications are electronic components,

springs and heat exchangers.

Brass is an alloy of copper and zinc.

Bronze is an alloy of copper and tin.


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Nickel (Ni) has strength, toughness, and

corrosion resistance to metals. Used in stainless steels and nickel-base

alloys.

Alloys are used for high temperatureapplications, such as jet-engine componentsand rockets.


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Superalloys are high-temperature alloys

use in jet engines, gas turbines andreciprocating engines.


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Titanium (Ti) is expensive, has high strength-to-weight ratio and corrosion resistance.

Used as components for aircrafts, jet-engines,

racing-cars and marine crafts.


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Refractory metals have a high melting pointand retain their strength at elevatedtemperatures.

Applications are electronics, nuclear powerand chemical industries.

Molybdenum, columbium, tungsten, andtantalum are referred to as refractory metal.


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1. Beryllium2. Zirconium

3. Low-melting-point metals:

- Lead- Zinc- Tin

4. Precious metals:- Gold- Silver

- Platinum


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1. Shape-memory alloys (i.e. eyeglass frame,helical spring)

2. Amorphous alloys (Metallic Glass)

3. Nanomaterials

4. Metal foams


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Ceramics Traditional ceramics

New ceramics

Glass


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Traditional ceramics clays: kaolinite

silica: quartz, sandstone

alumina

silicon carbide

New ceramics oxide ceramics : alumina

carbides : silicon carbide, titanium carbide, etc.

nitrides : silicon nitride, boron nitiride, etc.


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Glass products window glass

containers

light bulb glass

laboratory glass glass fibers

optical glass

Glass ceramics - polycrystalline structure


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Thermoplastics

Thermosets

Elastomers


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Thermoplastics- reversible in phase by heating andcooling. Solid phase at room temperature and liquidphase at elevated temperature.

Thermosets- irreversible in phase by heating and

cooling. Change to liquid phase when heated, thenfollow with an irreversible exothermic chemicalreaction. Remain in solid phase subsequently.

Elastomers- Rubbers


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Acetals

Acrylics - PMMA Acrylonitrile-Butadiene-Styrene - ABS

Cellulosics

Fluoropolymers - PTFE , Teflon

Polyamides (PA) - Nylons, Kevlar Polysters - PET

Polyethylene (PE) - HDPE, LDPE

Polypropylene (PP)

Polystyrene (PS) Polyvinyl chloride (PVC)


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Amino resins Epoxies

Phenolics

Polyesters Polyurethanes

Silicones


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Natural rubber

Synthetic rubbers butadiene rubber butyl rubber chloroprene rubber

ethylene-propylene rubber isoprene rubber nitrile rubber polyurethanes silicones

styrene-butadiene rubber thermoplastic elastomers


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Metal Matrix Composites

Ceramic Matrix Composites

Polymer Matrix Composites


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Metal Matrix Composites (MMC)Mixture of ceramics and metals reinforced by strong, high-

stiffness fibers

Ceramic Matrix Composites (CMC)Ceramics such as aluminum oxide and silicon carbide

embedded with fibers for improved properties, especiallyhigh temperature applications.

Polymer Matrix Composites (PMC)Thermosets or thermoplastics mixed with fiber

reinforcement or powder.


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1D fibre

Woven fabric

Random fibre


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