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MANUFACTURINGPROCESSES

- AMEM 201 –

Lecture 2: Industrial Materials & their Properties

DR. SOTIRIS L. OMIROU

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Choosing materials

What is it used for?

Why choose that material?

What is it?

What materials are used?

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A saucepan for cooking

plasticmetal

conductor insulator

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A dustpan and brush for cleaning

plasticplastic

light and rigid flexible

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A glass for drinking

glass

waterproof

easy to clean

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A lightbulb for seeing in the dark

metalglass

transparent conductor

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Criteria for selecting the right material:

Properties of the material

Cost

Industrial Materials

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Industrial Materials Four basic categories:

– metals & alloys– ceramics– polymers– composites

Other useful materials are:

natural rubber/leather, glass, wood, cotton, silkand wool

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Industrial Materials

Alloys are composed of two or more elements (at least one element is metal)Alloys can be divided into two basic groups:

1. ferrous (iron alloys) 2. Nonferrous

Examples of ferrous alloys:Steel is an alloy of iron and carbon (0.02 to 2 %). It may also have manganese, chromium and nickel to enhance the properties of the metal

Cast iron is also an alloy of iron, carbon (2 to 4 %) and silicon (0.5 to 3 %)

Examples of nonferrous alloys:Bronze is an alloy consisting primarily of copper, commonly with about 12% tin and often with the addition of other metals (such as aluminium, manganese, nickel or zinc)

Brass is a metal alloy made of copper and zinc (usually over 30%)

Metals: iron, aluminium, copper, silver, nickel, cobalt, magnesium, etc.

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Ceramics: Compounds of metallic and nonmetallic elements – oxygen, nitrogen, and carbon.

Types:

– Traditional ceramics – clay for brick, tile and pottery, silica for glass products and alumina and silicon carbide for abrasives used for grinding

– Newer ceramics – tungsten carbide and titanium carbide for cutting tools and grinding abrasives

– Crystalline ceramics are formed from powders and then sintered

* Sintering – heating to a temperature below the melting point to achievebonding between the powders

Industrial Materials

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Polymers

– Compounds consisting of carbon plus one or more other elements such as hydrogen, nitrogen, oxygen, and chlorine

– Thermoplastic polymers soften when heated and when cooled, they are hard again –polyethylene bags, PVC pipes and nylon

– Thermoset polymers char and burn when heated – plastic cups and dishes made of melamine.

Compositescomposite material is a mixture of two or more materials with properties superior to the

materials of which it is made, ex. Concrete (rocks, sand and cement)

- reinforced plastics

Industrial Materials

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Properties of Materials

Materials are chosen for their characteristics or properties.

Examples:– glass for windows– plastic for insulators– copper for electrical wires.

Common properties:– strength – hardness– density– ability to conduct electricity / heat– resistance to corrosion

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Mechanical properties of materials

Strength, Toughness, Hardness, Ductility,Elasticity, Fatigue and Creep

Chemical properties

Oxidation, Corrosion, Flammability, Toxicity, …

Physical properties

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

Properties of Materials

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Properties of Materials

Mechanical properties determine the behavior of a material when subjected to mechanical forces

STRENGTH is the ability of a material to keep its own shape when a force is applied. There are four kinds of forces:

Tension is a force that pulls on a piece of material, e.g. pulling aspring

Compression is a force that pushes on or squeezes a material,e.g. squeezing s sponge

Shear force acts on a material like a pair of scissors. One part of the material slides in one direction and the other part slides inthe opposite direction

Torque or torsion is the twisting force, e.g. using a wrench to turn a bolt

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Properties of Materials

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TENSION TEST

Most common mechanical stress-strain test

Used to ascertain several mechanical properties that are important in design

A specimen is deformed, usually to fracture, with a gradually increasing tensile load that is applied uniaxially along the long axis of the specimen.

Properties of Materials

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The specimen is mounted by its ends into the holding grips of the testing apparatus

Tensile testing machine– To elongate the specimen at

a constant rate– To continuously and

simultaneously measure the instantaneous load and the resulting extension

– Load using load cell– Extension using

extensometer

Takes few minutes and is destructive.

TENSION TEST

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Engineering Stress (σ) = Instantaneous applied load (F) / Original Area (Ao)

Engineering strain (ε) li = instantaneous length lo = original length

0AF

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ll

llli

Stress and Strain

Compression Test (Similar to tensile test, compressive load)

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Properties of MaterialsStress – Strain Diagram

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Failure in Tension, Young’s modulus and Tensile strength

Properties of Materials

In the linear elastic range: Hooke’s law

= E ε

E: Young’s modulus

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– Toughness is the ability of a material to absorb energy without breaking.

Toughness is an estimate of how much energy is consumedbefore the material fractures.

Toughness = the strain energy = area under the stress-strain curve

Properties of Materials

Mechanical properties: TOUGHNESS

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• Toughness is approximated by the area under thestress-strain curve.

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smaller toughness

polymers

Engineering tensile strain,

Engineering tensile stress,

smaller toughness (ceramics)

larger toughness(metals)

Mechanical properties: TOUGHNESS

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Ductility is the ability of a material to undergo permanent deformation through elongation (reduction in cross-sectional area) or bending at room temperature without fracturing. Opposite of brittleness.

Ductility = 100 x (Lf – Lo)/Lo

Examples

High ductility: platinum, steel, copper

Good ductility: aluminum

Low ductility (brittle): chalk, glass, graphite

Mechanical properties: DUCTILITY

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Mechanical properties: HARDNESS (animation)

Definition: resistance to plastic deformation by indentation

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Mechanical properties: HARDNESS (animation)

Definition: resistance to plastic deformation by indentation

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Mechanical properties: HARDNESS (animation)

Definition: resistance to plastic deformation by indentation

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Mechanical properties: HARDNESS (animation)

Definition: resistance to plastic deformation by indentation

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Widely used for testing metals and nonmetals of low to medium hardness

A hard ball is pressed into specimen surface with a load of 500, 1500, or 3000 kg

Brinell Hardness Test - Description

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Brinell Hardness

)( 222

ibbb DDDDFHB

Where,

HB = Brinell Hardness,

F = indentation load, kg

Db = diameter of ball, mm,

Di = diameter of indentation, mm

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Modes of fatigue testingModes of fatigue testing

Mechanical properties: FATIGUE

The phenomenon leading to fracture under repeated or fluctuating stress. Fatiguefractures are progressive beginning as minute cracks and grow under the action of fluctuating stress

Try to break a paper clip by using a cyclic loading;notice the appearance and propagation of cracks

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Mechanical properties: CREEP

If a material is kept under a constant load over a long period of time,it undergoes permanent deformation. This phenomenon is seen in manymetals and several non-metals.

For most materials, creep rate increases with increase in temperature.

The phenomenon does not have much direct implication in manufacturing,but has significant use in design of parts that, for example, carry a load

permanently during their use.

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– Materials that offer very little resistance to the flow of electricity are conductors, e.g. silver and copper

– Materials that resist the flow of electricity most strongly are insulators, e.g. plastic and rubber

Electrical properties

Thermal properties

Properties related to the ability of a material to conduct heat.Copper and aluminum are the two best conductors of heatInsulation is a layer of material used to prevent the movement of heat

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Physical properties:

Density = ρ = mass/volume

Applications:

Why is steel a good material for the wrecking ball used to demolish old buildings?

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Melting pointThis is the temperature at which the material changes phase from solid to liquid.

Physical properties:

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Specific heat - definition

The amount of heat energy that will raise the temperature of aunit mass of the material by 1°C.

Physical properties:

How specific heat affects machining and forming processes:

In machining and forming processes, a lot of heat is generated due to deformation and friction between the tool and workpiece.

If the specific heat of the work piece is low, then its temperature will rise very rapidly, resulting in poor surface finish. So extra or more efficient coolants may be required.

Likewise, if the specific heat of the tool material is low, the tool will heat up rapidly, leading to lower tool life.

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Physical properties:

Thermal expansion - definition

Application example :

The linear coefficient of thermal expansion is defined as theproportional change in a material’s length when its temperaturechanges by 1°C:

coefficient of linear thermal expansion = α = ΔL/(L ΔT)

In machine tools where different components are made of different materials, the assembly may jam, or become too loose and vibrate, when the temperature changes. Their design must account and compensate for the different rates of thermal expansion for the materials.

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Summary

Knowledge of materials’ properties is required to

Select appropriate material for design requirementSelect appropriate manufacturing processOptimize processing conditions for economic manufacturing…

Materials have different mechanical, physical, electrical properties

Reference: Chapter 2, Chapter 3, Mfg Engg & Tech, Kalpakjian & Schmid