1a Properties Spectrum of Materials_s1-s20

1 MBB3023 Course Outcomes

Apply knowledge of materials properties for engineering design and applications.

Select suitable materials for a given engineering application.

Interpret and analyze materials testing data.

Identify the appropriate material testing standards.1

2

3

4

At the end of the course, the students should beable to:

2

Metals and

Alloys

Ceramics

and GlassesPolymers

Composites

Wire-

reinforced

cement

(Cermet)

Filled polymers

CFRP GFRP

Steel-cord

tyres

3 Role of Materials in Product Success

Failure of products:

1. Insufficient design

2. Insufficient properties

“Design flaws occurs because the designers and tool fabricators never use the product - common in large corporations.”

Insufficient properties is a materials

engineering issue.

Properties: characteristic that

distinguish and identify a material.

Originate in the nature of material

at the atomic or molecular level.

Material properties

Chemical Mechanical Physical

4 Material properties

Chemical Mechanical Physical Thermal •Material

characteristics that

relates to the

structure of

materials, its

formation from the

elements, and its

reactivity with

chemicals, other

materials, and

environment.

•The

characteristics of

a material that

are displayed

when a force is

applied to the

material.

•Characteristics

of materials that

relate to the

interaction of

these materials

with various

forms of energy

and with human

senses.

Procurement/Manufacturing considerations are not listed in property handbooks

and not even legitimate category by most standards. However the available shapes,

sizes, surface Texture, tolerances on materials are often the most important selection

factors.

•The properties

of a material

change with

temperature,

usually for worst.

Start to creep or

oxide/degrade.

5 Materials Property Spectrum

Composition

Microstructure

Phases

Grain Size

Corrosion Resistance

Inclusions

Tensile/compressive

Toughness

Ductility

Fatigue

Hardness

Creep resistance

Shear strength

Available Shapes,

Sizes, Surface

Texture

Manufacturing

Tolerances

Composition

Fillers, Crystallinity

Molecular weight

Flammability

Spatial configuration

Chemical resistance

Tensile/compressive

Heat distortion

Pressure-velocity limit

Toughness, Stress

Rupture, Creep

Manufacturing tolerances,

Stability, Available Sizes,

moldability, surface

texture

Composition

Porosity

Grain size

Crystal Structure

Corrosion Resistance

Tensile/compressive

Fracture toughness

Transverse rupture

Hardness

Available Shapes,

Sizes, Surface Texture

Manufacturing

Tolerances, Stability

Composition

Matrix/reinforcement bond;

Volume fraction of

reinforcement;

Reinforcement nature

Tensile/compression

Fracture toughness

Creep resistance

Reinforcement orientation

Available shape and Sizes

Manufacturing tolerances

Stability

• Specific heat

• Coefficient of

Thermal

Expansion

• Thermal

conductivity

• Heat

distortion

temp

• Glass

transition

temp

• Magnetic

• Electrical

• Optical

• Acoustic

• Gravimetric

• Color

CHEMICAL PHYSICAL MECHANICALProcurement/ Manufacturing considerations

ME

TA

LS

PO

LY

ME

RS

CE

RA

MIC

SC

OM

PO

SIT

ES

6 “Properties-Product Design Relationship”

How the

properties of

engineering

materials

affect the way

in which

products are

designed.

Properties

Bulk mechanical properties

INTRINSIC ATTRIBUTIVE

Bulk non-mechanical properties

Surface properties

Price and Availability

Production properties: ease

of mfg, fabrication,

joining, finishing

Aesthetic properties:

appearance, texture, feel

7 “Properties-Product Design Relationship” How the Mechanical Properties of engineering materials affect the

way in which products are designed.

•“Elastic” means it springs back when released;

•Elastic stiffness – resistance to bending is set partly by its shape – thin strips are easy to bend – partly by a property of the material itself - its Elastic Modulus, E.

•Materials with high E, like steel, are intrinsically stiff; those with low E, like PE, are not.



•Permanent deformation is related

to strength not stiffness.

•Permanent bent depends on its

shape and its Yield Strength , y.

•Large y (Ti) is hard to deform

permanently, even E is not high

•Low y like lead is deformed easily

•When metals deformed they

getting stronger („work

hardening‟) but there is limit called

Tensile strength, ts after this limit

the materials fails (the amount of

stretches before it breaks is called

“ductility”.



•Fracture suddenly before it

acquires a permanent bend.

•No permanent deformation -

y is not the right property.

•Resistance of materials to

cracking and fracture is

measured instead by Fracture

Toughness, K1c.

•Steels are tough – have high

K1c; glass is brittle – low K1c



Inadequate Stiffness

(E too low)Inadequate

Strength (y low)

Inadequate

Fracture &

Toughness

(K1c too low)

Inadequate

Density

( too high)


How the Thermal Properties of engineering materials affect the way in

which products are designed.

1. The strength of materials fails, it starts to „creep‟

(to sag slowly over time), it may oxidize, degrade or

decompose (figures).

This means that there is a limiting temperature called

the Maximum Service Temperature, Tmax, above which

its use is impractical.




2. Most materials expand when they are heated, but by different amount depending on their Thermal Expansion Coefficient,. The expansion is small but its consequences can be large. E.g. buckling of the rod. (the rod is constrained and then heated – the expansion forces the rod against the constraint, causing it to buckle). E.g: railway tracks.




High Conductivity,

3. Some materials-metals-feel cold; others-wood-feel warm. This feel has to do with

two thermal properties of materials: Thermal Conductivity, and Heat Capacity. -

measures the rate at which heat flows through the material when one side is hot and

the other cold: High is needed in conducting heat from one place to another

(cooking pans, radiators, heat exchangers). Low is useful in insulate homes,

reduce energy consumptions of refrigerators and freezers and enable space vehicles

to re-enter the earth’s atmosphere.

When time is limited, Heat Capacity, Cp is matter. It measures the amount of heat

that it takes to make the temp. of material rise by a given amount.

14 The Price & Availability of Materials

Consider how the materials used for building bridges in Cambridge

have changed over the centuries. Fig. 1.2 (Queens’ Bridge) suggests,

until 150 years or so ago wood was commonly used for bridge

building. It was cheap, and high-quality timber was still available in

large sections from natural forests. Stone, too, as the picture of Clare

Bridge (Fig. 1.3) shows, was widely used. In the 18th century the

ready availability of cast-iron, with its relatively low assembly costs,

led to many cast-iron bridges of the type exemplified by Magdalene

Bridge (Fig. 1.4). Metallurgical developments of the later 19th century

allowed large mild-steel structures to be built (the Fort St. George

Footbridge, Fig. 1.5). Finally, the advent of cheap reinforced concrete

led to graceful and durable structures like that of the Garret Hostel

Lane bridge (Fig. 1.6).

“This evolution clearly illustrates how availability influences the

choice of materials. Nowadays, wood, steel and reinforced concrete

are often used interchangeably in structures, reflecting the relatively

small price differences between them. The choice of which of the

three materials to use is mainly dictated by the kind of structure the

architect wishes to build: chunky and solid (stone), structurally

efficient (steel), slender and graceful (pre-stressed concrete.”

Fig. 1.2

Fig. 1.3

Fig. 1.4

Fig. 1.5

15 Mechanical Properties of Materials

Learning Objectives: students should be able to:

1. Achieve an understanding of the difference between

strength and toughness.

2. Gain a secure knowledge of tensile testing and its

product.

3. Learn how to use mechanical properties in materials

selection and failure analysis.

16 Spectrum of Mechanical Properties

Mechanical properties

Strength

Tensile

Yield

Compression

Flexural

Shear

Creep

Stress rupture

Formability

% elongation;

% reduction area;

Bend radius

Stiffness

Modulus of elasticity

Flexural modulus

Toughness

Impact strength; Notch sensitivity; Critical stress intensity factor

Durability

Hardness; Wear resistance; Fatigue strength

17

What is tensile testing?

What is it used for?

How does it work?

Important parts on a tensile tester:

– Specimen‟s pulling/pushing mechanism

– Grips

– Extensometer

– Fixtures

Type of loading

Definition of elastic modulus

Yield strength

Tensile strength

Determining percent elongation

True stress and strain

Poisson‟s ratio

Tensile Testing

18 Tensile Test

The key mechanical properties obtained from a Tensile Test:1-Modulus of Elasticity (E); 2-Yield Strength (Y.S).3-Tensile Strength (TS); 4-Ductility, 100xєfailure (elastic recovery occurs after fracture); 5-Toughness (measured under load; hence the dashed line is vertical)

19 The tensile test is the most common test for determining such mechanical properties of materials as strength, ductility, toughness, elastic modulus, and strain-hardening capability.

20 Significance of Stress-Strain Data

Parameter Description

Modulus of

elasticity

Used to measure the relative stiffness of materials.

Yield strength(YS) Design stresses must be lower than the YS to ensure

that a part does not fail by plastic deformation. Shear

strength may be estimated from this YS.

Ultimate tensile

strength (UTS)

The ultimate tensile stress is the maximum stress

observed in a tensile test. Necking begins when the

value is reached.

UTS/YS ratio The ratio provides an indication of the degree of work

hardening that has occurred.

% elongation Indication of material ductility and toughness

% reduction in area Indication of material ductility and toughness

General shape of

curve

Area under the curve provides a relative indication of

material toughness. Interstitial activity in the material

can be observed. Relative level of work hardening are

assessed.

1a Properties Spectrum of Materials_s1-s20

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