PROPERTIES OF MATERIALS

Mechanical Properties Physical PropertiesContd .. From lecture 3

Non-Ferrous Metals

Aluminium

• Predominantly used in aerospace industry ( 80.0% weight / commercial aircraft ) in the form of Al/Al alloy

• Al has emerged as a valuable source of metal for the automobile industry too .

Duralumin

Titanium• Properties between those of steel and Al. • Strong, lightweight, corrosion resistance. • Mechanical properties are retained up to

5350C.• Problems with Ti:

– Chemically very active in molten state, absorbing O2 or N2 from air

– Difficult and costly to produce.

NiTi Shape memory

Actuators

High Temperature Metals/Alloys

• Jet engines, gas turbines, rocket and nuclear applications require materials– high strength, – creep resistance – corrosion resistance

at temperatures in excess of 1100oC .• Future jet engine temperatures may be

well above 1400oC

Superalloys• Ni, Fe, Ti and Co form the base of these

materials– Aerospace: Ti- based superalloys (Al, C, Mo,

V)– Turbine blades are Ni-based (Fe, Cr)

Refractory Metals• Nb (2470oC), Mo (2610oC),Tantalum

(3000oC), W (3410oC).

Defence Met. Res. Lab (DMRL), Hyderabad

High Temperature Metals/Alloys

Ni-based superalloy

1 cm

Ceramics• Compounds of metallic and non–metallic

elements. Often in the form of oxides, carbides and nitrides

Characteristics • Very high Melting temperature (>1500OC)• Compressive strength can be 5 to 10

times of tensile strength. • Very Brittle. Some ceramics like SiC and

SiN offer moderate toughness.• Low thermal and electrical conductivity

• Al2O3, SiO2, UO2

• SiC, TiC, WC• TiN, BN• Kaolinite (Al2Si2O5(OH)2) • Hydroxyapatite (Ca10(PO4)3(OH)2

Sialon(Si-Al-N) : It is stronger than steel extremely hard and as light as aluminium

Orthopedic application: Hydroxyapatite

Composite Materials• Heterogeneous solid consisting of two or

more different materials that aremechanically or metallurgically bonded

Advantages• Can combine conflicting properties such

as ductility and strength/hardness,resulting in a new material with a uniquecombination of:– Low weight – Stiffness, strength and creep resistance

Classification• Laminar/layer composites

– Plywood: layers of wood bonded together with their grain orientations at different angles

• Improves strength and fracture resistance• Reduces swelling and shrinkage

– Safety glasses(wind shield): Adhesive layer placed between two pieces of glass

• Retains fragments when glass is broken

Steel-Polyurea

• Particulate Composites– Discrete particles of one material surrounded

by matrix. Common example is concrete– Hard particles-soft matrix

• Pronounced strengthening, better creep resistance, toughness

WC in Co

Carbon-Carbon Composite

Stealth Aircraft(Hypersonic)

C-C compositeBlue: Carbon fiberBrown : SiC

PROPERTIES OF MATERIALS

Mechanical Properties Physical Properties

Material property should be compatible with:

• Service conditions to which the component will be subjected to.

• Manufacturing process

Mechanical Property : Loading

Tensile Compressive Shear

Mechanical Property : Tensile Test

V

Load cells Extensometer

Engineering stress:

Engineering strain:

o

o

L LeL−

=

Original area

S = F/A0

Definition of Parameters

Engineering stress – strain curve

Engineering stress – strain curve

UTS

Engineering stress – strain curve

Definiciones

– Yield strength (Y)• Stress at which plastic deformation starts to occur

– Young’s modulus (E) S = E·e

• The slope of the linear elastic part of the curve

– Ultimate tensile strength (UTS)• Maximum engineering stress• Stress at which necking or strain localization occurs

– 2% Offset yield strength Y(0.002)

O

Max LoadUTSA

=

Parameters

Tension test sequence

Figure 2.2 (a) Original and final shape of a standard tensile-test specimen. (b) Outline of a tensile-test sequence showing stages in the elongation of the specimen.

Note: In this figure, length is denoted by lower case l.

Tension test sequence

Necking

Ductility– Ductility: Measure of the amount of plastic

deformation a material can take before it fractures.

• % Elongation to Fracture:

– % El is affected by specimen gage length. Short specimens show larger % El

• % Reduction in Area

– No specimen size effect when area in necked region is used

% 100O Fr

O

A AA xA−

=

% 100f O

O

L LEl x

L−

=

Typical mechanical properties at RT

METALS (WROUGHT) E (GPa) Y (MPa) UTS (MPa) (ELOGATION POISSO’S(%) in 50 mm RATIO (v)

Aluminum and its alloys 69-79 35-550 90-600 45-5 0.31-0.34Copper and its alloys 105-150 76-1100 140-1310 65-3 0.33-0.35Lead and its alloys 14 14 20-55 50-9 0.43Magnesium and its alloys 41-45 130-305 240-380 21-5 0.29-0.35Molybdenum and its alloys 330-360 80-2070 90-2340 40-30 0.32Nickel and its alloys 180-214 105-1200 345-1450 60-5 0.31Steels 190-200 205-1725 415-1750 65-2 0.28-0.33Stainless Steels 190-200 240-480 480-760 60-20 0.28-0.30Titanium and its alloys 80-130 344-1380 415-1450 25-7 0.31-0.34Tungsten and its alloys 350-400 550-690 620-760 0 0.27

NONMETALLIC MATERIALS

Ceramics 70-100 - 140-26000 0 0.2

Diamond 820-1050 - - - -Glass and porcelain 70-80 - 140 0 0.24Rubbers 0.01-0.1 - - - 0.5Thermoplastics 1.4-3.4 - 7-80 1000-5 0.32-0.40Thermoplastics, reinforced 2-50 - 20-120 10-1 -Thermosets 3.5-17 - 35-170 0 0.34Boron fiber 380 - 3500 0 -Carbon fibers 275-415 - 2000-5300 1-2 -Glass fibers (S, E) 73-85 - 3500-4600 5 -Kevlar fibers (29, 49, 129) 70-113 - 3000-3400 3-4 -Spectra fibers (900, 1000) 73-100 - 2400-2800 3 -

True Stress and True Strain

M. P. Groover, “Fundamentals of Modern Manufacturing 3/e” John Wiley, 2007

True stress:

True strain:

Instantaneousarea

t

True Stress (σt) & Strain (ε)

• More Accurate Measurement

• True Stress

• True Strain

P

P

l 0l

A

0A

x

y

AP

AreaeousInsForce

==tantan

σ

⎟⎠⎞

⎜⎝⎛=⎟

⎠⎞

⎜⎝⎛=⎟

⎠⎞

⎜⎝⎛=⎟⎟

⎠

⎞⎜⎜⎝

⎛=

DD

DD

AA

ll 0

200

0

ln2lnlnlnε

t

Engineering Stress (S) /Strain (e) vs. True Stress (σ) /Strain (ε)

True Stress & Engineering Stress (Up to necking)

True Strain & Engineering Strain (Up to necking)

Conservation of volume:

A·l = A0·l0

t

True Stress (σt) & Strain (ε)

Comparision between True stress-Strain and Engg.Stress –strain curve

(UTS)

t

σe = eE