ta 201 l4
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PROPERTIES OF MATERIALS
Mechanical Properties Physical PropertiesContd .. From lecture 3
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Non-Ferrous Metals
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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 .
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Duralumin
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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.
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NiTi Shape memory
Actuators
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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
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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).
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Defence Met. Res. Lab (DMRL), Hyderabad
High Temperature Metals/Alloys
Ni-based superalloy
1 cm
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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
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• 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
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Orthopedic application: Hydroxyapatite
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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
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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
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• 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
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Carbon-Carbon Composite
Stealth Aircraft(Hypersonic)
C-C compositeBlue: Carbon fiberBrown : SiC
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PROPERTIES OF MATERIALS
Mechanical Properties Physical Properties
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Material property should be compatible with:
• Service conditions to which the component will be subjected to.
• Manufacturing process
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Mechanical Property : Loading
Tensile Compressive Shear
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Mechanical Property : Tensile Test
V
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Load cells Extensometer
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Engineering stress:
Engineering strain:
o
o
L LeL−
=
Original area
S = F/A0
Definition of Parameters
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Engineering stress – strain curve
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Engineering stress – strain curve
UTS
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Engineering stress – strain curve
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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
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Tension test sequence
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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
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Necking
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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−
=
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Typical mechanical properties at RT
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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 -
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True Stress and True Strain
M. P. Groover, “Fundamentals of Modern Manufacturing 3/e” John Wiley, 2007
True stress:
True strain:
Instantaneousarea
t
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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
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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
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True Stress (σt) & Strain (ε)
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Comparision between True stress-Strain and Engg.Stress –strain curve
(UTS)
t
σe = eE