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I. IntroductionMECE 3245 Materials Science Lab
About the Course
Materials Science Lab - MECE3245
1 hour lectures 8- 3 hour Experiments
Wednesdays 2:30-3:30 pmE223-D3
Fridays W249-D3
2- quizzes
Fridays W249-D3
copyright © 2008 by Li Sun
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I. IntroductionMECE 3245 Materials Science Lab
Lab Experiments
Basic Phenomena:
Mechanical Behavior • Phase diagrams• Recrystallization of Brass
• Tensile Testing• Charpy toughness testing• Fatigue of metal• Creep
Microstructure / Property Control
• Age Hardening• Heat treatment of Steel
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I. IntroductionMECE 3245 Materials Science Lab
Lectures
Basic Phenomena Review: Mechanical behavior:
Crystallography / dislocationsPhase EquilibriaDiffusion
Tensile stress-strainToughnessFatigue
Thermo-mechanical control of microstructure
Work hardeningHeat treatment
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I. IntroductionMECE 3245 Materials Science Lab
Lab Schedule
Lecture 01/17 Wednesday, 5-8 lectures depend on progress
First lab starts on Feb, 2nd
02/02 Lab 102/09 Lab 202/16 Lab 302/23 Lab 403/02 Quiz03/09 Open
03/12-03/17 Spring Break03/23 Lab 503/30 Lab 604/06 Lab 704/13 Lab 804/20 Quiz
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I. IntroductionMECE 3245 Materials Science Lab
Lab Organization
• Phase diagrams• Recrystallization of Brass• Fatigue of metal• Heat treatment of Steel
• Tensile Testing• Charpy toughness testing• Age Hardening• Creep
Three sessions: 9am-noon, 1-4pm, 4-7pm
Once you sign-up for one session, you can not switch to other two.
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I. IntroductionMECE 3245 Materials Science Lab
Sign-up
Three sessions: A, B, C
Each session has four groups: 1, 2, 3, 4
Four student per group
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I. IntroductionMECE 3245 Materials Science Lab
What do you need to do?
• Sign-up for the lab section.• Get your Materials Science textbook out (Calister)• Get familiar with the lab manual before each experiment• Read lab report format and requirement
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I. IntroductionMECE 3245 Materials Science Lab
Mechanical Properties of Solids
copyright © 2007 by Li Sun
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I. IntroductionMECE 3245 Materials Science Lab
Mechanical Properties
Materials response to external mechanical forces.
• Stress and strain: What are they and why are they used instead of load and deformation?• Elastic behavior: When loads are small, how deformation occurs? What materials deform least?• Plastic behavior: At what point does permanent deformation occur? What materials are most resistant to permanent deformation?
• Toughness and ductility: What are they and how do we measure them?
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I. IntroductionMECE 3245 Materials Science Lab
Engineering Stress and StrainF
F
l0
ll0
F
F
lx
y
zO
0
0
0 lll
ll i −=
∆=ε
0AF
=σ (N/m2)
Original cross-section area
l0 : initial length,li : final length
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I. IntroductionMECE 3245 Materials Science Lab
Shear and Torsional Stress and Strain
0AF
=τ (N/m2)
θγ tan= no unitF
F
θ
T
φ
T: torqueφ: twist angle
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I. IntroductionMECE 3245 Materials Science Lab
Typical Tensile Test Curves
σ
0
ceramic
metal
polymer
ε
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I. IntroductionMECE 3245 Materials Science Lab
Stress-Strain Testing• Typical tensile test
machine
specimenextensometer
• Typical tensile specimen
gauge length
Fig 6.2, 6.3
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I. IntroductionMECE 3245 Materials Science Lab
Stress-strain Curve and Sample Deformation
0ε
σ
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I. IntroductionMECE 3245 Materials Science Lab
Linear Elastic Properties
• Modulus of Elasticity, E:(also known as Young's modulus)
• Hooke's Law:
σ = E ε σ
Linear-elastic
E
ε
F
Fsimple tension test
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I. IntroductionMECE 3245 Materials Science Lab
Elastic and Plastic Deformation2. Small load
Fd
Bonds stretch
return to initial
3. Unload1. Initial
1. Initial
elastic + plastic
3. Unload
plasticd
Planes still stretched
2. large load
F
d
Bonds stretch + Planes stretch
Elastic means reversible!
Plastic means permanent!
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I. IntroductionMECE 3245 Materials Science Lab
Important Concepts Associated with the σ-ε Curve
Tensile strength: maximum stress on the σ-ε curve.
σTSσy
σf
0 εYield strength: stress when plastic deformation begins to progress.
Fracture strength: stress when fracture happens.
Resilience: strain energy stored per unit volume in material up to yielding point.
Toughness: strain energy stored per unit volume in material up to fracture point.
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I. IntroductionMECE 3245 Materials Science Lab
Important Concepts Associated with the σ-ε Curve - continued
Ductility: Percentage of plastic strain at fracturePercentage of area reduction at the fracture surface
I.. %100%0
0 ×⎟⎟⎠
⎞⎜⎜⎝
⎛ −=
lll
EL f
0 ε
σ
l0
lf
εTS
• When ε<εTS, elongation is uniform along the whole test sample.• When ε>εTS, necking happens, and significant part of plastic deformation happens in the neck region. For short gauge the percentage of elongation will be larger than in long specimen.
%EL is sample length sensitive
II.. %100%0
0 ×⎟⎟⎠
⎞⎜⎜⎝
⎛ −=
AAA
RA f
%RA is sample length insensitive
0 ε
σ
l0
lf
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I. IntroductionMECE 3245 Materials Science Lab
True Stress and true Strain
Engineering stress and engineering strain
0AF
=σ0
0
0 lll
ll i −=
∆=ε
0 ε
σ
With respect to original cross-section area and length
True stress and true strainWith respect to instantaneous cross-section area and sample length
0ln0 0
1lildlil
l ldT =∫ ∫== ε εε
iT A
F=σ
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I. IntroductionMECE 3245 Materials Science Lab
Relation between σ and σT , ε and εTc
iAF
T =σ0
lnlil
T =ε0
0
0 lll
ll i −=
∆=ε
0AF
=σ
Under uniaxial loading and there is not volume change during deformation,
00lAlA ii =
llli ∆+= 0
lllAAi ∆+
=0
00
0ln
lil
T =ε
00ln
lill
T+
=ε
⎟⎟⎠
⎞⎜⎜⎝
⎛+=
01ln
lil
00
0 )(lA
llFAF
iT
∆+==σ
⎟⎟⎠
⎞⎜⎜⎝
⎛ ∆+=
01
llσ
)1( εσσ +=T )1ln( εε +=T
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I. IntroductionMECE 3245 Materials Science Lab
Stress-strain Curve
0 ε
σEngineering
True
The true stress increases with increasing strain during the plastic deformation. This is the strain hardening behavior.
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I. IntroductionMECE 3245 Materials Science Lab
Strain Hardening
• Curve fit to the stress-strain response:
σT = K εT( )n
“true” stress (F/A) “true” strain: ln(L/Lo)
hardening exponent:n = 0.15 (some steels) to n = 0.5 (some coppers)
• An increase in σy due to plastic deformation.σ
ε
large hardening
small hardeningσy0
σy1