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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
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
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
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
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.
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
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
I. IntroductionMECE 3245 Materials Science Lab
Mechanical Properties of Solids
copyright © 2007 by Li Sun
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?
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
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
I. IntroductionMECE 3245 Materials Science Lab
Typical Tensile Test Curves
σ
0
ceramic
metal
polymer
ε
I. IntroductionMECE 3245 Materials Science Lab
Stress-Strain Testing• Typical tensile test
machine
specimenextensometer
• Typical tensile specimen
gauge length
Fig 6.2, 6.3
I. IntroductionMECE 3245 Materials Science Lab
Stress-strain Curve and Sample Deformation
0ε
σ
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
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!
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.
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
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
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
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.
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