Transcript MSE527

MSE 527
Fall 2011
MSE 527- Mechanical Behavior of Materials
Time: Wed 18:30-19:50 PM, Room JD1504
Lecture units: 2.0, Lab design units: 1.0
A survey of relationships between mechanical behavior and materials structure. Elements of creep, fracture
and fatigue of metals, ceramics, and composites. Introduction to applied fracture mechanics and
environmentally assisted cracking laboratory methods for evaluating structural property relationships, fracture
toughness measurements and failure analysis using Scanning Electron Microscopy.
Textbook: R. W. Hertzberg, Deformation and Fracture Mechanics of Engineering Materials,
4th Ed., J. Wiley & Sons, 1996.
Instructor: Dr. Behzad Bavarian
Dept. of Manufacturing Systems Engineering and Management
Office: JD3513, 818/677-3917
Email: [email protected]
Office Hour: W 5:30-6:15PM
Course Description:
Prerequisites: MSE 227 and MSE 227L
The main techniques used in this course, center around the application of scientific principles to real-life
situations. Library research is necessary to develop most of the topic discussions. The course covers
dislocation theory and plastic deformation in order to explain strengthening mechanisms in different materials.
Materials applications in elevated temperature are studied to understand the design criteria for these
applications.
Fundamentals of fracture mechanics, microstructure aspects of fracture toughness, transition temperature,
environment-assisted cracking, and fatigue crack propagation is discussed to be able to design based on the
damage tolerant concept, and failure analysis using scanning electron microscopy.
This course requires extensive design problem solving, technical presentation, and a term paper on a current
topic in materials application or design.
Final Exam December 14, 2011 8:00PM – 10:00 PM
Course Method and Expectations:
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The main techniques to be used in this course, center on the application of scientific principles to real-life situations.
Library research is necessary to develop most of the topic discussions.
•
Grading Policy
•
Homework
10%
•
Mid-term Exam
30%
•
Term project
15%
•
Final Exam
45%
Grading System:
•
Letter Grades
•
A Outstanding
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B Excellent
•
C Acceptable
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D Passing
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F Failure
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Plus/Minus Grading
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Grade Points
4.0
3.0
2.0
1.0
0.0
Last day to drop: Friday, Sept. 16, 2011
References:
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1. D. Callister, Jr. Fundamentals of Materials Science and Engineering, J. Wiley & Sons, NY, 2nd Ed. 2005.
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2. G. E. Dieter, Mechanical Metallurgy, McGraw-Hill, NY, 1994.
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3. V. J. Colangelo and F.A. Meiser, Analysis of Metallurgical Failures, J. Wiley & Sons, NY, 1987.
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4. ASM Metals Handbook, Volume 11, Failure Analysis and Prevention, Metals Park, 1986.
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5. R. M. Caddell, Deformation and Fracture of Solids, 1980.
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6. A. G. Guy, Elements of Physical Metallurgy, 1984.
• Materials science deals with basic knowledge
about the internal structure, properties and
processing of materials.
• Materials engineering deals with the application
of knowledge gained by materials science to
convert materials to products.
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Materials Science
Materials Science and
Engineering
Basic
Knowledge
of
Materials
Resultant
Knowledge
of Structure and
Properties
Materials Engineering
Applied
Knowledge
of Materials
Types of Materials
• Metallic Materials
 Composed of one or more metallic
elements.
 Example:- Iron, Copper, Aluminum.
 Metallic element may combine with
nonmetallic elements.
 Example:- Silicon Carbide, Iron Oxide.
 Inorganic and have crystalline structure.
 Good thermal and electric conductors.
Metals and Alloys
Ferrous
Eg: Steel,
Cast Iron
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Nonferrous
Eg:Copper
Aluminum
Types of Materials
• Polymeric (Plastic) Materials
 Organic giant molecules and mostly
noncrystalline.
 Some are mixtures of crystalline and
noncrystalline regions.
 Poor conductors of electricity and hence
used as insulators.
 Strength and ductility vary greatly.
 Low densities and decomposition
temperatures.
 Examples :- Poly vinyl Chloride (PVC),
Polyester.
 Applications :- Appliances, DVDs,
Fabrics etc.
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Types of Materials
• Ceramic Materials
 Metallic and nonmetallic elements are chemically
bonded together.
 Inorganic but can be either crystalline,
noncrystalline or mixture of both.
 High hardness, strength and wear resistance.
 Very good insulator. Hence used for furnace lining
for heat treating and melting metals.
 Also used in space shuttle to insulate it during exit
and reentry into atmosphere.
 Other applications : Abrasives, construction
materials, utensils etc.
 Example:- Porcelain, Glass, Silicon nitride.
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Types of Materials
• Composite Materials




Mixture of two or more materials.
Consists of a filler material and a binding material.
Materials only bond, will not dissolve in each other.
Mainly two types :o Fibrous: Fibers in a matrix
o Particulate: Particles in a matrix
o Matrix can be metals, ceramic or polymer
 Examples : Fiber Glass ( Reinforcing material in a polyester
or epoxy matrix)
 Concrete ( Gravels or steel rods reinforced in
cement and sand)
 Applications:- Aircraft wings and engine,
construction.
1-8
Types of Materials
• Electronic Materials
 Not Major by volume but very
important.
 Silicon is a common electronic
material.
 Its electrical characteristics are
changed by adding impurities.
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 Examples:- Silicon chips,
transistors
 Applications :- Computers,
Integrated Circuits, Satellites etc.
Future Trends
• Metallic Materials
 Production follows US economy closely.
 Alloys may be improved by better
chemistry and process control.
 New aerospace alloys being constantly
researched.
o Aim: To improve temperature and corrosion
resistance.
o Example: Nickel based high temperature
super alloys.
 New processing techniques are
investigated.
o Aim: To improve product life and fatigue
properties.
o Example: Isothermal forging, Powder
metallurgy.
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 Metals for biomedical applications
Future Trends
• Polymeric (Plastic Materials)
 Fastest growing basic material (9%
per year).
 After 1995 growth rate decreased
due to saturation.
 Different polymeric materials can
be blend together to produce new
plastic alloys.
 Search for new plastic continues.
1-12
Future Trends
• Ceramic Materials
New family of engineering ceramics are
produced last decade
 New materials and applications are constantly
found.
 Now used in Auto and Biomedical
applications.
 Processing of ceramics is expensive.
 Easily damaged as they are highly brittle.
 Better processing techniques and high-impact
ceramics are to be found.
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Future Trends
• Composite Materials
 Fiber reinforced plastics are primary
products.
 On an average 3% annual growth from
1981 to 1987.
 Annual growth rate of 5% is predicted
for new composites such as
Fiberglass-Epoxy and Graphite-Epoxy
combinations.
 Commercial aircrafts are expected to
use more and more composite
materials.
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Future Trends
• Electronic Materials
 Use of electronic materials such as
silicon increased rapidly from 1970.
 Electronic materials are expected to play
vital role in “Factories of Future”.
 Use of computers and robots will
increase resulting in extensive growth in
use of electronic materials.
 Aluminum for interconnections in
integrated circuits might be replaced by
copper resulting in better conductivity.
1-15
Future Trends
• Smart Materials : Change their properties by
sensing external stimulus.
 Shape memory alloys: Strained material reverts
back to its original shape above a critical
temperature.
 Used in heart valves and to expand arteries.
 Piezoelectric materials: Produce electric field
when exposed to force and vice versa.
 Used in actuators and vibration reducers.
MEMS and Nanomaterials
• MEMS: Microelectromechanical systems.
 Miniature devices
 Micro-pumps, sensors
• Nanomaterials: Characteristic length < 100
nm
 Examples: ceramics powder and grain size <
100 nm
 Nanomaterials are harder and stronger than
bulk materials.
 Have biocompatible characteristics ( as in
Zirconia)
 Transistors and diodes are developed on a
nanowire.
SUMMARY: BONDING
Type
Bond Energy
Comments
Ionic
Large!
Nondirectional (ceramics)
Covalent
Variable
Directional
large-Diamond semiconductors, ceramics
small-Bismuth
polymer chains)
Metallic
Variable
large-Tungsten
small-Mercury
Nondirectional (metals)
smallest
Directional
inter-chain (polymer)
inter-molecular
Secondary
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FACE CENTERED CUBIC
STRUCTURE
(FCC)
• Close packed directions are face diagonals.
--Note: All atoms are identical; the face-centered atoms are shaded
differently only for ease of viewing.
• Coordination # = 12
Adapted from Fig. 3.1(a),
Click on image to animate
(Courtesy P.M. Anderson)
Callister 6e.
6
BODY CENTERED CUBIC
STRUCTURE (BCC)
• Close packed directions are cube diagonals.
--Note: All atoms are identical; the center atom is shaded
differently only for ease of viewing.
• Coordination # = 8
Adapted from Fig. 3.2,
Click on image to animate
(Courtesy P.M. Anderson)
Callister 6e.
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HEXAGONAL CLOSE-PACKED
STRUCTURE (HCP)
• ABAB... Stacking Sequence
• 3D Projection
• 2D Projection
A sites
B sites
A sites
Adapted from Fig. 3.3,
Callister 6e.
• Coordination # = 12
• APF = 0.74
10
• Stress-Strain
Mechanical Testing and Properties
•
Tensile Strength  Tensile Test
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Flexural Strength  Bend Test for brittle materials
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Hardness  Hardness Test
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Toughness  Impact Test
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Fatigue Life  Fatigue Test
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Creep rate  Creep Test
Tensile Test
Engineerin g stress   
F
A0
Engineerin g strain   
l  l0
l0
Mechanical Testing and Properties
Tensile Test & the properties obtained from the Tensile Test
Engineerin g stress   
F
A0
Engineerin g strain   
l  l0
l0
•Note: in Metals, Yield stress is usually the stress required for dislocations to slip.
Tensile Test & the properties obtained from the Tensile Test
Note: Young’s modulus is a measure of the stiffness of the material.
Tensile Test & the properties obtained from the Tensile Test
Er=1/2(yield strength)(strain at yielding)
Poisson' s ratio :  
  lateral
 longitudinal
Tensile Test & the properties obtained from the Tensile Test
Er=1/2(yield strength)(strain at yielding)
  lateral
Poisson' s ratio :  
 longitudinal
Tensile Test & the properties obtained from the Tensile Test
Effect of Temperature
The Bend Test for Brittle Material
•Due to the presence of flaw at the surface,
in many brittle materials, the normal tensile
test cannot easily be performed.
The Bend Test for Brittle Material
Flexural strength 
3FL
, where F is fracture Load.
2
2 wh
The Bend Test for Brittle Material
where  is deflection
True Stress-True Strain
F
Engineerin g stress   
A0
l  l0
Engineerin g strain   
l0
F
True stress   t  '
A
l
dl
l'
A0
True strain   t    ln( )  ln( ' )
l l
l0
A
'
0
The Hardness Test
Brinell Hardness : HB 
F
( / 2) D( D  D 2  Di2 )
The Hardness Test
6.7 The Impact Test  impact strength
To evaluate the brittleness of a material subjected to a sudden blow.
6.7 The Impact Test  impact strength
Impact strength vs. Temperature
Note: BCC metals have transition temperature, but most FCC metals do not.
6.7 The Impact Test  impact strength
Yield Strength: A > B
Impact Strength: B > A
The Fatigue Test  Fatigue Life, Fatigue Strength
The Fatigue Test
S-N curve
The Creep Test:
Apply stress to a material at an elevated temperature
Creep: Plastic deformation
at high temperature
• a typical creep curve showing the strain produced as
a function of time for a constant stress and temperature.
The Creep Test: