MSE 527

Fall 2011

MSE 527- Mechanical Behavior of Materials Time: Wed 18:30-19:50 PM, Room JD1504Lecture units: 2.0, Lab design units: 1.0A 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 BavarianDept. of Manufacturing Systems Engineering and ManagementOffice: JD3513, 818/677-3917Email: bavarian@csun.eduOffice Hour: W 5:30-6:15PM

Course Description:Prerequisites: MSE 227 and MSE 227LThe 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:• 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 Grade Points• A Outstanding 4.0• B Excellent 3.0• C Acceptable 2.0• D Passing 1.0• F Failure 0.0• Plus/Minus Grading

• Last day to drop: Friday, Sept. 16, 2011

References:• 1. D. Callister, Jr. Fundamentals of Materials Science and Engineering, J. Wiley & Sons, NY, 2nd Ed. 2005.• 2. G. E. Dieter, Mechanical Metallurgy, McGraw-Hill, NY, 1994.• 3. V. J. Colangelo and F.A. Meiser, Analysis of Metallurgical Failures, J. Wiley & Sons, NY, 1987.• 4. ASM Metals Handbook, Volume 11, Failure Analysis and Prevention, Metals Park, 1986.• 5. R. M. Caddell, Deformation and Fracture of Solids, 1980.• 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.

Resultant Knowledge

of Structure and Properties

Applied Knowledge

of Materials

Materials ScienceMaterials Science and

Engineering Materials Engineering

Basic Knowledge

ofMaterials

1-4

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

NonferrousEg:CopperAluminum

1-5

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.

1-6

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.

1-7

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 matrixo Particulate: Particles in a matrixo 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.

Examples:- Silicon chips, transistors Applications :- Computers, Integrated

Circuits, Satellites etc.

1-9

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.

Metals for biomedical applications

1-11

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 MaterialsNew 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.

1-13

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.

1-14

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.

14

Type

Ionic

Covalent

Metallic

Secondary

Bond Energy

Large!

Variablelarge-Diamondsmall-Bismuth

Variablelarge-Tungstensmall-Mercury

smallest

Comments

Nondirectional (ceramics)

Directionalsemiconductors, ceramics

polymer chains)

Nondirectional (metals)

Directionalinter-chain (polymer)

inter-molecular

SUMMARY: BONDING

6

• Coordination # = 12

Adapted from Fig. 3.1(a), Callister 6e.

(Courtesy P.M. Anderson)

• Close packed directions are face diagonals.--Note: All atoms are identical; the face-centered atoms are shaded differently only for ease of viewing.

FACE CENTERED CUBIC STRUCTURE (FCC)

Click on image to animate

• Coordination # = 8

8

Adapted from Fig. 3.2, Callister 6e.

(Courtesy P.M. Anderson)

• Close packed directions are cube diagonals.--Note: All atoms are identical; the center atom is shaded differently only for ease of viewing.

BODY CENTERED CUBIC STRUCTURE (BCC)

Click on image to animate

10

• Coordination # = 12

• ABAB... Stacking Sequence

• APF = 0.74

• 3D Projection • 2D Projection

A sites

B sites

A sites Bottom layer

Middle layer

Top layer

Adapted from Fig. 3.3, Callister 6e.

HEXAGONAL CLOSE-PACKED STRUCTURE (HCP)

• Stress-Strain

Mechanical Testing and Properties

• Tensile Strength Tensile Test

• Flexural Strength Bend Test for brittle materials

• Hardness Hardness Test

• Toughness Impact Test

• Fatigue Life Fatigue Test

• Creep rate Creep Test

Tensile Test

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Mechanical Testing and Properties

Tensile Test & the properties obtained from the Tensile Test

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•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)allongitudin

lateralratiosPoisson

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Tensile Test & the properties obtained from the Tensile Test

Er=1/2(yield strength)(strain at yielding)

allongitudin

lateralratiosPoisson

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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

Load. fracture is where,2

3 strength Flexural

2F

wh

FL

The Bend Test for Brittle Material

deflection is where

True Stress-True Strain

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)ln()ln( strain True

stress True

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The Hardness Test

)()2/(HB :Hardness Brinell

22

iDDDD

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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:

• a typical creep curve showing the strain produced as a function of time for a constant stress and temperature.

Apply stress to a material at an elevated temperature

Creep: Plastic deformation at high temperature

The Creep Test: