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MATERIAL SCIENCE

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Week Subjects

1Introduction, Definition, Benefits of Material Knowledge,Standards

2 Micro Structure of Materials:Atom, Interatomic Bonds, Atomic Arrangement, CrystalStructure, Amorphous Structure

3 Crystallographic Directions, Interatomic Spacing,Relations between bonds and properties

4 Physical Properties of Materials : Bulk Density, SpecificWeight, Compactness, Porosity, Water Absorption,

Saturation Degree

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References John, V.B., Introduction to engineering materials,

second edition, ELBS, Macmillan, 1983.

Mamlouk, M.S., Zaniewski, J.P., Materials for civiland construction engineers, second edition,Pearson Prentice Hall, 2006.

Onaran, K., Malzeme Bilimi, Bilim teknik yaynevi,8. Bask, 2000, in Turkish.

Postacolu, B., Cisimlerin Yaps ve zellikleri, ITUY., 1981.

Material Science Lecture notes, KTU.

Material Science Lecture notes, YTU.

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Material

Material is anything made of matter,constituted of one or more substances.

Wood, cement, hydrogen, air and waterare all examples of materials.

Materials are the parts required to makesomething else, from buildings and art tostars and computers.


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Material Science

Materials science is an interdisciplinaryfield applying the properties of matter tovarious areas of science and engineering.This scientific field investigates therelationship between the structure ofmaterials at atomic or molecular scalesand their macroscopic properties.

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A material can be anything: a finishedproduct or an unprocessed raw material.

Raw materials are first extracted orharvested from the earth and divided intoa form that can be easily transported andstored, then processed to produce semi-finished materials.

These can be input into a new cycle ofproduction and finishing processes tocreate finished materials, ready fordistribution, construction, andconsumption.

Raw materials and processing

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Some Examples of Materials

Common civil engineering materials:

Concrete

WoodSteel

aggregates

masonry

asphalt

glass

polymers

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Examples forsome common

civil engineeringmaterials


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Concrete

Concrete is used more than any otherman-made material in the world. As of2006, about 7.5 billion cubic meters ofconcrete are made each yearmore thanone cubic meter for every person on Earth.

Cement Sand Aggregates Water

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Wood

Wood is a hard, fibrous tissuefound in many plants. It has been

used for hundreds of thousandsof years for both fuel and as aconstruction material. It is anorganic material composed ofcellulose fibers (which are strongin tension) embedded in a matrix

of lignin which resistscompression.

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Steel

Steel is an alloy thatconsists mostly of iron

and has a carboncontent between 0.2%

and 2.1% by weight,depending on thegrade. Carbon is themost common alloyingmaterial for iron.

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CLASSIFICATION OF MATERIALS

A) According to their use and purposes:

Structural materials: Materials with highmechanical properties used for load bearing purposes;i.e. Concrete, steel, wood, stone, brick, etc.

Decorative materials: Materials used fordecoration purposes; i.e. Gypsum, wood, stone, paint,etc.

Protective materials: Materials that protect thestructure from any deterious effects such as heat, water,

moisture, solutions, etc. (i.e. paint, stone, heat and

water insulation materials, bitumen, etc.)


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B) According to their deformations: Elastic materials: If a material exhibits true elastic behavior, it

must have an instantaneous response (deformation) to load,and the material must return to its original shape when the loadis removed. Most metals exhibit elastic behavior, at least at low

stress levels. Rubber is also an el astic material. Plastic materials: Clay and fresh concrete are examples for

plastic materials. Plastic behavior indicates permenantdeformation of the specimen so that it does not return to itsoriginal shape when the load is rem oved.

Elastoplastic Materials: For some materials, as the stressapplied on the specimen is increased, the strain willproportionally increase up to a point; after this point the strainwill increase with l ittle additional stress. In this case, the materialexhibits linear elastic behavior followed by plastic response. Thestress level at which the behavior changes from elastic toplastic is the elastic limit. When the load is removed from thespecimen, some of the deformation will be recovered andsome of the deformation will remain. (i.e. steel)

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C)According to their physical structure

Homogeneous materials: Materials that have auniform composition throughout its structure (i.e. steel ).

Heterogeneous materials: Materials that arecomposed of dissimilar parts (i.e. wood).

Isotropic materials: Materials whose properties areidentical in all directions (i.e. steel).

Anisotropic materials: Properties of anisotropicmaterials depend on the directions (axis). Wood is an

example for anisotropic materials.

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Ceramics: Ceramic materials are formed by acombination of ionic and covalent bonds. Ceramicsencompass a broad range of materials, including

glass, fired clay products - bricks, concrete, rocks,porcelain, etc. These materials have high strengthand stiffness but their lack of fracture toughness(1/50 of metals) limits their use in engineeringapplications. Ceramic materials tend to fracture in abrittle manner rather than to have plasticdeformation. They can be used as abrasivematerials in industry (Al2O3). They are also durable tohigh temperatures (refractory materials). Ceramicmaterials do not conduct heat and electricity wellsince they have no free electrons.

C) According to their chemical structure

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Metals: The chemical definition of a metal is an element withone, two, or three valance electrons. These elements bond intoa mass with metallic bonds. Due to the nature of metallicbonds, metals have a very regular and well-defined structure.They conduct heat and electricity well (by free electrons).Metals generally have the capability to make plasticdeformations. (i.e. copper, gold, iron, etc.)

Polymers: Polymers are organic or synthetic materialscomposed of long molecules of covalent bonded nonmetallicelements such as C, H, O, N, Cl. Polymers can be classified asthermoplastics (polystyrene, PVC), thermosets (epoxy),elastomers or rubbers (elastic materials) and natural materials(wood). Examples: polystrene, PVC, rubber, wood, etc.

Composites: The need for materials with proporties not foundin conventional materials, combined with advances intechnology, have resulted in combining two or more materialsto form what are called composite materials. These materialsusually combine the best properties of their constituents andfrequently exhibit qualities that do not even exist in theirconstituents. Examples: concrete, reinforced concrete, etc.
http://en.wikipedia.org/wiki/File:Blue_and_white_vase_Jingdezhen_Ming_Yongle_1403_1424.jpg


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AtomThe atom is a basic unit of matter that consists of a densecentral nucleus surrounded by a cloud of negatively

charged electrons. The atomic nucleus contains a mix ofpositively charged protons and electrically neutral

neutrons and both of these particle types make up themass of the atom (atomic weight -AW). One mole of anysubstance will always contain the same number ofmolecules, and the number of molecules contained in a

mole is given by the universal constant, Avogadrosnumber (AN=0,602*1024).

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Bonding Between Atoms

(Strong bonds-Weak bonds)

Ionic BondAn ionic bond is a type of chemicalbond formed through an electrostatic

attraction between two oppositelycharged ions. Ionic bonds are formedbetween a cation, which is usually a

metal, and an anion, which is usually anonmetal. Since these bonds are

based on the transfer of electrons, theyhave no directional nature.

Na++Cl- NaCl

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Covalent bondA covalent bond is a form of chemical bonding that ischaracterized by the sharing of pairs of valance electronsbetween atoms. The atoms that are covalently bonded will

each contribute at least one electron to the bond and the shared

electrons may be considered to belong to both atoms. Thesebonds are highly directional. In materials such as diamond

(very hard, high melting temperature), the covalent bondsare very strong. (i.e. HF, HCl)

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Metallic bondMetallic bond is found in metals

and their alloys. The metallic

bond forms when atoms give up

their valence electrons, which

form an electron sea. The

positively charged atom cores

are bonded by mutual (karlkl)

attraction to the negatively

charged electrons.Metallic bonds

are non directional.


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Van der Waals bonds (Weak Bonds)

In addition to the primary types ofinteratomic bonding, there also existweaker bonds, owing to the polarisation(kutuplama) of atoms or molecules.These weaker bonds, based onelectrostatic attraction, are generallyknown as van derWaals forces.

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Molecule

A molecule may consist of atoms of a

single chemical element, as with oxygen(O2), or of different elements, as withwater (H2O).

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Valance Electrons

The electrons that occupy the outermost orbit

are known as valence electrons. The number

of valence electrons cant be greater than 8.

These electrons determine; chemical

properties, type of bonding, mechanical

properties, electrical, optical, thermal

properties.

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Atomic Arrangement/Amorphous andCrysttalline Structure

Atomic arrangement or order plays an important role in

determining the microstructure and behavior of a solid

material. Some arrangements permit exceptionalductility, whereas others yield exceptional strength. Ifthe atoms or molecules in a material are randomly

arranged with no regular crystal structure, such

materials are amorphous. If the constituent atoms or

molecules of a material are arranged in a definite

symmetrical pattern, such materials are crysttalline.


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Unit Cell

The unit cell is the basic structural unit orbuilding block of the crystal structure.

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Types of Crystal Systems

There are seven crystal systems;Sizes Angles

Triclinic abc

Monoclinic abc ==900

Rhombohedral a=b=c ==900

Hexagonal* a=bc ==900,=600

Orthorhombic abc ===900

Tetragonal a=bc ===900

Cubic a=b=c ===900

* Another system is sometimes used to define hexagonal form. Inthis system reference is made to four axes, namely, threecoplanar axes, a1, a2, and a3, all of equal length and inclined at1200 to each other, and a fourth axis, of length c, mutuallyperpendicular to the other three axes

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Lattice systems

These lattice systems are a grouping of crystalstructures according to the axial system used

to describe their lattice. Each lattice systemconsists of a set of three axes in a particulargeometrical arrangement. There are sevenlattice systems. They are similar to but not

quite the same as the seven crystal systemsand the six crystal families

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The 7 lattice systems

(From least to most symmetric)

1.Ttriclinic

2. Monoclinic

simple base-centered


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3. Orthorhombic

simple base-centered body-centered face-centered

4. Rhombohedral

5. Tetragonal

simple body-centered

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6. Hexagonal

7. Cubic

simple (SC) body-centered (bcc) face-centered (fcc)

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The Simple Cubic Crystal Structure

The crystal structure is imaginary for puremetals; there is no common engineering

materials have this crystal structure. Theatoms are situated at each corner of this cube.

a is the edge length of cube (isknown as lattice parameter) r isthe atomic radius

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Atomic Packing Factor

The atomic packing factor (APF) or packing fraction is the fraction ofvolume in a crystal structure that is occupied by atoms. It isdimensionless and always less than unity. For practical purposes, theAPF of a crystal structure is determined by assuming that atoms arerigid spheres. The radius of the spheres is taken to be the maximal

value such that the atoms do not overlap. For one-component crystals(those that contain only one type of atom), the APF is representedmathematically by

where Natomsis the number of atoms in the unit cell,Vatom is the volume of an atom, andVunit cellis the volume occupied by the unit cell.


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Body-centered cubic crystal structure (BCC)

The primitive unit cell for the body-centered cubic

(BCC) crystal structure contains nine atoms: oneon each corner of the cube and one atom in thecenter. Because the volume of each corner atom isshared between adjacent cells, each BCC cellcontains two atoms.

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Body-centered cubic crystal structure (BCC)

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Face Centered Cubic (FCC)

Atoms are arranged at the corners and center of

each cube face of the cell.

Atoms are assumed to touch along facediagonals

Bonding Forces and Energy Well

(a) The dependence of attractive, repulsive and net forces as a function of interatomic

separation for two isolated and adjacent atoms.

(b) The dependence of net potential energy as a function of interatomic separation for twoisolated and adjacent atoms.

ro (ao) is the equilibrium

spacing. The exact

shape of the energy wellis important in

determining severalphysical and mechanicalproperties. The deeper

the well (Emin ) thehigher the melting andvaporization

temperatures, the higher

the cohesive strengthand the higher the E.Thermal expansion is

inversely correlated withEmin.

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Material Melting Temp.

(T, oC)

Thermal Expansion

Al 660 22x10-6

Fe 1538 12x10-6

Melting temperatures and thermal expansion coefficients ofAl and Fe.

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Imperfections In Crystal Structures

1. Point Defects:Point defects: 1.Vacancy (bo ke),

2.Self interstitial atom is an extra atom

that has crowded its way into an interstitialvoid in the crystal structure. Self interstitial

atoms occur only in low concentrations in

metals because they distort (bkmek) andhighly stress the tightly packe d lattice

structure. , 3.Substitutional impurity atom

(Yer alan atomu) replaces or substitutes

for the host atoms, 4.Interstitial impurity

atoms (ara yer atomu) are much smaller

than the atoms in the bulk matrix. They fit

into the open space between the bulk

atoms of the lattice structure. i.e.: the

carbon atoms that are added to iron to

make steel.

Fig. Point Defects

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2. Line Defects (Dislocations)

The most common type of linedefect within a crystal is a

dislocation. A dislocation is aone-dimensional defectaround which some of theatoms are misaligned. Two

types: edge and screwdislocation. Dislocationscontribute metals plastic

deformation capability.

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3. Surface Defects

Surface defects are the boundaries that seperate a material intoregions, each region having the same crystal structure but

different orientations. Among these imperfections external

surfaces and grain boundaries are the most important ones. Agrain boundary is the surface that seperates the individual grains

and is a narrow zone in which the atoms are not properly spaced.

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Crystallographic Directions and Planes

Every point within a unit cell can beidentified in terms of the coefficient alongthe three coordinate axes. The origin is

0,0,0; the far corner of the unit cell is 1,1,1regardless of the crystal system.

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Crystallographic Directions

A Crystallographic direction is defined as a line between twopoints or a vector. Indices of directions are the shorthandnotation used to describe these directions. The following steps

are utilized in the determination of the three directional indices:

A vector of convenient length is positioned such that it passes

through the origin of the coordinate system. The length of the vector projection on each of the three axes is

determined.

These three numbers are multiplied or divided by a commonfactor to reduce them to the small est values.

The three indices, not seperated by commas(,), are enclosed insquare brackets [uvw]. The u, v, w , integers correspond to theprojections along the x, y and z axes respectively.

Negative indices are also possible, which are represented by abar over the appropriate index.

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Crystallographic Planes

The orientations of planes for a crystal structure are representedin a similar manner:

The length of the planar intercept for each axis is determined in

terms of the lattice parameters a, b, c. Teh reciprocals of these numbers are taken. A plane that

parallels an axis may be considered to have an infiniteintercept, and therefore a zero index.

If necessary these three numbers are changed to the set ofsmallest integers by multiplication or division using a commonfactor.

The integer indices, not seperated by commas, are enclosedwithin parantheses, thus (hkl).

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Linear and Planar Atomic Densities

Linear density corresponds to the fractionof line length that passes through atomcenters. Planar density is simply thefraction of total crystallographic planearea that is occupied by atoms.

L.A.D.=Number of atoms/Unit Length (atom/cm)

P.A.D.=Number of atoms/Unit Area (atom/cm2)

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Properties of materials will be examined in two topics;physical and mechanical.

2. PROPERTIES OF MATERIALS

2.1. Physical Properties

As in all solid materials, basic physical properties in

construction materials are weight, volume, density,specific

gravity, permeability, color, etc.

All construction materials except glass and metals moreor

less contain voids; and are effected by water and vapor.

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Pore properties include; ratio of pores, their size and

characteristic (being enclosed or open).

2.1. Physical Properties / Pore structure

Pores in Porous Materials

Distribution of pores in a solidmedium can be;

Regular or irregularConnected ordisconnected

Open or enclosed.

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Physical parameters of porous materials are;

Unit weight of the material; density (),

Unit weight of the sol id part; specific gravity (),

Compactness ratio; compactness (k),

Ratio of total pores; porosity (p),

- Open pores, water absorption by mass and byvolume,

- Capillary pores, capillary water absorption (K)

Permeability

2.1. Physical Properties

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a) Unit Weight (Density) (, g/cm3)

Density () is defined as the dry weight (Wo) of a given volume

(Vt) of a material.

Density has a strong relation with strength and thermalconductivity.

=t

o

V

W

2.1. Physical Properties / Density

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b) Specific gravity (, g/cm3)

=

0

0

v

w

2.1. Physical Properties / Specific gravity

Specific gravity is the dry weight (Wo) of a

given volume of the solid phase (Vd) of a

material.

c) Compactness ratio (k)

The ratio of solid volume of a ma terial (Vd) to its total volume (Vt)

and can also be calculated by dividing density () by specific

gravity ().

d) Porosity (p)

The ratio of the pore volume (V b) to the total volume (Vt) of the

material. Porosity can be determined by several methods such as;

gas expansion method, mercury injection method, density methods,

water absorption methods or statistical methods. Porosity (%p)

defines total pores, whereas effective porosity (%pe) defines open,

interconnected and continuous pores.

t

d

VVk%

k

V

Vp

t

b 1%

2.1. Physical Properties / Compactness ratio and porosity

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f) Absorption by volume (%av, Effective porosity)

The ratio of the increase in mass to the to the totalvolume.

2.1. Physical Properties / Absorption

e) Absorption by mass (%am): The ratio of the increase inmass to the mass of the dry sample.

0

0

W

WWa SSDm

V

WWa SSDv

0

WSSD: The weight of the sample in the SSD state

W0: The weight of the sample in oven dry state

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f) Capillary Water Absorption (K)

Defined as the absorbed water amount (Q) from unit surface area (A) ofa material in unit time (t).

K= Q2

/ (A2

t)

Capillary water absorption Coefficient (K) is determinedexperimentally as a

function of time and surface area that contacts with water.

Sample: Cross Section Area, A (cm 2)Weight, W0(g)

t0 W0 Q0= 0t1 W1 Q1=W1-W0t2 W2 Q2=W2-W0

tn Wn Qn=Wn-W0

Fig: Capillary water absorption

test

2.1. Physical Properties / Capillarity

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tF

QK

. Capillarity Coefficient : ).(

.

2

2

2

s

cm

tF

QK

K

hH

K

Qt s

22

max ).%(Rise time of water by capillarity:

2.1. Physical Properties / Capillarity

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Permeability

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Permeability in fluid mechanics and the earth sciences (symbolizedas k) is a measure of the abil ity of a porous material (often, a rock

or unconsolidated material) to allow fluids to pass through it.

Water Permeability

Water permeability of a material is expressed by the coefficient ofwater permeability, which is measured by determining the rate of

water flow through the material under pressure.

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