Chapter 1- Material Engineering Concept-Print

7/22/2019 Chapter 1- Material Engineering Concept-Print

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CHAPTER 1- MATERIALS

ENGINEERING CONCEPTS

New Words

Characteristic: c tnh Property: Tnh cht Behavior: ng x, trng thi Mechanical property: Tnh cht c hc Physical property: Tnh cht vt l Aesthetic property: Tnh thm m Loading condition: iu kin gia ti Stress-Strain: ng sut-Bin dng

Elastic behavior: ng x n hi Elastoplastic: n hi do Viscoelastic: n hi nht Work: Cng Energy: Nng lng Failure: S ph hoi Rupture: Ph hoi t gy Fracture: Ph hoi nt gy Fatigue: Mi Yield: Chy Buckling: Bd do un dc Static load: Ti trng tnh Dynamic load: Ti trng ng

Periodic load: Ti trng theo chu k Random load: Ti trng ngu nhin Transient load: Ti trng ngn hn tc th Yield strength: Cng chy (gii hn chy) Ultimate strength: Cng cc hn (gii hn

bn) Breaking strength: Cng ph hoi Modulus of elasticity: M un n hi Modulus of resilience: Cng bin dng n hi Initial tangent modulus: M un tip tuyn

ban u Tangent modulus: M un tip tuyn Secant modulus: M un ct tuyn Chord modulus: M un theo dy cung Proportional limit: Gii hn t l Elastic limit: Gii hn n hi Endurance limit: Gii hn bn mi


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New Words Strain hardening: Cng ngui Strain softening: Brittle material: VL gin Ductile material: VL do Creep: T bin Viscous flow: Dng nht Relaxation: Chng (ng sut) Factor of safety: H s an ton Density: Khi lng n v Unit weight: Trng lng n v Specific gravity: T trng Deteriorate: Xung cp (do lo ha + s

dng) Degradation: Xung cp (do lo ha, phong

ha)

Corrosion: n mn Erosion: Xi mn Abrasion: Mi mn (b mt) Wear: Mi mn (gia cc VL) Surface texture: Cu trc b mt

Smooth texture: B mt nhn Rough texture: B mt th rp Raw material: VL th (VL u vo) Manufacture: Sn xut Place: Maintenance: Bo dng Fabricate: Ch to Erect: Lp rp Live cycle: Vng sng, chu k hot ng Sample: Mu Specimen: Mu Toughness: bn dai Hardness: cng b mt

Stiffness: cng n hi Impact Strength: Cng va p Bonding Strength: Cng dnh kt

Outlines

1.1 Materials and Types

1.2 Properties of Materials

1.2.1 Mechanical properties

1.2.2 Non-mechanical properties

1.2.3 Other criteria

1.3 Selection of Materials


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1.1 Materials and Types

Materials and TypesCriteria Name

Uses Building (Construction) Materials: Materials that are used in constructionindustry, such as cement, steel, concrete, stones, aggregates, plastics,asphalt, ceramic, wood, glass,Raw Materials: Natural products or materials that are transformed throughmanufacturing processEx: Iron ore; Limestone; Coal; Petroleum.Repair Materials: Materials used to repair a deteriorating structure ofconcrete, masonry,.Ex: Rubber; Asphalt; Cement mortar; Concrete.Waste Materials (by-product): The waste matter obtained from amanufacturing process.Ex: Fly-Ash; Silica fume; Slag.

Based on thepredominant type ofbond

Metallic (Metals): Steel, cast iron, wrought iron, aluminum Metallic bond.Inorganic solids (Ceramic Materials): Portland cement concrete, bricks,cinder blocks, glass, aggregate, rock product Covalent and Ionic bond.Organic solids (Polymer): Asphalt, plastic, wood Covalence bond.


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Materials and Types

Criteria Name Name

Metallic (Metals) Generally classified as ferrous and nonferrous metals.- Ferrous metals: are iron-carbon alloys with small amount of sulfur,phosphorous, silicon, and manganese.Ferrous metals come in 3 forms: Steel; Cast Iron, and Wrought Iron.- Nonferrous metals: Copper; Nickel; Zinc; Aluminum; andMagnesium.

Inorganic solids

(Ceramic Materials)- Glasses Based on silica: This is a special type of inorganic solids,they dont develop a crystalline structure, it has amorphous structure,but it is very stable at atmospheric temperature.- Vitreous ceramics: Fired clay products such as bricks, pottery- High- performance ceramics: Highly refined inorganic solids used forspecialty applications.- Cement and concrete- Rock and minerals

Materials and TypesCriteria Name

Organic solids

(Polymer)

Is defined as any material that belongs to a group of carbon-containing

materials, natural or manmade, that have macromolecular structure.

Most polymers are plastic, they can be easily bent into different

shapes.

-Thermoplastic(Asphalt): At low temperature secondary bonds adherethe chains, upon heating the secondary bonds melt and thethermoplastics become a viscous material.-Thermoset (Epoxy, polyester): Made of a resin and a hardener thatchemically react to harden. In the formation of solid, the carbon chainsare cross-linked to form stable compounds that do not soften uponheating.-Elastomers or rubbers: At atmospheric temperature the secondarybonds have melted. The cross-linking enables the material to return toits original shape when unloaded.-Natural materials (Wood): Wood is the primary material of interest,which is composed of cellulose, lignin, and protein


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Crystalline and Non-crystalline (Amorphous)

Example of a crystalline atomicstructure. Four grains are

illustrated. In each grain, theatoms form an orderly lattice.

Example of an amorphousstructure. The atoms are

arranged in a random fashion.

When a crystalline material is heated, the atoms receive the energy and begin tovibrate. With increase in temperature, the movement (or vibration) become veryenergetic and the material melts. In the liquid form, the atoms move very freely andare arranged quite randomly, and the material is said to be amorphous.

Criteria Name Name

The arrangement ofatoms

Amorphous: The atoms are arrangedalmost randomly

Crystalline: The atoms are arrangedorderly .

The deformationbefore failure

Brittle: Materials with little plasticdeformation before failure.

Ductile: Materials with noticeable plasticdeformation before failure.

The materialproperties

Isotropic: Material properties are thesame in all directions.

Anisotropic: Material properties aredifferent in directions.

The materialcomposition

Homogeneous: Material compositionis the same throughout.

Heterogeneous: Material compositionis not the same throughout.

Conductivity Insulators: Materials that are

provided for sound, thermal (heat) orelectrical insulation.

Conductors: Materials that are

provided for sound, thermal (heat) orelectrical conduction.

Construction Cast in place Precast

Resist force Structural Materials Non-Structural Materials

Method ofManufacture

Natural Materials: Materials areavailable in the nature (Naturallyoccurring)

Manufacturing (Processing) Materials

(or Synthetic, or manmade Materials):

Materials are produced through theprocess of converting raw materials orcomponents.


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Cast in place

Precast


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Materials and Types

Criteria Name

Others Cementitious Materials: Materials in which the principal binder isPortland cement or another type of hydraulic cement.Masonry Materials: Materials used for construction of masonry,including stone, block, brick, and mortar.Elastic Materials: Materials have ability to deform under a loadwithout a permanent set or deformation upon the release of theload. Ex: Springs, rubber bands.Plastic Materials (Plastics): Plastics are organic-based materialsderived primary from the petrochemical industry, they can be easilybent into different shapes.Plastics are also defined as synthetic organic materials that can be

molded under heat and pressure into shape that will be retainedafter removal of heat and pressure.Divided into two types: Thermoplastic and thermosetting.Viscous Materials:

Magnetic Materials:

Electronic Materials:

1.2 Properties of Materials


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Types of Materials Properties

1. Mechanical properties: How does material respond to the externalload? (Describe the behavior of material under external load)Stress-Strain relation: Elastic and plastic behavior; Elastic Modulus;Strength (Shear, compressive and tensile), hardness,..

2. Non-mechanic Properties: Refer to the characteristics of material,other than load response

Physical properties: Properties derived from the physicalstructure. Ex: Surface characteristic (color, dimension);Weight; Density

Chemical properties: Determine the way a materialbehaves in a chemical reaction (acidity, alkalinity, corrosionresistance)

Thermal properties: Thermal expansion; Thermalconductivity; Melting point; Electrical and magnetic properties: Conductivity Optical and Acoustic properties:

3. Other criteria: Aesthetic property; Economic Factors; Production andconstruction consideration.

1.2.1 Mechanical Properties

I. Loading conditions

II. Stress-Strain relations

III. Stiffness (rigidity)

IV. Elasticity and Plasticity

V. Strength

VI. Hardness

VII. Toughness

VIII. Creep and Relaxation

IX. Failure and Safety


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I. Loading condition

Forces, Loads, Stresses

Forces: A forceis a push or pull upon an object resulting from the object's

interaction with another object.

In physics, a force is any influence that causes an object toundergo a certain change, either concerning its movement,direction, or geometrical construction.

Compression, tension, torsion, etc

Loads:

A term frequently used in engineering to mean the force exertedon a surface or body.

Forces dead loads, live loads, wind loads, etc

Stresses (Internal Forces) Describe the measure of a force acting on a unit area

Compression, tension, torsion, shear, bending, etc

Tension Test

Compression Test

Flexure Test


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I. Loading condition

1. Static loading: Implies a sustained loading of the structure over aperiod of time, slowly apply without shock or vibration

Dead load: The own load of elements such as columns, beams, arches,.of structure (the weight of structure itself)

Other gravity load: Weight of the external thing on an object such asfurniture, people, goods, snow,.... on the structure.

2. Dynamic loading (live load): Implies a shock or vibration loading in thestructure.

- Periodic load: The load repeat itself with time (Ex: Rotating equipment in

the building)- Random load: The load pattern never repeat (Ex: Earthquake)

- Transient load: The load applies over a short time interval, after which thevibration decay until the system returns to a rest condition (Ex: Transientload of trucks on the bridge)

External Load (P)

Stress =P/A

Deformation (L or )

Strain = L/L

Poinssons ratio= -(l/ a)

Elasticbehavior

Elastoplasticbehavior

Viscoelasticbehavior

- Elastic Modulus: formaterial that display linear

behavior- Other types of modulus:for materials that do notdisplay linear behavior

-Yield strength; Ultimatestrength; Modulus of

resilience and Toughness.

Stress-Strain relation

II. Stress-Strain Relations (S-S Relation)

Stress:Describe the measure of a force acting on a unit area.

(Stress=Load/Area)

Deformation:Indicate the change in form of the body.

Strain:Indicate the deformation per unit length.

(Strain = change in length/original length)


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II. Stress-Strain Relation


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Some Definitions

Elastic limit: The stress level at which the behavior change from

elastic to plastic.

Proportional limit: The stress level at which the behavior change

from linear to non-linear.

Yield Point: The first stress, at which deformation continues without

increase in loading.

Yield strength (y): The stress at which yield is initiated.

Ultimate strength (u): The stress corresponding to the maximum

load applied to the specimen.

Breaking strength (b): The stress corresponding to rupture

II. Stress-Strain Relations (S-S Relation)


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Yield stress (strength): Identified by offset method andextension method

- Offset yield stress (strength): A specified offset ismeasured, and a line with a equal to the initial tangentmodulus is drawn through this point. The point where thisline intersects the stress-strain curve is the offset yield stress.

- Extension yield stress (strength): The point where a vertical

projection, at specified level, intersects the stress-strain curveis the extension yield stress.

How to determine the Yield Strength?


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Some Definitions

Modulus of elasticity:- Modulus of Elasticity in tension- Modulus of Elasticity in compression- Modulus of Elasticity in shear (Modulus of Rigidity - G)

Poissons ratio (): Lateral strain/axial strain (0.15 0.40) Modulus of elasticity or Youngs Modulus (E) (For materials exhibitlinear elastic behavior): The ratio of stress over strain below theproportional limit.

=E

a

l

=

Youngs Modulus - E

0.00

10000.00

20000.00

30000.00

40000.00

50000.00

60000.00

0. 00 20 000. 00 4 0000. 00 60000. 00 80000. 00 100000 .0 0 1200 00. 00 1400 00. 00 160 000. 00

Gauge

Strain Gauge


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4 methods to determine the Modulus for materials that do not display any

linear behavior:

- Initial Tangent Modulus - Tangent Modulus

- Secant Modulus - Chord Modulus

III. Stiffness (Rigidity)

The resistance of a material to deflection is calledstiffness or rigidity. Steel is stiffer or more rigid thanaluminum.

Stiffness is measured in term of Modulus of Elasticity E.

At a given level of stress, more strain less stiff, lessstrain more stiff The higher the value of the ElasticModulus, the stiffer the material. E is the ratio of stressover strain.


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IV. Elasticity and Plasticity

Elasticity of a material is its power of coming back to itsoriginal position after deformation when the stress or loadis removed. Elasticity is a tensile property of its material.

The plasticity of a material is its ability to undergo some

degree of permanent deformation without failure. Plasticdeformation will take place only after the elastic rangehas been exceeded.


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Elastic and Elastoplastic Behavior

Elastic behavior: If the material exhibits true elasticbehavior, it must have instantaneous response(deformation) to load, and the material must return to itsoriginal shape when the load is removed.

Elastoplastic behavior: An elastoplastic materialexhibits the linear elastic behavior followed by plasticresponse.

If the load is removed after the plastic deformation, someof the deformation will be recovered and some of thedeformation will remain.

Elastoplastic Behavior

Example of loading and unloading on Stress-Strain

curve of Plastic material


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V. Strength It is the resistance offered by a material when subjected

to external loading. So, stronger the material the greaterthe load it can withstand.

Depending upon the type of load applied the strengthcan be tensile, compressive, shear or torsion.

The maximum stress that any material will withstandbefore destruction is called its ultimate strength.

VI. Hardness

Hardness is closely related to strength. It is the ability ofa material to resist scratching, abrasion, indentation, orpenetration.

It is directly proportional to tensile strength and ismeasured on special hardness testing machines bymeasuring the resistance of the material againstpenetration of an indentor of special shape and materialunder a given load. The different scales ofhardness are Brinell hardness, Rockwell hardness,Vickers hardness, etc.


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VI. Toughness

The toughness of a material is its ability to withstand bothplastic and elastic deformations. The toughness is the ability of a material to support loads after

yielding or crack. Toughness is a measure of the amount of energy a material

can absorb before actual fracture or failure takes place. Thework or energy a material absorbs is called modulus oftoughness

Ex: If a load is suddenly applied to a piece of mild steel andthen to a piece of glass the mild steel will absorb much moreenergy before failure occurs. Thus, mild steel is said to be

much tougher than a glass. Toughness is measured by a special test on Impact TestingMachine or byThe area under the stress-strain diagram

The strength is increased, but the toughness may bereduced

VI. Toughness


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- Creep: Associated with long termdeformation and can occurs inmetals, ionic and covalent crystal, and amorphous materials (Ex:

Concrete can creep over period of decades)In materials science, creep is the tendency of a solid material to moveslowly or deform permanently under the influence of stresses. Itoccurs as a result of long term exposure to high levels of stress thatare below the yield strength of the material. Creep is more severe inmaterials that are subjected to heat for long periods, and near meltingpoint. Creep always increases with temperature.

- Relaxation: Dissipation of stresses with time.



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Failure occurs when a member or structure no longer perform thefunction for which it was designed.

Failure of a structure can take several modes including:- Fracture (rupture): A brittle material typically fractures suddenly when thestatic stress reaches the strength of the material. The ductile material mayfracture due to excessive plastic deformation.

- Fatigue: Repeated stresses can cause a material to fail at a stress well belowthe strength of the material. The number of application a material can withstanddepend on the stress level relative to the strength of the material Endurancelimit: Stress level below which fatigue does not occur

- Yielding: This failure happens in ductile materials, and it spreads throughoutthe whole structure, which results in a total collapse.

- Buckling: Long and slender member subjected to axial compression may faildue to buckling.

- Excessive deformation: Depending on the function of the member.



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StressAllowable

StressUltimate

SafetyofFactor

a

u==

=

FS

FS

Structural members ormachines must bedesigned such that theworking stresses are less

than the ultimate strengthof the material.

Factor of safety considerations:

Uncertainty in material properties

Uncertainty of loadings

Uncertainty of analyses

Number of loading cycles Types of failure

Maintenance requirements anddeterioration effects

importance of member tointegrity of whole structure

Risk to life and property

Influence on machine function



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1.2.2 Non-mechanical Properties

I. Density and Unit weight

II. Thermal expansion

III. Surface characteristics

The weight of materials is animportant design consideration.(Weight is usually taken to mean thesame as mass)

Three general terms used todescribe the mass, weight and volume

relationship:

- Density: Mass per unit volume (pcf)

- Unit weight: Weight per unit volume

- Specific gravity: The ratio of themass of a substance to the mass of anequal volume of water at a specifictemperature. This equivalent to thedensity of material divided by thedensity of water

= .g

Where:

= Unit weight

= Density (Unit mass)

g= Acceleration of gravity

- For solid materials, such as metals,the unit weight, density and specificgravity have the same numericalvalue.

- For other materials, voids in thematerials require definitions forvariety of densities and specificgravity



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Liquid Material

Density (Khi lng ring)

Density of water =1Mg/m3=1000kg/m3=1ton/m3=62,4lb/ft3


Solid Material

Khi lng ring

Specific Mass

Trng lng ringSpecific Weight

T trng (t khi)Specific Gravity

Khi lng n v(Khi lng th tch, Dung khi)

Unit Mass

Trng lng n v(Trng lng th tch, dung trng)

Unit Weight

Denstiy


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Bulk (porous) Materials

Khi lng ringSpecific Mass

Trng lng ringSpecific Weight

T trng (khi) tuyt iApparent Specific Gravity

Khi lng n v - ht(Khi lng th tch - ht)

Unit Mass - OD v SSD

Trng lng n v - ht(Trng lng th tch - ht)

Unit Weight - OD v SSD

Density

OD v SSD

T trng (khi) htBulk Specific Gravity (OD v

SSD)

Khi lng n v xp(Khi lng th tch xp)

(Bulk) Unit Mass

Trng lng n v xp(Trng lng th tch xp)

(Bulk) Unit Weight

Bulk Density

All materials expand astemperature increases and contractas temperature falls.

The amount of expansion per unitlength due to one unit of temperatureincrease is expressed as thecoefficient of thermal expansion ().This parameter is very important inthe design of structure.

In case the structure is composedof different materials that are boundtogether, if are different, thematerial will strain at different rate cause stresses in the material leaddirectly to fracture.

Stresses can also be developed asa result of a thermal gradient in thestructure.

II. Thermal expansion

o

V

o

L

V

TV

L

TL

=

=

Where:

L= Linear coefficient of thermal expansion

V= Volumetric coefficient of thermal expansion

L= Change in the length of specimen

T= Change in temperature

V= Change in the volume of specimen

Lo= Original length of specimen

Vo= Original volume of specimen


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III. Surface characteristics

All materials deteriorate over the service lives. The mechanismscontributing to the deterioration of a material differ depending onthe characteristics of the material and the environment. The surfaceproperties of materials, that is interest of civil engineers include:

Corrosion and degradation:- Corrosion process is the loss of material, either by dissolution or by the

formation of nonmetallic scale of film. Ex: Metals and ceramics- Degradation is the effects of solvent and ultraviolet radiation on the material.

Ex: Asphalt

Abrasion and Wear resistance:- Important properties of materials applying for resisting dynamic load

Surface texture:- Smooth texture of aggregate particle improve workability of Portland concretemixture.

- Rough texture of aggregate particle provide a stable asphalt concrete pavement

1.3. Other criteria

I. Aesthetic: How does the structure look?

II. Economic Factor: Factors that should be considered in theselection of the material include:

- Availability and cost of raw materials

- Manufacturing cost

- Transportation- Placing

- Maintenance Economic selection of material have to consider life cycle, not only

initial cost

III. Production and Construction: Implies the ability of fabricateand erect the material into the desired shape and requiredspecification


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1.3 SELECTION OF MATERIALS

Structural Materials must perform the followingfunctions:

Carry prescribed loads

Satisfy serviceability and durability requirements

Be aesthetically pleasing: How beautiful does the

building look like? Be economically practical: Availability of raw materials;

Manufacturing cost; Transportation cost; Maintenancecost.

Be environmentally friendly: LEED buildings(Leadership in Energy and Environmental Design)


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MATERIALS SELECTION FLOWCHART

Available materials

Materials A, B, C, D,..

Select a material for consideration

Does the material satisfy strength requirement?

Does the material satisfy serviceability requirement?

Are aesthetic qualities of material acceptable?

Does the material satisfy cost constraints?

(Material cost plus construction cost)

Does the use of material cause environmental problems andhazards?

Select the material

59

Yes

Yes

Yes

Yes

No

No

No

No

No

Yes

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Chapter 1- Material Engineering Concept-Print