properties and characteristics of engineering materials

8/11/2019 Properties and Characteristics of Engineering Materials

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PROPERTIES ANDCHARACTERISTICS

MATERIALS


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Physical Propertie


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Phase Transformation

Temperatures

Transitions from solid to liquid, fromliquid to vapor, from vapor to solidand visa versa

The phase transition temperature where a solidchanges to a liquid is called the melting point.

The temperature at which the vapor pressure of aliquid equals 1 atm (101.3 kPa) is called theboiling

point.

The temperature at which a solid, glassy materialbegins to soften and flow is called theglass

transition temperature.


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Density

Substance

Air 0.

Gasoline 0.

Wood

0.Water (ice) 0.

Water (liquid) 1.

Aluminum 2.

Steel 7.

Silver 10

Lead

11

Mercury 13

Gold 19

It is defined as the ratio of anobjects mass to its volume.

Densityis a function of the mass ofthe atoms making up the materialsand the distance between them.


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Specific Gravity

Specific gravity is the ratio of density of a substance compardensity of fresh water at 4C (39 F). At this temperature thewater is at its greatest value and equal 1 g/mL.


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Thermal Conductivity

MaterialThermal Conductivity

W/m, oK

Air at 0 C 0.024

Aluminum 205.0

Brass

109.0

Concrete

0.8

Copper 385.0

Glass, ordinary 0.8

Gold 310

Ice 1.6

Iron -

Lead 34.7

Polyethylene HD

0.5

Polystyrene expanded 0.03

Silver 406.0

Styrofoam 0.01

Steel 50.2

Water at 20 C -

Wood 0.12-0.04

Thermal conductivity () is the intrinsicproperty of a material which relates its

ability to conduct heat.

Thermal conductivity is defined as thequantity of heat (Q) transmitted through aunit thickness (L) in a direction normal to a

surface of unit area (A) due to a unittemperature gradient (T)under steady

state conditions

= Q L/ (A T)


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Linear Coefficient ofThermal Expansion

Materiala

(m/m/oK

Aluminum 23.8 x 10-6

Concrete 12.0 x 10 -6

Copper 17.6 x 10 -6

Brass 18.5 x 10 -6

Steel 12.0 x 10 -6

Timber

40.0 x 10-6

Quartz Glass 0.5 x 10 -6

Polymeric Materials 40-200 x 10 -6

Acrylic

75.0 x 10 -6

The linear coefficient of thermalexpansion ( a) describes the relativechange in length of a material per degreetemperature change.

the ratio of change in length ( Dl) to the

total starting length (li) and change intemperature ( DT).


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Electrical Conductivity andResistivity

Electrical conductivity is a measure of how well amaterial accommodates the movement of anelectric charge. It is the ratio of the current densityto the electric field strength.

Electrical resistivity is the reciprocal of conductivity.It is the is the opposition of a body or substance tothe flow of electrical current through it, resulting ina change of electrical energy into heat, light, orother forms of energy.


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Magnetic Permeability

. It is a constant of proportionality that exists between magninduction and magnetic field intensity.

. The permeability factors of some substances change with rifalling temperature, or with the intensity of the applied mag


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Mechanical Propert


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Strength or Loading

The strength of a material is the resistanceof a force to an object.

Five fundamental loading conditions;

Tension

Compression

Bending

Shearing

torsion


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Tension

Tension is the type of loading in which the two sections of material on

plane tend to be pulled apart or elongated.


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Compression

Compression is the reverse of tensile loading and involves pressing thtogether.


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Bending

Loading by bending involves applying a load in a manner that causes a mcurve and results in compressing the material on one side and stretching

other.


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Shearing

Shear involves applying a load parallel to a plane which caused the matof the plane to want to slide across the material on the other side of th


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Torsion

Torsion is the application of a force that causes twisting in a material


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Tensile Properties

Elastic limitis the greatest stress the materialcan withstand without any measurable

permanent strain remaining on the completerelease of load.

Yield strengthis the stress required to produce asmall-specified amount of plastic deformation.

Proportional limit is the highest stress at whichstress is linearly proportional to strain.

Ultimate tensile strength is an engineering valuecalculated by dividing the maximum load on amaterial experienced during a tensile test by theinitial cross section of the test sample.

True fracture strength is the load at fracturedivided by the cross sectional area of the sample.


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Ductility

The ductility of a material is a measure ofthe extent to which a material will

deform before fracture.


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Toughness

The ability of a metal to deformplastically and to absorb energy in the

process before fracture.


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Fatigue Properties

Fatigue cracking results from cyclic stresses that are below ttensile stress, or even the yield stress of the material.

The name fatigue is based on the concept that a material b

tired and fails at a stress level below the nominal strength material.


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Hardness

Hardness is the resistance of a material to localized deformatterm can apply to deformation from indentation, scratching,bending. In metals, ceramics and most polymers, the deformconsidered is plastic deformation of the surface.


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Elasticity & Plasticity

Elasticity is the property by which amaterial is enabled to return exactly toits original shape on removal of astraining force, a very importantproperty in materials.

Plasticity is the reverse of elasticity; aplastic material will retain exactly theshape it assumes under load when theload is removed.


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Chemical Properti


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Acidity or

BasicityDefinitions of acids and

Arrhenius

Substanc

produc

H+in solutio

Bronsted Proton dono

Lewis

Electrophi

Acidity and basicityas electrophile(electron loving sites)

and nucleophile(positive or nucleiloving sites) in order to cover most

reactions.


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Corrosion

Corrosion involves the deteriorationof a material as it reacts with itsenvironment. Corrosion is theprimary means by which metalsdeteriorate. Corrosion literallyconsumes the material reducingload carrying capability and causing

stress concentrations


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Two Chemical

Processes of Corrosion

1) Oxidationis the process of strippingelectrons from an atom. The oxidationprocess takes place at an area known asthe anode.

2)Reductionoccurs when an electron isadded to an atom. reduction occurs whenan electron is added to an atom. At thecathode, the corresponding reductionreaction takes place and consumes the freeelectrons.


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Composition

The presence of various elemental and chemical componemixture is called composition.

properties and characteristics of engineering materials

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