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MNIT, Jaipur

Departmentof 

metallurgical and materials engineering

  Presentation on

Classification of engineeringmaterials

Submitted to :-

Dr.V.K.Sharma(Associate Professor)

Submitted by :-

Rajat GoelM.tech(Ist year)

(2011PMT5175)

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Classification ofEngineering

materials

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METALS POLYMERS CERAMICS COMPOSITES

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Classifications & Specifications of Metallic Materials

Major characteristics of metallic materials arecrystallinity, conductivity to heat and electricity andrelatively high strength & toughness.Classification: systematic arrangement or division ofmaterials into group on the basis of some commoncharacteristicGenerally classified as ferrous and nonferrous

Ferrous materials-iron as the base metal,range from plain carbon (>98% Fe) to high alloysteel (<50% alloying elements)

Nonferrous materials consist of the rest of themetals and alloys

Eg. Aluminum, magnesium, titanium & theiralloys

 Metal / Metallic materials

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Within each group of alloy, classification can be

made according(a) chemical composition, e.g. carbon content oralloys content in steels;(b) finished method, e.g. hot rolled or cold rolled;

(c) product form, e.g. bar, plate, sheet, tubing,structural shape;(d) method of production, e.g. cast, wroughtalloys.

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Designation: identification of each class by a

number, letter, symbol, name or a combination.Normally based on chemical composition ormechanical properties.Example : Table 2.1 designation systems for steel

System used byAISI

&SAE

: 4, or 5 digits whichdesignate the alloy composition.1st two digits indicate Alloy systemLast two or three digits nominal carbon content inhundredths of a percent

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Manufacturing consideration

Majority of metallic components are wrought or cast

Wrought :usually stronger and more ductile than cast.

Available in many shapes & size tolerance

Hot worked products:

Tolerance are wider thus difficult for automaticmachining

Poor surface quality, esp. in sheet/wire drawing

Cold worked product:

Narrow toleranceResidual stress cause unpredictable size changeduring machining

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Weldability – a function of material composition. Sostructure involve welding of the components need to

consider. Also for other joining means.Machinability:

Important if large amounts of material have to beremoved

improvement by heat treatment or alloying elements

Economic aspects:

material able to perform function at lowest cost

Plain carbon steel & cast iron are the least expensive

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Classifications of Polymers

Polymer – low density, good thermal & electricalinsulation, high resistance to most chemicals andability to take colours and opacities.

But unreinforced bulk polymer are mechanicallyweaker, lower elastic moduli & high thermalexpansion coefficients.

Improvement Reinforced variety of fibrous

materials Composites (PMC).

Polymers

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Thermoset & thermoplastic

Differ in the degree of their inter-molecular

bondingThermoplastic-little cross bonding betweenpolymer, soften when heated & harden whencooled

Thermoset-strong intermolecular bonding whichprevents fully cured materials from softeningwhen heated

Rubber are similar to plastic in structure and thedifference is largely based on the degree ofextensibility or stretching.

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Advantages : ease of manufacturing & versatility.

Can manufacture into complicated shapes in one

step with little need for further processing orsurface treatment.

Versatility : ability to produce accuratecomponent, with excellent surface finish and

attractive color, at low cost and high speedApplication: automotive, electrical & electronicproducts, household appliance, toys, container,packaging, textiles

Basic manufacturing processes for polymer parts areextrusion, molding, casting and forming of sheet.

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Design consideration for polymer

Structural part/When the parts is to carry load

Should remember the strength and stiffness ofplastics vary with temperature.

T room data cannot be used in design calculation if

the part will be used at other temp.Long term properties cannot be predicted from short

term prop. Eg. Creep behavior

Engineering plastics are britle (notched impactstrength < 5.4 J/cm)

Avoid stress raiser

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Classification of Ceramic Materials

Ceramics – inorganic compounds of one or more metalswith a nonmetallic element. Eg Al2O3, SiC, Si2N3.

Crystal structure of ceramic are complexThey accommodate more than one element of

widely different atomic size.The interatomic forces generally alternate betweenionic & covalent which leave few free electrons

usually heat & electrical insulators.

Strong ionic & covalent bonds give high hardness,stiffness & stability (thermal & hostile env.).

Ceramics

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Structure:

(1) Amorphous or glass-short range order, (2)crystalline (long range order) & (3) crystallinematerial bonded by glassy matrix.Classification:

Whitewares, glass, refractories, structural clayproducts & enamels.Characteristics:

Hard & brittleness,

low mechanical & thermal shockHigh melting pointsThermal conductivities between metal & polymer

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Design consideration for ceramicsBritle, low mechanical & thermal shock-need specialconsideration

Ratio between tensile strength, modulus of rupture &compressive strength ~ 1:2:10. In design, load ceramicparts in compression & avoid tensile loadingSensitive to stress concentration

Avoid stress raiser during design.Dimensional change take place during drying and firing,should be considerLarge flat surface can cause wrapping

Large changes in thickness of product can lead tononuniform drying and cracking.Dimensional tolerances should be generous to avoidmachining

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Introduction

A composite material can be broadly defined as anassembly two or more chemically distinct material,having distinct interface between them and actingto produce desired set of properties

Composites – MMC, PMC & CMC.

The composite constituent divided into two

Matrix

Structural constituent / reinforcement

Composites

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Properties / behavior depends on properties, size& distribution, volume fraction & shape of theconstituents, & the nature and strength of bondbetween constituents.

Mostly developed to improve mechanicalproperties i.e strength, stiffness, creep resistance& toughness.

Three type of composite

(1) Dispersion-strengthened,

(2) Reinforcement – continuous & discontinuous(3) Laminated (consist more than 2 layersbonded together).

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Designing with composite

A composite materials usually are more expensive on a

cost.Used when weight saving is possible when the relevantspecific property (property/density) of thecomposite is better than conventional material

E.g. specific strength (strength/density), specificelastic modulus ( elastic modulus/density)

Efficient use of composite can be achieved bytailoring the material for the application

E.g., to achieve max. strength in one direction in afibrous composite, the fibers should be wellaligned in that direction

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If composite is subjected to tensile loading,important design criterion is the tensile

strength in the loading directionUnder compression loading, failure by bucklingbecome important

Fatigue behavior:

Steel- show an endurance limit or a stress belowwhich fatigue does not occur

Composite-fatigue at low stress level becausefibrous composites may have many crack, whichcan be growing simultaneously and propagatethrough the matrix

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THANK YOU