BITS PilaniPilani Campus

Materials Science & Engineering

Dr. Subrata Bandhu GhoshDepartment of Mechanical Engg.

BITS Pilani, Pilani Campus

Welcome to the fascinating andexceedingly interesting world of

“Engineering Materials”!

BITS Pilani, Pilani Campus

TODAY’S LECTURE

• Aims and Scopes• Classification to Materials• Recommended Text and Reference Books

BITS Pilani, Pilani Campus

Introduction to diverse kinds of engineering materials

Overview of what determines the properties ofmaterials and how we engineer them

Structure of materials and various length scales

Properties of materials: elasticity, plasticity, fracture

Processing of materials: metals, ceramics, polymers& composites

Selection of materials and design of engineeringcomponents

Destructive and nondestructive testing techniques

What will you learn?

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Metallic Materials

Glass and Ceramic Materials

Polymeric Materials

Composite Materials

Electronic Materials

Natural materials

Classes of Materials

Three maintypes of

materials

Other typesfor modernengineeringtechnology

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Smart Materials

Nanomaterials

Advanced Materials

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These materials are inorganic substances that are composed ofone or more metallic elements and may also contain somenonmetallic elements.Metallic elements: Fe, Cu, Al, Ni and TiNonmetallic elements: C, N, OMetals have a crystalline structure in which the atoms arearranged in an orderly manner. Structurally, atoms in metalsnormally adopt one of three common arrangements:hexagonal close-packed (hcp), cubic close-packed (fcc) orbody centred cubic (bcc).

Metallic Materials

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The valence electrons occupy a conduction band, whichmeans that they are delocalised throughout the structure(accounting for the high thermal and electricalconductivity of metals).Metallic bonding is strong.Metals in general are good thermal and electrical conductors.Many metals are relatively strong and ductile at roomtemperature, and many maintain good strength even athigh temperature.Metals in their alloyed and pure forms are used in numerousindustries including aerospace, biomedical, semiconductor,electronic, energy, civil structural and transport.

Metallic Materials

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Glasses and Ceramics are inorganic compounds that are nonmetallic. Ceramics are crystalline, and so have a regularrepeating unit throughout their structure, while glasses arenon-crystalline (normally termed “amorphous”).Structurally ceramics and glasses may be formed from eitherionic or covalent bonds and so have strong bonds betweenatoms.Most ceramic materials have high hardness and hightemperature strength but tend to be brittle (little or nodeformation prior to fracture).Advantages of ceramic materials for engineering applicationsinclude light weight, high strength and hardness, good heatand wear resistance, reduced friction and insulativeproperties.

Glass and Ceramic Materials

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Traditional ceramic materials include clay and stone.Glasses and Ceramics include cements and concretesas well as a range of compounds that are becomingincreasingly used for high-technology applicationssuch as diamond, alumina (e.g. sapphire),magnesia, silica glasses and silicates, siliconcarbide and silicon nitride.These new generation ceramic materials are calledengineering ceramics, structural ceramics oradvanced ceramics. They have higher strength,better wear and corrosion resistance andenhanced thermal shock resistance.

Glass and Ceramic Materials

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Ceramic materials can be applied to aerospace, metalmanufacturing, biomedical, automobile and numerousother industries.The two main drawbacks for this class of materials are thatthey are (1) difficult to process into finished products andare therefore expensive and (2) brittle and have lowfracture toughness compared to metals.If techniques for developing high toughness ceramics aredeveloped further, these materials could show atremendous upsurge for engineering applications.

Glass and Ceramic Materials

BITS Pilani, Pilani Campus

Polymers are built up from (normally organic) monomericbuilding units. The bonding within the polymer chainconsists of strong covalent bonds. However, the bondingbetween chains is far weaker (Van der Waals type).The long-flexible chains may be arranged completely randomly(giving an amorphous polymer) or in a regular chain-foldingpattern (leading to crystalline regions within the polymer).The detailed properties of a particular polymer will depend onfactors such as chain length, crystallinity and the presence ofany cross-linking between the chains.The strength and ductility of polymeric materials vary greatly.Because of the nature of their internal structure, mostpolymeric materials are good insulators and are used forelectrical insulative applications.

Polymeric Materials

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Polymeric materials have low densities and relatively lowsoftening or decomposition temperatures.Examples of important polymers are polyethylene (PE),polymethylmethacrylate (PMMA, perspex), nylon,polystyrene (PS), polyurethane (PU) and polyvinylchloride(PVC)

Polymeric Materials

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A composite material may be defined as two or morematerials(phases or constituents) integrated toform a new one.The constituents keep their properties and theoverall composite will have properties differentthan each of them.Most composite materials consist of a selected filleror reinforcing material and a compatible matrix orresin binder to obtain the specific characteristicsand properties desired.

Composite Materials

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Composites include glass-fibre reinforced polymers(denoted GFRP, such as fibreglass), carbon-fibrereinforced polymers (CFRP), filled polymers and afew composites of ceramics and metals (cermets).Composite Materials

BITS Pilani, Pilani Campus

Electronic materials are not a major type of material byproduction volume but are an extremely important type ofmaterial for advanced engineering technology.Eletronic material: Silicon, GermaniumMicroelectronic devices have made possible such newproducts as communication satellites, advancedcomputers, handheld calculators, digital watches androbots.Electronic materials will play a vital role in the “factories ofthe future” in which almost all manufacturing may be doneby robots assisted by computer-controlled machine tools.

Electronic Materials

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These are often classed as a separate category, but allnatural materials really fit into one of the others.Examples of natural materials are wood, stone, bone,leather and cotton.Natural Materials

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Smart materials have the ability to sense externalenvironmental stimuli (temperature, stress, light,humidity, and electric and magnetic fields) andrespond to them by changing theirproperties(mechanical, electrical or appearance),structure or functions.Smart materials consists of sensors and actuators.The sensory component detects a change in theenvironment, and the actuator componentperforms a specific function or a response.

Smart Materials

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For instance, some smart materials change or produce colourwhen exposed to changes in temperatures, light intensity,or an electric current.Some smart materials that can function as actuators areshape-memory alloys and piezoelectric ceramics.Shape-memory alloys are metal alloys that, once strained,revert back to their original shape upon an increase intemperature above a critical transformation temperature.The change in shape back to the original is due to a change inthe crystal structure above the transformationtemperature.

Smart Materials

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Nanomaterials are generally defined as thosematerials that have a characteristic lengthscale(that is, particle diameter, grain size, layerthickness etc) smaller than 100 nm. Nanomaterialscan be metallic, polymeric, ceramic, electronic, orcomposite.

Nanomaterials

BITS Pilani, Pilani Campus

• William F. Smith, Javed Hashemi and RaviPrakash, Materials Science and EngineeringIn SI Units, McGraw-Hill Companies, New DelhiFourth Edition, Special Indian Edition, 2008

Recommended Textbook

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Basic References

• William D CalisterJr. Materials Science andEngineering: An Introduction, John Wiley & Sons,Singapore, Sixth Edition, (2003)

• E Paul Degarmo, J T Black, Ronald A Kohser, ”Materialsand Processes in Manufacturing’, John Wiley & Sons,Singapore, Ninth Edition, (2004)

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