Presentation OnClassification Of MaterialsPresented ByGulfam Hussain
Classification Of MaterialsThere are different types of materials such as :1- Metals and Alloys2- Ceramics3- Polymers (Plastics)4- Semiconductors5- Composite Materials
IntroductionWhat is Material ?“The matter from which different things can be made iscalled material .”It consists of physical objects. Sincemetallic materials are extensively used forload-bearing applications, their mechanical propertiesare of great practical interest. Webriefly introduce these here. The term “stress” refers toload or force per unit area.
“Strain” refers to elongation or change indimension divided by the original dimension.Applicationof “stress” causes “strain.” If the strain goes awayafter the load or applied stress isremoved, the strain is said to be “elastic.” If thestrain remains after the stress is removed,the strain is said to be “plastic.”When thedeformation is elastic, stress and strain arelinearlyrelated; the slope of the stress-strain diagram isknown as the elastic or Young’s modulus.The level of stress needed to initiate plasticdeformation is known as the “yield
The maximum percent deformation that can beachieved is a measure of the ductility of a metallicmaterial. These concepts are discussed further inChapters 6 and 7.1-Metals and AlloysMetals and alloys includesteels, aluminum, magnesium,zinc, cast iron, titanium, copper, and nickel. An alloy isa metal that contains additions ofone or more metals or non-metals. In general, metalshave good electrical and thermal conductivity.Metals and alloys have relatively high strength, highstiffness, ductility or formability,
They are particularly useful for structural or load-bearing applications. Although pure metals areoccasionally used, alloys provide improvement in aparticular desirable property or permit bettercombinations of properties.Metals & Alloys Examples OfApplicationsPropertiesCopper Electrical conductorwireHigh electricalconductivity,good formabilityGrey Cast Iron Automobile engineblocksCastable,machinable,vibration-dampingAlloy Steel Wrenches,automobile chassisSignificantlystrengthened byheat treatment
2-Ceramics :Ceramics can be defined as inorganiccrystalline materials. Beach sandand rocks are examples of naturallyoccurring ceramics. Advanced ceramics arematerialsmade by refining naturally occurringceramics and other special processes.Advanced ceramicsare used in substrates that house computerchips, sensors and actuators, capacitors,wireless communications, spark plugs,inductors.
Some ceramics are used as barrier coatings to protectmetallic substrates in turbine engines. Ceramics arealsoused in such consumer products aspaints, plastics, and tires, and for industrialapplicationssuch as the tiles for the space shuttle, a catalystsupport, and the oxygen sensors used in cars.Traditional ceramics are used to makebricks, tableware, toilets, bathroom sinks, refractories(heat-resistant material), and abrasives. Ingeneral, due to the presence of porosity (smallholes), ceramics do not conduct heat well; they mustbe heated to very high temperatures before melting.
We normally prepare fine powders of ceramics andconvert these into different shapes. New processingtechniques make ceramics sufficiently resistant tofracture that they can be used in load-bearingapplications, such as impellers in turbine engines.Ceramics have exceptional strength under compression.Can you believe that an entire fire truck can besupported using four ceramic coffee cups?Ceramics Examples OfApplicationsPropertiesAl2O3, MgO, SiO2 Refractories(i.e. Heat-resistant lining offurnaces) for containingmolten metalThermallyinsulating,Withstandhigh temperatures &Relatively inert to moltenmetalBarium Titanate Silica Capacitors formicroelectronics, OpticalHigh ability to storecharge & Low optical
3-Polymers :Polymers are typically organic materials. They areproduced using aprocess known as polymerization. Polymericmaterials include rubber (elastomers) and manytypes of adhesives. Polymers typically are goodelectrical and thermal insulators.Although theyhave lower strength, polymers have a very goodstrength-to-weight ratio. Theyare typically not suitable for use at hightemperatures.
Many polymers have very good resistanceto corrosive chemicals. Polymers havethousands of applications ranging frombulletproofvests, compact disks (CDs), ropes, and liquidcrystal displays (LCDs) to clothes andcoffee cups. Thermoplastic polymers, inwhich the long molecular chains are notrigidly connected,have good ductility and formability;thermosetting polymers are stronger butmorebrittle because the molecular chains aretightly linked.
Polymers are used inmany applications, including electronic devices.Thermoplastics are made by shaping their moltenform. Thermosets are typically cast into molds.Plastics contain additives thatenhance the properties of polymers.Polymers Examples OfApplicationsPropertiesPolyethylene Food packaging Easily formed intothin, flexible,airtight filmEpoxy Encapsulation ofintegrated circuitsElectrically insulatingandmoisture-resistantPhenolics Adhesives for joiningplies in plywoodStrong, moistureresistant
SemiconductorsDefinition of SemiconductorA materials product - usually comprised of silicon -which conducts electricity more than an insulator butless than a pure conductor, such as copper andaluminum is known as semiconductor..Semiconductors are usually very small and complexdevices, and can be found in thousands of productssuch as computers, cell phones, appliances, andmedical equipment.
Metals tend to be good conductors of electricity becausethey usually have "free electrons" that can move easilybetween atoms, and electricity involves the flow ofelectrons. While silicon crystals look metallic, they are not, infact, metals. All of the outer electrons in a silicon crystal are involvedin perfect covalent bonds, so they cant move around. A pure silicon crystal is nearly an insulator -- very littleelectricity will flow through it. But we can change all this through a process calleddoping. A diode is the simplest possible semiconductordevice, and is therefore an excellent beginning point ifwe want to understand how semiconductors work. Semiconductor diodes are used as rectifier.
In some semiconductors, the level ofconductivity can be controlled to enableelectronic devices such astransistors, diodes, etc., that are used to buildintegrated circuits.In many applications, we need large singlecrystals of semiconductors.These are grown from molten materials. Often, thin films of semiconducting materials
Composite Materials:The main idea in developing composites is to blendthe properties of different materials.These are formed from two or morematerials, producing properties not found in anysingle material.Concrete, plywood, and fiberglass are examples ofcomposite materials.Fiberglass is made by dispersing glass fibers in apolymer matrix.The glass fibers make the polymer stiffer, withoutsignificantly increasing its density.
With composites, we can produce lightweight, strong,ductile, temperature-resistant materials or we canproduce hard, yet shock-resistant, cutting tools thatwould otherwise shatter.Advanced aircraft and aerospace vehicles rely heavilyon composites such as carbon fiber reinforcedpolymers .Sports equipment such as bicycles, golf clubs, tennisrackets, and the like also make use of different kinds ofcomposite materials that are light and stiff.
The X-wing for advanced helicopters relies on a material composed of acarbon fiberreinforcedpolymer. (Courtesy of Sikorsky Aircraft Division – United TechnologiesCorporation.)