Advanced Engineering materials

1. Advanced Engineering materials

2. Types of Materials • Ceramics • Low density • High melting point • Very high elastic modulus • Unreactive • Brittle • Polymers • Very low density • Low melting point • Low elastic modulus • Very reactive • Ductile and brittle types • Organics • (wood, paper, textiles) • Sustainable • Recyclable • Biodegradable • Easily worked • Flammable • Share properties of composites Metals • High density • Medium to high melting point • Medium to high elastic modulus • Reactive • Ductile

3. Metals and Alloys Metals are the most common of the elements. Strong, with good conductivity for electricity and heat. Mostly easily worked. • Bronze for spearheads and axes • Steel • Aluminium, Magnesium • Titanium: as strong as steel but 45% lighter • Shape memory alloys

4. Polymers Flexible Thermoplastic (PE, PU) Rigid Thermosets (EP, PF) Rigid Thermoplastic (PVC, PS) Elastomers or rubbers

5. A ceramic is a composite consisting of hard granules bound together by a ‘glue’ often like glass. Examples: Stone Limestone (CaCO3) Sandstone (SiO2) Granite (aluminosilicates) Cement and Concrete Mixtures of lime (CaO), silica (SiO2) and alumina (Al2O3) The CaO reacts with water and carbon dioxide from the air to form Ca2CO3 (limestone) Ceramics

6. Microstructure of ceramics Pottery ceramic Engineering ceramic – Al2O3

7. Properties of ceramics • Extremely hard and resistant to wear • Very high melting point • Resistant to chemical attack • High compressive strength • Low and variable tensile strength • Low density ( as compared to steel) • Ceramic components are not easy to make because of their high mp and hard/brittle so can’t be machined.

8. Organic materials • Have been used since the stone age eg wood or bone handle for stone axe. • Fibre for ropes • Sinew for bow string • Timber for houses and furniture • Paper and cardboard for packaging • Composites e.g. srbp for electrical components • Glues and varnishes

9. Wood • Has a grain structure with directionally oriented fibers • High compressive strength • Good tensile strength along grain axis • Weak across grain • Prone to decay and infestation eg woodworm – however look at timber used for staithes at Dunston

10. In its most basic form a composite material is one which is composed of at least two elements working together to produce material properties that are different to the properties of those elements on their own. The properties of a material depend on the kind of stress it is exposed to. For example concrete has a good compressive strength, but a low tensile strength. This is overcome by reinforcing with steel rods - making a composite. Composites

11. Types of stress Tension Compression Shear Flexion

12. Tensile strength and tensile modulus Tensile strength Tensile modulus (stiffness)

13. Three main groups of engineering composites • Polymer matrix composites • Metal matrix composites • Ceramic matrix composites

14. Polymer matrix composites These are the most common composites in use today. Also known as FRP - Fibre Reinforced Polymers (or Plastics) these materials use a polymer-based resin as the matrix, and a variety of fibers such as glass, carbon and Aramid (Kevlar) as the reinforcement.

15. Resin systems such as epoxies and polyesters have limited use for the manufacture of structures on their own, since their mechanical properties are not very high when compared to, for example, most metals. However, they have other desirable properties for engineering, particularly their ability to be easily formed into complex shapes. PMC Bulk material

16. Reinforcement Materials such as glass, aramid (kevlar), carbon and boron have extremely high tensile and compressive strength but in ‘solid form’ these properties are not readily apparent. This is due to the fact that when stressed, random surface flaws will cause each material to crack and fail well below its theoretical breaking point. To overcome this problem, the material is produced in fiber form, so that, although the same number of random flaws will occur, they will be restricted to a small number of fibers with the remainder exhibiting the material’s theoretical strength.

17. Crack propagation in bulk reinforcement material

18. Crack propagation in fiber reinforcement material When stressed individual fibres may break at a flaw, but the overall strength of the material is not prejudiced as the matrix bonds the remaining fibres together. Even quite short fibre whiskers or particles can enhance the strength of the matrix, particularly with respect to tensile and flexural stresses.

19. Matrix and reinforcement combined • When the resin systems are combined with reinforcing fibers such as glass, carbon and Aramid (Kevlar), exceptional properties can be obtained. • The resin matrix spreads the load applied to the composite between each of the individual fibers and also protects the fibers from damage caused by abrasion and impact. • High strengths and stiffness, ease of moulding complex shapes, high environmental resistance all coupled with low densities, make the resultant composite superior to metals for many applications.

20. Properties of PMC’s Since PMC’s combine a resin system and reinforcing fibers, the properties of the resulting composite material will combine some of the properties of the resin on its own with those of the fibers on their own.

21. Metal matrix composites Increasingly found in the automotive industry, these materials use a metal such as aluminium as the matrix, and reinforce it with particles or fibers such as silicon carbide SiC. Particulate SiCp/Al and whisker SiCw/Al were extensively characterized and evaluated during the 1980s. MMC’s can also use continuous fibre reinforcement (e.g. Graphite / Aluminium or Graphite / Magnesium) Expensive and difficult to produce, MMC’s are mainly used where their special benefits (e.g. weight saving) outweigh cost considerations – such as on the space shuttle.

22. Metal matrix composites • Composites with aluminium and magnesium matrices have been investigated extensively, and recently steel matrix composites have gathered increased interest. • In these composites, stainless steels, tool steels and precipitation hardened steels have been used as the matrix material. • The particulate reinforcements can be oxides (Al2O3, Y2O3), carbides (TiC, Cr3C2, VC, NbC), nitrides (TiN, Si3N4), and borides (TiB2, CrB2).

23. Ceramic matrix composites Ceramics have a high compressive strength but low tensile strength. Combining with a high tensile reinforcement gives very strong hard materials. Used in high temperature environments, such as jet engines, CMC’s use a ceramic as the matrix and reinforce it with short fibres, or whiskers such as those made from silicon carbide and boron nitride.

24. Super hard coatings About coatings: • Diamond • B-C-N (Boron – Carbon – Nitrogen) coatings • Ti – B – N and Ti – B – C – N • Biocompatible super hard coatings for medical devices

25. Nanostructured materials

26. Fullerenes: Molecular structures of carbon • ‘Fullerenes’ is a generic term for the third carbon molecule that follows graphite and diamond. • Fullerenes are composed of a network structure, either in a spherical or a tubular form, where 60 or more carbon atoms are strongly bonded together. • The atoms that make up Fullerenes are the same carbon atoms as those in graphite. • C60 is one of the representative examples, and is a spherical aggregate of 60 carbon atoms, with a diameter of approximately 0.7 nanometers (one nanometer equals 1/1,000,000,000 meter).

27. Fullerene structures

28. Applications of fullerenes • Electrochemical properties – use in batteries and fuel cells • Gas Storage properties – storage of hydrogen • Mechanical properties – lubricants and super hard materials • Electrical properties – superconductors • Optical properties

29. Carbon nanotubes • Carbon nanotubes are fibers with a tensile strength many times that of steel • They are being postulated as a solution to the construction of a ‘space elevator’ where a geostationary satellite is tethered to the earth, and elevators run up and down the cable raising materials into orbit.

30. Aerogels • Made of inexpensive silica, aerogels can be fabricated in slabs, pellets, or most any shape desirable and have a range of potential uses. By mass or by volume, silica aerogels are the best solid insulator ever discovered. Aerogels transmit heat only one hundredth as well as normal density glass. Sandwiched between two layers of glass, transparent compositions of aerogels make possible double-pane windows with high thermal resistance. Aerogels alone, however, could not be used as windows because the foam-like material easily crumbles into powder. Even if they were not pulverized by the impact of a bird, after the first rain they would turn to sludge and ooze down the side of the house.

31. Aerogels as insulators • Aerogels are a more efficient, lighter-weight, and less bulky form of insulation than the polyurethane foam currently used to insulate refrigerators, refrigerated vehicles, and containers. • They have another critical advantage over foam. Foams are blown into refrigerator walls by chlorofluorocarbon (CFC) propellants, the chemical that is the chief cause of the depletion of the earth's stratospheric ozone layer. According to the Environmental Protection Agency, 4.5 to 5 percent of the ozone shield over the United States was depleted over the last decade.

32. Facts about aerogels • They are 39 times more insulating than the best fibreglass insulation. • They are 100 times less dense than glass. • A wafer thin layer is sufficient to protect a hand from a blowtorch just inches away from it. • A block the size of a person weighs less than a pound, looks like it would blow away in a slight breeze, yet could support a small car. • They were used as insulation on the rover vehicle of the Mars Pathfinder. • The Marshall Space Flight Center has already provided specifications for aerogels to over 50 companies and research institutes for products as diverse as diving suits, industrial insulation, medical containers and windows. • The value of the worldwide market for low-cost aerogels is projected to reach $10 billion by the year 2005.

33. Applications of aerogels • Solid insulation • Silica aerogels are very light in weight and have an R-value up to R25 per inch • Electrodes for batteries • Vanadium oxide aerogels have very promising properties for use in Lithium cells

34. Today’s news Organic-inorganic hybrids • Under investigation by Prof J McKenzie at UCLA • Textile composites • Organic composites • Geopolymers – a better cement / concrete • Conjugated polymers • For semiconductors and light emitting devices

35. Resources • www.azom.com A to Z of materials • http://www.seas.ucla.edu/ms/ • http://www.plasticsusa.com/polylist.html datasheets for all common plastics • http://www.materials.ac.uk/ • http://bell-labs.com/org/physicalsciences/