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assignment 1 , bit dull :-) Purely a presentation - internal links don't work!

assignment 1 , bit dull :-) Purely a presentation - internal links don't work!

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6505 assignment 1 interactive resource Presentation Transcript

  • 1. 6505 Assignment 1 Interactive Resource Anton Taverne April 6th 2012
  • 2. IntroductionEngineers must make informed decisions about how items can best be constructed.A thorough understanding of materials is thus an essential part of an Engineering Studiescourse, as indicated by the following Course Outcomes. Table 1: Syllabus Outcomes P1.2 explains the relationship between properties, structure, uses and applications of materials in engineering H1.2 differentiates between the properties and structure of materials and justifies the selection of materials in engineering applications P2.1 describes the types of materials, components and processes and explains their implications for engineering development H2.1 determines suitable properties, uses and applications of materials, components and processes in engineering (Board of Studies 2011 pp 11,12) 2
  • 3. Explicit or implied reference to engineering materials appears in all of the modules in the syllabus. Table 2 Syllabus Content Relevant modules (Preliminary) (HSC) Personal and public Telecommunicatio Braking systems Civil structures ns engineering fundamentals Aeronautical engineering engineering Engineering Engineered Biomedical transport products Syllabus topics classification of materials • properties of materials • • • • structure of materials • • • • metals • • • • • • forming processes • • • • polymers • • • • • ceramics • • • • composites • • • • modification of materials • • • engineering applications of materials • • • recyclability of materials • • materials for braking systems • historical developments of products • • construction & processing materials used over time • • •(Board Of Studies 2011) 3
  • 4. About this resourceIt contains information about polymers and plain carbon steel, including: general structure properties applications methods of modifying the structure, and hence the properties methods of shaping and forming the material into useful productsIt combines explanatory material with tables summarizing significant features, givingstudents an overview, and links to other resources.Activities vary from simple identification exercises to questions requiring synthesis ofconcepts, encouraging further research, so that the course outcomes are met, and studentscan answer the question ….. “What should I use to make this?” 4
  • 5. PolymersPolymers are long chain molecules consisting of repeating units called monomers.They are covalent compounds, typically involving a carbon backbone and other non-metal elements.Carbon has 6 protons in the nucleus and therefore 6 electrons, 2 locked up in the inner shell and 4 in the outer shellavailable for forming bonds. The outer shell of carbon can accommodate 8 electrons. Hydrogen has one electron in itsouter shell, which can accommodate 2 electrons. For both atoms to have a stable arrangement of electrons, with fullouter shells, electrons are shared.Fig 1 Electron Sharing in Covalent Bonds Surrounding each central carbon atom are 8 electrons – 4 from its own outer shell, 1 from each neighboring carbon and 1 from each neighboring hydrogen. (The end carbons have a single electron available for forming a bond with the next available ethylene molecule, breaking one of its double bonds) The covalent structure means polymers do not normally conduct electricity. 5
  • 6. Polymers can be classified in different ways.Table 3 Polymer ClassificationsAddition CondensationThermosetting Thermoplastic ElastomerHomopolymers Copolymers …On to Crystallinity … 6
  • 7. Addition Polymers (1)Addition polymers are formed when the double bond of each monomer is broken, allowing the monomers to join.The process of polymerization is typically initiated with a peroxide molecule to break the first bond. The mostcommon addition polymers are made from ethylene molecules, in which one or more of the original hydrogen atomsin ethylene have been replaced.For example: polypropylene is formed from ethylene with a hydrogen atom substituted by a methyl group. Fig 2 Addition polymerisation 7
  • 8. Addition Polymers (2)Two of the factors that influence the properties of polymers are branching and substitution.If the long carbon chains have extensive branching, it is difficult for the branches to get close together. The dispersionforces that attract molecules to each other are therefore quite weak. For example low density polyethylene (LDPE)has extensive branching, has a low density and therefore floats in water, and is quite flexible, making it useful forwrapping. High density polyethylene (HDPE) is much more rigid and does not float readily in water. Fig 3 Branching LDPE HDPE In Polystyrene, there is a large, flat benzene ring with many electrons on each monomer. This allows for much stronger dispersion forces between the polymer strands, making polystyrene a very hard and rigid polymer. The Chlorine atoms in Polyvinylchloride makes PVC, used extensively in downpipes and drainage pipes, fire resistant, rigid and somewhat brittle. 8
  • 9. Condensation PolymersCondensation Polymers are usually formed from two different monomers, typically with water as a by-product.Polyesters can be made from alcohols and carboxylic acids Fig 4 Polyesters The properties of condensation polymers are further influenced by the lengths of the carbon chains between the functional groups, the presence of other atoms and the extent of hydrogen bonding between the strands. For example, in polyamides, there is a relatively positive hydrogen atom attached to the nitrogen and a relatively negative oxygen atom. The hydrogen from one strand is attracted to the oxygen of the other by relatively strong ‘hydrogen bonding’. Fig 5 Polyamides In polyesters there are no such relatively positive hydrogen atoms. 9
  • 10. Homopolymers and CopolymersHomopolymers - one type of monomer, e.g. polyethylene.Copolymers - two or more monomers arranged in different possible ways.Fig 6 Copolymer structures (Course Notes)Alternating: Block: Random: Graft:X XXOXOXOX OXXXXOXXXX OOXOOXXXOXX OOOOOOOOO X X X 10
  • 11. Thermosoftening polymers, Thermosetting polymers and ElastomersThermoplastics have weak bonds between the strands. Heating allows the molecules to disentangleand move around. On cooling, the plastic resolidifies in its new shape.When thermosetting plastics are heated, chemically active sites on the chains form strong bondsbetween the chains, resulting in a three-dimensional amorphous (non-crystalline) structure that cannotbecome soft again.Elastomers (rubbers) can be stretched, (firstly untangling the chains, then stretching the bonds holdingthe chains together), and will return to their original shape when released.Thermosetting rubbers typically have crosslinks formed by sulfur atoms.Within the structure of thermoplastic elastomers are strong, rigid ‘domains’ which prevent sliding atroom temperature, and flexible chains that give it the rubber qualities. At sufficiently hightemperatures, they deform in the manner characteristic of thermoplastics.(Course notes) 11
  • 12. CrystallinityPolymer strands may be tangled in a seemingly random fashion (amorphous regions) or with themolecules neatly ordered and packed close together (crystalline regions).The latter restrict movement and are denser, with reduced optical clarity.Plastics with a lot of crystallinity will shrink more on cooling, and will be more rigid, brittle and lessductile.(Course notes) Fig 7 Crystallinity Crystalline regions Amorphous regions 12
  • 13. ModificationsThe properties of specific polymers can be modified in several ways. (Course notes) Table 4 Effect of modifications on properties Modification Comment Longer chains Increase tensile strength Branching Increase tensile strength and stiffness, reduce density Large groups of atoms in chain Increase stiffness Cross-linking Increase rigidity More crystalline regions Higher density, tensile strength and rigidity Orientation of the molecules Different properties in different directions Copolymerisation Various effects Blending Various effects Additives : Stabilisers Protect from UV Plasticisers Increase flexibility and mouldability Flame retardants Reduce flammability Pigments and dyes Provide colour Fillers : These can greatly reduce the cost Glass fibres Increase impact and tensile strength Mica Reduce electrical conductivity Graphite Reduce friction Wood flour Increase tensile strength Gas Produce foams Carbon black Strengthen and protect from UV 13
  • 14. Activities for PolymersActivity 1: Match the desired properties with the purpose of the polymer, and suggest suitable polymers. Research the structural features of the polymer that contribute to the relevant property. Activity2: Suggest appropriate objects that could be formed using the forming methods described. Activity 3: Explore the Macrogalleria website. Find examples of polymers relevant to engineering, focusing on how their structures relate to their properties and uses. http://www.pslc.ws/macrog.htm 14
  • 15. METALSIn metal atoms there are typically very few electrons in the outer shell.To achieve the more stable inert gas electron configuration, metals tend to losethese outer electrons.Metals can be visualized as positive metal ions in a ‘sea’ of delocalized electrons.These electrons move freely, making metals good conductors of electricity.Other typical metal properties (malleability, ductility, thermal conductivity) resultfrom the relative mobility of metal ions that are surrounded by very small freeelectrons compared to the lack of mobility of those surrounded by large anions, asfound in ionic compounds like salt.When different metals combine, there are no discrete molecules or fixed ratios ofpositive and negative ions. A wide range of ‘alloys’ (not ‘compounds’) can thus beformed. 15
  • 16. STEEL STEEL is an alloy of Iron with up to 2% Carbon. The iron exists in one of two allotropic forms – Austenite (FCC)- which exists at high temperatures Ferrite (BCC) at low temperatures. Martensite (BCT) forms if hot steel is cooled quickly. Carbon becomes trapped in the FCC structure as iron tries to form the BCC structure, causing distortion and internal stresses.Fig 7Face Centered Cubic<http://ecee.colorado.edu/~bart/book/fcc.gif > Fig 8 Body Centered Cubic <http://ecee.colorado.edu/~bart/book/bcc.gif> Fig 9 Body Centered Tetragonal <://www.tf.uni-kiel.de/matwis/amat/def_en/kap_1/illustr/bravais5.gif > 16
  • 17. Factors influencing the properties of steelCarbon contentAtoms other than iron and carbon (Not included here)The way the atoms are arranged in microstructuresThe grain size and grain flowHow it has been treatedHow it has been shaped and formed …on to cutting methods …… 17
  • 18. Carbon ContentTable 7 Categories of steel and their uses (Scanned from Copeland Vol 1 p.95) 18
  • 19. Microstructures Table 8 Steel microstructures: (Copeland 1 p 95) Name Alias Structure T Dissolved C Properties Effect on steel Austenite Gamma iron FCC >723 degrees < 2% Soft, ductile NA at room T Ferrite Alpha iron BCC As steel cools .. <0.025% Soft, ductile Cementite Iron Carbide (Fe3C) Hard, brittle Hardness up, toughness, and ductility down Pearlite Layers of 0.83% cementite and ferrite Martensite BCT Rapid quenching >0.03% < 1.3% Hard Greater hardness, brittle Fig 11 Martensite Fig 10 Plain Steel Microstructures Microstructure (Scanned from Copeland (2000) p.93) (Scanned from Course Notes)Activity 4: Use the data in table 8 to explain the trends observed in figure 12 Fig 12 (Scanned from Copeland (2000) p.93) 19
  • 20. Grain size and UniformityHaving a uniform grain size makes the steel easier to machine.Smaller grains make the steel harder and stronger, but less ductile.Larger, regular grains allow easier movement of the grains. Grain flow continuity Steel that has been forged into shape (left) with continuous grain flow is stronger than steel that has been cut to shape (right). Fig 13 Grain flow 20
  • 21. Modifications (1)Work hardening If a metal is bent or beaten at temperatures below its recrystallisation temperature, atoms slip along shear planes, distorting the metal. Discontinuities in the crystal structure allow slip to occur more easily, by moving the discontinuities through the structure. With greater deformation, the discontinuities can become jammed, restricting the movement of atoms, resulting in greater hardness prior to fracture. ( Copeland 2000, p 66) Recrystallisation When the steel is heated sufficiently and allowed to cool, any grains that were work hardened or stressed are replaced by unstressed grains, whose axes are approximately the same length. Recrystallisation reduces internal stresses, hardness and strength, while it increases ductility and grain size. (Course notes) 21
  • 22. Modifications (Heat)Table 9 : Heat treatment of steels (Course notes)Annealing Relief stresses Uniform grain structure Soften the metal for further working or machining Process Effect Comments Full Heat to red heat, Form austenite on heating, pearlite /ferrite Effect depends on C% (900degrees) then cool very or pearlite or pearlite/cementite slowly Process / subcritical ~600 deg Ferrite recrystallised pearlite remains Not as soft as full annealing Cool in air elongated Spherodising High C > 0.3 % content Kept Produces spheres of cementite Easy to machine. Hard brittle speroids at ~680 several hours then pushed away by cutting tool edge. cool slowlyNormalising To red heat, then cool in air Small, uniform grain Improve machinability so faster coolingHardening Red heat, quick cool Forms martensite Hard, brittle Not much use.Tempering Heat hardened steel to Carbon atoms escape from martensite to Lowers tensile strength / hardness but more below 723 degrees, form fine cementite ductile, impact resistance “soaking”, slow coolingCase or surface hardening Keeps the core soft and tough, gives the surface greater wear resistance carburising Red heat, soak in Carbon- Increase C content of surface rich atmosphere flame For large objects. C% > 0.3 induction Passing electric current Smaller objects. C% > 0.3 through nitriding Change surface composition by diffusing Nitrogen into hot steel 22
  • 23. Annealing Activity (part 1) 23
  • 24. Annealing Activity (part 2) 24
  • 25. Forming and Shaping Sandcasting Casting Activity 6: Videos Hot Working Drawing Spinning Image from Powder Processing http://i1.ytimg.com/vi/XcxDY7vQnPo/default.jpg Investment castingActivity 7: Find suitable examples of steel items made with each method, and indicate why that method is appropriate. Consider factors such as the intricacy of the component, Image from the finish produced and the run size. http://i1.ytimg.com/vi/tyrXq_u1OH0/default.jpg 25
  • 26. Cutting Methods Activity 8a: Video Water jet Image from http://www.youtube.com/watch?v=wPYwrFwQrN4Activity 8b: Find examples of items cut by the different methods described, indicating why the method is particularly suitable for that item. 26
  • 27. Joining MethodsMaterials can be joined by: introducing another substance that : reacts chemically to form a strong bond that melts and resolidifies melting and solidifying the materials themselves at their boundary Activity 9b: Recommend and justify joining methods for the different applications Activity 9a: videos Arc Welding Friction Welding Image from Image from http://i1.ytimg.com/vi/Te http://i2.ytimg.com/vi/- BX6cKKHWY/default.jpg aEuAK8bsQg/default.jpg 27
  • 28. APPLICATIONSActivity 10: Identify the relevant properties of, and the type of steel typically used for a range of engineering purposes. Indicate how the steel is best treated for the application. 28
  • 29. Bibliography and ReferencesREADING:Board of Studies, New South Wales (2011) “Engineering Studies Syllabus Stage 6” Retrieved February 10th, 2012 fromhttp://www.boardofstudies.nsw.edu.au/syllabus_hsc/pdf_doc/engineering-studies-st6-syl-from2013.pdfCopeland, P. L. (2005) Engineering Studies: The definitive Guide Volume 2 . (2nd ed.). Helensburgh, NSW: Anno Domini 2000 Pty LtdCopeland, P. L. (2000) Engineering Studies: The definitive Guide Volume 1. Helensburgh, NSW: Anno Domini 2000 Pty LtCourse Notes 2011: “1. Engineering Materials and Applications” EDUC6505 Engineering Education Studies 2 University of NewcastleMetcalfe, P. & Metcalfe, R. (2009) Excel Senior High School Engineering Studies. (2nd ed.). Glebe, NSW: Pascal Press VIDEOS http://www.youtube.com/watch?v=_FIsrYzyvlg&feature=player_detailpage Water Jet http://www.youtube.com/watch?v=XcxDY7vQnPo&feature=player_detailpage Sand casting http://www.youtube.com/watch?feature=player_detailpage&v=tyrXq_u1OH0 Investment casting http://www.youtube.com/watch?v=TeBX6cKKHWY&feature=player_detailpage Plasma arc http://www.youtube.com/watch?feature=player_detailpage&v=-aEuAK8bsQg Friction welding 29