ENCN221

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Marciaho
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269337
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ENCN221
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2014-04-07 06:26:55
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ENCN221
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  1. Ionic Bond Energy
    • Large
    • Non Directional
    • High/Low E.N
  2. Covalent Bond Energy
    • Variable
    • High E.N
  3. Metallic Bond Energy
    • Variable
    • Non Directional
    • Low E.N
  4. Secondary Bond Energy
    • Smallest
    • Directional
    • Interaction Polymer
    • Intermolecular
  5. Ceramic Bond Type
    Ionic and Covalent
  6. Polymers Bond Type
    Covalent and Secondary
  7. Ceramics Bond Energy and Properties
    • Large Melting Temperature
    • Large Energy
    • Small Thermal Coeffecient
  8. Metals Bond Energy and Properties
    • Moderate Melting Temperature
    • Moderate Energy
    • Moderate Thermal Coeffecient
  9. Polymers Bond Energy and Properties
    • Small Melting Temperature
    • Small Energy
    • Large Thermal Coefficient
  10. Ceramics Density and why
    • Mid Density
    • Less dense packing
    • Lighter elements
  11. Metals Density and why
    • High Density
    • Close packing
    • Often Large atomic mass
    • Often same element = same radii
    • Simplest crystal structure
  12. Polymers Density and why
    • Low density
    • Low packing (amorphous)
    • Lighter elements (CHO)
  13. Body Centred Cubic Properties
    incl APF and L
    • 9 Atoms
    • Centre of lattice and each corner
    • Equiv no. of atoms =2
    • APF = 0.68
    • L = 4R = Root 3 a
  14. Face Centred Cubic Properties
    • 14 atoms
    • Centre of each face
    • Each corner
    • Equvi no. of atoms = 4
    • APF = 0.74
    • L= r = 2 root 2
  15. Hexagonal Close Pack Properties
    • 17 atoms
    • Centre plane
    • Centre top and bottom face
    • Each corner
    • Equiv no. of atoms = 6
    • APF = 0.74
  16. Equiv no. of atoms for each type
    • BCC =2
    • FCC=4
    • HCP =6
  17. Atomic Packing Factor Equation
    • Volume of atoms in unit cell divided by volume of unit cell 
    • 0.52 for a simple cubic structure
  18. APF for each type
    • BCC - 0.68
    • FCC -0.74
    • HCP - 0.74
  19. Density Equation
    nA/(Vc*Na)
  20. Single vs Polycrystal Properties
    • Single: 
    • Properties vary with direction ANISOPTROPIC
    • Poly Crystal:
    • If grains random: ISOTROPIC
    • If grains textured: ANISOTROPIC
  21. Isotopic
    When properties of material are independent of direction
  22. Anisotropic
    When properties are different
  23. Bulk Modulus (K)
    Measure of substance;s resistance to uniform  compression. The pressure increase need to to deform
  24. Shear Modulus (G)
    aka Modulus of rigidity, the ratio of shear stress to shear strain
  25. Poisson's Ration and equation (2)
    Ratio of the contraction or transverse strain (normal to load) to extension or axial strain ( in direction of load)

    • V= (3K-2G)/(GK +2G) 
    • E = 2G(1+V)
  26. Poisson's ration for metals ceramics and polymers
    • Metals V= 0.33
    • Ceramics V=0.25
    • polymers V=0.40
  27. Ductility
    Plastic tensile strain @ failure

    • %EL = LF-l0/l0 x100
    • %RA = A0-AF/A0 x 100
  28. Toughness definition and for each material
    • Approcimated by area under stress strain curve
    • Energy require to fracture specimen
    • Metals: Large Toughness
    • Ceramics : Small Toughness
    • Polymers: Very Small Toughness
  29. Brittle energy
    Elastic Energy
  30. Ductile Energy
    Plastic and elastic energy
  31. Resilience (Ur) definition and equation
    • Ability to store energy
    • Energy require to reach yield point

    Ur = 1/2 Stress(y) Strain (y)
  32. Yield Strength
    Stress at which noticeable (strain =0.002) plastic deformation has occurred.
  33. Proportional limit
    Point on graph between linear and non linear behaviour
  34. Elastic Limit (yield point)
    Point between elastic and plastic behaviour, max stress for full recovery
  35. Yielding
    Strain continues with little or no increase in strength
  36. Ultimate stress
    Max strength on curve
  37. Tensile Strength
    • Max strength on curve.
    • Metals: Occurs when noticeable necking starts
    • Polymers occurs when polymer backbone chains are aligned and about to break
  38. Hardness definitions and what it means
    • Resistance to permanently indenting surface
    • Large hardness means
    •      Resistance to plastic deformation
    •      Better wear properties
    • Can be correlated to yield and tensile strength
  39. Fracture Mechanisms
    • Ductile Fracture
    • Occurs with plastic deformation

    • Brittle Fracture
    • Little or no plastic deformation
    • Catastrophic
    • Sudden failure when static stress = strength
  40. Stress corrosion cracking
    and requirements
    Form of cracking produced by chemical attack at tip of stress crack. 

    • 1) Susceptible material
    • 2) Environment
    • 3) Stress
  41. Ductile vs Brittle
    • Ductile
    • Much plastic deformation
    • Dull appearance
    • Cross section reduced by necking
    • Crack growth slow

    • Brittle
    • Little plastic deformation
    • Shiny appearance
    • Cross section not reduced by necking
    • Cracks grow rapidly - loud
  42. Transition Temperature 
    Above and Below
    • Above
    • High toughness- take high energy
    • MCV - ductile
    • Large plastic deformation

    Below

    • low toughness
    • Fracture occurs by cleavage
    • Small plastic deformation
  43. Time Dependent Response
    Amount of deformation depends of duration of load
  44. Creep definition and types
    occurs at what melting temp
    • Long term deformation, can be in metals, timber, concrete. 
    • Primary, secondary and tertiary
    • T> 0.4
  45. Viscous flow
    Amorphous materials can be under short term flow
  46. Primary creep
    Slope decreases with time
  47. Secondary creep
    steady state
  48. Tertiary creep
    Creep rate increase with time
  49. Relaxation
    Stresses dissipate with time.
  50. Viscoslasticity
    Exhibits both viscous and elastic response. Delayed response to load
  51. Rheology definition and 3 elements
    Study of flow of materials. Provides relationship between deformation and load over time.
  52. Hookean
    Perfectly elastic material. Response to force is instantaneous and deformation completely recovered.
  53. Newtonian
    Perfectly viscous behaviour. Force is proportional to length of time of applied force/ When removed, element retains deformed shape.
  54. St Venant
    Deformation only occurs once the force exceeds tat which resists deformation
  55. Flow processes
    • Concrete has resistance to flow- yield stress. 
    • Stickiness - plastic viscosity (mew) - slope of line
  56. Material variability (3)
    • Inherent Variability
    • Variance caused by sampling method
    • Variance associated with the way test is conducted
  57. Sampling must be (3)
    • randomly selected
    • representative of whole lot
    • Quantify the characteristics of population

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