ENCN221
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Ionic Bond Energy
 Large
 Non Directional
 High/Low E.N


Metallic Bond Energy
 Variable
 Non Directional
 Low E.N

Secondary Bond Energy
 Smallest
 Directional
 Interaction Polymer
 Intermolecular

Ceramic Bond Type
Ionic and Covalent

Polymers Bond Type
Covalent and Secondary

Ceramics Bond Energy and Properties
 Large Melting Temperature
 Large Energy
 Small Thermal Coeffecient

Metals Bond Energy and Properties
 Moderate Melting Temperature
 Moderate Energy
 Moderate Thermal Coeffecient

Polymers Bond Energy and Properties
 Small Melting Temperature
 Small Energy
 Large Thermal Coefficient

Ceramics Density and why
 Mid Density
 Less dense packing
 Lighter elements

Metals Density and why
 High Density
 Close packing
 Often Large atomic mass
 Often same element = same radii
 Simplest crystal structure

Polymers Density and why
 Low density
 Low packing (amorphous)
 Lighter elements (CHO)

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

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

Hexagonal Close Pack Properties
 17 atoms
 Centre plane
 Centre top and bottom face
 Each corner
 Equiv no. of atoms = 6
 APF = 0.74

Equiv no. of atoms for each type

Atomic Packing Factor Equation
 Volume of atoms in unit cell divided by volume of unit cell
 0.52 for a simple cubic structure

APF for each type
 BCC  0.68
 FCC 0.74
 HCP  0.74

Density Equation
nA/(Vc*Na)

Single vs Polycrystal Properties
 Single:
 Properties vary with direction ANISOPTROPIC
 Poly Crystal:
 If grains random: ISOTROPIC
 If grains textured: ANISOTROPIC

Isotopic
When properties of material are independent of direction

Anisotropic
When properties are different

Bulk Modulus (K)
Measure of substance;s resistance to uniform compression. The pressure increase need to to deform

Shear Modulus (G)
aka Modulus of rigidity, the ratio of shear stress to shear strain

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= (3K2G)/(GK +2G)
 E = 2G(1+V)

Poisson's ration for metals ceramics and polymers
 Metals V= 0.33
 Ceramics V=0.25
 polymers V=0.40

Ductility
Plastic tensile strain @ failure
 %EL = LFl0/l0 x100
 %RA = A0AF/A0 x 100

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

Brittle energy
Elastic Energy

Ductile Energy
Plastic and elastic energy

Resilience (Ur) definition and equation
 Ability to store energy
 Energy require to reach yield point
Ur = 1/2 Stress(y) Strain (y)

Yield Strength
Stress at which noticeable (strain =0.002) plastic deformation has occurred.

Proportional limit
Point on graph between linear and non linear behaviour

Elastic Limit (yield point)
Point between elastic and plastic behaviour, max stress for full recovery

Yielding
Strain continues with little or no increase in strength

Ultimate stress
Max strength on curve

Tensile Strength
 Max strength on curve.
 Metals: Occurs when noticeable necking starts
 Polymers occurs when polymer backbone chains are aligned and about to break

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

Fracture Mechanisms
 Ductile Fracture
 Occurs with plastic deformation
 Brittle Fracture
 Little or no plastic deformation
 Catastrophic
 Sudden failure when static stress = strength

Stress corrosion cracking
and requirements
Form of cracking produced by chemical attack at tip of stress crack.
 1) Susceptible material
 2) Environment
 3) Stress

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

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

Time Dependent Response
Amount of deformation depends of duration of load

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

Viscous flow
Amorphous materials can be under short term flow

Primary creep
Slope decreases with time

Secondary creep
steady state

Tertiary creep
Creep rate increase with time

Relaxation
Stresses dissipate with time.

Viscoslasticity
Exhibits both viscous and elastic response. Delayed response to load

Rheology definition and 3 elements
Study of flow of materials. Provides relationship between deformation and load over time.

Hookean
Perfectly elastic material. Response to force is instantaneous and deformation completely recovered.

Newtonian
Perfectly viscous behaviour. Force is proportional to length of time of applied force/ When removed, element retains deformed shape.

St Venant
Deformation only occurs once the force exceeds tat which resists deformation

Flow processes
 Concrete has resistance to flow yield stress.
 Stickiness  plastic viscosity (mew)  slope of line

Material variability (3)
 Inherent Variability
 Variance caused by sampling method
 Variance associated with the way test is conducted

Sampling must be (3)
 randomly selected
 representative of whole lot
 Quantify the characteristics of population