ENCN221
Card Set Information
Author:
Marciaho
ID:
269337
Filename:
ENCN221
Updated:
2014-04-07 06:26:55
Tags:
ENCN221
Folders:
ENCN221
Description:
ENCN221
Show Answers:
Ionic Bond Energy
Large
Non Directional
High/Low E.N
Covalent Bond Energy
Variable
High 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
BCC =2
FCC=4
HCP =6
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= (3K-2G)/(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 = LF-l0/l0 x100
%RA = A0-AF/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