Midterm 265 Flashcards
(208 cards)
1
Q
Engineering Stress (σ)
A
Force per unit area - σ = F/A - from axial loading (tension/compression) - Pa = N/m²
2
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Engineering Strain (ε)
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Change in length per unit of original length - ε = Δl/l - unitless
3
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Shear Stress (τ)
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Shear force per unit area - τ = F/A - Pa = N/m²
4
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Shear Strain (γ)
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Change in length per unit of original length caused by shear force - γ = tan(θ) = w/l - θ is angle of shear deformation
5
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Elastic Deformation
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Stress-strain relationship is proportional upon loading/unloading, not permanent, caused by small changes in atomic spacing and stretching of atomic bonds
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Linear Elastic Deformation
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Straight-line relationship between stress and strain
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Non-Linear Elastic Deformation
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Nonlinear (curved) relationship between stress and strain
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Modulus of Elasticity (E)
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Slope of the linear elastic region of the stress-strain curve - E is the modulus of elasticity (Young’s Modulus)
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Poisson’s Ratio (ν)
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Ratio of axial to lateral strain - ν = -εx/εz = -εy/εz - z (axial direction), x+y (lateral directions)
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Shear Modulus (G)
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Slope of the shear stress versus shear strain curve in the elastic region - G = τ/γ
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Isotropic
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Having material properties that are independent of direction and the same in each direction
12
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Relationship between E and G (Isotropic Materials)
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E = 2G(1 + ν)
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Anisotropic
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Elastic material properties depend on crystallographic direction; more parameters are required to describe behavior
14
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Polycrystalline Materials Assumption
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Crystal orientation is often random; isotropic material behavior can be assumed
15
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Plastic/Elasto-plastic Deformation
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Stress-strain relationship upon loading/unloading is non-proportional; bonds are broken and new bonds are made
16
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Proportional Limit (P)
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Defines transition from linear to non-linear elastic behavior; somewhere below yield stress - MPa
17
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Yield Stress (σy or fy)
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Defines the transition between elastic and plastic behavior; important design parameter
18
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Determining Yield Stress
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0.2% rule - parallel line drawn through point corresponding with 0.002 strain at zero load, intersection with stress-strain curve is taken as yield stress
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Strain Hardening
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Further increase in stress in plastic region
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Ultimate Tensile Strength (UTS) (σu or fu)
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Maximum tensile stress
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Necking
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Localized narrowing of specimen after ultimate tensile strength (UTS)
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Fracture
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Total failure of the specimen; fracture strength = stress at fracture
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Strain Gauges
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Devices that convert tension and compression forces that can be converted into resistance
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Load Cell
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Arrangement of four strain gauges arranged in a Wheatstone bridge
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True Stress (σT)
σT = σE(1+εE)
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True Strain (εT)
εT = ln(1+εE)
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True vs Engineering σ + ε
Approximation is good enough under normal conditions; questionable after ultimate tensile stress due to necking
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Ductility
How much plastic deformation a material can undergo before fracture - measured as %EL
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Percent Elongation (%EL)
%EL = ([lf - lo]/lo) - percentage of plastic strain at fracture, lo (initial strain gauge length), lf (gauge length after fracture)
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Percent Reduction (%RA)
%RA = ([Ao - Af]/Ao) - percent reduction in x-section area, doesn't depend on a gauge length
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Brittle
Materials that fracture with little deformation
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Resilience
Capacity of a material to absorb energy during elastic deformation
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Modulus of Resilience (Ur)
Strain energy per unit volume required to load a material up to the point of yielding
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Ur Assuming Linear Elastic Behaviour
Ur = 0.5σyεy
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Toughness
Capacity of a material to absorb energy up to fracture; area under the stress-strain curve up to fracture
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Hardness
A measure of material resistance to local penetration or scratching
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Ways to Measure Hardness
Moh's scale, Brinell hardness number (HB), Rockwell hardness tests
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Moh's Scale
Based on the ability of one material to scratch softer material; scale of 1-10
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Brinell Hardness Number (HB)
Measure of the size of indentation made from a 10mm diameter steel/tungsten carbide sphere under load
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Rockwell Hardness Test
Determined by measuring depth of penetration of indenter subjected to a prescribed load
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Time-Dependent Deformations
Anelastic deformation, creep
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Anelastic Behaviour
Time dependent elastic behaviour; time needed for full rebound upon unloading
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Creep
Permanent time-dependent deformation; visco-elastic behaviour
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Fracture (Ductile/Brittle)
Separation of a body into two or more pieces
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Ductile Fracture
Evidence of plastic deformation; necking, cup + cone surface, irregular fibrous appearance
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Stages of Ductile Fracture
1. Formation of microvoids, 2. Coalescence of microvoids, 3. Crack propagation, 4. Fracture
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Brittle Fracture
No sign of plastic deformation; little to no prior deformation, rapid crack propagation occurs, grainy texture (change in cleavage planes), breaking of atomic bonds
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Charpy V-Notch Test
Means of determining impact energy or 'notch toughness'; impacting specimen with a weighted pendulum, causing fracture at notch, measure of how far pendulum continues to swing beyond point of impact
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Purpose of Impact Fracture Testing
Model conditions under which 'brittle fracture' is most likely; low temp, high strain rate + triaxial stress state
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Ductile to Brittle Transition Temp
Determined from impact fracture test; transition is pronounced for low strength steels that have a BCC crystal structure
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Design Against Ductile Fracture
Limit the load level so that: σ < Fy --> P < A*Fy
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Factor of Safety (Ductile Fracture)
P < [A*Fy]/f.s., where f.s. > 1; the less that is known about parameters, the bigger f.s. should be
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Limit States Design Approach
±dPd + ±lPl < ¦AFy, where ± = load factor (> 1), ¦ = resistance factor (< 1), d = dead loads, l = live loads
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Stress Concentration Factor (σm)
For an elliptical hole - σm = (1 + 2sqrt(a/Δ))σo, a = 1/2 of hole width, Δ = notch radius
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Stress Intensity Factor (K)
Measure of the 'crack driving force' - K = Yσsqrt(π*a), Y = correction factor
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Material Fracture Toughness (Kc)
Material property affected by: 1. temperature, 2. strain rate, 3. grain size
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Fracture Mechanics-Based Design
K1c > Yσsqrt(π*a), K1c refers to mode 1 crack
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Mode 1 Fracture
Crack that results in an opening
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Mode 2 Fracture
Fracture caused by sliding (shearing)
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Mode 3 Fracture
Fracture caused by tearing (shearing)
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Correction Factor (Y)
Takes into account: true crack shape, effect of finite plate dimensions, effect of a non-uniform stress distribution
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Rheological Models
Used to model mechanically the time dependent behaviour of materials
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3 Basic Elements of Rheological Models
1. Hookean, 2. Newtonian, 3. St. Venant - combined in series or parallel to define material behaviours
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Hookean Element
Represents a perfectly linear elastic material - deformation is completely recovered following unloading, modeled as a linear spring, deformation if proportional to force F by a constant M
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Newtonian Element
Represents a perfectly viscous material - deformation remains following unloading, modeled as a dashpot/shock absorber, deformation is proportional to amount of time force is applied
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St. Venant Element
Represents the force required to overcome the static friction - modeled as a sliding block on friction, unrealistic element and is always combined with other basic elements
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Maxwell Model
Total deformation = sum of deformation of individual elements - made of a spring and dashpot element - in series
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Kelvin Model
Total deformation = sum of deformation of individual elements - made of a spring and dashpot element - in parallel, force starts in dashpot and ends up in the spring --> stop deforming
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Burger's Model
Shows 3 phases of behaviour: 1. Instantaneous deformation, 2. Combined deformation, 3. Continued constant deformation - combines Maxwell and Kelvin models in series
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Prandtl Model
Represents elastic-perfectly plastic materials - when small load is applied, material responds elastically until it reaches yield point, after that material exhibits plastic deformation - combines St. Venant and Hookean elements in series
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Strain Hardening Power Law
σT = K*εT^n - K and N are constants
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Fatigue
Failure at relatively low stress levels of structures that are subjected to cyclic stresses - formation of cracks as a result of repeated application of loads - fails at stress levels less than tensile strength - with no prior warning
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3 Stages of Fatigue Failure
1. Crack initiation, 2. Crack propagation, 3. Final failure
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Crack Initiation
Cracks normally initiate at stress concentrations - cyclic loading produces microscopic surface discontinuities due to dislocation slip
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Crack Propagation
Crack surface characterized by striations - corresponds with crack growth per cycle, can be counted to estimate the number of cycles to grow cracks from one depth to another
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Final Failure
Occurs rapidly once crack reaches critical size - can be ductile or a brittle fracture
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Stress Cycles (N)
Unit of measure for determining when fatigue failure will occur
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S-N Curve Approach
Conducting fatigue tests in a lab - plot the results as log(σ) vs. log(N) - S-N curve is the line of best fit of the data, the higher the stress range -> lower fatigue life
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Fatigue Life
Number of cycles (N) until failure
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Fatigue Strength
Stress range Δσ to cause failure
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Low Cycle Fatigue
N = 10^4 to 10^5 - high stress range - some plastic deformation
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High Cycle Fatigue
N > 10^5 - low stress range - elastic loading only
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Fatigue Limit
Stress range where fatigue life is practically infinite - ferrous alloys have a fatigue limit, non-ferrous alloys do not
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Factors Affecting Fatigue Life
1. Stress range, 2. Mean stress level, 3. Surface conditions, 4. Stress concentration, 5. Surface treatment - polishing (smoother), grinding (removes defects), shot peening (increases fatigue life, decreases mean stress)
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Fatigue Life (Notch Effects)
Fatigue life decreases with notch sharpness - notch sharpness increases Kt - fillet
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Miner's Sum
Used to predict fatigue life under variable amplitude loading conditions - D = Σni / Ni - ni = actual number of cycles at given stress range, Ni = number of cycles that would cause failure at stress range, failure: D > 1
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Cycle Counting Methods
1. Rainflow, 2. Reservoir, 3. Range-mean
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S-N Curves - Pros
Simple, widely used - curves can be refined over time with new test results - considers crack initiation + propagation
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S-N Curves - Cons
Gives no information about crack size/crack growth rate vs. time - can't be used to evaluate remaining fatigue life when a crack is detected or to determine optimal inspection frequency
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Where Are Fatigue Cracks Most Likely to Form?
At the welds, which contain defects + are located at sudden changes in geometry
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3 Types of Primary Chemical Bonds
1. Ionic, 2. Covalent, 3. Metallic - determined by valence electrons
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Net Force (F) Between 2 Atoms
Fn = Fa + Fr - Fa = attractive forces, Fr = repulsive forces at equilibrium - Fa + Fr = 0 --> Force (F) vs. Atomic Spacing (r)
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Potential Energy (E) Between 2 Atoms
E = +F dr - net energy --> En = +Fn dr = +Fa dr + +Fr dr --> En = (-A/r) + (B/r^n) --> Potential Energy (E) vs. Atomic Spacing (r)
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Ionic Bond
Between metallic and non-metallic elements - predominant bonding type in ceramic materials - non-directional - brittle, insulative, strong
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Bonding Energy (Ionic Bonds)
Attractive energy: Ea = -A/r - A = constant, repulsive energy: Er = B/(r^n) - B = constant - n = 8
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Covalent Bond
Electrons are shared between neighboring electrons - between non-metallic atoms - polymeric materials - directional - large range in bond strength --> # of bonds possible = 8 - N' --> N' = # of valence electrons
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Metallic Bond
Electrons are not associated with a particular atom, free to drift through entire metal - non-valence electrons and nuclei form ionic cores w/ net positive charge - free electrons act as a glue to hold ion cores together - non-directional - high electrical + thermal conductivity
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Secondary Bonds
Van Der Waals - generally very weak bonding energy - no electrons are exchanged/shared
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Fluctuating Dipole Bonds
Electrons moving within an atom - when 2 stable atoms are close - they may interact cooperatively
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Polar Molecule-Induced Dipole Bonds
When a polar molecule is bonded with another polar molecules, opposite end - responsible for high boiling points
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Potential Energy (E)
Measure of the separation resistance of adjacent atoms - measure of material stiffness - in the same range for ceramics + metals (non directional bonding) - weaker for polymers (directional)
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Material Structures
1. Crystalline structures, 2. Non-crystalline structures, 3. Amorphous
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Crystalline Structures
Atoms in repeating pattern over large atomic distances - atoms position themselves upon solidification
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Unit Cells
Small repeating entities based on lines of symmetry
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Coordination #
# of atoms touching a given atom
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Atomic Packing Factor
Volume of atoms in unit cell/ total unit cell volume
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Parameter 'a'
Length of cube side
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Parameter 'R'
Atomic radius
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Most Common Crystal Structures
1. Face centre cubic (FCC), 2. Body centre cubic (BCC), 3. Hexagonal close-packed (HCP)
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Face Centre Cubic (FCC)
Cubes with atoms at each corner and at centres of each face - ie: aluminum, copper, nickel, silver - a = 2.828*R - n = 4 whole atoms/unit cell - coordination # = 12 - APF = 0.74
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Body Centre Cubic (BCC)
Cube with atoms at each corner and one atom at centre - ie: iron, chromium, tungsten - a = 2.309*R - n = 2 atoms/unit cell - coordination # = 8 - APF = 0.68
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Hexagonal Close Packed (HCP)
Hexagonal unit cell - ie: zinc, titanium, cobalt - n = 6 atoms/unit cell - coordination # = 2 - APF = 0.74
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Theoretical Density Calculation
Á = (nA)/(VcNa) - Á = density - n = # atoms per unit cell - A = atomic weight - Vc = unit cell volume - Na = avogadro's number
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Chemical Impurities
Solid solutions contain impurity atoms/ions which alter the structural regularity of materials - always present in real materials
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Types of Chemical Impurities
1. Substitutional, 2. Interstitial
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Hume-Rothery Rules for Substitutional Solid Solutions
1. <15% difference in atomic radius, 2. Same crystal structure, 3. Similar electronegativities, 4. Similar valence - if one rule is violated, only partial solubility is possible
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Interstitial Impurities
Difference between atom sizes is large - solubility is limited in this case
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Types of Defects
1. Point, 2. Line, 3. Planar defects
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Point Defects
Occur due to thermal vibration of atoms above absolute zero - vacancy defects, self-interstitial defects
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Linear Defects
Associated primarily with mechanical deformation - referred to as 'dislocations'
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Types of Linear Defects
1. Edge, 2. Screw, 3. Mixed
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Burger's Vector
Displacement vector necessary to close mxn loop around defect
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Edge Dislocation
Burger's vector --> perpendicular to dislocation line
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Screw Dislocation
Burger's vector --> parallel to dislocation line
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Mixed Dislocation
Burger's vector --> fixed in space
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Types of Planar Defects
1. Material surfaces, 2. Grain boundaries, 3. Tilt boundaries, 4. Twin boundaries
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Material Surfaces
Atoms not bonded to maximum number of neighbours - higher energy state (surface energy) - materials tend to minimize surface energy - minimum = surface area/volume
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Grain Boundaries
As crystal grows, it establishes its own orientation in space - more difficult for last atom to take up a position --> results in transition zone (grain boundary) --> atoms are more strained (higher energy)
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Tilt Boundaries
Accommodated by a few isolated edge dislocations
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Twin Boundaries
Low energy state since boundary atoms occupy normal atom positions on both sides of boundary - produced by applied mechanical shear force
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Diffusion
Material transport by atomic motion
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Mechanisms for Diffusion in Metals
1. Vacancy diffusion, 2. Interstitial diffusion
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Vacancy Diffusion
Interchange of atoms between normal lattice positions + adjacent vacancies
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Interstitial Diffusion
Migration of atoms from one interstitial position to an adjacent one
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Fick's First Law (Steady State)
J=-D(dC/dx) - J = diffusion flux [kg/m²*s] - D = diffusion coefficient [m/s²] - C = concentration [kg/m³] - x = distance within solid [m]
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Fick's First Law (for Linear Concentration Profile)
dC/dx = Δc/Δx = (Ca - Cb)/(xa-xb) - C = concentration [kg/m³] - x = distance within solid [m]
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Fick's Second Law (Non-Steady State)
(Cx - Co)/(Cs - Co) = 1-erf[x/2sqrt(D*t)] - C = concentration [kg/m³] - x = distance within solid [m] - D = diffusion coefficient [m/s²] - t = time (s) - erf = gaussian error function
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Plastic Deformation (in Perfect Crystals)
Can be explained by the 'slip' movement or large number of dislocations - all metals + alloys contain some dislocations introduced during solidification - yielding of a crystal is caused by shear stresses
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Peierls-Nabarro Stress
Stress required for dislocation motion - σ = GEXP(-2π*a/[(1-ν)*b]) - a = b
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Direction of Dislocation Motion
Edge dislocations: parallel to the slip direction, Screw dislocations: perpendicular to the slip direction, Mixed dislocations: inbetween
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Characteristics of Dislocations
1. Strain fields exist around dislocations --> affects mobility of dislocations + ability to multiply, 2. Strain fields present for: Edge dislocations: tensile, compressive + shear strains, Screw dislocations: only shear strains, 3. During plastic deformation the number of dislocations increases dramatically as a result of: - dislocations multiplying + forming grain boundaries - surface irregularities - internal defects
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Plastic Deformation (Polycrystalline Materials)
In each grain of a polycrystalline material, there are preferred slip planes in the crystal structure - direction of pref. slip plane varies from one grain to another • overall distortion of the material is due to the distortion (elongation) of individual grains • during deformation, grain boundaries do not come apart - neighbouring grains constrain each other • polycrystalline materials tend to be stronger than their single-crystal equivalents • fine grain materials tend to be stronger
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Strengthening Mechanisms
- Dislocations generated through plastic slip - dislocation strain interactions are repulsive - dislocations interact, interfere + pile up - dislocation movement is obstructed by other dislocations, impurities + grain boundaries - strain hardening results
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Results of Strain Hardening
Upon unloading, dislocation movement cannot be reversed - when a load is reapplied, no plastic deformation occurs until previous max stress is reached --> yield stress increases
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Degree of Cold Work
%CW = [(Ao-Ad)/Ao] - Ao = original, Ad = deformed area
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Purpose of Strain Hardening
Enhance the yield strength of metals during fabrication
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Methods of Work Hardening
1. Tensile pre loading, 2. Cold rolling, 3. Forging, extrusion + drawing
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How Do Grain Boundaries Strengthen Materials
--> provide resistance to dislocation movement - stronger than coarse grained materials b/c larger boundary area
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How to Regulate Grain Size
By controlling the rate of solidification/annealing
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Solid Solution Strengthening
High purity metals = weaker than metals w/ impurities --> b/c they form a substitutional/interstitial solid solution + obstruct dislocation movement
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Substitutional Impurities
Smaller impurity --> tensile lattice strains, Larger impurity --> compressive lattice strains
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Annealing
Process of reheating to return the material properties of cold worked metal to return to its pre-worked state
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Annealing Process
1. Recovery, 2. Recrystallization, 3. Grain growth
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1. Recovery
Thermal energy is supplied to the cold-worked metal --> causes rearrangement of dislocations into lower energy configurations through atomic diffusion - rate of diffusion is dependent on temperature - accompanies by reduction in σy + increase in ductility --> # of dislocations decreases
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2. Recrystallization
New strain-free equiaxed grains, w/ lower dislocation density are formed - driving force = difference in internal energies of strained + unstrained materials - new small grains begin to form + grow until it completely consumes the parent material - accompanied by further reduction in σy + increase in ductility
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3. Grain Growth
Strain-free grains continue to grow if left at an elevated temperature - driving force = increase in grain size resulting in a decrease in the total grain boundary area --> reduction in total energy - results in decrease in strength results
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Equilibrium Phase Diagram
Material properties depend on atomic + microscopic structure - tool for explaining the development of microstructure - solutions consist of components - (solutes + solvents consist of pure metal + compounds)
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Phase
A homogeneous, physically/chemically distinct region of matter
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One Component Phase Diagrams
3 controllable parameters 1. Temperature - plotted, 2. Pressure - plotted, 3. Composition - fixed - data is determined experimentally
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Invariant Point
Point where all 3 phases are in equilibrium
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Two Component (Binary) Phase Diagrams
Isomorphous (complete solid solution) systems - 2 components (A+B), fully soluble - pressure is held constant @ 1atm
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Binary Phase Diagrams: Possible Phases
- Liquid (L), - Solid (α), - Liquid + Solid (L + α)
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Eutectic Systems
- No solubility 2 components (A + B), not soluble possible phases: 1. Liquid (L), 2. Liquid + Solid (L + A), 3. Liquid + Solid (L + B), 4. Solid (A + B)
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Eutectic System - Some Solubility
2 components (A + B), partially soluble α - mostly A, β - mostly B possible phases: 1. Liquid (L), 2. Liquid + Solid (L + α), 3. Liquid + Solid (L + β), 4. Solid (α + β)
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Solus Line
Line between 2 solid phases - ie. between α + β
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Ferrite (α iron)
Exists at room temperature - stable - BCC crystal structure - magnetic, soft, ductile
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Austenite (γ iron)
Pure iron transforms into austenite at 912° C - FCC crystal structure - non-magnetic - not stable below 727°C
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Ferrite (δ iron)
Forms at 1394° C, melts at 1538 °C - BCC crystal structure
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Cementite/Iron Carbide (Fe3C)
Forms at concentration of 6.70% carbon, very hard + brittle - metastable
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Metastable
Gradually transforms into α iron + graphite
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Iron-Carbon Alloy Types
1. Iron --> 0-0.008% C, 2. Steel --> 0.008-2.14% C, 3. Cast iron --> 2.14-6.7% C
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Development of Microstructure
1. Eutectic point, 2. Eutectoid point
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Eutectoid Cooling
Results in pearlite
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Pearlite
Layers of ferrite and cementite
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Hypo-eutectoid Cooling
Primary/pro-eutectoid α + pearlite
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Hyper-eutectoid Cooling
Primary/pro-eutectoid cementite + pearlite
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Isothermal Transformation (T-T-T) Diagrams
Time-temperature-transformation diagrams - used to predict phase transformations while temperature is held constant
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Iron-Carbon Eutectoid Reaction
Diffusional reaction - rate depends on atom migration which depends on temperature
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Products of Eutectoid Reaction
1. Coarse pearlite, 2. Fine pearlite, 3. Bainite
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Coarse Pearlite
At high temperatures - diffusion rates are higher - atoms travel more + faster - layers are thicker --> resulting in coarse pearlite
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Bainite
Like pearlite, very fine + needle like - not layered - occurs at temperatures below the 'nose' of the isothermal transformation diagram
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Martensite
Forms when austenite is rapidly cooled - non-equilibrium single phase which eventually decomposes into ferrite + cementite - forms when quenching rate is fast enough to prevent carbon diffusion
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Product of Non-diffusional Reaction
Martensite
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Spheroidite
Forms when a steel alloy w/ pearlitic/bainitic microstructure is held for a long time at a temperature below eutectoid temp. - not shown on the T-T-T diagram
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Continuous Cooling Transformation(C-C-T) Diagrams
Modified T-T-T diagrams used to predict transformations under steady cooling by shifting curves down and to the right - longer times and lower temperatures
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Martensite
Quenching produces:
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Faster Cooling Produces
Pearlite + martensite
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Normalizing or 'Air Cooling' Produces
Fine pearlite
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Annealing or 'Furnace Cooling' Produces
Coarse pearlite
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Effects of Non-eutectoid Composition on C-C-T Diagrams
- If a composition other than eutectoid (0.76% C) is used, a proeutectoid phase will also be present - curves corresponding w. the proeutectoid transformation can be shown on T-T-T or C-C-T diagrams
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Effects of Other Alloying Elements on C-C-T Diagrams
Change in the shape of the T-T-T or C-C-T diagrams - ie shifting the nose of the diagram to the right - ie formation of a separate bainite 'nose'
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Tempering
Heat treatment @ 250-650°C - improves ductility + relieves internal stresses or any temp. below eutectoid temperature - used for martensite (too brittle)
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To Make Tempered Martensite
1. Quench to make martensite, 2. Reheat and hold temp. for a period of time
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Increasing Carbon Content Results In
Increase in strength + hardness - decreases ductility
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How Steel is Made
1. Iron ore, coke + lime are mixed in a blast furnace to produce liquid iron, 2. Liquid iron is passed through Basic Oxygen Steelmaking (BOS) furnace - to reduce carbon content, 3. Secondary processing - further cleaning the steel + refine chemical composition, 4. Steel is continuously cast into solid slabs, blooms or billets - hot rolled into more useful shapes
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Final Processing of Steel Includes
- Shaping (cold rolling), - Machining (drilling), - Joining (welding, bolting), - Coating (galvanizing), - Heat treatment (tempering), - Surface treatment (shot peening)
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Advantages of Ferrous Alloys
- High strength to weight ratio --> light structures, - Recyclable, - Abundance of iron, - Relative economy of refining process, - Versatility
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Disadvantage of Ferrous Alloys
- Corrosion susceptible, - Cast iron (cast = brittle, easily melted)
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Wrought Iron
Wrought = easily deformed - low in C content
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Cast Iron
Cast = brittle, but easily melted - high in C content
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Low-Carbon Steel
- Typically pearlite-ferrite microstructure - difficult to form martensite - soft, weak, highly ductile ex: car bodies, structural applications, pipelines
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High Strength Low Alloy (HSLA) Steel
- More corrosion resistant - other alloys compose up to 10% - higher material strength
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Medium-Carbon Steel
- Commonly: tempered martensite microstructures ex: railway wheels + tracks, gears, crank-shafts and other machine parts
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High-Carbon Steel
- Hardest, strongest + least ductile steel - wear resistance, sharp cutting edges possible ex: tool + die steels
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Stainless Steel
- Highly corrosion resistance - can be martensitic, ferritic or austenitic - can be magnetic - cannot be heat treated, only cold worked ex: used in high temp. environments (jet engines)
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Structural Steel Naming
Ex. 350W (very common) yield strength: Fy = 350MPa letters: denote treatment
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Rebar
Steel bars used to reinforce concrete - hot rolled from steel billets
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Steel in Prestressed Concrete
Steel used in prestressing wires + strands have higher strength than structural steel/rebar - high carbon steel and wires are cold worked to achieve required material strength
