Grain BoundariesGrain Boundaries
Ni-Base Superalloy Waspalloy
50µm
high-angle grain boundary (>15°)
low-anglegrain boundary
Properties of Materials Properties of Materials
• Mechanical Properties
• Elastic• Plastic• Viscoelastic• Creep
• Testing methods
The Tensile TestThe Tensile Test
F o rc e
sp e c im e n
stress =F/A
strain =l-l0/l0
Al 0
l
The Tensile TestThe Tensile Test
Elastic DeformationElastic Deformation
re p u ls iv e
a ttra c tiv e
n e t e n e rg y
e n e rg y /fo rc e
r 0 distance r
r0
F
F
Force=dE/dr
Elastic constants (isotropic case)Elastic constants (isotropic case)
• Stress – strain / shear stress – shear strain
• Young’s modulus• Shear modulus• Poisson ratio
In order to completely describe the elastic behavior of a solid 2 of these constants need to be known!
1G2E
Yield Strength Yield Strength YY 0.002 strain offset yield-point phenomenon
(C steels, dislocations are pinned by C)
Y
Y
The Stress-Strain CurveThe Stress-Strain Curve
stress
strain
necking
engineering stress
true stress
Materials Selection ChartsMaterials Selection Charts
Strength [MPa]
Density [1000kg/m³]
Plastic Deformation – Dislocation GlidePlastic Deformation – Dislocation Glide
shear stress
Plastic Deformation – Dislocation GlidePlastic Deformation – Dislocation Glide
=>macroscopicdeformation
Plastic Deformation – Dislocation GlidePlastic Deformation – Dislocation Glide
dislocation motion
Plastic DeformationPlastic Deformation
shear stress
F
F
Some concluding words on dislocationsSome concluding words on dislocations
• Strengthening mechanisms
• Grain size reduction (Hall-Petch equation)
• Solid solution strengthening• Strain hardening
dk y0y
Mechanical testing Mechanical testing
• Hardness• Vickers• Rockwell• … Nanoindentation
• Ductility• Toughness• Creep • Fatigue
Vickers Microhardness TestingVickers Microhardness Testing
length of the diagonals d1 and d2
Rockwell Hardness Testing (HRC)Rockwell Hardness Testing (HRC)
scale
indenter (120° diamond pyramid)
specimen
DuctilityDuctility
stress
strain
%EL, percent elongation
%RA, percent reduction in area
brittle
ductile
Charpy Impact TestingCharpy Impact Testing
hammer
impact energy Av=mg(h-h´)specific ak=Av/A0
(DIN 50115)
T-Dependence of T-Dependence of AAvv
BDTT
Cleavage Fracture at Low Cleavage Fracture at Low TemperaturesTemperatures
Deformation at Elevated Deformation at Elevated Temperatures: CreepTemperatures: Creep
Creep TestingCreep Testing
sp e c im e n
w e ig h ts
s tra in g a u g e
fu rn a c e
t
ddt
Fatigue Loading during ServiceFatigue Loading during Service
Fatigue TestingFatigue Testing
Fatigue TestingFatigue Testingpush-pullrotating-bending
counter
load
servohydraulic actuator
Fatigue-Testing: The S/N DiagramFatigue-Testing: The S/N Diagram
400
500
600
700
800
900
1000
1100
1200
1000 10000 100000 1000000 10000000 100000000
Bruchlastspielzahl N B
Bie
ge
spa
nn
un
g
[MP
a]
Dauerfestigkeit
stress amplitude [MPa]
cycles to failure N
fatigue limit
total life design
Fracture MechanicsFracture Mechanics
F
F
F
F
m o d e I m o d e II m o d e II I
KIc represents resistance to brittle fracture [MPam0.5]
Determination of Determination of KKIcIc using Compact using Compact
Tension (CT specimens)Tension (CT specimens)
extensometer
force
displacement
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