Transcript Rasterelektronenmikroskopie - uni

Grain Boundaries
high-angle grain boundary (Q>15°)
Ni-Base Superalloy Waspalloy
low-angle
grain boundary
50µm
Properties of Materials
•
Mechanical Properties
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Elastic
Plastic
Viscoelastic
Creep
Testing methods
The Tensile Test
stress s=F/A
Force
specimen
A
l l0
strain e=l-l0/l0
The Tensile Test
Elastic Deformation
energy/
force
repulsive
F
Force=dE/dr
r0
r0
distance r
net energy
attractive
F
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!
E  2G1  
Yield Strength sY
0.002 strain offset
yield-point phenomenon
(C steels, dislocations are pinned by C)
sY
sY
The Stress-Strain Curve
true stress
stress
engineering stress
necking
strain
Materials Selection Charts
Strength
[MPa]
Density [1000kg/m³]
Plastic Deformation – Dislocation Glide
shear stress t
Plastic Deformation – Dislocation Glide
=>macroscopic
deformation
Plastic Deformation – Dislocation Glide
dislocation motion
Plastic Deformation
F
shear stress t


F
Some concluding words on dislocations
•
Strengthening mechanisms
• Grain size reduction (Hall-Petch equation)
s y  s0  k y d
• Solid solution strengthening
• Strain hardening
Mechanical testing
•
Hardness
• Vickers
• Rockwell
• … Nanoindentation
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Ductility
Toughness
Creep
Fatigue
Vickers Microhardness Testing
length of the diagonals d1 and d2
Rockwell Hardness Testing (HRC)
scale
indenter
(120° diamond pyramid)
specimen
Ductility
%RA, percent reduction stress
in area
ductile
brittle
%EL, percent elongation
strain
Charpy Impact Testing
impact energy Av=mg(h-h´)
specific ak=Av/A0
hammer
(DIN 50115)
T-Dependence of Av
BDTT
Cleavage Fracture at Low
Temperatures
Deformation at Elevated
Temperatures: Creep
e
Creep Testing
de/dt
specimen
furnace
weights
e
t
strain gauge
Fatigue Loading during Service
Fatigue Testing
Fatigue Testing
rotating-bending
push-pull
load
counter
servohydraulic actuator
Fatigue-Testing: The S/N Diagram
stress amplitude [MPa]
Biegespannungs [MPa]
1200
1100
1000
900
800
total life design
700
600
500
Dauerfestigkeit
fatigue limit
400
1000
10000
100000
1000000
Bruchlastspielzahl N B
cycles
to failure N
10000000
100000000
Fracture Mechanics
KIc represents resistance to brittle fracture [MPam0.5]
modeI
modeII
F
F
m
Determination of KIc using Compact
Tension (CT specimens)
force
extensometer
displacement