Grain Boundaries

1
Grain Boundaries
high-angle grain boundary (Qgt15)
2
Properties of Materials

• Mechanical Properties
• Elastic
• Plastic
• Viscoelastic
• Creep
• Testing methods

3
The Tensile Test
4
The Tensile Test
5
Elastic Deformation
distance r
6
Elastic constants (isotropic case)

• Stress strain / shear stress shear
  strain
• Youngs modulus
• Shear modulus
• Poisson ratio
• In order to completely describe the elastic
  behavior of a solid 2 of these constants need to
  be known!

7
Yield Strength sY
yield-point phenomenon (C steels, dislocations
are pinned by C)
0.002 strain offset
8
The Stress-Strain Curve
stress
necking
strain
9
Materials Selection Charts
Strength MPa
Density 1000kg/m³
10
Plastic Deformation Dislocation Glide
11
Plastic Deformation Dislocation Glide
gtmacroscopic deformation
12
Plastic Deformation Dislocation Glide
dislocation motion
13
Plastic Deformation
shear stress t
14
Some concluding words on dislocations

• Strengthening mechanisms
• Grain size reduction (Hall-Petch equation)
• Solid solution strengthening
• Strain hardening

15
Mechanical testing

• Hardness
• Vickers
• Rockwell
• Nanoindentation
• Ductility
• Toughness
• Creep
• Fatigue

16
Vickers Microhardness Testing
17
Rockwell Hardness Testing (HRC)
scale
indenter (120 diamond pyramid)
specimen
18
Ductility
stress
strain
19
Charpy Impact Testing
impact energy Avmg(h-h) specific akAv/A0
hammer
(DIN 50115)
20
T-Dependence of Av
21
Cleavage Fracture at Low Temperatures
22
Deformation at Elevated Temperatures Creep
23
Creep Testing
24
Fatigue Loading during Service
25
Fatigue Testing
26
Fatigue Testing
rotating-bending
push-pull
load
counter
servohydraulic actuator
27
Fatigue-Testing The S/N Diagram
stress amplitude MPa
cycles to failure N
28
Fracture Mechanics
KIc represents resistance to brittle fracture
MPam0.5
29
Determination of KIc using Compact Tension (CT
specimens)