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