Fatigue initiation
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Fatigue Initiation . Makes up some 90% of the total fatigue life Little has been understood about it Experimental fatigue testing of components is very costly. Image - Wikipedia. 3. Oxygen Free High Conductivity Annealed Copper. Initially strain free Simple FCC structure

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Fatigue Initiation

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Fatigue initiation

Fatigue Initiation

  • Makes up some 90% of the total fatigue life

  • Little has been understood about it

  • Experimental fatigue testing of components is very costly

Image - Wikipedia

3


Oxygen free high conductivity annealed copper

Oxygen Free High Conductivity Annealed Copper

Initially strain free

Simple FCC structure

Single phase material

99.95+% purity

5


Mechanical test rig setup

Mechanical test rig setup

6


Fatigue initiation

Image of Spray Pattern for Digital Image Correlation

3.3mm

7

3.3mm


Fatigue initiation

Digital Image Correlation

Before tensile test

After tensile test

8


Fatigue initiation

Vector Map of Pattern Displacements

144

3.3mm

120

Displacement /pixel

9

3.3mm


Cyclic strain map for 20cycles

Cyclic Strain Map for 20Cycles

1.6

0.8

0

10


Cyclic strain map for 200 cycles

Cyclic Strain Map for 200 Cycles

1.6

1.6

0.8

0

1.6

0.8

0

1.6

0.8

0

0.8

0

11


Cyclic strain map for 2000 cycles

Cyclic Strain Map for 2000 Cycles

1.6

0.8

0

12


Fatigue initiation

1.6

Cyclic Strain Maps from Digital Image Correlation

0.8

20 cycles

200 cycles

2000 cycles

0

13

Eyy %


Fatigue initiation

Surface Relief – Appearance of Persistent Slip Bands PSBs

PSBs

Grain

Boundary

14

After 2200 cycles

100μm


Kikuchi diffraction pattern

Kikuchi Diffraction Pattern

15


Kikuchi diffraction pattern1

Kikuchi Diffraction Pattern

16


Ebsd image of microstructure after 200 cycles

EBSD Image of Microstructure after 200 Cycles

17


Fatigue initiation

Geometrically Necessary Dislocation GND Distribution

200 cycles

ρGND

10μm

18


Fatigue initiation

2000 cycles

ρGND

10μm

19


Fatigue initiation

0

2

20

200

2000

cycles

Scalebar

25μm

16

ρGND

20

12


Project overview

Project Overview

Digital Image Correlation

Evolution of surface strain distribution

Mechanical testing

and

empirical lifing

Dislocation accumulation

High resolution EBSD map

Crystal Plasticity Simulation

Physical understanding

and

Improved life prediction

21


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