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Understanding Fatigue Initiation and Dislocation Behavior in Annealed Copper via Digital Image Correlation

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This project explores the intricate mechanisms of fatigue initiation, which constitutes about 90% of total fatigue life but remains poorly understood. Utilizing experimental fatigue testing methods proves to be costly. Employing Digital Image Correlation (DIC), we analyze mechanical performance and dislocation behaviors in high-conductivity annealed copper, including microstructural changes through Electron Backscatter Diffraction (EBSD). Our findings focus on the evolution of surface strain distribution across various cyclic loading scenarios to enhance life prediction models in mechanical components.

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Understanding Fatigue Initiation and Dislocation Behavior in Annealed Copper via Digital Image Correlation

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  1. 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

  2. Oxygen Free High Conductivity Annealed Copper Initially strain free Simple FCC structure Single phase material 99.95+% purity 5

  3. Mechanical test rig setup 6

  4. Image of Spray Pattern for Digital Image Correlation 3.3mm 7 3.3mm

  5. Digital Image Correlation Before tensile test After tensile test 8

  6. Vector Map of Pattern Displacements 144 3.3mm 120 Displacement /pixel 9 3.3mm

  7. Cyclic Strain Map for 20Cycles 1.6 0.8 0 10

  8. 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

  9. Cyclic Strain Map for 2000 Cycles 1.6 0.8 0 12

  10. 1.6 Cyclic Strain Maps from Digital Image Correlation 0.8 20 cycles 200 cycles 2000 cycles 0 13 Eyy %

  11. Surface Relief – Appearance of Persistent Slip Bands PSBs PSBs Grain Boundary 14 After 2200 cycles 100μm

  12. Kikuchi Diffraction Pattern 15

  13. Kikuchi Diffraction Pattern 16

  14. EBSD Image of Microstructure after 200 Cycles 17

  15. Geometrically Necessary Dislocation GND Distribution 200 cycles ρGND 10μm 18

  16. 2000 cycles ρGND 10μm 19

  17. 0 2 20 200 2000 cycles Scalebar 25μm 16 ρGND 20 12

  18. 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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