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Incubation & Nucleation Validation Study

Incubation & Nucleation Validation Study. SIPS TIM, October 22 nd 2007 Cornell and RPI. Eight peer-reviewed journal papers will be produced from the SIPS-related work being completed by Cornell and our M&S colleagues:

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Incubation & Nucleation Validation Study

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  1. Incubation & Nucleation Validation Study SIPS TIM, October 22nd 2007 Cornell and RPI

  2. Eight peer-reviewed journal papers will be produced from the SIPS-related work being completed by Cornell and our M&S colleagues: • January, 2008 – “A geometric approach to creating and meshing statistically accurate finite element models of AA7075-T651 microstructures” • January, 2008 – “A geometric approach to modeling microstructurally small crack fatigue crack formation part I: probabilistic simulation of constituent particle cracking in AA7075-T651” • May, 2008 – “A three-dimensional multiscale procedure for microstructurally small fatigue crack nucleation” • May, 2008 – “A geometric approach to modeling microstructurally small crack fatigue crack formation part II: verification and validation of incubation and nucleation criteria” • July, 2008 – “A geometric approach to modeling microstructurally small crack fatigue crack formation part III: simulation of stage I, intra-granular crack propagation in AA7075-T651” • January, 2009 – “A geometric approach to modeling microstructurally small crack formation, part IV: simulation of stage I, trans-granular crack propagation in AA7075-T651” • March, 2009 – “A geometric approach to modeling microstructurally small crack formation, part V: probabilistic simulation of stage I crack propagation in AA7075-T651” • May, 2009 – “A geometric approach to modeling microstructurally small crack formation, part VI: a probabilistic multiscale method for predicting microstructurally small fatigue life of AA7075-T651

  3. Outline • Previous Work • Incubation Filter • Nucleation Damage Metrics • Calibration & Validation • Objectives • Microstructure Replication Process • Model Generation • Preparation & Analysis • Results & Observations

  4. Previous Work: Incubation Filter ND RD Determine particle strength,scr~ KIC / sqrt(particle size) sp scr no yes

  5. Max. accumulated slip on a single system: Max. accumulated slip on a single plane: Total accumulated slip: Work-based damage: Fatemi-Socie damage: Previous Work: Nucleation Damage Metrics Definitions of relevant slip-based damage metrics: Criterion: Nucleation occurs when Di ≥ Di,0

  6. Calibration & Validation: Objectives Calibrate incubation & nucleation criteria: • Using 1 experimental observation of crack incubation, back calculate the parameter ‘C’ • Using 1 experimental observation of crack nucleation, calibrate the parameter ‘Di,0’ for each damage metric Using 13 additional observations, validate incubation criterion assumptions : • Maximum particle stress is accurately obtained when: • idealizing particle as an ellipsoid • only attaching the surrounding grain • Parameter ‘C’ is a material constant Evaluate nucleation criteria using 5 additional observations: • Do any of the 5 slip-based damage metrics predict nucleation events for all observations?

  7. Outline 7 • Previous Work • Incubation Filter • Nucleation Damage Metrics • Calibration & Validation • Objectives • Microstructure Replication Process • Model Generation • Preparation & Analysis • Results & Observations

  8. Microstructure Replication Process Detailed Microstructure OIM SEM Physical Data (from Northrop Grumman) Particle Particle • Take detailed microstructure from EBSD/OIM • Generate a simplified microstructure derivative based on phenomenological information • Assign crystal plasticity model, with measured orientations, to each grain • Mesh and apply notch strain Computational Modeling • Test effect of simplifying the microstructure by comparing with results from detailed geometry • Record results, check for mesh convergence, and note numerical advantages for each simplified microstructure derivative

  9. Model Generation: Detailed Microstructure

  10. Model Generation: Simplified Microstructure Derivatives No Small Grains @ Distance Surrounding Grains Only All Grains No Small Grains Small Grains Above/Below

  11. Model Generation: Automated Routine

  12. Preparation and Analysis: Mesh All grains Surrounding grains only

  13. Preparation and Analysis: Notch Strain Questions for Northrop Grumman Inc.: What is the exact notch strain for the first load cycle? What is the notch strain history for subsequent load cycles?

  14. Results and Observations sxx MPa Surrounding Grains Only All Grains 75 mm 100 mm Coarse Mesh Medium Mesh Fine Mesh x

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