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

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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

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

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4 p cr no yes RD ND Determine particle strength, cr ~ K IC / sqrt(particle size) Previous Work: Incubation Filter

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

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

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

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8 Physical Data (from Northrop Grumman) Computational Modeling Generate Model Prepare and Analyze Record and Observe SEM OIM Particle Detailed Microstructure 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 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 Microstructure Replication Process

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9 Model Generation: Detailed Microstructure

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

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11 Model Generation: Automated Routine

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12 All grainsSurrounding grains only Preparation and Analysis: Mesh

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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?

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Coarse MeshMedium Mesh xx MPa 100 m 75 m x Surrounding Grains Only All Grains Fine Mesh Results and Observations 14

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