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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

Incubation & Nucleation Validation Study

SIPS TIM, October 22nd 2007

Cornell and RPI

slide2
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
outline
Outline
  • Previous Work
    • Incubation Filter
    • Nucleation Damage Metrics
  • Calibration & Validation
    • Objectives
  • Microstructure Replication Process
    • Model Generation
    • Preparation & Analysis
    • Results & Observations
previous work incubation filter
Previous Work: Incubation Filter

ND

RD

Determine particle strength,scr~ KIC / sqrt(particle size)

sp scr

no

yes

slide5
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

slide6
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?
outline1
Outline

7

  • Previous Work
    • Incubation Filter
    • Nucleation Damage Metrics
  • Calibration & Validation
    • Objectives
  • Microstructure Replication Process
    • Model Generation
    • Preparation & Analysis
    • Results & Observations
slide8
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
slide10
Model Generation: Simplified Microstructure Derivatives

No Small Grains @ Distance

Surrounding Grains Only

All Grains

No Small Grains

Small Grains Above/Below

slide12
Preparation and Analysis: Mesh

All grains

Surrounding grains only

slide13
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?

slide14
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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