Post on 19-Dec-2015
Nov. 9, 2006
DDSim: A Next Generation Damage and
Durability Simulator
Presenting: John EmeryAdvising and Supporting: Prof. Tony Ingraffea, John Dailey Jr.,
Gerd Heber, Wash Wawrzynek
funded through NASA’s Constellation University Institutes Project.
2John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Outline for the Talk
The Big Picture & Overview DDSim Level I – Reduced-order filter
InputApproachResults & Performance
Level II – Automated crack insertion ApproachResults
Level III – Multiscale simulationStatistically accurate microstructural geometryMultiscale implementation
Conclusions
3John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
DDSim
Finite element model of structure including boundary/environmental conditions
Material system & pertinent microstructural statistics
Best available physics-based damage models
Random input
Time to failure, N
Probabilistic life prediction
The Big Picture
P
4John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Overview of the Hierarchical Approach
Level I: A fast, analytical, reduced-order filter to determine life-limiting hot-spots in complex structures
Level II: Traditional continuum fracture mechanics, FRANC3D, to compute the life of the structure consumed by growth of microstructurally large cracks (NMLC)
Level III: Multiscale simulation to compute the life of the structure consumed by incubation, nucleation and propagation of microstructurally small cracks (NMSC)
Assumption: Ntotal = NMLC + NMSC
A multiscale approach with 3 hierarchical levels:
5John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Models and Parameters for Fracture and Damage Mechanics
• Models for fatigue crack growth (NASGRO equation*)
• Statistical material data & initial damage size
Database from FEM without damage
• Mesh
• Field information
• Boundary conditions
Stress field contour plot: Rib-stiffened element
*Forman & Mettu, Fracture Mechanics: Twenty-second Symposium, Vol. 1, ASTM STP 1131
A (slide 6)
DDSim Level I: Input
B (slide 9)
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ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Life prediction contour ploton original FE Mesh
(29,072 surface nodes, average ai=2.76e-4 in)
• Analytical solutions & field data from undamaged FEM used to estimate service life limited by damage at a large number of possible origins (mesh nodes).
Key Ideas for Level I:High Volume, High Automation, Probabilistic, &
Conservative First Order Analysis
• These damage origins do NOT become part of the geometrical model in Level I.
• These damage origins do NOT interact with each other.
• These simplifications readily allow parallel processing.
How to map:
Stress Life prediction?• Initial flaw size from statistical
distribution (eg. particle x-sectional area).
Stress field contour plot: x-section A (previous), Rib-stiffened element
DDSim Level I
7John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Conservative SIF History
0.0
30.0
60.0
90.0
0.00 0.10 0.20
a_DDSim b_F3Db_DDSim a_F3D
Crack length, (in)S
tres
s in
tens
ity f
acto
r, (
ksii
n)Principal stress on a
thermomechanically loaded part (courtesy of FAC)
DDSim Level I is designed to provide conservative estimates of K (compared with FRANC3D here).
a
b
8John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Under Fatigue spectrum Nodes (i.e. initial flaw locations): 63,974 Random initial flaws (from particle filter): 10,000 No. of processors @ 3.6GHz w/ 2GB RAM: 16 Min & Max computed life (cylces): 18542 - 99,999 Processing time (hr:mm): 5:48
Level I Results & Performance
Particle diameter, (in)
0
0.25
0.5
0.75
1
1.00E-05 1.00E-04 1.00E-03
Particles
Broken
Pro
babi
lity
of o
ccur
renc
e
Life prediction contour plot w/ 10,000 initial flaws
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ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Fully 3D crack growth simulation at “hot spots”: • Explicit representation of crack surface in FE model geometry• Automatically inserted at “hot spots” determined by Level I analysis
Level I Life prediction contour plot (x-section B slide 5)
Automatically inserted, grown and remeshed crack
DDSim Level II
10John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
0
10000
20000
30000
40000
0.015 0.065 0.115 0.165
Level I, aLevel I, bLevel II, aLevel II, bLevel II, m
Level II Results
Crack paths
b
m
a
Low fidelity NMLC = 803 cycles, High fidelity NMLC = 4070 cycles
Crack length, (in)
N, (
load
cyc
les)
NMLC = 4070
Level I predictions
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ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Representative digital microstructure
With a first order, probabilistic analysis completed, focus on the “hot spots” to increase the accuracy of the NMSC
prediction using:
• Representative digital microstructure • Best available physics • Multiscale simulation• High performance parallel computing
DDSim Level III: Multiscale Simulation
Life contour plot from initial prediction
Focusing on a “hot spot”, rectangular void for PC model
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ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Crack Incubation Crack Nucleation Crack Propagation
Level III: Microstructurally Small Damage
Important geometrical features: Grains Particles
Damage processes and events: (a) Crack incubation process – damage accumulation until the
particle cracks (b) Crack nucleation event – (c) Microstructurally small crack propagation – process of
crack growth within grains and across grain boundaries
a
b
c
10 m
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ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Level III: Current Microstructural Geometry Models
The lumber model (right) approximates the average grain size and aspect ratios of AA 7075 in a randomly assorted stack
The rolled Voronoi model (right) is our most statistically accurate geometry for rolled AA 7075, approximating grain morphology and average size.
The Voronoi model (left) approximates random crystallographic structure of an unrolled alloy
14John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
DDSim Level III: Multiscale Simulation
Life contour plot from initial prediction
Focusing on a “hot spot”, rectangular void for PC model
Multiscale model = Continuum + structure!
Representative digital microstructure
15John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
DDSim Level I provides a high volume, highly automated, probabilistic, and conservative life prediction (Ntotal) for real structures & locates areas of high interest for the Level II & III simulations
Level II uses the current best practice fracture mechanics life predictions methodologies for high fidelity NMLC
The Level III microstructural models incorporate state-of-the-art physics and accounts for microstructural stochasticity for high fidelity NMSC.
DDSim, as a multiscale system, will provide microstructurally educated life predictions for real structures.
Conclusions
Our assumption is: Ntotal = NMLC + NMSC
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ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Safety slides
Intentionally blank
17John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Metallic Composite
0.6 mm
Dissimilar materials…similar microstructural geometrical features
Level III: Microstructural Geometry and Damage
50 mMetallic micrographs courtesy of A. Rollett, CMU.
Composite micrographs from: Nicoletto G., Enrica R., Composites: Part A, 35, 2004, 787 – 795, & S. Stanzl-Tschegg, personal communication
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ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Level III: Particle Crack Incubation Criterion
Affect of grain orientation on particle stress, 3 categories:
High stress orientation Intermediate stress orientation Low stress orientation
xx
High orientation
Low orientation Intermediate orientation
• Particle aspect ratio• Grain orientation• Strain level
Pro
babi
lity Particle Tensile Stress (σxx)
Probability Density Function
Particle Tensile Stress
Pro
babi
lity
19John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Currently, we have these loose ends:
Monte Carlo simulation is feasible for the low fidelity life prediction of DDSim Level I, however, it is NOT feasible for the multi-scale simulation
One microstructural model requires millions of DOF
Required number of samples makes MC intractable
Level II computes the life consumed by continuum length scale damage evolution
Level III computes the life consumed by micro-scale damage evolution
Putting It All Together
Recall our assumption was: Ntotal = Nmacro + Nmicro
20John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Low fidelity life predictor:
DDSim Level I
Low fidelity life prediction
Damage site iterator:
DDSim Level II, Nmacro
Combine conditional probabilities
“predictor”
“corrector”
Multi-scale simulation:
DDSim Level III, Nmicro
Bayesian estimation
)@|( DSaNP imicro
Low fidelity “prior” conditional life cdf
nodes
iiitotalT aPaNPNP )()|()(
)@|( DSaNP imicro
High fidelity “post” conditional life cdf
Random input
High fidelity High fidelity life predictionlife prediction
Putting It All Together
N
P
N
P
N
P
N
P
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ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
3-D Continuum Model 3-D Continuum Field Analysis 3-D Realistic Microstructure Model
Analyze microstructure for to capture
microstructural damage evolution,
update continuum damage state and fields
Apply B.C.’s from Macroscale Model
Simulate damage evolution:steam enhanced delamination
(with models from collaborating CUIP IFST teams)particle debonding/cracking
crystal plasticity/cohesive constitutive modelsintra/intergranular microcracking
Level III: Multi-scale
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ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
Close-Up of Bolt-Holex (ksi)
Continuum Scale
Continuum Model
E=10,500 ksi
=0.33
45.17 ksi
Gather Boundary Conditions and Apply to Polycrystal Model
Polycrystal Model
Polycrystal Scale
x (ksi)
Calculate New Modulus for Each Gauss Point in the Continuum
Model
Grain Boundary Decohered
E=10,500 +/- 1,000 ksi
=0.33
tp=72.5 ksi
Update Stiffness
Level III: Multi-scale, 2D Example
x
y
23John Emery & Tony IngraffeaCornell University
ASME International Mech. Eng. Congress and Expo DDSim: A Damage and Durability Simulator
x
Updated Continuum Model
Smeared Crack
Level III: Multi-scale, 2D Example
x
y