Crack Trajectory Prediction in Thin Shells Using FE Analysis

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Crack Trajectory Prediction in Thin Shells Using
FE Analysis

• 6th International Conference on Computation of
  Shell and Spatial Structures
• Cornell University and NASA Langley Research
  Center
• A.D. Spear1
• J.D. Hochhalter1
• A.R. Ingraffea2
• E.H. Glaessgen3

1 Graduate Research Assistant, Cornell
University 2 Principal Investigator, Cornell
University 3 Grant Monitor, NASA Langley Research
Center
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Outline

• Motivation objectives
• Point-source damage HOW TO LAND SAFELY?
• Fatigue damage HOW MANY MORE FLIGHTS?
• Relevant past work
• Improvements in physics-based modeling
• Incorporating the nano- micro-scales
• Current technical challenges

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Point-source damage HOW TO LAND SAFELY?
Airbus A300 damaged by surface-to-air missile
www.youtube.com/watch?vDUstvXSytRc
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Point-source damage Objectives

• Develop finite element-based analyses to predict
  growth of point-source damage within airframe
  structures under realistic conditions and in
  real-time
• Interface real-time damage assessment with
  control systems to provide a damage-dependent
  flight envelope to restrict structural loads in
  the presence of severe damage

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Point-source damage Technical approach
Generic aircraft component damaged by
surface-to-air missile
Airbus A300 damaged by surface-to-air missile

• Integrate information from on-board sensors to
  characterize damage
• Develop interface with control system

Response surface
Reduced model

• Recast structural component as a lower order
  model (i.e. equivalent plate)
• Get the sensor description of inflicted damage
  and compute updated allowable load in real-time

• Parameterize damage configurations
• Store a response surface of computed allowable
  load given the damage configuration and query in
  real-time

Damaged Area
www.youtube.com/watch?vDUstvXSytRc
http//www.free-online-private-pilot-ground-school
.com/aircraft-structure.html
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Point-source damagePredicting damage
configurations
Before Impact
Projectile
Projectile
45 degrees
0 degrees
After Impact
T. Krishnamurthy and J.T. Wang, NASA Langley
Research Center
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Point-source damage Response surface method
Original Load Allowable
Global Finite Element Model
Decrease Load Allowable
YES
Store New Load Allowable in Response Surface
Extract Local Boundary Conditions
NO
Catastrophic Crack Growth?
Parameterized Damage State
Local Finite Element Model
Explicit Crack Growth Simulation
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Outline

• Motivation objectives
• Point source damage HOW TO LAND SAFELY?
• Fatigue damage HOW MANY MORE FLIGHTS?
• Relevant past work
• Improvements in physics-based modeling
• Incorporating the nano- micro-scales
• Current technical challenges

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Fatigue damage HOW MANY MORE FLIGHTS?
Small cracks start at each rivet hole
April 28, 1988. Aloha Airlines Flight 243 levels
off at 7,000 meters...
25 mm
then link to form a lead crack
The plane, a B-737-200, had flown 89,680
flights, an average of 13 per day over its 19
year lifetime. A high time aircraft has flown
60,000 flights.
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Displacement in z-direction
Fatigue damage Relevant past work
inch
-0.16
FRANC3D-ABAQUS interface for crack growth
simulation
Global-Local Hierarchical Modeling

• Maximum tangential stress for crack trajectory
• Experimental determination of phenomenological
  material constants
• - crack tip opening angle, CTOA
• - critical radius, rc

Initial crack
z
-1.10
measured
Internal cabin pressure, P

• What about
• -slanted crack growth?
• influence of fundamental fatigue damage
  mechanisms?
• the inherent stochastic nature?

predicted
ui
ui
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Improvements in physics-based modeling Modeling
crack front with 3D finite elements
Shell-to-solid couple
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Improvements in physics-based modeling Modeling
crack front with 3D finite elements
RD
SEMs of 7075-T651 (R. Campman, CMU)
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Improvements in physics-based modeling
Considering common damage mechanisms
7075-T651
Loading Direction

• (a) Incubation the process that leads to the
  first appearance of a cracked particle
• (b) Nucleation the appearance event of a crack
  in the matrix
• (c) Propagation the process of crack extension
  governed by microstructural heterogeneities
• Stage I Slip along a single band
• Stage II Slip along multiple bands, causing
  crack propagation subnormal to the global tensile
  direction

(a)
(b)
(c)
b
10 mm
a
c
Stage I/II illustration from C. Laird, 1967.
SEM/OIM courtesy of Northrop Grumman Corporation
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Improvements in physics-based modeling
Incorporating the nano- micro-scales

• FCC polycrystal plasticity for grains linear
  elastic, isotropic for particles
• 1 Cycle _at_ 1 strain in simple tension, along
  RD-axis

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Improvements in physics-based Modeling
Incorporating the nano- micro-scales
Molecular dynamics simulation
Grain Boundary
Crack
Incubated crack
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Technical Challenges

• Incorporating nano- micro-scale simulation in a
  computationally feasible manner
• Determination of damage configurations and
  assessment during flight
• Better physical understanding of the governing
  mechanisms for crack growth
• Why does CTOA appear to work?
• Interpolating between damage states
• Development of real-time interface with control
  system

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Backups
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Fatigue damage Past work
Build global model
Stress/Stability Analysis
Define sub-model
ABAQUS batch
FRANC3D Geometric Crack Representation
View stress intensity factors/CTOAs
Crack growth / remesh
Insert flaw / mesh
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Combine the length scales
Analyze with continuum FEA
Generate Realistic Microstructure (MS)
Model at component scale
A
C
B
F
Simulate MS damage evolution Particle/grain
boundary cracking, intra/intergranular crack
growth
Return Damage State and Prognose
Remaining Strength/Life
D
Apply B.C.s from Full-scale Model
E
Bozek, J.E. (2007) A 2D Multiscale Procedure for
Fatigue Crack Nucleation, Cornell University.
Masters Thesis
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