Transcript Crack Trajectory Prediction in Thin Shells Using FE Analysis

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
Outline
• Motivation & objectives
i. Point-source damage: HOW TO LAND SAFELY?
ii. 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?v=DUstvXSytRc
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Point-source damage:
Objectives
1) Develop finite element-based analyses to
predict growth of point-source damage within
airframe structures under realistic conditions
and in real-time
2) Interface real-time damage assessment with
control systems to provide a damagedependent 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
Stiffeners
Idealized
Damage
Skin
• Integrate information from
on-board sensors to
characterize damage
• Develop interface with
control system
Reduced
Responsemodel
surface
• Parameterize
Recast structural
damage
component
as a lower order
configurations
Response surface
equivalent
plate)
• model
Store a(i.e.
response
surface
of
• Get
the sensor
description
computed
allowable
load
of
inflicted
damage and
given
the damage
compute
updated
allowable
configuration
and query
in
Damaged Area
load
in real-time
real-time
www.youtube.com/watch?v=DUstvXSytRc
http://www.free-online-private-pilot-ground-school.com/aircraft-structure.html
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Point-source damage:
Predicting 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
Parameterized
Damage
State
Extract Local
Boundary
Conditions
Catastrophic
Crack Growth?
Local Finite
Element
Model
Explicit Crack
Growth
Simulation
NO
Store New Load
Allowable in
Response
Surface
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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?
April 28, 1988. Aloha Airlines Flight 243
levels off at 7,000 meters...
Small cracks start at each rivet hole…
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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Fatigue damage:
Relevant past work
[inch]
-0.16
Displacement in
z-direction
FRANC3D-ABAQUS interface
for crack growth simulation
Global-Local
Maximum tangential
stress for
Initial crack
Hierarchical Modeling
crack trajectory
Experimental determination of
phenomenological material
constants:
- crack tip opening angle, CTOA
- critical radius, rc
Internal cabin
What about
pressure,
P
-slanted crack growth?
-influence of fundamental fatigue
damage mechanisms? ui
-the inherent stochastic nature?
ui
z
-1.10
measured
predicted
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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
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SEM’s of 7075-T651 (R. Campman, CMU)
Improvements in physics-based modeling:
Considering common damage mechanisms
Loading
Direction
7075-T651
•
•
•
(a)
(b)
(c)
b
(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
10 mm
a
c
Stage I/II illustration from:
250 mm
C. Laird, 1967.
Cycle:
3000
10001
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 @ 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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