Aluminum Honeycomb Characterization and
Modeling for Fuze Testing D. Peairs, M. Worthington, J. Burger, P. Salyers, E. Cooper
May 16, 2012
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This presentation consists of L-3 Communications Corporation general capabilities
information that does not contain controlled technical data as defined within the
International Traffic in Arms (ITAR) Part 120.10 or Export Administration Regulations
(EAR) Part 734.7-11.
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Motivation
• Need: Rapid evaluation of fuze models in impact with honeycomb materials
• Large expense of fuze testing in actual penetration and launch environments.
• Airgun testing used to simulate environments
• Pulse characteristics controlled by honeycomb materials.
• Shell model of honeycomb is too computationally intensive for many iterations
Aluminum Honeycomb Material
• Primarily two current types used at L3-FOS:
“ Mitigator” and “Backstop”
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Mitigator Backstop
Foil Layers Foil
Thickness
Density Crush
Strength
Mitgator >2 .006 in 0.0166 lb/in3 >80,000 lbs
Backstop 1 .002 in 0.0045 lb/in3 >1000 lbs
Mitigator after impact
1/8” pre-crush
Material Model Description
• LS-DYNA Explicit FEA • Equilibrium with applied forces not maintained - update stiffness matrix in small
steps
• Timestep controlled by element size and wavespeed
• MAT_026, Mat_126 (honeycomb, modified honeycomb) options • Separate stress-relative volume curves allowed for normal and shear stress
direction (3 normal, 3 shear directions)
• Mat_026 uncoupled, nonlinear behavior for normal and shear stresses
• Mat_126 can model off axis loading, shear and normal curves can be coupled
• Two almost independent phases: Not Compacted, Fully Compacted
• Extrapolated yield stresses should not be negative
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Shkolnikov, 7th International LS-DYNA Users Conference
Crush Strength
EUncompressed
Efully compressed
Displacement/Strain
Forc
e/S
tress
Sample Preparation
• Cylindrical mitigator sectioned to determine
compressive, shear properties in primarily axial,
theta, radial directions
• Samples bonded to rigid face plates for shear.
5 6 Jan 2011
Sample Geometry Compression 1Adirection T= direction AA= LCA
L-3 Proprietary Information
4 in.
6 in.
0.5 in.
Axial configuration
load
6 Jan 2011
Compression specimen 3adirection W or L= direction BB or CC= LCB or LCC, primarily radial direction
L-3 Proprietary Information
0.27”2”
6”
1”
3.87”
load
2”
load
Axial
Primarily
Radial
Shear Sample Preparation
• Steel face plates
• Hysol EA 9360 adhesive • 5000 psi lap shear strength
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6 Jan 2011
Shear specimen 1adirection WT or LT= direction AB or AC= LCAB or LCCA, primarily radial axial or theta axial
L-3 Proprietary Information
4”
6”
load
load
0.75”
2”1”
Example sectioning for shear (primarily
circumferential-axial direction)
Example shear specimen(primarily
axial-circumferential direction)
Testing
• Quasistatic loading • 6 Mitigator specimens, 2 Backstop specimens
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Shear testing
• No mitigator shear tests reached crushing portion of response
• Backstop shear test did not reach fully compressed response
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Test Data Reduction
• Same number of data points desired for
each load/relative volume relationship
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Ensures that extrapolation
do not extend into
negative stress region
Used for
Uncompressed
modulus
Shear Data Estimation
• Ratio of Backstop shear/compressive properties used to estimate Mitigator Shear/compressive properties
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Material Model Input
• 4 curves used to describe crush strength • Axial
• Primarily radial
• Primarily circumferential
• Shear (1 instead of maximum of 3)
• 4 uncompacted Moduli
• Compressive modulus and Poisson’s Ratio from Aluminum for fully compacted condition
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FEA Model Set-up
• Solid elements
• Applied axial displacement applied to top surface
• 5 in. at constant rate
• BC’s – Nodes around center
hole at top and bottom fixed in transverse direction
– Bottom face fixed in axial direction
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Initial Modeling Results MAT_26
• No precrushed section causes
crushing to initiate in multiple
layers • Precrushed layer not modeled
• Insufficient face constraints and
multiple crushing locations can
cause bending/buckling
• No strain rate dependence
included
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Initial Modeling Results MAT_26
• Initial stress increase in entire structure similar to test results
• Early termination because of poor model stability
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MAT_126 (Modified Honeycomb) Model
• Switch to nonlinear spring element (type 0) • Allows large deformations
• Increased stability
• Load curves input in strain instead of relative
volume
• Material response during and after crushing
follows load curve • Post crush material properties ignored
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MAT_126 Model Results
• Response matches test curve (as expected)
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High Speed Impact
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Shell Model
• Very good correlation to test results
– Computationally intensive
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MAT_126 results
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• ~85% reduction in run time from shell element mitigator model
• Run time now controlled by elements in device under test
• Honeycomb on honeycomb contact modeled
Stiffened Mat_126
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Model Results Comparison
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-1600
-1400
-1200
-1000
-800
-600
-400
-200
0
200
0 0.0005 0.001 0.0015 0.002 0.0025 0.003
Nest Velocity by Mitigator Type
Shell
MAT_126 (w/Backstop)
MAT_126 (Stiffened)
-20000
0
20000
40000
60000
80000
100000
120000
140000
160000
0.00E+00 5.00E-04 1.00E-03 1.50E-03 2.00E-03 2.50E-03 3.00E-03
Mitigator Crush Force by Type
Shell
MAT_126 (w/Backstop)
MAT_126 (Stiffened)
Comparison with Test Data
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Conclusion
• Honeycomb material model is part of
ongoing efforts at L-3 FOS to continuously
improve modeling capabilities of all factors
affecting fuze survivability.
• Material model significantly reduces runtime
while maintaining acceptable accuracy.
• Reduced run time allows increased model
iteration and increased understanding of
response.
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