Aluminum Honeycomb Characterization and Modeling for Fuze Testing D. Peairs, M. Worthington, J. Burger, P. Salyers, E. Cooper

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L-3 Communications Corporation general capabilities

technical data as defined within the International

1 Aluminum Honeycomb Characterization and Modeling for Fuze Testing D. Peairs, M. Worthington, J. Burger, P. Salyers, E. Cooper May 16, 2012 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 or Export Administration Regulations (EAR) Part

Airgun testing used to simulate environments Pulse characteristics controlled by

2 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 2

Aluminum Honeycomb Material Primarily two

0166 lb/in 3 >80,000 lbs Backstop 1.002 in 0.

3 Aluminum Honeycomb Material Primarily two current types used at L3-FOS: Mitigator and Backstop Foil Layers Foil Thickness Density Crush Strength Mitgator >2.006 in lb/in 3 >80,000 lbs Backstop in lb/in 3 >1000 lbs 1/8 pre-crush Mitigator Mitigator after impact Backstop 3

4 Force/Stress 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 Crush Strength E fully compressed E Uncompressed Displacement/Strain Shkolnikov, 7 th International LS-DYNA Users Conference 4

Sample Preparation Cylindrical mitigator sectioned to determine compressive, shear

3a direction W or L= direction BB or CC= LCB or LCC, primarily radial direction Axial

5 Sample Preparation Cylindrical mitigator sectioned to determine compressive, shear properties in primarily axial, theta, radial directions Samples bonded to rigid face plates for shear. Sample Geometry Compression 1A direction T= direction AA= LCA load Compression specimen 3a direction W or L= direction BB or CC= LCB or LCC, primarily radial direction Axial configuration 0.5 in. load Axial 6 in in. Primarily Radial 6 load L-3 Proprietary Information 6 Jan 2011 L-3 Proprietary Information 6 Jan

6 Shear Sample Preparation Steel face plates Hysol EA 9360 adhesive 5000 Shear psi lap specimen shear 1a strength direction WT or LT= direction AB or AC= LCAB or LCCA, primarily radial axial or theta axial load 2 1 L-3 Proprietary Information 6 load Example sectioning for shear (primarily circumferential-axial direction) 6 Jan 2011 Example shear specimen(primarily axial-circumferential direction) 6

7 Quasistatic loading Testing 6 Mitigator specimens, 2 Backstop specimens 7

8 Shear testing No mitigator shear tests reached crushing portion of response Backstop shear test did not reach fully compressed response 8

9 Test Data Reduction Same number of data points desired for each load/relative volume relationship Ensures that extrapolation do not extend into negative stress region Used for Uncompressed modulus 9

10 Shear Data Estimation Ratio of Backstop shear/compressive properties used to estimate Mitigator Shear/compressive properties 10

11 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 11

12 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 12

13 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 13

14 Initial Modeling Results MAT_26 Initial stress increase in entire structure similar to test results Early termination because of poor model stability 14

15 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 15

16 MAT_126 Model Results Response matches test curve (as expected) 16

17 High Speed Impact 17

18 Shell Model Very good correlation to test results Computationally intensive 18

19 MAT_126 results ~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 19

20 Stiffened Mat_126 20

21 Model Results Comparison Nest Velocity by Mitigator Type Mitigator Crush Force by Type Shell MAT_126 (w/backstop) MAT_126 (Stiffened) Shell MAT_126 (w/backstop) MAT_126 (Stiffened) E E E E E E E-03 21

22 Comparison with Test Data 22

23 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. 23

Numerical simulation of wood filled impact limiter with LS-DYNA

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