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Development, optimization, and design for robustness of a novel FMVSS 201 U energy absorber David M. Fox US Army RDECOM-TARDEC COM: (586) 574-3844 DSN: 786-3844 Email: david.m.fox1 @us.army.mil

Development, optimization, and design for robustness of a ... · FMVSS 201 U energy absorber David M. Fox US Army RDECOM-TARDEC COM: (586) 574-3844 DSN: 786-3844 Email: david.m.fox1

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  • Development, optimization, and design for robustness of a novel FMVSS 201 U energy absorber

    David M. Fox US Army RDECOM-TARDEC

    COM: (586) 574-3844 DSN: 786-3844

    Email: david.m.fox1 @us.army.mil

  • Report Documentation Page Form ApprovedOMB No. 0704-0188Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering andmaintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information,including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, ArlingtonVA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if itdoes not display a currently valid OMB control number.

    1. REPORT DATE 15 MAY 2006

    2. REPORT TYPE Briefing Charts

    3. DATES COVERED 08-01-2006 to 25-04-2006

    4. TITLE AND SUBTITLE Development, optimization, and design for robustness of a novel FMVSS201U energy absorber

    5a. CONTRACT NUMBER

    5b. GRANT NUMBER

    5c. PROGRAM ELEMENT NUMBER

    6. AUTHOR(S) David Fox

    5d. PROJECT NUMBER

    5e. TASK NUMBER

    5f. WORK UNIT NUMBER

    7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) U.S. Army TARDEC,6501 East Eleven Mile Rd,Warren,Mi,48397-5000

    8. PERFORMING ORGANIZATIONREPORT NUMBER #15848

    9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) U.S. Army TARDEC, 6501 East Eleven Mile Rd, Warren, Mi, 48397-5000

    10. SPONSOR/MONITOR’S ACRONYM(S) TARDEC

    11. SPONSOR/MONITOR’S REPORT NUMBER(S) #15848

    12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited

    13. SUPPLEMENTARY NOTES For 2006 LS-DYNA INTERNATIONAL USER’S CONFERENCE

    14. ABSTRACT briefing charts

    15. SUBJECT TERMS

    16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT

    Public Release

    18. NUMBEROF PAGES

    33

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    a. REPORT unclassified

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    Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

  • Introduction

    • Significant opportunity to improve vehicle occupant safety

    • Reduce impact severity between occupant heads and vehicle interiors

    • Rigid body panels

    • Used plastic deformation of mild steel fins and cover sheet to absorb impact energy

  • Absorber construction

    • 0.5 inch wide mild steel fins

    • Connected with a mild steel web

    • Sandwiched between mild steel surface panel and rigid armor

  • LS-DYNA absorber model

    • Connected fin I web assembly to cover sheet using spot welds

    • Used SPC to anchor fins at interface between absorber and rigid panel

    • Type 13 contacts between the various assembly components

    • Nominal 3 mm mesh

    • Steel was modeled using MAT24

  • Impact test simulation

    • FMVSS 201U

    • Component level, 10 inch X 10 inch surface

    • FTSS v. 3.6 free motion headform

    • 15 mph initial velocity

    • 20° angle between velocity and surface

  • Optimization problem

    • Minimize crush space subject to the constraint that H IC( d) < 700

    • Independent variables: - crush space

    -spacing between fins

    -shell thickness of fin, web, and cover sheet

  • Head Injury Criterion (HIC)

    HIC ==max t I ,t 2

    2 .5

    rtz a(r)dr J,l

    HIC(d) == 0.75446 (HIC)+ 166.4

    01 Typical Impact Event c 160r------"--'-------~---------,

    ----z-140 m12o c

    2 100 co (i) 80 Q) (.) 60 (.)

    ~ 40 c ~ 20 ;:}

    ~ %~o.-oo2~o-.oo~4-o.o~oe-o.o-oa-o-.o1-0.0-12 -0.0-14-o~.o 1=eo=.o1=a~o.o2

  • Optimization technique • Closely followed Stander and Craig (LS-OPT)

    successive response surface method • Iterative sequence of linear least squares

    response surfaces • Chose D-Optimal subsets of 33 full factorial

    basis designs • D-Optimal subsets contained seven

    combinations of the three design factors • 15 iterations of 7 runs each; 105 simulations

    overall

  • Convergence to optimum values

    Initial Optimum

    Crush space (inch) 0.875 0.8044 Fin spacing (inch) 0.875 0.9446 Fin I web I cover shell thickness (inch) 0.0285 0.02616 RIC( d) 737 699

  • Convergence - crush space and

    0.95

    :2 0.9 (,.) c: -Cll ::I (ij 0.85 > ... Cll -c: ~ 0.8

    0.75

    0.7

    • spactng

    A / ~/ ~ I \ I

    - -------, -- -I \ I \

    \ ~ '"-- ..... ..... v v 0 2 4 6 8 10 12 14 16

    Iteration

    1-+- Crush space -Fin spacing I

  • Convergence - shell thickness

    -.t:. () c:

    0.029

    0.0285

    :.:;. 0.028 Q) :::J iU > s 0.0275 -c: Q) ()

    ::! 0.027 Q) c:

    .ll:! ()

    ;s 0.0265 Qj .t:. en

    0.026

    0.0255

    -

    1\

    \ \ I \ \ I \ v

    0 2

    A

    ~ /~ ..---_.._----,

    ~ ~ ~ ....... -a

    4 6 8 10 12 14 16

    Iteration

  • Acceleration - time history for optimum design

    160

    140

    120

    - 100 ~ c: 0

    ~ 80 ... (I)

    Gi (,)

    lil 60

    40

    20

    0

    r

    f\ ) 1\

    \ l_ 1\. v \f\ I \

    N \ \ \ ~ .....,

    ~ J 1"-----0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02

    time (s)

  • Variability I robustness Cube Plot (data means) for HIC(d)

    tB 1699.022 I

    Spacing ~ ~--------

    / I

    Crush Space

    0.02485 0.8446

    • 23 full factorial about optimum • Optimum design settings ± 5°/o

    e Centerpoint e Factorial Point

  • Initial design interaction

    Interaction Plot (data means) for HIC(d)

    0.8974 0.9446 0.9918 0.02485 0.02616 0.02747

    ________. .___________ Crush Space

    • • Or - -----o.--

    .....

    Spacing ~ •

    Thickness

  • Crush space- thickness interaction

    §150 r----+----~4-~-~----r----+---~~ c: 0

    ~ Q)

    ~ 1 00 +----7f-+-t-'+-----l-() C'CS

    0 ~---+----4---~~--~----+-~~~

    0.002 0.004 0.006 0.008 0.01 0.012 0.014

    t (s)

    - low crush space- low th HIC(d)=818

    - low crush space - hi th HIC(d)=756

    -hi crush space - low th HIC(d)=709

    hi crush space - hi th HIC(d)=688

    • Lower shell thickness increases propensity toward "bottoming out"

    • Lower crush space tends to increase mean deceleration

  • y

    HIC(d) = 688, first peak I I SAE J 1 000 Filtered Acceleration Time=3.499797 ·•o..-------------,

    100

    - 80 s c: 2 ;;; a; c; .., ., 0

    •O

    1-·,1

    o-l----.J~~~---.-------:--~.::::==;==--.--......,j o ooo2 ono.c- ono' oooa 001 001.2 oo,~ o.o1e- oo·a on:z

    Time (s)

  • HIC(d) = 688, second peak I I SAE J1 000 Filte red Acceleration Time= 7.499736 ··~~.------------,

    10D

    1-.,1 y

    20

    +

    ~+----,.L~~~~~~--=-~ o ooo:: ooo..: oote oooa 001 oo1: oou o.C 1 ~ oo1s oo2 Time (s)

  • Improve design Cube Plot (data means) for HIC(d)

    m 1699.022 I

    Spacing ~ ~--------

    / I

    Crush Space

    0.02485 0.8446

    $ Centerpoint

    e Factorial Point

    • -5°/o increase in crush space should enable HIC(d) < 700 • Use 0.84 crush space face as starting point

  • 0.858

    0.856

    0.854

    :2 .~ 0.852 -Q) (.)

    [ 0.85 Ill

    ..c: Ill 2 0.848 u

    0.846

    0.844

    0.842

    v

    0

    Design improvement

    / ~

    / ~ r----/ -

    ._____

    I I

    I

    1 2 3 4 5 6 7

    Iteration

    • Used interpolation process keeping spacing and thickness fixed • Found new crush space to ensure HIC(d) < 700 for nominal

    parameter settings + 5°/o

  • 710

    708

    706

    704

    :0 u 702 ::I:

    700

    698

    696

    694

    r ·-

    1\

    \

    0

    Design improvement

    \ \

    \

    \ \ / -- ---------1 \ ~ ~ v

    1 2 3 4 5 6 7

    Iteration

  • Improve design Cube Plot (data means) for HIC(d)

    l699.022 I

    Spacing ~ ~--------

    / I

    Crush Space

    $ Centerpoint e Factorial Point

    • -5°/o increase in crush space should enable HIC(d) < 700 • Use 0.84 crush space face as starting point

  • Improved design Cube Plot (data means) for HIC(d)

    Spacing ~ ~--------

    / I

    Crush Space

    • New nominal design settings + 5°/o

    EB Centerpoint

    e Factorial Point

    • Moderate(- 0.1 inch) increase in nominal crush space yields HIC(d) < 700

  • Improved design interaction

    Interaction Plot (data means) for HIC(d) 0.8974 0.9446 0.9918 0.02485 0.02616 0.02747

    ~ ~ Crush Space

    . --- . -->---- >" - -Spacing /

    Thickness

  • Response surfaces for the improved design

    • Sampled by means of uniform designs

    • Developed response surfaces via Kriging

    • Factorial simulation results were used to compare fidelity of Kriging response surfaces generated in various ways

  • Kriging

    p

    Y krige == fJ k Jk ( X ) + Z ( X ) k==l

  • Kriging models

    • Compared results for surfaces generated with -constant

    -first order polynomial

    -quadratic polynomial

    • Gaussian correlation function

    • Three different sample sizes- 9, 17, and 30

  • Goodness-of-fit estimates

    Maximum Error= max Ykrige,i- Y factoriaZ,i

    ( ) 1/2

    RMSE = L Y krige, i - Y factorial, i . n l

  • Comparison of maximum error

    First Order Quadratic Sample size Constant Polynomial Polynomial

    9 42.70 29.52 -

    17 125.28 37.44 34.92

    30 53.39 30.08 18.66

  • Comparison of root mean square error (RMSE)

    First Order Quadratic Sample size Constant Polynomial Polynomial

    9 24.36 18.36 -

    17 60.50 16.00 19.02

    30 23.95 15.04 10.67

  • Kriging model contours

    Spacing = 0.95 (5°/o lower than nominal value)

    0. 950 +-------'...___,.. __ ~......_____, __ __,...,.____;___;_,~"---'1,.~ 0.950 0.975 1.000

    Crush Space 1.025 1.050

  • Kriging model contours

    {II {II (I)

    1.050

    1.025

    .§ 1.000 u

    ~

    0.975

    0.950 0.950

    Spacing= 1.00 (nominal value)

    0.975 1.000 Crush Space

    1.025 1.050

    HIC(d)

    • < 580 • 580 - 600

    600 - 620

    620 - 640 640 - 660

    • 660 - 680

    • > 680

  • Kriging model contours

    0.950 0.950

    Spacing = 1.05 (5°/o higher than nominal value)

    0.975 1.000 Crush Space

    1.025 1.050

  • Conclusions • It's possible to very efficiently optimize an energy

    absorber design using - the LS-DYNA explicit finite element code - the successive response surface method algorithm

    • Use of classic factorial techniques in combination with Kriging response surfaces can - guide improvement of product robustness - offer insight into the nature of a product and its performance

    variability

    • An enlightened combination of these techniques enables, if nothing else, valuable and relatively inexpensive insight into the feasibility and behavior of various design concepts.