Component Cushion Test Development - PowerPoint PPT Presentation

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Component Cushion Test Development

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Dynamic test based on ASTM D 3574-03 (IFD Test) Utilize high ... Outlying data point in second plot due to difference in 1-g cushion deflection under ATD load ... – PowerPoint PPT presentation

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Title: Component Cushion Test Development


1
Component Cushion Test Development
  • Presented at the Fourth International Fire and
    Cabin Safety Research Conference
  • November 18, 2004
  • Lisbon, Portugal
  • Steve Hooper, PhD
  • and
  • Marilyn Henderson
  • J.B. Dwerlkotte Assoc., Inc.
  • Wichita, KS
  • USA
  • 316-269-6970, ext 14
  • Email shooper474_at_earthlink.net

2
Outline
  • Motivation to develop component test
  • Review dynamic seat certification requirements
  • Background
  • Review foam material properties
  • Describe a dynamic component test method
  • Material test results
  • Correlate with dynamic sled (seat) test results
  • Present proposed component test method
  • Summary and conclusions

3
Motivation to Develop Component Test
  • Seat Cushions are a significant maintenance item
  • Typical life 3-5 years
  • Cushions identical to the original cushions not
    always available
  • Full-scale seat tests are destructive
  • Airlines are not willing to obtain / destroy
    seats for full-scale tests
  • Bottom cushion design strongly influences lumbar
    load
  • During 14-G download tests
  • Component tests are useful in validating dynamic
    simulations of seats / restraints / and occupants

4
Download Test Description
  • Test Conditions
  • 14g triangular pulse, tr 0.08s (peak g), DV
    35 fps
  • Applied 90 deg to flight path vector
  • Pass / Fail Criteria
  • Lumbar Load 1500 lb.

Amdt. 25-64, 53 FR 17646, May 17, 1988
5
Background Foam Material Properties
  • Gibson and Ashby describe foam compression as
  • Three significant regions
  • Two significant material properties eD and spl
  • Some matls exhibit a work hardening response
  • As shown on the right


6
Background Foam Material Properties
  • Upper R.H. portion of curve is an artifact of the
    test
  • Not a Material Property

7
Background IFD Test
  • ASTM D3574 Indentation Force Deflection (IFD)
    Test
  • Measure Resistive Force at 25 and 65 deflection
    of cushion thickness
  • 7 ½-in (190.5-mm) Diameter Specimen
  • Static loading
  • No unloading measurements

8
Background Other Efforts
  • Lim method developed during the FAA / NASA AGATE1
    Program
  • Addressed rate effects
  • Hooper and Henderson developed dynamic component
    test
  • Included diaphragm in the test article definition
  • Lims method not documented in the public
    literature
  • Not validated as a robust method
  • Hooper and Hendersons method
  • Too expensive (diaphragm issue)
  • These investigators identified the significance
    of the densification strain on lumbar load during
    dynamic seat tests

9
Description of Dynamic IFD Test
  • Dynamic test based on ASTM D 3574-03 (IFD Test)
  • Utilize high-rate servo hydraulic test stand
  • 220 kip load frame
  • 110 kip actuator
  • 10 kip piezoresistive load cell
  • MTS Testar-IIm Controller
  • MTS Multi-Purpose Testware (MPT) software
  • Sampling rate 12,288 samples/sec

10
Fixture Design
Dimensions in inches
11
Test Stand Performance
Position
Velocity
Unfiltered Data
12
Test Description
  • Test articles fabricated and supplied by three
    aircraft seat cushion suppliers
  • Monolithic (nonflotation) cushions
  • 4 polymers
  • 3 densities (3.1 4.4 lb/ft3)
  • 3 thicknesses
  • Laminated (flotation) cushions
  • 3 laminates
  • 2 polymers comfort foam
  • 3 polymers flotation foam
  • 3 densities (comfort foam)
  • Same matl as used in monolithic specimens
  • Flotation foam thickness established to satisfy
    TSO-C72c
  • 3 densities (1.4 2.6 lb/ft3)
  • 3 thicknesses
  • The entire test matrix was not tested

13
Test Results Monolithic Materials
14
Test Results Laminated Materials
15
Stress- Strain Curve - Monolithic Foam
16
Stress-Strain (cont.)
  • Shifting the unloading curves to a common stress
    value produces a common stress-strain curve

17
14-g Sled Tests
  • 14-g sled tests were conducted of a limited
    number of cushions

18
Correlation of Sled Results w/ Matl Properties
2-in. monolithic
3.25-in. monolithic
  • Matl plotted in black produced highest lumbar
    load in every test
  • Blue and red curves (matls) always in same
    relative position on s-e curve and always
    produced lower lumbar loads.

19
Comparison of Static and Dynamic Test Results
  • Measurable rate effects may include
  • Increased plateau strength
  • Reduced apparent densification strain

20
Correlation of Sled Results w/ Matl Properties
(cont.)
21
Effect of thickness on lumbar load
  • Caution this trend is probably material
    specific
  • Points to importance of Densification Strain

22
Correlation of Sled Results w/ Matl Properties
2-in. laminated
4-in. laminated
  • Matl plotted in black produced highest lumbar
    load in every test
  • Blue and red curves (matls) always in same
    relative position on s-e curve and always
    produced lower lumbar loads.

23
Physical Explanation of Results
  • 14-g tests of an ATD installed in a Rigid iron
    seats with no cushion produce lumbar loads lt1000
    lb.
  • The F d curve of this steel cushion lies above
    all of the foam cushion curves
  • Consider the performance of a very soft cushion
    that is installed on the iron seat
  • This cushion is so soft that it is completely
    consolidated under the ATDs 1-g preload
  • But, the F d curve to the right of the
    consolidation strain is nearly as stiff as the F
    d curve for steel
  • Therefore, the lumbar load for this cushion will
    approach 1000 lb. as well

24
Regression Analysis
  • Outlying data point in second plot due to
    difference in 1-g cushion deflection under ATD
    load
  • Quadratic curve selected as the Criterion Curve

25
Criterion Curve
  • Definition Criterion Curve
  • The load-deflection curve for a specified cushion
    thickness that produces the largest lumbar load

26
Criterion Stress Log Strain Curve
27
Proposed Component Test Method
  • Perform dynamic component test of Certified
    Cushion Specimen
  • Compute criterion curve for specimen thickness
  • From stress log strain curve
  • Compare F - d data for certified cushion with
    criterion curve
  • If above, then show replacement cushion in Usable
    Region

Monolithic or Laminated Cushions
28
Proposed Component Test Method (cont.)
  • If below, then show replacement cushion in Usable
    Region

Monolithic Cushions Only
29
Evaluation Region
  • The Usable Region is determined by analyzing the
    position of the F - d curves in the Evaluation
    Region

30
Ineligible Material
31
Static Requirement
  • Replacement cushion specimen displacement under
    130-lb. Load must be equal to, or greater than,
    the corresponding displacement of the original
    certified cushion

32
Acknowledgements
  • This research was funded by the FAA William J.
    Hughes Technical Center by a subcontract through
    the National Institute for Aviation Research at
    Wichita State University.
  • Mr. Timothy G. Smith, FAA COTR
  • Dr. John Tomblin, WSU P.I.
  • The authors would like to acknowledge the
    contributions of
  • Ms. Lamia Salah and Wadii Benjilany of Wichita
    State
  • Mr. Rick DeWeese and David Moorcroft of FAA CAMI
  • Mr. Mike Thompson of the FAA Transport Aircraft
    Directorate
  • Mr. Matt Riggins and Mr. Habtom Gebremeskel of
    JBDA
  • The late Van Gowdy, who contributed to the design
    of this research.

33
Summary Conclusions
  • High-rate material tests were performed of
    typical flotation and nonflotation seat cushions
  • Seat cushions exhibit a measurable rate
    sensitivity
  • The material properties from these tests were
    qualitatively correlated with lumbar loads
    measured during dynamic seat tests
  • These results point to the existence of a F - d
    curve that maximizes the lumbar load for a
    specified cushion thickness
  • These results show that a replacement cushion can
    be designed that will produce a lumbar load that
    is equal to, or less than, the lumbar load
    produced by an original certified seat cushion
  • The replacement cushion does not have to exhibit
    properties that are identical to the original
    certified cushion
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