# Presentation: 418884

## 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@earthlink.net**

## 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**

## 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**

## Download Test Description

**Test Conditions**
**14g triangular pulse, t****r**** = 0.08s (peak g), ********V = 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]**

## Background – Foam Material Properties

**Gibson and Ashby describe foam compression as**
**Three significant regions**
**Two significant material properties:  ********D**** and ********pl**
**Some mat’ls exhibit a “work hardening” response**
**As shown on the right **

- *

## Background – Foam Material Properties

**Upper R.H. portion of curve is an artifact of the test**
**Not a Material Property**

## Background – IFD Test

**ASTM D3574 Indentation Force Deflection (IFD) Test**
**Measure Resistive Force at 25 and 65% deflection of cushion thickness**
**7 1⁄2-in (190.5-mm) Diameter Specimen**
**Static loading**
**No unloading measurements**
**	****	****	**

## Background – Other Efforts

**Lim method developed during the FAA / NASA AGATE****1**** Program**
**Addressed rate effects**
**Hooper and Henderson developed dynamic component test**
**Included diaphragm in the test article definition**
**Lim’s method not documented in the public literature**
**Not validated as a robust method**
**Hooper and Henderson’s method**
**Too expensive (diaphragm issue)**
**These investigators identified the significance of the densification strain on lumbar load during dynamic seat tests****	**

## 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 **

## Fixture Design

- Dimensions in inches

## Test Stand Performance

- Unfiltered Data

**Position**

**Velocity**

## 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/ft****3****)**
**3 thicknesses**
**Laminated (flotation) cushions**
**3 laminates**
**2 polymers comfort foam**
**3 polymers flotation foam**
**3 densities (comfort foam)**
**Same mat’l 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**

## Test Results – Monolithic Materials

## Test Results – Laminated Materials

## Stress- Strain Curve - Monolithic Foam

## Stress-Strain (cont.)

**Shifting the unloading curves to a common stress value produces a common stress-strain curve**

## 14-g Sled Tests

**14-g sled tests were conducted of a limited number of cushions**

## Correlation of Sled Results w/ Mat’l Properties

**Mat’l plotted in black produced highest lumbar load in every test**
**Blue and red curves (mat’ls) always in same relative position on ******** curve and always produced lower lumbar loads.**

**2-in. monolithic**

**3.25-in. monolithic**

## Comparison of Static and Dynamic Test Results

**Measurable rate effects may include:**
**Increased plateau strength**
**Reduced apparent densification strain**

## Correlation of Sled Results w/ Mat’l Properties (cont.)

## Effect of thickness on lumbar load

**  ****Caution:  this trend is probably material specific**
**  ****Points to importance of Densification Strain**

## Correlation of Sled Results w/ Mat’l Properties

**2-in. laminated**

**4-in. laminated**

**Mat’l plotted in black produced highest lumbar load in every test**
**Blue and red curves (mat’ls) always in same relative position on ******** curve and always produced lower lumbar loads.**

## Physical Explanation of Results

**14-g tests of an ATD installed in a Rigid “iron seats” with no cushion produce lumbar loads <1000 lb.**
**The F – ******** 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 ATD’s 1-g preload**
**But, the F – ******** curve to the right of the consolidation strain is nearly as stiff as the F – ******** curve for steel**
**Therefore, the lumbar load for this cushion will approach 1000 lb. as well**

## 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***

## Criterion Curve

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

## Criterion Stress – Log Strain Curve

## 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 - ******** data for certified cushion with criterion curve**
**If above, then show replacement cushion in ****Usable Region**

**Monolithic or Laminated Cushions**

## Proposed Component Test Method (cont.)

**If below, then show replacement cushion in ****Usable Region**

**Monolithic Cushions Only**

## Evaluation Region

**The Usable Region is determined  by analyzing the position of the F - ******** curves in the Evaluation Region**

## Ineligible Material

## 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 **

## 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.**

## 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 - ******** 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**