# Presentation: 007182

## Development of a Lab-Scale Flame Propagation Test for Composite Fuselages

## Introduction

**With the increased use of non-traditional materials for modern aerospace applications, fire test methods must be continually updated and re-evaluated in order to maintain a high level of passenger safety**
- Application of fire tests to modern materials
- Re-evaluation of pass/fail criteria
- Introduction of new safety threats with new materials
- Develop new standards or test methods to address these issues
**Composite materials (carbon fiber-epoxy) are being used in places where aluminum was traditionally used **
- Fuselage skin
- Structural members – stringers and formers
- Seat frames
- Fuel tanks
**There is a need to evaluate the fire properties of these materials to ensure there is not a decreased level of safety **

## Composite Fuselage

**There is a need to evaluate the fire properties of a composite fuselage**
- Burnthrough
- Toxicity
- In-flight burnthrough
- Flame propagation
**This objective of this study is to determine whether a composite fuselage will pose a flame propagation hazard**
- Identify potential scenarios where a threat may be present
- Evaluate threat with full or intermediate scale test
- Analyze results to determine if there is an increased risk
- Use full/intermediate scale test results to develop a lab-scale test for future certification purposes

## Evaluation of Flame Propagation Risk

**An intermediate scale test was performed using the foam block fire source**
**Different configurations of the fire source, thermal acoustic insulation, and composite panel were attempted**
**Test results indicated that the material being evaluated did not present a flame propagation hazard**
**Other composites or composites of varying thicknesses may pose a threat**

## Development of Lab-Scale Test

**Use the results from previous intermediate scale test as a baseline for a “pass”**
- The intermediate scale test results were used to certify that specific material for use in aircraft
- The intermediate scale test will not suffice for certification, however, as it is a large test and takes time and money to perform
- Certification tests must be performed when varying the material (different epoxies, thicknesses, etc.)
- The lab scale test must provide the same discretion as the intermediate scale test, but be more efficient to perform
**Radiant Panel Test Apparatus**
- The radiant panel test is very useful for evaluation flame propagation tendencies for materials
- The test is a “surface” test, as radiant heat and the burner impingement are applied to the material surface
- Material thickness and thermal conductivity play a large role in this test
- Test parameters must be adjusted to account for composite materials of varying thicknesses (warm-up time, flame exposure time, radiant heat energy, etc.)
- Task here is to determine if the radiant panel test will be useful for evaluating the flame propagation threat of composite materials

## Previous Work on Composites

**FAA Report DOT/FAA/AR-07/57 (Quintiere et al.) entitled “*****Flammability Properties of Aircraft Carbon-Fiber Structural Composite”***
**Investigated a material manufactured by Toray Composites America to meet Boeing Material Specification 8-276**
**Key objective was to investigate the heating and burning properties of the material with various methods**
- Cone calorimeter
- Microscale combustion calorimeter
- Thermogravimetric analysis
- Differential scanning calorimeter
- Flame spread apparatus
- Thermal conductivity apparatus
- OSU and smoke chamber

## Material Details

**Toray Composites, BMS 8-276**
- [-45, 0, 45, 90]2s 16 plies
- Material is composed of carbon fibers (7μm dia.) and resin
- 3.2 mm thick (0.125 in.)
- Density = 1530 kg/m3 (95.5 lb/ft3)
- 60% by volume carbon fibers
- Resin density = 1220 kg/m3 (76 lb/ft3)
- Typical char fraction of resin ~ 25%

## Properties

**Resin is primary fuel for reactions**
- Escapes the material through pores in the matrix
- Heating causes material to swell as internal pressures rise
- Flame jets can protrude from the material due to pressure release
- Properties change as material changes in shape
- Density decreases
- Thermal conductivity of matrix decreases
- Both flaming and non-flaming combustion can occur
- Resin can produce flaming combustion
- Char and carbon can smolder on the surface without flame
**Thermal conductivity was measured with a home-built apparatus**
- Measurements were made over a range of temperatures relevant to combustion
- Heat loss errors were found with the apparatus, possibly up to 20% difference
- More accurate methods are needed
- Despite the errors, the dependency of thermal conductivity on temperature is clear

## Flame Spread Experiments

**Critical heat flux was found from cone calorimeter measurements**
- Piloted ignition:  17.5 kW/m2 (1.5 BTU/ft2s)
- Non-piloted ignition:  31.5 kW/m2 (2.8 BTU/ft2s)
**Apparatus was developed in the work of Panagiotou and Quintiere**
- Vertically mounted specimen
- Surface exposed to radiant heat is 6 x 25 cm (2.4” x 9.8”)
- Pre-heat time of 4 min was used to create thermal equilibrium on sample surface (found from critical heat flux for piloted ignition)
- Flame spread is only a function of heat flux for this pre-heating condition, as flame speed is dependent upon surface temperature
**Key findings**
- Exposed heat flux of 1.25 BTU/ft2s
- Pilot flame in contact entire test
- Flame spread of approx 7” over 2 1⁄2 min
- Pyrolysis spread of approx 12.6” over 2 1⁄2 min

## Preliminary FAATC Measurements

**BMS 8-276, 0.125” thickness, 20” x 9.5”**
**Radiant Panel Test, configured for 25.856(a)**
- 1.5 BTU/ft2s at zero position
- 15 sec. pilot flame application
- Result:  No propagation, no after flame
- 4 min. pre-heat, 30 sec. pilot flame application
- Result:  No propagation, no after flame
- Turned sample 180°, 30 sec. pilot flame application (~6 min pre-heat)
- Result:  3 sec. after flame, no propagation
- Re-applied flame for 1 min
- Result:  6 sec. after flame, no propagation
- Damaged Panel, 15 sec. pilot flame application
- 19 sec. after flame, no propagation
- Pilot flame applied to rear edge of panel, 15 sec pilot flame application
- Result:  >15 sec. after flame, no propagation

## Configuration 1

- 15 sec. flame application
- No propagation or after flame

## Configuration 2

- 4 min. pre-heat
- 30 sec. flame application
- No propagation or after flame

## Configuration 3&4

- Rotated sample 180°, -> ~6 min pre-heat
- 30 sec. flame application
- 3 sec. after flame no propagation
- Re-applied flame for 1 min
- 6 sec. after flame, no propagation

## Configuration 5

- Damaged Panel
- 15 sec. flame application
- 19 sec. after flame, no propagation

## Configuration 6

- Pilot flame applied to edge
- 15 sec. flame application
- >15 sec. after flame, no propagation

## Summary of Initial Testing

**Results:**
- Test conditions for 25.856(a) are not severe enough to produce any result
- 4 minute pre-heat not sufficient to produce any result
- ~6 minute pre-heat was able to produce short after flame
- Delamination and damage to panel caused significant after flame
- Application of flame to edge of panel caused significant after flame
- After flame seems to behave like a candle, where fuel is drawn to the flame through the panel like a candle
- Combustible gases seem to escape through the edges, which causes after flame at the edge
- Sample frame should be constructed to completely block off the edges and only allow for surface to be exposed

## Status

**Work is in the initial phase right now**
**Initial work will involve tooling with the radiant panel and different composite material plaques to observe how the material behaves in this test**
- Vary sample size, thicknesses
- Vary radiant heat and flame exposure times
**Gather samples of different composite materials for intermediate and lab scale tests**
**Perform intermediate and lab scale tests, change test parameters such that the intermediate and lab scale results correlate**

## Questions or Comments?

**Contact:**
**Robert Ochs**
**DOT/FAA Tech Center**
**Bldg. 287**
**Atlantic City Int’l Airport, NJ  08405**
**(609)-485-4651**
**robert.ochs@faa.gov**