does an appropriate test protocol exists for characterizing the … · 2007-11-30 · 1. damage...

13 Nov 2007 Halpin & H. Kim 1

Does An Appropriate Test Protocol Exists

for Characterizing the Hail Ice Threat

Environment in Support of the Damage

Tolerance Requirements?

Comparison of current test

concepts and a recommendation.


Issue: Test Protocol Simulating

Hail Ice Damage• Real hail ice in its naturally occurring state is nearly

impossible to test– complex internal structure and shape – typically oblate

spheroid that is spherically layered or agglomerated

– dense frozen, porous, and liquid regions – density (reported inliterature)

– layers 170 – 920 kg/m3

– overall observed 870 – 920 kg/m3

• SIMULATED HAIL ICE (SHI) is manufactured in the lab:frozen water cast into spheres; density ~ 920 kg/m3

– unfilled ice – monolithic, flat, and spherically layered

– cotton filled per ASTM F320 spec (windshield testing)

Monolithic, or Single Cast Flat-Wise Layered Spherically Layered

Firing

Orientation

Objective of study: comparison of

impact damage initiation to composite

panels by cotton-filled and unfilled

simulated hail ice (SHI)

50.8 mm Ball with 8 g Cotton Fill

Cotton-Filled Ice


Comparison of Two Hail Ice Test Protocols:

The Cotton Reinforced Ice Does Not Reproduce Typical Hail Induced

Material-structural Damage (data by H Kim)

ASTMF320

FiberRupture &Puncture

P&W Hail Ice

Test, INITIAL

Delamination &

Resin Cracking


Impact DamageSize vs. KE

(data by H Kim)

0 40 80 120 160 200

Projectile Kinetic Energy (ft-lbf)

0

2

4

6

8

10

12

14

16

De

l am

ina

tio

n C

i rcu

mf. o

r C

r ack L

en

gth

(in

.)

Unfilled - No Damage

Unfilled

Clean Hole - DiameterSame as Ice

1.68 in. Ice

2.0 in. Ice

1.5 in. Ice

Woven Carbon/Epoxy Panels:0.065 to 0.075 in.

Ice:1.68 in. Unfilled1.5 and 2.0 in. Cotton-Filled

Cotton-Filled

- Penetration

FTE - cotton

FTE - Ice

- Delamination

Unfilled - Cracking

Cotton-Filled - No Damage

Cotton-Filled Cracking


A Head-to-Head Diagnostic Test: Private

Communication

(The Nature of the Impactor Makes a Difference!)

• Simulated hail ice, no damage observed at 500 in-lbs

– Damage threshold ~380 ft-lbs (4567 in-lbs)

• ASTM F320 composite reinforced ice

– Damage threshold ~44 ft-lbs (528 in-lbs)

– Damage size estimate >1 inch

• FFA-2 lead ball simulated FOD & runway debris.– Damage threshold ~10 to 18 ft-lbs (~180 to 220 in-lbs)


Comparison: Parametric Estimates and Diagnostic Test Conditions for the

ASTM F320 2.4 Inch Diameter Ball, & Simulated Natural Ice using the P&W.

ASTM 320

Test

Natural Ice Test

Prediction

SHI Test, No Damage

•FFA-2 Lead Ball Simulated FOD &Runway Debris.


Illustration of the Influence of Test Simulation Methodology on the Thickness

of a Typical Pressurized Structure: The ASTM F320 Cotton Composite

Reinforced Test Ball Is Significantly More Damaging That Simulated Hail Ice.

An Inappropriate Test Protocol, ASTM F320 Adds Weight but May Not

Provide Improved Damage Tolerance (Reduced CAI & Fatigue Sensitivity).


In Early 1980’s Pooled Data From Falling Weight Testing Was Used to

Correlate CAI Capability Resulting From a Combination of

Delamination, Resin Cracking & Fiber Breaking

• Delamination & Resin Cracking Produces Lower CAI CapabilityThan Fiber Breaking


Different Damage Morphologies May Have Different CAI Strengths:

Notional Illustration

ASTMF320

FiberRupture &Puncture

P&W Hail Ice

Test, INITIAL

Delamination

& Resin

Cracking


Cotton-Filled Ice PenetrationType V Damage Mode – Clean Hole (data by H Kim)

• Target: 8-ply woven carbon/epoxy plate, quasi-isotropic, 0.065 in. Thickness, held by picture-

frame fixture having 11x11 in. Opening and providing clamped b.C. (With in-plane freedom)

• Projectile: 2.0 in. Dia. Ice with cotton fill per ASTM F320, vo = 283 ft/s, KE = 186.6 ft-lbf

• Result: type V damage mode – clean hole penetration of size roughly same as projectile dia.

Impact-Side ViewBack-Side

View

Liberated Panel

Fragments,

Recovered Ice Ball


Cotton-Filled Ice PenetrationType IV Damage Mode – Large Cracking (data by H Kim)

• Target: 8-ply woven carbon/epoxy plate, quasi-isotropic, 0.065 in. Thickness, held bypicture-frame fixture having 11x11 in. Opening and providing clamped b.C. (With in-planefreedom)

• Projectile: 2.0 in. Dia. Ice with cotton fill per ASTM F320, vo = 183 ft/s, KE = 77.1 ft-lbf

• Result: type IV damage mode – thru penetration with large cracking patterns, ~ 13.1 totalcrack length

Impact-Side

ViewBack-Side

View


Comparison: Cotton-Fill vs. Unfilled Damage at ~180 ft-lbf(data by H Kim)

0.065 in. thick panel impacted byASTM F320 Cotton-Filled IceBall, 2.0 in. Dia.

vo = 283 ft/s, KE = 186.6 ft-lbf

Damage: clean hole penetration ~ 2in. diameter

0.072 in. thick panel impacted by

Unfilled Ice Ball, 1.68 in. Dia.

vo = 370 ft/s, KE = 179.4 ft-lbf

Damage: penetration with large

cracking ~ 13 in. tot. crack length

Both Images Panel Back-Side View


Fuel Tank - Tire Rupture Performance Requirements in AC25.963-1(A Positive Example)


Compliance Testing Performed at a Structural Configuration Level.

Properties of the Impacting Rubber Disk Comparable to Tire Tread

Used for the Aircraft Per the Performance Requirement.


Structural Capacity for Impact Threats Characterized With Test

Articles Representative of Aircraft Design and

Impacting Objects Relevant to the Threat


Suggested Test Standard:

Common Format - Performance Based &

Relevant to Damage Tolerance Needs

• Bird Strike– ASTM 330-89 modified

– Far Part 25 (no airframerequirement?)

• Weight-Size - 90%

• Velocity, VC

– Performance Focus• Bird carcass

• Gel Pack

– Document Threat

– Other

• Hail Strike– ASTM 330-89 modified

– Far Part 25 (no airframerequirement?)

• Weight-Size - 90%

• A/C Velocity, VC &

• Hail Terminal velocity

– Performance Focus• Simulated Hail Ice

– Document Threat

– Other


Comparative Test Program Recommended

• 1960 through the 1980 for bird strike

– Bird carcass & Gel Pack calibration

– Competitive test & simulation model development

– EU investments 1990’s into 2005

• AC5.963-1 good example; tire rupture performancerequirement

• Lightning requirements - performance focus?

• Activity similar to birdstrike recommended for the hail icethreat

– Natural ice versus Simulated Hail Ice

– Competitive test & simulation model development

• Document in common location

– Requirements for airframe (fragmented)

– Characterization of threat environments

– Acceptable test protocol(s)


!Sandwich" Construction:

Honeycomb Sandwich Construction Increases Vulnerability


Summary: Ice Impacts on Composites


SUMMARY

1. Damage Thresholds should be the bases for the dimensioning of laminatesexposed to hail and other impact threats (the damage thresholds will dependon the nature of the threat, FOD is different that hail ice, than the ASTM ball,than the rubber puck for tire damage, ---.

2. The threat environments need to be quantified, agreed to, and kept up todate. They are independent of platforms.

(Good data base for the US But need data for international locations.)

JOINT INTERNATIONAL EFFORT?

A data base need; hail & operational velocities, ---.

3. Defense of a design is the responsibility of the OEMs including test &analysis methods.

(Realistic test protocols are available.)

4. Inspection for Cause; Hail example, triggered by extreme Rogue weatherconditions, and a defined operating period allowing short term operationsbefore repair, dependent upon severity of damage as defined by the Pxxinternal load conditions or Allowable Damage Limits.

This perspective would utilize a “Self Evident Rogue Event” instead of “SelfEvident Damage” as a criteria condition. The dent has been a “Self EvidentDamage” criteria condition BUT is not a sufficient basis for a preventivedesign & maintenance concept.

does an appropriate test protocol exists for characterizing the … · 2007-11-30 · 1. damage...

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