FAA Workshop for Composite Damage Tolerance and ... Damage Tolerance... · AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3

Damage Tolerance Methodology - ESAC - Ref. X029PR0608046 - Issue 1

Damage Tolerance Methodology

Chicago, IL

Prepared by Emilie MORTEAU, Chantal FUALDES

Presented by

Chantal FUALDESAirbus Head of Composite stress analysis Composite Senior Expert

FAA Workshop for Composite Damage Tolerance and Maintenance July 19-21, 2006

Composites @ Airbus

July 2006Damage Tolerance Methodology - ESAC - Ref. X029PR0608046 - Issue 1 Page 2© A

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Main principles in Damage tolerance methodologyR

EG

UL

AT

ION

RE

GU

LA

TIO

N

ANALYSISANALYSIS--

FATIGUEFATIGUE& DAMAGE& DAMAGE

TOLERANCETOLERANCEEVALUATIONSEVALUATIONS

ININ--SERVICESERVICEEXPERIENCEEXPERIENCE

TEST RESULTS TEST RESULTS ––

BUILDING BLOCK APPROACHBUILDING BLOCK APPROACH


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CONTENT

1. AIRBUS Damage tolerance philosophy1. Damage Detectability2. Impact threat3. Large Damage4. Hail5. Manufacturing defects6. No-growth / Fatigue

2. Test Pyramid3. Analysis4. Key messages


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CONTENT




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1- AIRBUS Damage tolerance philosophy

DT Philosophy to answer to requirement and means of compliance


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CONTENT




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1.1- Damage detectability

Damage detectability

•Damage metric

•BVID definition

•Large VID definition

•Supporting tests and analysis

•Relaxation behaviour


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4For Airbus composite parts (CWB, Keel Beam, aileron, spoiler, HTP, VTP, LGD, etc)

relevant impacts for DT analysis are from maintenance i.e. tool drop, removable panel drop, and in a smaller extent from operation by runway debris (LGD), 4Shape of damage can be simulated by low impactor diameter (diameter

generally used for composite test and DT substantiation is from 6 to 25mm), and 4Resulting damages have similar diameter, mainly the dent depth (and crack length for edges), and depend on the impact energy

For transverse impact, the damage metric used for detectability is the

dent depth

For edge impact, the damage metric used for detectability is the dent

depth and/or cracks length

Has to be revisited for composite fuselage application for consistency

with impact sources (ground handling)Damage metric


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The minimum impact damage surely detectable by scheduled inspection

4Dent depth criterion as a damage metric is widely used for composites. (It is acceptable to use additional criteria (not just dent depth) when establishing the limit of detectability, if this is justified by appropriate testing)4It corresponds to a probability of detection of 90% with an interval of confidence of 95%.4It provides a reasonable level of robustness for the structure design

–the aim is to sustain UL with BVID

Two values for the BVID criterion are established dependent on the visual inspection type : DET and GVI

BVID definition


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is technology and structure dependant

4Damage size associated to walk-around is considered on a case-by-case basis

4 Typically « penetration »

Example for a sandwich structure

Large VID definition


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DET Inspection§Detection of damages on different composite panels (size: from 100*100mm to 0.8m², painted or not, glossy or mat,white, grey, blue or green paint, primer) §Duration of inspection : not limited§Distance of inspection : 50 cm§Lighting condition : available lighting+grazing light (if required)§Several impactor diameter : 6mm and 16mm§A total of 902 inspections

GVI Inspection§Inspection on large panel (8m*1.2 m)§Two configurations : horizontal or vertical panels§Distance of inspection : 1m§Duration of inspection : 30sec/panel§Artificial lighting representative of Natural daylight§Several impacts on painted panel: from 0.3mm deep to perforation§Several impactor diameter : from 6 to 120mm§A total of 240 inspections

FOR BVID TRANSVERSE IMPACT

Supporting tests and analysis and in-service survey


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( )

∫ ∫∞−

−

∞−

−−−

==>j

jd

md

ymd

j dyeddeddPσ

σ

πσπ

log

22

log

det

2

2

2

21

)(log.2

1)(

33.2)95/50()95/99(

)95/50(

:

aLogaLogaLogm

depthdentd

−=

=

σBVID

Results of inspection were statistically processed using a search for maximum plausibility type approach.

The analytical POD function used is the Log Normal cumulative distribution



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85% of collected impact damages (dent) (around 1000 damage records) detected through GVI inspection (A, C check, daily, weekly, etc) are below Airbus established detectability threshold

Airbus BVID(GVI) is consistent with Airline survey findings

Survey in European airlineCumulative curve of dent depth

0,00%

20,00%

40,00%

60,00%

80,00%

100,00%

120,00%

0,00 0,50 1,00 1,50 2,00 2,50 3,00 3,50 4,00 4,50 5,00 5,50 6,00 6,50

Dent depth (mm)

Po

urc

enta

ge

of

dam

ages

wit

h d

ent

less

than

d

Example for GVI inspection


Airbus BVID (GVI)


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The relaxation is the phenomenon that leads to damages that become less detectable over time: a damage being detectable at time of impact, can become undetectable after an interval of inspection due to mechanical, thermal cycling, wet and ambient ageing and temperature.

Material A

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

0,90

After impact After 20 mn After 48H After WA Beforefatigue

After110cycles

0,6Fr

After fatigue

Event

Den

t dep

th e

volu

tion

(mm

)

18J impact+WA70/95%HR1500h and fatigue (r=10c/c) at 20°

18J impact+WA70/95%HR1500h and fatigue (r=10c/c) at -40°

18J impact+WA70/95%HR1500h and fatigue (r=-1 t/c)at 20°


20J impact+WA70/95%HR1500h and fatigue (r=10c/c) at -40°20J impact+WA70/95%HR1500h and fatigue (r=-1 t/c)at 20°


23J impact+WA70/95%HR1500h and fatigue (r=10c/c) at -40°23J impact+WA70/95%HR1500h and fatigue (r=-1 t/c)at 20°

Influent parameters were studied, the wet ageing until saturation covers all environmental and mechanical effects during the aircraft life.For tests, impact inflicted to the structure takes into account the relaxation of the dent under environmental conditions.

Hot/wet ageing

Relaxation behaviour


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CONTENT




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1.2- Impact threat

Impact threat

•Impact threat definition

•Typical impact threat

•Supporting data and analysis


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1.2- Impact threat

The impact threat is the mathematical description of impact severities associated to their probability of occurrence. It is supported by extensive survey of in-service incidents.

External part•Typical impact threat:

35J 10-5 /FH (static cut-off)90J 10-9 /FH (damage tolerance cut-off)

•HTP root/Rear fuselage skin140J 10-5 /FH (static cut-off)

•Doorway zones132,5J 10-5 /FH (static cut-off)238,5J 10-9 /FH (damage tolerance cut-off)

Note : for some structures where a low impact threat can be anticipated (eg x >2,7), then the energy associated to a realistic event could be low.

1510)(jE

x

jj EEp−−

=≥

fhJEPj /10)30( 5−=≥

fhJEPj /10)90( 9−=≥with x=3, giving

Impact threat definition

Typical impact threatRef: Effect of low velocity impact damage on primary aircraft structures – the certification issue; Aug 1999, J. Rouchon


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1.2- Impact threat

4A survey on wing impact damage, covering the whole Airbus types, totalling 18,740,000 flight hours and 9,800,000 flight cycles4A similar survey extended the data to the fuselage, covering A320 family, totalling 1,140,000 flight hours 4A similar survey covering the whole aircraft covering A320 family, totalling 500,000 flight hours4And another source of data was a survey, totalling 10,330,000 flight hours

Extensive survey available from which the current impact threat is derived.

Impact threat parameters have a solid foundation, new in-service data, additional applications (A380 for example) and associated in-service history should lead to future updates with a more complete understanding of damage threats.

Supporting data and analysis


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CONTENT




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1.3- Large Damage

• Large Damage Capability, LDC: not realistic damage

Design precautions to protect against the unknown.

• Design precautions

4 Fail Safe demonstration on main joint areas: hinged structures, high load introduction (disconnection of one load path) …

4 In addition, for each typical technology / design, arbitrary typical damages are assumed for LDC assessment, such as: – Stringer disbond analysis for co-bonded technology – Missing fasteners at load introduction area– Large hole in typical area


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CONTENT




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1.4- Hail

• Hailstorms data is based on meteorological survey defining:

4 Size of hailstones :– Standard hailstorm, (Dia 10mm) for a P of 50% of hailstorms– Rare hailstorm, (Dia 25mm) for a P of 5% of hailstorms– Extremely rare hailstorm, (Dia 50mm) for a P of 0.1% of hailstorms.

4 Concentration per unit area: number of hailstones impacting a surface based on the size of the storm.

4 Velocities for the energy of hails impact on ground and flight conditions.

• Structure Damage tolerance approach, 2 points are considered:

4 Unloaded Structure, hail on ground for commercial aspect– Showers of Dia 10 and 50 mm ( 33m/s; 32 Joules)

4 Loaded structure, hail in flight considered in damage tolerance analysis (Energy, loading, risk analysis)– Tests determine the structure behaviour


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CONTENT




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1.5- Manufacturing defects

• Allowable manufacturing defects accounted for in the static demonstration

Size and type4 Inherent to manufacturing process4 Established through quality assurance plan4 Quantified for each sizing criteria

• Manufacturing defects included in the building block demonstration from coupon to full scale test


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CONTENT




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1.6- No-growth / fatigue

Means of compliance AMC25-6034 § 6.2.1 Structural details, elements, and subcomponents of critical structural

areas should be tested under repeated loads to define the sensitivity of the structure to damage growth. This testing can form the basis for validating a no-growth approach to the damage tolerance requirements.[…]

4 § 6.2.3 …The evaluation should demonstrate that the residual strength of the structure is equal to or greater than the strength required for the specified design loads… For the no-growth concept, residual strength testing should be performed after repeated load cycling.

Tests performed for compliance4 No initiation of damages checked defining good design practices4 Critical Non detectable damage/defects under repeated loads

during one DSG4 Critical detectable damage under repeated loads during at least one

interval of inspection4 A residual test after cycling to validate required design loads


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CONTENT




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2- Test Pyramid

•Verify analysis methods

•Verify FEM predicted stress/strain distribution

•Verify predicted failure modes

BUILDING BLOCK APPROACH

COUPONS

DETAILS

ELEMENT

SUBCOMPONENT

COMPONENT

FULL SCALE

•Allowable validation against coupon and smaller specimen

•At detail level, ‘B’ values are determined if test results are used in the analysis. (1 or more typical feature per specimen)

•Statistical treatment: large and small populations ‘B’ value

•In general 1 typical feature per specimen (hole,lay up, impact damage…)

•Determine environmental effects (moisture, thermal…)


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• Purpose4 Assess laminate design value (CAI, TAI, ShAI & failure criterion

including environmental conditions)4 hundred of specimens4 Statistical treatment to obtain design values based on MIL-HDBK-17

2- Test Pyramid for Damage tolerance

Coupons & details tests

ShAI specimen after failure

CAI or TAI specimens after impact


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• Purpose4 Verify strength of critical design details (hole edge impact, top stringer

impact, ply drop off with impact, etc)4 Obtain design values for these critical designs (Statistical treatment

based on small sample law)4 Tenths of specimens

Element tests

Top stringer impacted after compression failure Compression specimen with impact in the

hole radius


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• Purpose4 Verify design concept4 Validate method

(analytical, complex loading, etc)

4 Validate fatigue behaviour

4 Few specimens

Sub-Component tests

Stiffened panel with stringer edge impact loading with

combined compression/pressure


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Component & Full-scale tests• Purpose

4 Validate the stress GFEM analysis4 Prove the behaviour of the structure4 Show compliance with Regulations. For instance

– Limit load strength without detrimental deformations– Ultimate load strength (with BVID damages and allowable manufacturing defects in

critical location)– Fatigue and damage tolerance requirements (no generation of new damages and no

growth of damages) with BVID, manufacturing defect, VID and large damage in critical location

4 Validate in-service repair solutions

Example of full scale test


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CONTENT




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3- Analysis

The damage tolerance method4 Dent depth versus impact energy4 Damage size versus impact energy4 Residual strength versus damage size4 Failure criterion

Relies on coupons&detail tests of the test pyramidAnd is enhanced at higher level of the test pyramid

Parameters accounted for4 Material differences4 Laminate thickness4 Lay-up and stacking sequence4 Hot/wet4 Support condition for impact4 Net section for residual4 Scatter (B-value)4 etc


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3- Analysis

Dent depth prediction example

( )conditionsboundarythMatEfd .,,,=

+ Relationship between Dent depth after relaxation and dent depth just after impact

Qualification test results QI(4mm) AR/RT

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

0 10 20 30 40 50 60 70

Energy (J)

Den

t de

pth

afte

r im

pact

(m

m)

prediction material 1

Test points Material 1



Material 2: thickness effect

0

0,5

1

1,5

2

2,5

0 10 20 30 40 50 60 70

Impact energy (J)

dent

dep

th a

fter

impa

ct (

mm

)

test points 4mmprediction 4mmtest point 4,5mmprediction 4,5mmtest points 5mmprediction 5mm


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3- Analysis

Delaminated area prediction example

( )uplayconditionsboundarythMatEfSd −= ,.,,,Qualification test results QI(4mm) AR/RT

0

200

400

600

800

1000

1200

1400

1600

0 10 20 30 40 50 60 70

Energy (J)

Del

amin

ated

are

a (m

m²)



prediction material 2Test points Material 2


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3- Analysis

Compression after impact prediction example

( )uplayngconditionithMatSdfEpsCAI −= ,,,, Test results AR/RT

2000

3000

4000

5000

6000

7000

8000

0 500 1000 1500 2000 2500 3000

Delaminated area (mm²)

Lo

ss o

f st

rain

in c

om

pre

ssio

n

Material 1 prediction QI 4mm thick

Material 1 Test points QI 4mm thick

Material 2 prediction oriented lay-up 8mm thick

Material 2 Test points oriented lay-up 8mm thick


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CONTENT




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4- Key messages

ü Airbus Damage tolerance methodology relies on

Ø Mature design practicesØ Extensive tests to support analysisØ Robust impact survey based on in-service experience

ü Airlines cooperation, by rigorous inspections reporting , enables Airbus to design more durable and damage tolerant Composite Structures

Ø Impact threat understandingØ Detectability assessment


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© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.

This document and all information contained herein is the sole property of AIRBUS S.A.S.. No intellectual property rights are granted by the delivery of this document or the disclosure of its content. This document shall not be reproduced or disclosed to a third party without the express written consent of AIRBUS S.A.S. This document and its content shall not be used for any purpose other than that for which it is supplied.

The statements made herein do not constitute an offer. They are based on the mentioned assumptions and are expressed in good faith. Where the supporting grounds for these statements are not shown, AIRBUS S.A.S. will be pleased to explain the basis thereof.

AIRBUS, its logo, A300, A310, A318, A319, A320, A321, A330, A340, A350, A380, A400M are registered trademarks.

Documents

FAA Workshop for Composite Damage Tolerance and ... Damage Tolerance... · AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3