Airbus Composites - Damage Tolerance Methodolgy - Fualdes

Chicago, IL

FAA Workshop for Composite Damage Tolerance and Maintenance July 19-21, 2006 Prepared Prepa red by Emilie MORTE MORTEAU, AU, Chantal FUALDES FUALDES

Presented by

Chantal FUALDES Airbus Head of Composite stress analysis Composite Senior Expert

Composites @ Airbus Damage Tolerance Methodology Damage Damage Tolerance Methodolo Methodology gy - ESAC ESAC - Ref. X029PR0608 X029PR0608046 046 - Issue 1

Main principles in Damage tolerance methodology IN IN--SERVICE EXPERIENCE

N O I T A L U G E R

. t n e m u c o d y r a t e i r p o r p d n a l a i t n e d i f n o C . d e v r e s e r s t h g i r l l A . S . A . S S U B R I A ©

ANALYSIS ANALYSIS--

TEST RESULTS RESULTS – – BUILDING BLOCK APPROACH

Damage Tolerance Methodology - ESAC - Ref X029PR0608046 - Issue 1

FATIGUE & DAMAGE TOLERANCE EVALUATIONS July 2006

Page 2

Main principles in Damage tolerance methodology IN IN--SERVICE EXPERIENCE

N O I T A L U G E R


ANALYSIS ANALYSIS--

TEST RESULTS RESULTS – – BUILDING BLOCK APPROACH


FATIGUE & DAMAGE TOLERANCE EVALUATIONS July 2006

Page 2

CONTENT 1. AIRBUS Damage tolerance philosophy


1.

Damage Dam age Detec Detectabili tability ty

2.

Impact threat

3.

Large Damage

4.

Hail

5.

Manufacturing defects

6.

No-growth / Fatigue

2. Test Pyramid Analysis s 3. Analysi 4. Key messages


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1.

Damage Damage Detectab Detectability ility

2.

Impact threat

3.

Large Damage

4.

Hail

5.


6.

No-growth / Fatigue

2. Test Pyramid 3. Analysis 4. Key messages


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1- AIRBUS Damage tolerance philosophy DT Philosophy to answer to requirement and means of compliance



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1.

Damage Detectability

2.

Impact threat

3.

Large Damage

4.

Hail

5.


6.

No-growth / Fatigue



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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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1.1- Damage detectability Has to be revisited for composite fuselage application for consistency with impact sources (ground handling) (CWB, Keel Beam, aileron, spoiler, HTP, VTP, LGD, etc)

Damage metric

For Airbus composite parts 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), 4

Shape of damage can be simulated by low impactor diameter (diameter generally used for composite test and DT substantiation is from 6 to 25mm), and 4

Resulting damages have similar diameter, mainly the dent depth (and crack length for edges), and depend on the impact energy 4


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 Damage Tolerance Methodology - ESAC - Ref X029PR0608046 - Issue 1

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1.1- Damage detectability BVID definition The minimum impact damage surely detectable by scheduled inspection Dent 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 d esign 4

–the aim is to sustain UL with BVID . t n e m u c o d y r a t e i r p o r p d n a l a i t n e d i f n o C . d e v r e s e r s t h g i r l l A . S . A . S S U B R I A ©

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


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1.1- Damage detectability Large VID definition is technology and structure dependant

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

4


Typically « penetration »

Example for a sandwich structure


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1.1- Damage detectability Supporting tests and analysis and in-service survey 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)

FOR BVID TRANSVERSE IMPACT

§Several impactor diameter : 6mm and 16mm § A total of 902 inspections

GVI Inspection §Inspection on large panel (8m*1.2 m) . t n e m u c o d y r a t e i r p o r p d n a l a i t n e d i f n o C . d e v r e s e r s t h g i r l l A . S . A . S S U B R I A ©

§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


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1.1- Damage detectability Supporting tests and analysis and in-service survey 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

d j . t n e m u c o d y r a t e i r p o r p d n a l a i t n e d i f n o C . d e v r e s e r s t h g i r l l A . S . A . S S U B R I A ©

P det ( d > d j ) =

∫

−∞

−

1 2π .σ

e

log d j −m

(log d − m )2 2σ

2

σ

d (log d ) =

∫

−∞

1 2π

e

−

y 2 2

dy

d : dent depth m = Log ( a50 / 95) σ

=

Log (a 99 / 95) − Log (a 50 / 95)

BVID

2.33


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1.1- Damage detectability Supporting tests and analysis and in-service survey Example for GVI inspection Cumulative curve of dent depth


t n e d h t i w s e d g a n a m h a t d s f s o l e e g a t n e c r u o P

120,00% 100,00% 80,00% 60,00% 40,00% 20,00% 0,00%

BVID 0,00 0,50 Airbus 1,00 1,50 2,00 2,50 3,00 3,50 4,00 4,50 5,00 5,50 6,00 6,50 (GVI) Dent depth (mm)

Survey in European airline 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 Damage Tolerance Methodology - ESAC - Ref X029PR0608046 - Issue 1

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1.1- Damage detectability Relaxation behaviour 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.

18J impact+WA70/95%HR 1500h and fatigue (r=10 c/c) at 20°

Material A


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.

18J impact+WA70/95%HR 1500h and fatigue (r=10 c/c) at -40°

0,90 ) 0,80 m m0,70 ( n o 0,60 i t u l o 0,50 v e 0,40 h t p 0,30 e d t n 0,20 e D

20J impact+WA70/95%HR 1500h and fatigue (r=10 c/c) at 20° 20J impact+WA70/95%HR 1500h and fatigue (r=10 c/c) at -40° 20J impact+WA70/95%HR 1500h and fatigue (r=-1 t/c) at 20° 23J impact+WA70/95%HR 1500h and fatigue (r=10 c/c) at 20°

0,10 0,00 After impact After 20 mn

After 48H

After WA

Before fatigue

After After fatigue 110cycles 0,6Fr

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

18J impact+WA70/95%HR 1500h and fatigue (r=-1 t/c) at 20°

Hot/wet ageing

July 2006

23J impact+WA70/95%HR 1500h and fatigue (r=10 c/c) at -40° 23J impact+WA70/95%HR 1500h and fatigue (r=-1 t/c) at 20°

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1.


2.

Impact threat

3.

Large Damage

4.

Hail

5.


6.

No-growth / Fatigue



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1.2- Impact threat

Impact threat •Impact threat definition •Typical impact threat •Supporting data and analysis . t n e m u c o d y r a t e i r p o r p d n a l a i t n e d i f n o C . d e v r e s e r s t h g i r l l A . S . A . S S U B R I A ©


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1.2- Impact threat Impact threat definition 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. −5

p j ( E ≥ E j ) = 10 Ref: Effect of low velocity impact damage on primary aircraft structures – the certification issue; Aug 1999, J. Rouchon

− x −

E j 15

P j ( E ≥ 30 J ) = 10 / fh

with x=3, giving

P j ( E ≥ 90 J ) = 10 −9 / fh

Typical impact threat

External part


•Typical impact threat: 35J 10-5 /FH (static cut-off) 90J 10-9 /FH (damage tolerance cut-off) •HTP root/Rear fuselage skin 140J 10-5 /FH (static cut-off) •Doorway zones 132,5J 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.


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


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.


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1.


2.

Impact threat

3.

Large Damage

4.

Hail

5.


6.

No-growth / Fatigue



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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

4 . t n e m u c o d y r a t e i r p o r p d n a l a i t n e d i f n o C . d e v r e s e r s t h g i r l l A . S . A . S S U B R I A ©

Fail Safe demonstration on main joint areas: hinged structures, high load introduction (disconnection of one load path) … 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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1.


2.

Impact threat

3.

Large Damage

4.

Hail

5.


6.

No-growth / Fatigue



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1.4- Hail •

Hailstorms data is based on meteorological survey defining: 4

Size of hailstones : – – –

4

4

• . t n e m u c o d y r a t e i r p o r p d n a l a i t n e d i f n o C . d e v r e s e r s t h g i r l l A . S . A . S S U B R I A ©

Standard hailstorm, Rare hailstorm, Extremely rare hailstorm,

(Dia 10mm) for a P of 50% of hailstorms (Dia 25mm) for a P of 5% of hailstorms (Dia 50mm) for a P of 0.1% of hailstorms.

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

4

Showers of Dia 10 and 50 mm ( 33m/s; 32 Joules)

Loaded structure, hail in flight considered in damage tolerance analysis (Energy, loading, risk analysis) –

Tests determine the structure behaviour


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1.


2.

Impact threat

3.

Large Damage

4.

Hail

5.


6.

No-growth / Fatigue



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1.5- Manufacturing defects • Allowable manufacturing defects accounted for in the static demonstration Size and type 4 4 4


Inherent to manufacturing process Established through quality assurance plan Quantified for each sizing criteria

• Manufacturing defects included in the building block demonstration

from coupon to full scale test


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1.


2.

Impact threat

3.

Large Damage

4.

Hail

5.


6.

No-growth / Fatigue



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1.6- No-growth / fatigue Means of compliance AMC25-603 4

4


§ 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 nogrowth approach to the damage tolerance requirements.[…] § 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 compliance 4 No initiation of damages checked defining good design practices Critical Non detectable damage/defects under repeated loads 4 during one DSG Critical detectable damage under repeated loads during at least one 4 interval of inspection A residual test after cycling to validate required design loads 4


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1.


2.

Impact threat

3.

Large Damage

4.

Hail

5.


6.

No-growth / Fatigue



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2- Test Pyramid BUILDING BLOCK APPROACH

•Verify analysis methods •Verify FEM predicted stress/strain distribution FULL SCALE

•Verify predicted failure modes

COMPONENT

•Allowable validation against coupon and smaller specimen SUBCOMPONENT


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

ELEMENT

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

COUPONS


•In general 1 typical feature per specimen (hole,lay up, impact damage…) •Determine environmental effects (moisture, thermal…)

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2- Test Pyramid for Damage tolerance Coupons & details tests •

Purpose 4

Assess laminate design value (CAI, TAI, ShAI & failure criterion including environmental conditions)

4

hundred of specimens

4

Statistical treatment to obtain design values based on MIL-HDBK-17 CAI or TAI specimens after impact


ShAI specimen after failure


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2- Test Pyramid for Damage tolerance Element tests •


Purpose 4

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

Top stringer impacted after compression failure


Compression specimen with impact in the hole radius July 2006

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2- Test Pyramid for Damage tolerance Sub-Component tests •


Purpose 4

Verify design concept

4

Validate method (analytical, complex loading, etc)

4

Validate fatigue behaviour

4

Few specimens

Stiffened panel with stringer edge impact loading with combined compression/pressure


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2- Test Pyramid for Damage tolerance Component & Full-scale tests •

Purpose 4 4 4

Validate the stress GFEM analysis Prove the behaviour of the structure Show compliance with Regulations. For instance – – –

4


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

Validate in-service repair solutions

Example of full scale test


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1.


2.

Impact threat

3.

Large Damage

4.

Hail

5.


6.

No-growth / Fatigue



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3- Analysis The damage tolerance method Dent depth versus impact energy 4 Damage size versus impact energy 4 Residual strength versus damage size 4 Failure criterion 4 Relies on coupons&detail tests of the test pyramid And is enhanced at higher level of the test pyramid


Parameters accounted for Material differences 4 Laminate thickness 4 Lay-up and stacking sequence 4 Hot/wet 4 Support condition for impact 4 Net section for residual 4 Scatter (B-value) 4 etc 4 Damage Tolerance Methodology - ESAC - Ref X029PR0608046 - Issue 1

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3- Analysis Dent depth prediction example

d = f ( E , Mat , th, boundary.conditions) + Relationship between Dent depth after relaxation and dent depth just after impact Material 2: thickness effect

Qualification test results QI(4mm) AR/RT 2,5

4,5

test points 4mm prediction 4mm test point 4,5mm prediction 4,5mm test points 5mm prediction 5mm

4

prediction material 1 3,5

o C . d e v r e s e r s t h g i r l l A . S . A . S S U B R I A ©

2

Test points Material 1

) m m ( 3 t c a . t p n e 2,5 m m i u c r o e d t y r f 2 a t a e i r p h t o r p p d e 1,5 n a d l t a i t n n e e d i f n D1

) m m ( t c a1,5 p m i r e t f a h t 1 p e d t n e d

prediction material 2 Test points Material 2

0,5

0,5

0

0 0

10

20

30

40

50

60

Energy (J) Damage Tolerance Methodology - ESAC - Ref X029PR0608046 - Issue 1

70

0

10

20

30

40

50

Impact energy (J)

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60

70

3- Analysis Delaminated area prediction example

Sd = f ( E , Mat , th, boundary.conditions, lay − up ) Qualification test results QI(4mm) AR/RT 1600

1400


1200 ) ² m m1000 ( a e r a d 800 e t a n i m 600 a l e D


400


200

0 0

10

20

30

40

50

60

70

Energy (J)


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3- Analysis Compression after impact prediction example

EpsCAI = f (Sd , Mat , th, conditioni ng , lay − up ) Test results AR/RT 8000

Material 1 prediction QI 4mm thick 7000


Material 1 Test points QI 4mm thick

n o i s s e r 6000 p m o c n 5000 i n i a r t s f 4000 o s s o L

Material 2 prediction oriented lay-up 8mm thick Material 2 Test points oriented lay-up 8mm thick

3000

2000 0

500

1000

1500

2000

2500

3000

Delaminated area (mm²)


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1.


2.

Impact threat

3.

Large Damage

4.

Hail

5.


6.

No-growth / Fatigue



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4- Key messages ü Airbus Damage tolerance methodology relies on Ø

Mature design practices Ø Extensive tests to support analysis Ø 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 . t n e m u c o d y r a t e i r p o r p d n a l a i t n e d i f n o C . d e v r e s e r s t h g i r l l A . S . A . S S U B R I A ©

Ø

Impact threat understanding

Ø

Detectability assessment


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Airbus Composites - Damage Tolerance Methodolgy - Fualdes

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