Airbus Damage Tolerance Methodology

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1 Chicago, IL FAA Workshop for Composite Damage Tolerance and Maintenance July 19-21, 2006 Prepared by Emilie MORTEAU, Chantal FUALDES Presented by Chantal FUALDES Airbus Head of Composite stress analysis Composite Senior Expert Airbus Damage Tolerance Methodology Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1

2 Main principles in Damage tolerance methodology REGULATION IN-SERVICE INEXPERIENCE ANALYSIS-ANALYSIS TEST RESULTS BUILDING BLOCK APPROACH Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 FATIGUE & DAMAGE TOLERANCE EVALUATIONS July 2006 Page 2

3 CONTENT 1. AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3. Large Damage 4. Hail 5. Manufacturing defects 6. No-growth / Fatigue 2. Test Pyramid 3. Analysis 4. Key messages Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 3

4 CONTENT 1. AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3. Large Damage 4. Hail 5. Manufacturing defects 6. No-growth / Fatigue 2. Test Pyramid 3. Analysis 4. Key messages Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 4

5 1- AIRBUS Damage tolerance philosophy DT Philosophy to answer to requirement and means of compliance Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 5

6 CONTENT 1. AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3. Large Damage 4. Hail 5. Manufacturing defects 6. No-growth / Fatigue 2. Test Pyramid 3. Analysis 4. Key messages Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 6

7 1.1- Damage detectability Damage detectability Damage metric BVID definition Large VID definition Supporting tests and analysis Relaxation behaviour Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 7

1.1- Damage detectability Damage metric Has to be revisited for composite fuselage application for consistency with impact sources (ground handling) For Airbus composite parts (CWB, Keel Beam,

of damage can be simulated by low impactor diameter (diameter generally used for composite test and DT substantiation is from 6 to 25mm), and Resulting damages have similar diameter, mainly the dent

8 1.1- Damage detectability Damage metric Has to be revisited for composite fuselage application for consistency with impact sources (ground handling) For 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), 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 Resulting 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 Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 8

9 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) It corresponds to a probability of detection of 90% with an interval of confidence of 95%. It 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 Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 9

1.1- Damage detectability Large VID definition is technology and structure dependant Damage size associated to walk-around is considered on a

10 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 Typically «penetration» Example for a sandwich structure Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 10

1.1- Damage detectability Supporting tests and analysis and in-service survey DET Inspection Detection of damages on different composite panels (size:

8m², painted or not, glossy or mat, white, grey, blue or green paint, primer) Duration of inspection : not limited Distance of inspection : 50 cm

TRANSVERSE IMPACT GVI Inspection Inspection on large panel (8m*1.

11 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) Several impactor diameter : 6mm and 16mm A total of 902 inspections FOR BVID TRANSVERSE IMPACT 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 Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 11

12 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 P det ( d > d j ) = d j 1 2π. σ d : dent e ( log d m ) 2σ depth m = Log( a50/ 95) 2 2 d (log d ) = Log( a99/ 95) Log ( a 50/95) σ = 2.33 logd m σ j Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page π e 2 y 2 dy BVID

13 1.1- Damage detectability Supporting tests and analysis and in-service survey Example for GVI inspection Pourcentage of damages with dent less than d 120,00% 100,00% 80,00% 60,00% 40,00% 20,00% Cumulative curve of dent depth 0,00% 0,00 0,50 1,00 Airbus 1,50 BVID 2,00 2,50 3,00 3,50 4,00 4,50 5,00 5,50 6,00 6,50 (GVI) Dent depth (mm) Airbus BVID(GVI) is consistent with Airline survey findings 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 Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 13

14 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. 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. Dent depth evolution (mm) 0,90 0,80 0,70 0,60 0,50 0,40 0,30 0,20 0,10 0,00 Material A After impact After 20 mn After 48H After WA Before fatigue After 110cycles 0,6Fr After fatigue Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 14 Event Hot/wet ageing 18J impact+wa70/95%hr 1500h and fatigue (r=10 c/c) at 20 18J impact+wa70/95%hr 1500h and fatigue (r=10 c/c) at J impact+wa70/95%hr 1500h and fatigue (r=-1 t/c) at 20 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 J 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 23J impact+wa70/95%hr 1500h and fatigue (r=10 c/c) at J impact+wa70/95%hr 1500h and fatigue (r=-1 t/c) at 20

15 CONTENT 1. AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3. Large Damage 4. Hail 5. Manufacturing defects 6. No-growth / Fatigue 2. Test Pyramid 3. Analysis 4. Key messages Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 15

16 1.2- Impact threat Impact threat Impact threat definition Typical impact threat Supporting data and analysis Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 16

17 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. p ( E j E j Ref: Effect of low velocity impact damage on primary aircraft structures the certification issue; Aug 1999, J. Rouchon ) = 10 x 15 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) Impact threat definition E j with x=3, giving Typical impact threat 5 P j ( E 30J) = 10 / 9 P j ( E 90J) = 10 / 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. Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 17 fh fh

18 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, totalling 1,140,000 flight hours A similar survey covering the whole aircraft covering A320 family, totalling 500,000 flight hours And 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. Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 18

19 CONTENT 1. AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3. Large Damage 4. Hail 5. Manufacturing defects 6. No-growth / Fatigue 2. Test Pyramid 3. Analysis 4. Key messages Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 19

20 1.3- Large Damage Large Damage Capability, LDC: not realistic damage Design precautions to protect against the unknown. Design precautions 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 Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 20

21 CONTENT 1. AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3. Large Damage 4. Hail 5. Manufacturing defects 6. No-growth / Fatigue 2. Test Pyramid 3. Analysis 4. Key messages Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 21

22 1.4- Hail Hailstorms data is based on meteorological survey defining: 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. 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: Unloaded Structure, hail on ground for commercial aspect 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 Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 22

23 CONTENT 1. AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3. Large Damage 4. Hail 5. Manufacturing defects 6. No-growth / Fatigue 2. Test Pyramid 3. Analysis 4. Key messages Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 23

24 1.5- Manufacturing defects Allowable manufacturing defects accounted for in the static demonstration Size and type 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 Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 24

25 CONTENT 1. AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3. Large Damage 4. Hail 5. Manufacturing defects 6. No-growth / Fatigue 2. Test Pyramid 3. Analysis 4. Key messages Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 25

26 1.6- No-growth / fatigue Means of compliance AMC 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.[ ] 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 No initiation of damages checked defining good design practices Critical Non detectable damage/defects under repeated loads during one DSG Critical detectable damage under repeated loads during at least one interval of inspection A residual test after cycling to validate required design loads Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 26

27 CONTENT 1. AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3. Large Damage 4. Hail 5. Manufacturing defects 6. No-growth / Fatigue 2. Test Pyramid 3. Analysis 4. Key messages Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 27

2- Test Pyramid BUILDING BLOCK APPROACH FULL SCALE Verify analysis methods Verify FEM predicted stress/strain distribution Verify predicted failure modes COMPONENT SUBCOMPONENT Allowable validation

28 2- Test Pyramid BUILDING BLOCK APPROACH FULL SCALE Verify analysis methods Verify FEM predicted stress/strain distribution Verify predicted failure modes COMPONENT SUBCOMPONENT 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) ELEMENT DETAILS COUPONS 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 ) Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 28

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

29 2- Test Pyramid for Damage tolerance Purpose Assess laminate design value (CAI, TAI, ShAI & failure criterion including environmental conditions) hundred of specimens Coupons & details tests Statistical treatment to obtain design values based on MIL-HDBK-17 CAI or TAI specimens after impact ShAI specimen after failure Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 29

2- Test Pyramid for Damage tolerance Purpose Verify strength of critical design

Obtain design values for these critical designs (Statistical treatment based on

compression failure Compression specimen with impact in the hole radius Damage

30 2- Test Pyramid for Damage tolerance Purpose Verify strength of critical design details (hole edge impact, top stringer impact, ply drop off with impact, etc) Obtain design values for these critical designs (Statistical treatment based on small sample law) Tenths of specimens Element tests Top stringer impacted after compression failure Compression specimen with impact in the hole radius Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 30

loading, etc) Validate fatigue behaviour Few specimens

impact loading with combined compression/pressure Damage

31 2- Test Pyramid for Damage tolerance Purpose Verify design concept Validate method (analytical, complex loading, etc) Validate fatigue behaviour Few specimens Sub-Component tests Stiffened panel with stringer edge impact loading with combined compression/pressure Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 31

2- Test Pyramid for Damage tolerance Purpose Component & Full-scale tests Validate the stress GFEM analysis Prove the behaviour of the structure Show compliance with Regulations.

32 2- Test Pyramid for Damage tolerance Purpose Component & Full-scale tests Validate the stress GFEM analysis Prove the behaviour of the structure 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 Validate in-service repair solutions Example of full scale test Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 32

33 CONTENT 1. AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3. Large Damage 4. Hail 5. Manufacturing defects 6. No-growth / Fatigue 2. Test Pyramid 3. Analysis 4. Key messages Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 33

34 3- Analysis The damage tolerance method Dent depth versus impact energy Damage size versus impact energy Residual strength versus damage size Failure criterion Relies on coupons&detail tests of the test pyramid And is enhanced at higher level of the test pyramid Parameters accounted for Material differences Laminate thickness Lay-up and stacking sequence Hot/wet Support condition for impact Net section for residual Scatter (B-value) etc Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 34

35 3- Analysis Dent depth prediction example ( E, Mat, th, boundaryconditions) d = f. + Relationship between Dent depth after relaxation and dent depth just after impact Qualification test results QI(4mm) AR/RT Material 2: thickness effect 4,5 2,5 Dent depth after impact (mm) 4 3,5 3 2,5 2 1,5 1 0,5 0 prediction material 1 Test points Material 1 prediction material 2 Test points Material Energy (J) Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 35 dent depth after impact (mm) 2 1,5 1 0,5 test points 4mm prediction 4mm test point 4,5mm prediction 4,5mm test points 5mm prediction 5mm Impact energy (J)

36 3- Analysis Delaminated area prediction example Sd ( E, Mat, th, boundaryconditions. lay up) = f, Qualification test results QI(4mm) AR/RT Delaminated area (mm²) Energy (J) prediction material 1 Test points Material 1 prediction material 2 Test points Material 2 Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 36

37 3- Analysis Compression after impact prediction example Eps CAI ( Sd, Mat, th, conditioning lay up) = f, Test results AR/RT 8000 Material 1 prediction QI 4mm thick Loss of strain in compression Delaminated area (mm²) Material 1 Test points QI 4mm thick Material 2 prediction oriented lay-up 8mm thick Material 2 Test points oriented lay-up 8mm thick Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 37

38 CONTENT 1. AIRBUS Damage tolerance philosophy 1. Damage Detectability 2. Impact threat 3. Large Damage 4. Hail 5. Manufacturing defects 6. No-growth / Fatigue 2. Test Pyramid 3. Analysis 4. Key messages Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 38

39 4- Key messages Airbus Damage tolerance methodology relies on Mature design practices Extensive tests to support analysis Robust impact survey based on in-service experience Airlines cooperation, by rigorous inspections reporting, enables Airbus to design more durable and damage tolerant Composite Structures Impact threat understanding Detectability assessment Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 39

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.

40 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. Damage Tolerance Methodology - ESAC - Ref. X029PR Issue 1 July 2006 Page 40

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FAA Bombardier Composite Transport Workshop (Sept 15 17, 2015) Prepared: J. van Doeselaar/ S. Rabois/ J.L. Leon-Dufour Smart(er) testing Airbus perspectives Pyramid considering past experience, and use