Composite Materials: Developing Continued Airworthiness Issues Simon Waite... · TE.GEN.00409‐001...

TE.GEN.00409‐001

Composite Materials:

Developing Continued Airworthiness Issues

Dr. S. Waite Structures Expert, EASA

Technology Evolution – Impact on Airworthiness23-24th.September 2014, Windhoek, Namibia

19/09/2014 SIASA Workshop - Namibia 2014 2

Composite Safety Issues

Composite Design/Operation/Maintenance

Agenda:

‐ Change from metallic to composites structures – basics (new materials, new applications, new engineering properties…)

‐ Composite Design/Rules/Guidance (design certification/ continued airworthiness interface)

‐ Developing Operational/Maintenance related activities:

‐ HEWABI (High Energy Wide Area Blunt Impact) ‐ Bonded Structure and Repairs



Change from metallic to composites structures :– composite use is not new to aviation…

(established rotorcraft and small fixed wing use)

metals (Duralumin) start to dominate in 1917, – Junker J1 1917

bonded balsa plywood sandwich 1940

ATR otbd wing box

sandwich secondary structure ‐ primary control surfaces – PSE monolithic structure

A380 Glare crown

B787, A350 fuselages

A320 empennage

wood and fabricWright Flyer



Recognising the Transition from Traditional Materials to Composites:

What is new includes…

- extended, extensive, and large scale application of CFRP in largepassenger CS25 structure, including the pressure hull, and wing box

A350 XWB

Alu alloyCFRP MonolithicCFRP SandwichQuartz, Glass

19/09/2014 5

•Tensile Modulus/Specific Gravity MNm-2

•Ten

sile

Stre

ngth

/Spe

cific

Gra

vity

MN

m-2

•Titanium

•Carbon

•Steel

•Aramid

•Glass

•Boron

•Aluminium

•5,000 •10,000

•50

•100

•150

Advantages:

- high specific strength

- high specific stiffness

- good fatigue resistance

- but only if designed correctly

- loads understood (out of plane, low strain etc)

- undamaged

- coupling of other effects e.g. temperature and aging accounted for

Key Points: Anisotropic

Inhomogeneous


SIASA Workshop - Namibia 2014

Why is the aviation interested in using these materials?



What are the potentially significant differences between typical metal and composite engineering properties?

Strength/Stiffness v Ply Angle (non-dimensionalised)

Anisotropy: potentially difficult to predict:

- failure loads

- damage modes

- damage locations

Anisotropy: Significant strength/stiffness reduction with ply orientation relative to load



Damage – Inspection and Damage Tolerance:

Composites:

- relatively low out of plane, compressive, and shear strength

- impact sensitive

- strength/stiffness reduction for critical damage modes

- material relaxation

Anisotropy:

Potential for significant Barely Visible/Non-Visible Damage….




Metallic structure: Typically, crack growth (da/dN) vs stress intensity factor relationship is understood (empirically), damage detectable –maintenance schedule (MS) credit

metals

9

Brittle composite

Toughcomposite

Metal•B

Material BSteel 1.6Aluminium 2.2Carbon/Thermoplastic 6.1Carbon/Epoxy 12.2

da/dN

Gmax

2B

2B

PdNda

PGAGdNda

Solution :- ensure that when damage is present, G is below a threshold value for crack growth

Composite structure: Typically, crack growth (da/dN) not understood, some damages not detectable –mixed/competing damage modes. No‐Growth philosophy necessary to comply – substantiated damage threat survey necessary in MS development



19/09/2014 SIASA Workshop - Namibia 2014

composites

10

•sandwich core

•skins

•A•A •B

•skin and core penetration -

visible

•delamination – not visible

•different damage modes

* similar arguments regarding impactor: - radii (larger radius, blunter impact) - material (softer iced cotton ball v metallic)

Competing Damage Modes (some not visible):

‐ for robust structures ‐ this must be understood and enveloped by manufacturers for all reasonably expected threats for a range of impactor geometries, energies, stiffnesses etc

- potentially more critical undetectable damage modes at lower energy…


19/09/2014 SIASA Workshop - Namibia 2014

impact energy A > BA B

19/09/2014 11

Also*:- high engineering property data scatter (static & fatigue)

- environment (moisture/temperature – manufacture and in-service)

- poor heat and electrical conduction (lightning strike)

- fire behaviour (toxic fumes, fibre release, strength/stiffness)

- quasi-brittle (vulnerable to load peaks, impact damage, strain rate etc)

- failure mode changes/mixed modes (impact, fatigue growth etc)

- difficult to repair (drying, cleanliness etc)

* particularly for older materials and processes – large existing fleet

important to composites behaviour

Therefore, the regulators are interested…





- Engineering Properties are the result of Material and Process, typically completed late in the production cycle….

Engineering properties are built into part or repair

TRAINING!

closer co‐operation between stakeholders required –

suppliers, design, production, continued airworthiness, and

regulation

moves sensitive production type activities in challengingservice

environment!

SAFETY MANAGEMENT

SYSTEMS(SMS)

•13

EU ParliamentEU Council

EU Commission

EASA

•Bin

ding

EU Aviation Safety Regulations

•Non

-Bin

ding

13

Enhanced SMS - specific rules in development EASA Safety Plan: http://easa.europa.eu/sms/

Note: Safety Management System (SMS) already exists as implicit and explicit linkage between rulesand specifications

Composite Safety in Aviation



Safety managed in certification using extensive: - test/analysis pyramid - robust structure design philosophy- training:

‐ operator input essential

‐ impact threat can be an important driver for design and in‐service certification

‐ typically more integrated than for metallic structure



* Harmonised with FAA AC 20-107B

Damage Categories EASA AMC 20-29*:



Standardisation of Certification Requirements for Composites

Background:- limited existing composite specific rules/guidance

- use of composites must not reduce the existing acceptable level of safety

Existing Certification Rules/Guidance

‘CS 25.603: Materials (For Composite Materials see AMC 20-29)

The suitability and durability of materials used for parts, the failure of which could adversely affect safety, must…..’

- be based upon experience/test- conform to specifications (meeting design data)

- consider environmental effect (temperature, moisture etc)



Some high level Certification Specifications are already equipped to address the transition to some extent…

Initial Certification Driven Continued Airworthiness:

CS25.571: Damage-tolerance & fatigue evaluation of structure

‘(a) General. An evaluation of the strength, detail design, and fabrication must show that catastrophic failure due to fatigue, corrosion, or accidental damage, will be avoided throughout the operational life of the aeroplane…’

Historically: metal/fatigue/corrosion focused

‘transition’ - more extensive AD/ED focus (may be addressed at AMC level in Aging Aircraft NPA 2013-07)

…further industry/regulator developed guidance is necessary…

Environmental Damage ‐ ED Accidental Damage ‐ ADconverge with

MSG3 terminology(Maintenance Steering Group)

19/09/2014 18

Initial Certification Driven Continued Airworthiness:

CS 25.571: Damage Tolerance and Fatigue Evaluation of Structure:

‘(3)…..inspections or other procedures must be established as necessary to prevent catastrophic failure, and must be included in the Airworthiness Limitations Section of the Instructions for Continued Airworthiness required by CS 25.1529’

CS 25.1529: Instructions for Continued Airworthiness:

‘Instructions for Continued Airworthiness in accordance with Appendix H must be prepared’

Note: some change in balance/emphasis in the design/operating environment expected (assuming same ground crew capabilities as for metallic structure, e.g. inspector eye sight etc remains the same, and operators continue to wish to use Visual Inspection as primary means of inspection – typically 80‐90%, same vehicle drivers etc).




Figure 4 ‐ Schematic diagram of residual strength illustrating that significant accidental damage with “no‐growth” should not be left in the structure without repair for a long time.

similar to metallic fatigue crack behaviour



Several conditions are required to exist together for a safety risk from damages:

‐ event occurs &

‐ damaged produced&

‐ < UL capability (large damage, critical location, unsubstantiated mode/extent)

&‐ damage is not reported/ remains undetected

&‐ load event > Residual Strength capability (>LL)

‐ all of these conditions do occur (each occasionally, but typically not together)…..‐ combined, not enough data to meaningfully quantify ‐ most events not significant safety issue ‐managed within cert Cat. 1‐4, or Cat 5 (obvious)


e.g., impact event, poor bond

Potential safety threat conditions


‐ Cat 3/5?: Caution – safety is about more than damage detection!

‐ CS25 ‐ Horizontal Stab‐ external impact detected during minor input(Cat 3 type finding?)

‐ cosmetic repair completed‐ no internal inspection – Why?‐ severed skin/spar (PSE) found

at next heavy input

Safety Message: correct follow-up action is essential

Training and awareness of maintenance staff is essential!

Composite Safety Issues Follow‐up Actions



most events not a significant safety issues ‐managed within cert Cat. 1‐4, or Cat 5 (obvious).

‐ 30‐40+% airframe damages due to ground impact ‐ high economic cost (Euro 2‐4Bn/year!) ‐ potential safety risk – metal or composite

‐ 50% damages not found at time of event (metal or composite)

Safety requires:

‐ understanding of damage modes, e.g. notch/disbond

‐ manufacturer to understand design space, threats, operator capabilities etc

‐ some typical impact events may leave damages which may be visible in metallic structure, but may not be visible in composite – manufacturer to manage via Cat 1/2/3 substantiation using test pyramid for appropriate damage modes.



Cat 5 caution!: Threats to consider include…

‐ design certification cannot address someone walking away from obvious damage… metallic or composite!

‐ possible difference (composite v metal) ‐ extensive non‐visible damage is caused andresponsible/irresponsible individual is marginal regarding decision to declare event (‘blame culture’?), then no obvious damage may help to drive the decision the wrong way (again, increased training/awareness required)

LHR damage ‐ aft cargo bay skin cut not reported by responsible individual – but visible during push back



Cat 5 caution!: Threats to consider include…

‐ Poor ramp discipline ‐ loose items exposed to wind/jet blast can impact fuselage without witness, e.g. loose containers, stairs etc.

(note: recent NPA 2013‐02‐05 addressing engine, tire, and runway debris threats suggests wind/jet‐blast impact events are not statistically significant or easily defined)

see aerodrome regs



AMC 20‐29:

‘Pilots, ramp maintenance and other operations personnel that service aircraft should be trained to immediately report anomalous ramp incidents and flight events that may potentially cause serious damage to composite aircraft structures’

Operator Action: appropriate training!

Manufacturer Action:

‐manufacturer to show that no serious additional threat exists unless the level of damage is so obvious and so far beyond typical F&DT considerations that those responsible must be aware – understanding Cat 2/3 v Cat 5.

‐manufacturer development work‐ training support for operators (e.g. video, ramp damage checker etc)

Regulator Action:

‐ work with manufacturers and operators (e.g. via SAE CACRC) to ensure CS25 satisfied‐ R&D (public data, transparent discussion)‐ develop aerodrome/ground handling regs – see support slides‐ fleet leader/sampling process? (longer term issue – find AD/ED surprises ‐ cumulative BVID, degradation, repair interaction etc)



High Energy Wide Area Blunt Impact (HEWABI):

*[email protected]

HEWABI



HEWABI: Extensive test pyramid required: Current R&D:‐ shows sensitivity to configuration (see following slides)‐ difficult to represent aircraft level Boundary Conditions well in lower pyramid

Conclusion: R&D suggests high level pyramid testing required to understand configuration sensitivity (& support conventional F&DT work)

HEWABI



Public R&D (H. Kim, Bishop) intended to show that understanding design space is important wrt the potential for non‐visible damage resulting from HEWABI.

H.Kim ‐ Composite Skin/Str/Frame – significance of shear tie stiffness

compliant shear ties- no external visible damage

- internal disbondstiff shear ties

- some external visible damage- internal frame damage

HEWABI



Public R&D (H. Kim, Bishop) intended to show that understanding design space is important wrt the potential for non‐visible damage resulting from HEWABI.

Bishop ‐ Hybrid Structure ‐ Composite Skin/Str/Metallic Frame

impact = 2500 kg at 1 m/s.

compliant shear tie - no external visible damage- internal shear tie failures

- possible to manage as Cat 2

HEWABI



HEWABI ‐ Conclusions:

CS25 satisfied – but new technology application requires some change in design and maintenance culture and process, as expected

‐ manufacturers : ‐ extensive test and analysis pyramid ‐ all failure modes to be identified and understood (load, mode, location etc)‐ robust structure/ stable underlying failure modes‐ support operators training

‐ operators/maintainers ‐ workforce discipline is important ‐ operators/manufactures must address this by improving training/ awareness (prevent/detect/follow‐on actions)

Safety Message: improve training of ground crew/vehicle operators‐ easy long term economic and potential safety benefit – metallic or composite!

‐ regulators ‐ Harmonised Blunt Impact Policy planned ‐ Continued R&D

‘Acceptable’ level of safety is maintained by industry (all parts) /regulator collaboration (Safety Management System, including ‘engineering judgement’/‘common sense’)

HEWABI



Bonded Structure and Repairs:

co‐cured

co‐bonded

secondary bonded

Bonded Structure

1 or 2 cured or metal

1 and 2 cured or metal

neither 1 nor 2 cured


Many examples: e.g. AD2010-26-53 …emergency AD – significant failure during acceptance flight test – 7 foot skin disbond from the upper forward wing spar

Mandatory Occurrence Reports (MORs) & ADREP Incidents/Accidentssearch terms: composites, delaminations, and disbond

0

10

20

30

40

50

60

70

76-81 81-86 86-91 91-96 96-2001

2001-2006

2006-2011

Years (5yr totals)

No.

Occ

urre

nces

CAA UK M OR composites

CAA UK M OR composites,delaminat ion, disbond

EASA ADREP (globalCS25) incidents/accidentsdelaminat ion, disbond

*MOR (UK CAA CAP382) : prevent accidents/incidents…not to attribute blame/liability

significant incidents

Note: data needs further investigation: unacceptable ‘disbond’ – cause or witness?


Accident/ Incident data:

CAA-UK (MORs):- composites, delam, disbond- delam, disbond

EASA (ADREP):- delam, disbond

need to improve forensics & taxonomy

Bonded Structure


Several conditions are required to exist together for disbond or delamination to be a safety issue:

- a disbond/weak bond/delamination exists

&

- < UL capability (large damage/disbond, critical location)

&

- damage/defect remains undetected

&

- load event > Residual Strength capability (>LL)

- all of these conditions do occur (each occasionally, but typically not together…..

- not enough data to meaningfully quantify - most events not significant safety issue

(most applications have not been significant)

e.g. in-service disbond reported (repair/production issues) approx:

1 incident 10^6 hrs1 serious incident 10^8 /10^9 hrs

No fatal accidents(CAA-UK MOR & fleet data only)

However, some have(incidents beyond CAA – UK data)

1 serious incident/accident>10^8 hrs


repair orremanufacture?

Bonded Structure

19/09/2014 34

Load response – from time domain flutter analysis

Following A300 Rudder Loss (and sandwich repair issues):

- extensive Airbus work to understand Ground-Air-Ground (GAG) cycle (Airbus: Roland Thevenin, Ralph Hilgers presentations CMH-17 26-28/9/11 Delft)

- CMH-17 Disbond/Delamination Working Group* Activity (Airbus: NASA: Ronald Krueger)


* plan to extend WG activity to include non‐pressure cycle related GAG issues, monolithic structural bonding etc

typical existing fleet structure configurations

Composite Safety Issues Bonded Structure



Standardisation of Certification Requirements for CompositesHarmonised CM – Bonded Repair Size Limits (BRSL)*: (Draft for comment by 14th October 2014):

- reasons for repair limits not understood by some in the repair community

- ‘remanufacturing’ PSEs in a repair shop is not a good idea without TC-Holder approval

- ensure that principles of 23.573(a)(5) apply to BRSL

* Draft available for comment until 14th Oct: 2014:http://easa.europa.eu/documents/public-consultations/proposed-cm-s-005

component airworthiness is based upon:

- production standards plus repair based upon repair standards

- not production based upon repair standards!

Bonded Structure



…and repair standards need to be better than this!

Examples of poor bonded repair practice – Inboard Flap (Ref. DOT/FAA/AR-XX/XX Case Studies C. Seaton, S. Richter, L. Ilcewicz, T. Herrington)

NOT ACCEPTABLE!

Bonded Structure



Conclusions:

New technologies, e.g. new materials and new applications require:

- appropriate training and awareness (all parties, e.g. DOA, POA, Continued Airworthiness, Regulators)

- more integration between all parties – SMS!

- regulators developing policy and rules with industry

- HEWABI

- Bonded Repair Size Limits



Thank You…

QUESTIONS?



Residual Strength Requirements versus Additional Damage Size CMH-17 Fig. 12.2.2.3(a)

substantiate larger damagesthan expected

- correct modes important



Developing Operational Activities:



Support Slide : CAST GSWG*:

‐ developed ‘standardised’ Ground Handling training concepts/ syllabi.‐ adoption of minimum standards competence.‐ provide training material (ground crew and aircraft safety)

Ramp Resource Management (RRM):http://easa.europa.eu/essi/ecast/wp‐content/uploads/2013/01/RRM‐training‐syllabus‐supporting‐document‐NLR‐TR‐2012‐483‐tr.pdf

‐ research the effect of Human Factors ‐ ramp safety (icw Dutch CAA)

http://content.yudu.com/A24vd0/GHIApril2013/resources/index.htm?referrerUrl=http%3A%2F%2Fwww.groundhandling.com%2Fghipublication%2F Page 22

*European Strategic Safety Initiative (ESSI) European Commercial Aviation Safety Team (ECAST) Ground Safety Working Group (GSWG)



Support Slide : Aerodrome Operations:

http://www.easa.europa.eu/agency‐measures/docs/opinions/2013/01/Draft%20Commission%20Regulation%20on%20Aerodromes.pdf

Regulation (EC) No 216/2008 Annex.1 SUBPART E — AERODROME MANUAL AND DOCUMENTATION (ADR.OR.E)

ADR.OR.D.030 Safety reporting system …aerodrome operator shall establish and implement a safety reporting system for all personnel and organisations operating or providing services at the aerodrome, in order to promote safety at, and the safe use of, the aerodrome. ..(1) …mandatory reporting of any accident, serious incident and occurrence; (2) …safety reporting system may be used for the voluntary reporting of any defect, fault and safety hazard which could impact safety.

recenthigh-level related aerodrome regs



Support Slide : Aerodrome Operations:

ADR.OPS.B.015 Monitoring and inspection of movement area and related facilities (a) The aerodrome operator shall monitor the condition of the movement area and …related facilities and report on matters of operational significance, whether of a temporary or permanent nature, to the relevant air traffic services providers and aeronautical information services providers; (b) The aerodrome operator shall carry out regular inspections of the movement area and its related facilities.

ADR.OPS.B.025 Operation of vehicles The aerodrome operator shall establish and implement procedures for the training, assessment and authorisation of all drivers operating on the movement area.

Note: Direct Ground Handler regulation under discussion in EU. No text available yet (TBD)

recenthigh-level related aerodrome regs

now needs detailed guidance



Developing Training Activities:


Composite Repair StandardisationEASA and related activities

DOA 1 Product DOA 2 Product DOA 3 Product

PART 145 A PART 145 B PART 145 C

Design related activities:

‐ Harmonised (FAA/TCCA/EASA) Bonded Repair Size Limits (BRSL) Policy (2013)

‐ Operational Suitability Data (OSD) (link to CS‐MCSD , ARP6262, AC 65‐33 etc)

Maintenance related activities:

‐MDM.075 – add Bonding capability (Dx) to PART 145

‐ amend PART 66 ‘Cert Staff’ appendix / new CS‐MCSD (Maintenance Cert Staff Data) (2014)

‐ SAE CACRC TTG ‐ baseline training to support OSD

‐ CAIRe (icw EASA TAC) ‐ improve bonding process

Support Slide: Composites: Product Specific Needs v Standardisation (developing process)

Design ‐Maintenanceco‐ordination essential…



Standardisation of Certification Requirements for Composites:Composite Certification Training – historic:

Need for composite training/approvals?:

- rapid increased use of composites

- increasingly globalised and segmented industry

- engineering properties are built into part or repair

- need for knowledge has moved more towards maintenance

- processes different to metal, some sensitive, e.g. bonding

- potential for non-visible damage

- majority of workforce experienced with metals, not composites

Training



Standardisation of Certification Requirements for Composites:Training – historic: Limited composite specific regulations, e.g.

PART 66 ‘Certifying Staff’: 66.A.45 Type/task training and ratings ‘6.3 Aircraft Materials — Composite and Non-Metallic6.3.1 Composite and non-metallic other than wood and fabric’

SAE- CACRC – existing guidance: AIR5278: Composite and Bonded Structure Engineers: Training DocumentAIR5279: Composite and Bonded Structure Inspector: Training Document

Training/Approvals – recent:AIR4938A (draft): COMPOSITE AND BONDED STRUCTURE TECHNICIAN/SPECIALISTTRAINING DOCUMENTAIR 6262 (new): Basic Composite Repair Technician Certification StdAC 65-33 ‘Development of Training/Qualification Programs for Composite Maintenance Technicians’SAE AIR 5719* Teaching Points for an Awareness Class on "Critical Issues in Composite Maintenance and Repair“

* developed with SAE Commercial Aircraft Composite Repair Committee (CACRC)

no further information!

Training



Standardisation of Certification Requirements for Composites:Training – developing/future: Possible Building Blocks

RMT.0275* (MDM.075) ‘Specialised tasks other than NDT’‘There are a number of tasks which are performed independently of the aircraft type and for which an organisation approval is not available. Similarly to D1 (NDT) it could be also considered painting, weighing, welding, composite repairs’

- develop composite repair approval and/or training guidance wrt PART 145, PART M?

Operational Suitability Data (OSD - NPA)- TC-Holder responsibilities regarding supply of product specific information to operators necessary to ensure safe operation – composite damage reporting, repairs?

New EASA CS-MCS (Maintenance Certification Staff)?

SAE (CACRC) - develop supporting training guidance for AC 65-33, e.g. ARPs, AIRs?

need for separate approval and/or training?

Training

FAA - Overview of AVS Composite Plan

Based on safety management approach. The Plans are linked to:

Best Industry PracticesCertification and field experiencesResearchProjected technological advances in aircraft structure

Continuous Operational Safety (COS)

Certification Efficiency(CE)

Workforce Education (WE)

COS A: Bonded Repair CE A: Hybrid F&DT Substantiation WE A: Composite Manufacturing Technology

Metal Bond Quality Control CE B: Bolted Repair WE B: Composite StructuresTechnology

Sandwich Disbond Growth CE C: Composite QC WE C: Composite Maintenance Technology

COS B: HEWABI CE D: Advanced Composite Maintenance Composite Basics

COS C: Failure Analysis of Composites Subjected to Fire CE E: Bonded Structure Guidance Composite DER

CE F: General Composite Structure Guidance

Support to future COS Initiatives Aging Composite Aircraft Teardown Transport Crashworthiness

Lightning Protection

CMH-17 Revision H

- Harmonisation - Industry/Regulator Working Group - SMS


Composite Materials: Developing Continued Airworthiness Issues Simon Waite... · TE.GEN.00409‐001...

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