CMC FAA Certification

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Gateway Materials Technology

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39th Annual Conference on Composites, Materials and StructuresWorkshop on Certification of CMC Components for Aerospace ApplicationsJanuary 26-29, 2015, Cocoa Beach, FL

Federal Aviation Administration (FAA)

Airworthiness Certification –

The Process and the Challenge for CMC

Components in Commercial Aircraft

Stephen T. Gonczy, Stephen T. Gonczy, PhDPhD

Gateway Materials Technology, IncMount Prospect, IL

847-870-1621, [email protected]

KEYWORDS: ceramic matrix composite, airworthiness, certification, high temperature, design, testing, prodcution

Approved for public release and not subject to export control.

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Outline

● Introduction-- CMC Mechanical Properties

-- CMCs for Civil Air Transport

● FAA and Airworthiness

-- Certification and Airworthiness

-- 14 CFR Aeronautics and Space-- Critical Materials Regulations

● The FAA Certification Process

-- The Steps

-- The Documents and Guidelines

● Metals and PMC Certification

● CMC Certification-- Differences Compared to PMCs

-- The Challenges for CMCs

● Conclusions CMC Exhaust Seals in F414 Engine of F/A-18E/F (Super Hornet), The US Navy

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High Strain, Damage Tolerant Failure

CMCs exhibit improved strain (~0.5%) damage tolerant failurefrom a cumulative damage process, unlike monolithicadvanced ceramics that fracture catastrophically with lowstrain from a single dominant flaw.

Tensile Stress-Strain Diagrams for Two CMCs

High Density, High Modulus MI SiC Matrixw/ Fiber Interface Coating on Nicalon (WIC)

Porous, Low Modulus Al-Si-O MatrixNo Fiber Coating on Nextel 720 (WMC)

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CMC Benefits --High Temperatures and Lower Density

and No Cooling Compared to Metals

Improved Fuel Efficiency

Damage Tolerance Compared to

Ceramic Monoliths

CMC Applications in Turbines --

Exhaust Components Shrouds/Seals Combustors Stators/Vanes Rotors/Blades

Te

ns

ile

S

tre

ss

Temperature

Nickel Superalloy

Ceramic Matrix Composite

Improvement in Temp

Courtesy of GE Aircraft Engines

Ceramic Matrix Composites for Turbines

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An Added Stakeholder

Military Aircraft

Stakeholders

Air Force/Navy/ Army

Air FrameOEM

EngineOEM

CMCProducer

AirlinesAir

FrameOEM

EngineOEM

CMCProducer

Civilian Aircraft

Stakeholders

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FAA Responsibility and Roles

Federal Aviation AgencyMISSION -- is to provide the safest, most efficient aerospace system in the world.

Regulating civil aviation to promote safety –the safe manufacture, operation, and maintenance of civil aircraft.

Developing and operating a system of air traffic control and navigation for both civil and military aircraft

Regulating U.S. commercial space transportation Researching and developing the National Airspace System and civil aeronautics

Encouraging and developing civil aeronautics, including new aviation technology

Developing and carrying out programs to control aircraft noise and other environmental effects of civil aviation

Aircraft, Airports, Air traffic, Licenses and Certifications, Aviation Data, Regulations and Policies

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FAA Airworthiness Certificate

An airworthiness certificate is an FAA document which grants authorization to operate an aircraft in flight.

“airworthiness” is defined as “that condition of an aircraft, engine, propeller, appliance, or component part where it conforms to its approved type design and is in a condition for safe operation within allowable limits.”

Federal Aviation Regulations (14 CFR) –Part 21 -- Airworthiness Standards

Initial Airworthiness Certification and Airworthiness Operation

Safety

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But it is an absolutely essential part of the process of converting science and engineering into real-world technology with social and

economic benefit.

Warning!! Warning!!

The certification process is not exciting, fast, easy, or simple.

In fact, it is hard work, time-consuming, and extremely detailed.

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The Basis –Title 14 CFR

Federal Aviation Regulations –Title 14 Code of Federal Regulations (CFR)Aeronautics and Space Part 3 – General Requirements

Part 21 – Certification Procedures for Products and Parts

Part 25 – Transport Airplanes

Part 33 – Aircraft Engines

Part 34 – Fuel Venting and Emissions -- Turbines

Part 35 – Propellers

Part 35 – Noise Standards

Part 43 – Maintenance, Preventive Maintenance, Rebuilding, Alteration

Part 91 — General Operating and Flight Rules

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Title 14 CFR

14 CFR Sec. 25.601 -- General. -- The airplane may not have design features or

details that experience has shown to be hazardous or unreliable. The suitability of each

questionable design detail and part must be established by tests.

14 CFR Sec. 25.603 -- Materials. -- The suitability and durability of materials used

for parts, the failure of which could adversely affect safety, must--

(a) Be established on the basis of experience or tests;

(b) Conform to approved specifications (such as industry or military specifications, or Technical

Standard Orders) that ensure their having the strength and other properties assumed in the

design data; and

(c) Take into account the effects of environmental conditions, such as temperature and

humidity, expected in service.

14 CFR 25.605 - Fabrication methods.

[a) The methods of fabrication used must produce a consistently sound structure. If a fabrication

process (such as gluing, spot welding, or heat treating) requires close control to reach this

objective, the process must be performed under an approved process specification.

(b) Each new aircraft fabrication method must be substantiated by a test program.

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Title 14 CFR

§25.609 Protection of structure. Each part of the structure must—

(a) Be suitably protected against deterioration or loss of strength in service due to any cause, including—

(1) Weathering;

(2) Corrosion; and

(3) Abrasion; and

(4) Have provisions for ventilation and drainage where necessary for protection.

§25.629 Aeroelastic stability requirements.

(a) General. The aeroelastic stability evaluations required under this section include flutter, divergence, control reversal and any undue loss of stability and control as a result of structural deformation. The aeroelastic evaluation must include whirl modes associated with any propeller or rotating device that contributes significant dynamic forces. Compliance with this section must be shown by analyses, wind tunnel tests, ground vibration tests, flight tests, or other means found necessary by

the Administrator.

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Title 14 CFR

14 CFR Sec. 25.613 - Material strength properties and design values(a) Material strength properties must be based on enough tests of material meeting approved specifications to establish design values on a statistical basis.

(b) Design values must be chosen to minimize the probability of structural failures due to material variability. Except as provided in paragraph (e) of this section, compliance with this paragraph must be shown by selecting design values which assure material strength with the following probability:

(1) Where applied loads are eventually distributed through a single member within an assembly, the failure of which would result in loss of structural integrity of the component, 99 percent probability with 95 percent confidence.

(2) For redundant structure, in which the failure of individual elements would result in applied loads being safely distributed to other load carrying members, 90 percent probability with 95 percent confidence.

(c) The effects of temperature on allowable stresses used for design in an essential component or structure must be considered where thermal effects are significant under normal operating conditions.

(d) The strength, detail design, and fabrication of the structure must minimize the probability of disastrous fatigue failure, particularly at points of stress concentration.

(e) Greater design values may be used if a "premium selection" of the material is made in which a specimen of each individual item is tested before use to determine that the actual strength properties of that particular item will equal or exceed those used in design.

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Types of FAA Certificates and approvals

Part 21 – Certification Procedures for Products and Parts Type Certification (TC) – design certification for

new aircraft/airframes, engines, and propellers

Production Certificate (PC) – approval to manufacture parts, components and systems

Supplemental Type Certificate (STC) –certification of a modification of aircraft, engine, or propeller (design, manufacture and install)

Parts Manufacturer Approval – certify replacement parts (third party)

Technical Standard Order (TSO) – written specification published by FAA on materials, parts, and appliances.

Airworthiness Certificate (AC) – approval to operate a specific aircraft

Certification is for systems, components, and parts

(Commonly not for materials!)

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STCs and TSOs for PMCs

STC Examples for Composites

ST00405AT Design, fabricate, and install a composite fuselage interior liner with subcomponent composite circular supports (A2NM - Boeing Company, The 757-200)

SA02365AK Manufacture and installation of a carbon composite engine cowling

SA01289AT Manufacture of composite engine cowlings. (3A12 - Cessna Aircraft Company, The 172)

TSO Examples for Composites

TSO-C148 AIRCRAFT MECHANICAL FASTENERS

TSO-C90c CARGO PALLETS, NETS, AND CONTAINERS

TSO-C135 Transport Airplane Wheels and Wheel and Brake Assemblies

TSO-C28 AIRCRAFT SKIS

No STCs or TSOs for Ceramics that I found (June 2014).

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FAA Documents

FAA Policy Statement and Memos – policy directives and direction

FAA Orders -- procedural rules and regulations

FAA Advisory Circulars (AC) Guidance documents for all aspects of design, production, operation,

inspection, maintenance, and repair.

Primary guidance on certification

FAA Technical Standard Orders (TSO) minimum performance standard issued by the Administrator for specified

materials, parts, processes, and appliances used on civil aircraft.

FAA Airworthiness Directives – legally enforceable regulations issued by the FAA in accordance with 14

CFR part 39 to correct an unsafe condition in a product

Technical Reports

FAA and Industry Guide to Product Certification –A guide to the current certification process

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The FAA Approval Stages

1. Product Design Approval Type and Supplemental Type

Certificates,

Technical Standard Order

2. Production Approval Production Certificate and Parts

Manufacture Approval,

Technical Standard Order

3. Product Operation and Maintenance Approval Regulations, STCs, FAA Orders, and

Advisory Circulars

Aircraft Handbooks and Manuals

Airworthiness Directives

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The FAA Approval Process

Product Design (Type Certification) – a design that meets operational, safety, and durability requirements. (Integrated life design)

Functional design definition, validation, and documentation

Structural substantiation (static, operational temps)

Manufacturing process definition and documentation

Bonding/assembly/integration design and validation

Environmental exposure

Damage tolerance and degradation definition and assessment Impact events

Fatigue and creep

Fire protection and flammability

Lightening strikes

Crashworthiness

Assembly

Inspection and Repair

Part 21, subpart B, Type Certificates (sections 21.11 through 21.53)

FAA Order 8110.4c Type Certification (Mar 2007)

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Manufacturing Production Approval –a defined and controlled processthat produces parts that consistently meet design specifications and tolerances Process Definition and Verification

Critical Manufacturing Steps and Control

Quality Control System with Records

Defect Detection and Disposition

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Product Operation and Field Maintenance Approval Maintenance Procedures

Damage Tolerance and Degradation Definition –Components and Joints

Damage Detection, Inspection, and Assessment

Repair Criteria and Validated Methods

Life Prediction and Assessment

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The Supplemetal Type Certificate (STC) Process

The TC process is divided into five phases:

FAA TeamManagersStaff OfficersEngineersTech ExpertsInspectorsTesters

Applicant TeamManagersDesignersEngineersProducersInspectorsTesters

From FAA order 8110.4C (TYPE CERTIFICATION

AC 21-40a - Guide for Obtaining a Supplemental Type Certificate

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Tools for the Certification Process

Provided by reference, by industry, andin Advisory Circulars and Handbooks Industrial specifications and test standards

Design criteria, methods, and approaches

Physical test methods,

Analytical methods Design stress and thermal

Life Prediction,

Property data bases

Operational (flight) tests

Fabrication Process control methods

Inspection methods

Installation methods

Maintenance methods

Field Inspection and Repair methods

Safran Herakles -- CMC Cone and Mixer

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Metals in the FAA Process

Strong Historical basis – aluminum, steel, titanium, magnesium, etc. with mature, well established technology

Well-defined industrial specifications and test methods Composition, processing, properties by specification

Integrated and accepted in the FAA process

Well defined and certified design, production, andassembly methods

Well known inspection and repair techniques

Metallic Materials Properties Development & Standardization Handbook (MMPDS) -Design Allowables for Metals in Aircraft AMS Alloy Specification reference

Required property (tension, compression, shear, bearing)by ASTM tests.

Recommended properties ((fatigue, crack growth, fracture toughness, effect of temperature) by ASTM tests

Fastener and joint data

Aviation Maintenance Technician Handbook – General, FAA 8083-30. Chapter 5 Aircraft Materials, Processes, and Hardware

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Polymer Matrix Composites in the FAA Process

PMCs- New Materials with much more complex challenges, compared to metals Complexity, anisotropy, fabrication sensitivity

Tool design and fabrication process control

Different failure and damage modes and design methodologies

Different types of flaws and different inspection methods

Flammability, Humidity, thermal, UV, solvent

Different bonding and joining methods

Field inspection and repairability

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FAA Policy Statements for Composites

Static Strength Substantiation of Composite Airplane Structure

[PS-ACE100-2001-006, December 2001]

Final Policy for Flammability Testing per 14 CFR Part 23, Sections 23.853, 23.855 and 23.1359 [PS-ACE100-2001-002, January 2002]

Material Qualification and Equivalency for Polymer Matrix Composite Material Systems[PS-ACE100-2002-006, September 2003]

Bonded Joints and Structures - Technical Issues and Certification

Considerations [PS-ACE100-2005-10038, September 2005]

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FAA Advisory Circulars for Composites and Materials

AC 20-107B – Composite Aircraft Structure

AC 21-26 -- Quality Control for the Manufacture of Composite Structures

AC23-3 – Structural Substantiation of Secondary Structures

AC23-20 -- Acceptance Guidance on Material Procurement and Process Specifications for Polymer Matrix Composite Systems

AC 25.571 -1C -- Damage Tolerance and Fatigue Evaluation of Structure

AC 25.613-1 -- Material Strength Properties and Material Design Values

AC 35.37-1A -- Guidance Material for Fatigue Limit Tests and CompositeBlade Fatigue Substantiation

AC 500-009 -- Composite Aircraft Structure – Compliance Guidance

AC 21-40a - Guide for Obtaining a Supplemental Type Certificate

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FAA Technical Reports

“Fiber Composite Analysis And Design Volume II Structures” [DOT-FAA-CT-88-18, Nov. 1979)

"Certification Testing Methodology for Composite Structures, Volumes I and II" [DOT/FAA/CT-86/39, October 1986]

“Handbook: Manufacturing Advanced Composite Components for Airframes” [DOT/FAA/AR- 96/75, April 1997]

”Fiber Composite Analysis and Design, Volume I Composite Materials and Laminates” [DOT/FAA/CT-85/6 , Oct 1997]

"Advanced Certification Methodology for Composite Structures" [DOT/FAA/AR-96/111, April 1997]

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FAA Technical Reports “Guidelines and Recommended Criteria for the Development of a Material

Specification for Carbon Fiber/Epoxy Unidirectional Prepregs" [DOT/FAA/AR-02/109, March 2003]

“Guidelines for the Development of Process Specifications, Instructions, and Controls for the Fabrication of Fiber-Reinforced Polymer Composites" [DOT/FAA/AR-02/110, March 2003]

"Guidelines for Analysis, Testing, and Nondestructive Inspection of Impact-Damaged Composite Sandwich Structures" [DOT/FAA/AR-02/121, March 2003]

“Material Qualification and Equivalency for Polymer Matrix Composite Material Systems“ [DOT/FAA/AR-03/19, September 2003]

"Assessment of Industry Practices for Aircraft Bonded Joints and Structures" [DOT/FAA/AR-05/13, July 2005]

Aviation Maintenance Technician (AMT) Airframe Handbook Volume 2 (FAA-H-8083-31) , Chapter 7 Advanced Composites

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CMH-17 Composites Handbook

Purpose - The Composite Materials Handbook organization creates, publishes and maintains proven, reliable engineering information and standards , subjected to thorough technical review, to support the development and use of composite materials and structures

CMH - 17 provides technical guidance on material & process control, design, analysis, testing, structural substantiation and maintenance.

Six Volumes

Vol 1 PMC: Guidelines for Characterization of Structural Materials

Vol 2 PMC: Material Properties

Vol 3 PMC: Materials Usage,Design and Analysis

Vol 4 MMCs

Vol 5 CMCs

Vol 6 Structural Sandwich Composites

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CMH-17 PMC Handbook

Vol 1 PMC: Guidelines for Characterization of Structural Materials (156 Pages) 1. Objectives

2. Guidelines for Property Testing of Composites

3. Evaluation of Reinforcement Fibers

4. Matrix Characterization

5. Prepreg Materials Characterization

6. Lamina, Laminate and Special Form characterization

7. Structural Element Characterization

8. Statistical Methods

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CMH-17 PMC Handbook

Vol 2 PMC: Material Properties (671 pages)

General

Carbon Fiber Tape and Prepreg fabric data

Boron Fiber Tape and Prepreg fabric data

Glass Fibers Tape and Prepreg fabric data

Quartz Fiber Tape and Prepreg fabric data

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CMH-17 PMC Handbook

Vol 3 PMC: Materials Usage, Design and Analysis (852 pages) General Intro to Composite Structure Development Aircraft Structure Certification and Compliance Building Block Approach to Composite Structures Materials and Processes – Variability Effects QC of Production Material and Processes Design of Composites Analysis of Laminates Structural Stability Analyses Bonded Joint Design Bolted Joint Design Damage Resistance, Durability, Damage Tolerance Defects, Damage, and Inspection Supportability, Maintenance, and Repair Thick Section Composites Crashworthiness and Energy Management Structural Safety Management Environmental Management

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Ceramic Matrix Composites for Aircraft

Why not just use PMC rules for CMCs? Technically similar to PMCs in

Composite complexity, anisotropy, fiber architecture

High strength, High stiffness fibers

Production process sensitivity and variability

Different applications than PMCs

Hot structures (>500C) in or next to engines

Different than PMCs in

Different constituents

Brittle, low strain matrix with early damage accumulation

Broader range of constituents (Oxide, non-oxide, carbon, etc) and densification/consolidation methods (CVI, MI, PDC, sinter)

Added level of complexity with fiber interfaces, porosity, and MI metal.

Different degradation, damage, and failure mechanisms,

High Temperature (>500C) Life Prediction

High temperature bonding challenges

ND Inspection Challenges

Question of reparability

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Questions and Challenges in CMC Certification

For a specific CMC part, we have to show the FAA how the part --

is well-designed for operation, safety, and durability

risks are managed and life limits are determined.

is tested and analyzed to certify safety and life.

can be manufactured reliably with certified quality control.

variability is controlled and managed.

is inspected for flaws off the finish line.

is integrated and installed in the system (joining and assembly).

is maintained and inspected in service.

Is repaired or replaced in service.

CMC parts will have to be FAA certified. What does the FAA need to know to certify CMCs?

How does the FAA learn about CMCs so they can makeInformed decisions about CMC parts in the certification process.FROM THE OEM DESIGNER, THE CMC PRODUCER, AND THE CMC COMMUNITY

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Tools for the Certification Process

Develop, validate and document the CMC tools

Design criteria, methods and approaches

Physical test methods

Analytical methods – stress, thermal, life prediction

Degradation, damage, and failure mechanisms at different temperatures and environments

Property data bases

Process control techniques

Inspection methods (production line and field)

Maintenance and repair techniques

On-going interaction with FAA tech experts to inform them aboutCMC technology.

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Gateway Materials Technology CMH-17 CERAMIC MATRIX COMPOSITES

HANDBOOK

CMH-17 Volume 5, Ceramic Matrix Composites Part A. Introduction and Guidelines

History, applications, benefits of CMC systems CMC Systems & processing methods Fiber and reinforcement technology Interphase/Interface technology and approaches Fabrication and forming of fiber architecture Non-destructive evaluation methods

Part B. Design and Supportability CMCs for Aircraft Turbine Engines Design of Attachments for CMCs in Engines

Part C. Testing Physical Test Methods, ThermoMechanical

Part D. Data Requirements and Data SetsCMC Property Data includes SiC/SiC, Carbon/SiC, Oxide/Oxide, SiC/Si3N4

Appendix A. Derivation of the Residual Strength Reduction Expressions for LCF and Rupture Loadings

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References

http://www.faa.gov/

Title 14 CFR

Part 21, 14 CFR subpart B, Type Certificates (sections 21.11 through 21.53)

FAA Order 8110.4c Type Certification (Mar 2007)

FAA and Industry Guide to Product Certification (FAA Sep 2004)

Aircraft Structure Certification and Compliance (Chap 3, Vol 3 (PMC), CMH-17 Handbook)

Airworthiness: An Introduction to Aircraft Certification By Filippo De Florio (2006)

Aviation Maintenance Technician Handbook –FAA 8083-30.

FAA AC 21-23b, Airworthiness Certification of Civil Aircraft, Engine, Propellers, and Related Products Imported to the United States

FAA AC 21-40a, Guide for Obtaining a Supplemental Type Certificate

“Airworthiness Certification of Aircraft and Related Products” (FAA, July 2012)

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Summary of CMC Certification

1. FAA Certification of CMCs has to happen, if we want

CMCs on commercial planes.

2. There is so much CMC technology to validate and

document to obtain certification of a given CMC part.

We can use the PMC ACs and CMH-17 PMC handbook as

templates.

3. All the stakeholders need to work with FAA tech

experts now to keep them fully-informed and current

on CMC design, testing, production, inspection , and

support technology to support certification.