Msu composites2009

Composite Materials for Aircraft StructuresComposite Materials for Aircraft Structures

Dr. Douglas S. Cairns,Lysle A. Wood Distinguished Professor

Department of Mechanical and Industrial EngineeringMontana State Universityy

ME 463 Composites,Fall 2009Fall 2009

Lysle Wood Professor

• Goals of the Professorship– Make a positive and significant impact on aerospaceMake a positive and significant impact on aerospace

technology nationally and in Montana– Provide support for aerospace related faculty

d ldevelopment– Enhance student learning opportunities for aerospace

related engineering careersrelated engineering careers

Design and Analysis of Aircraft Structures 13-2

Cairns’ Background

• Began composites career in 1978 as a Staff Engineer at the University of Wyoming– Characterization of compression fatigue mechanisms of F18 vertical stabilizer

(AS1/3501-6) for NavyHygrothermal characterization of Carbon Glass and Kevlar with Hercules 3501 6 for– Hygrothermal characterization of Carbon, Glass, and Kevlar with Hercules 3501-6 for Navy and Army

• Senior Engineer, Hercules Aerospace, Magna UT (designed and analyzed space and aircraft structures manufactured from composite materials)

• Ph.D. in Aeronautics and Astronautics, MIT, thesis on damage resistance and gdamage tolerance due to impact damage in carbon/epoxy and kevlar/epoxy structures, research sponsored by FAA

• Manager of Composites Technology, Hercules Materials Company– US largest manufacturer of structural carbon fibers

materials for militar and commercial aerospace primar str ct ral applications– materials for military and commercial aerospace primary structural applications • Radius Engineering Board of Directors – since 1988• Joined Mechanical and Industrial Engineering at Montana State University in 1995,

began working on wind turbine blade structures, <$10/lb final part cost target based on aerospace technologyon aerospace technology

• Teamed with Boeing engineers to develop and implement Aircraft Structures course at MSU

• Former Chairman, AIAA Materials Technical Committee• Co-Chairman Damage Tolerance Committee NASA/ MIL HDBK 17 Composites


• Private Pilot Certificate, 2006• FAA Consultant for developing composite materials specifications for General

Aviation Aircraft

Introduction

• Composite materials are used more and more for pprimary structures in commercial, industrial, aerospace, marine, and recreational structures


Composites:

• Composites materials consist of a fibrous reinforcements bonded together with a matrix materialg

• Occur naturally in your bones, in wood, horns etc.• Allow the stiffness and strength of the material to change

with direction of loading


The Hierarchy for Advanced Structural Materials

• Begin as laboratory curiosity• Applications to expensive structures (often MilitaryApplications to expensive structures (often Military

Aerospace)• Applications to stuff rich people buy• Applications to things you and I can afford

K A ti R t i l lti t lKey Assumption: Raw materials are ultimately inexpensive and materials synthesis is ultimately inexpensivep


Case History- Aluminum

• At one time, more rare than gold and silver; Kings and Queens wanted aluminum platesp

• Very Expensive Applications– Art Deco furnishings in the 1920s and 1930s

Milit i ft d i WW II– Military aircraft during WW II

• Stuff that rich people buy (Post WW II through 1960s)– General Aviation– Boats– Bicycles

Toda• Today– Aluminum BBQ grills at K-Mart– Aluminum shower curtain rods at hardware store


Composites:

Fiberglass Fibers Kevlar FibersCarbon FibersFiberglass Fibers Kevlar Fibers


Radius Engineering- Salt Lake City, Utah

Radius developed the Trek carbon fiber bicycle used by Radius developed Swix carbon fiber

Gy y

Lance Armstrongski poles; have been used by Gold medal Olympic skiers since 1990s


Discussion Objective

• Provide a brief introduction to composite materials and structures in Airplane Structures p


Composites are Damage Tolerant

• F18 Midair Collision (Circa 2002, no injuries)


Composites are Damage Tolerant (cont.)


Composites are Damage Tolerant (cont.)


Composite Vertical Stabilizer and Rudder Damage


Composition of Composites

Fiber/FilamentReinforcement CompositeMatrix

• Good shear properties

Low density

• High strength

High stiffness

• High strength

High stiffness• Low density• High stiffness

• Low density

• High stiffness

• Good shear properties

• Low density


y

Carbon is the Emperor

Typical large tow properties


The Emperor’s New ClothesTwo Basic Facts Hamper Application of Carbon Fibers to Primary Structure

• Carbon Fiber is expensive; about 8X-10X E-glass fibersfibers

• Much more sensitive to fiber mis-alignment from gmanufacturing process


Not Just An Academic Exercise

Design and Analysis of Aircraft Structures 13-18Consequence of Misalignment in Large, Composite Structure

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The Emperor’s New ClothesTwo Basic Facts Hamper Application of Carbon Fibers to Primary Structure

updated 3:56 p.m. MT, Fri., Aug 14, 2009 Boeing Co. has discovered another problem with its long-delayed 787 jetliner,

prompting the aircraft maker to halt production of fuselage sections at a factory in Italy.

The Chicago-based company found microscopic wrinkles in the skin of the 787’s fuselage and ordered Italian supplier Alenia Aeronautica to stop making sections onfuselage and ordered Italian supplier Alenia Aeronautica to stop making sections on

June 23, spokeswoman Lori Gunter said Friday. Boeing has started patching the areas.

The plane, built for fuel efficiency from lightweight carbon composite parts, is a priority f B i it t l ith d i dli d id th l b l ifor Boeing as it struggles with dwindling orders amid the global recession.

http://www.msnbc.msn.com/id/32415601/ns/business-aviation/


Difficult to Control Manufacturing Defects in Production


Shorthand Laminate Orientation Code

Tapes or Undirectional Tapes

[45/0/-45/902 /-45/0/45

• Each lamina is labeled by its ply orientation.• Laminae are listed in sequence with the first number representing the

lamina to which the arrow is pointing.a a to c t e a o s po t g• Individual adjacent laminae are separated by a slash if their angles

differ.• Adjacent laminae of the same angle are depicted by a numerical

subscript indicating the total number of laminae which are laid up in sequence at that angle

[45/0/-45/90] s

sequence at that angle.• Each complete laminate is enclosed by brackets.• When the laminate is symmetrical and has an even number on each

side of the plane of symmetry (known as the midplane) the code may be shortened by listing only the angles from the arrow side to the

Tapes or undirectional tapes


midplane. A subscript “S” is used to indicate that the code for only one half of the laminate is shown.

Shorthand Laminate Orientation Code

Fabrics and Tapes and Fabrics

[(45)/(0)/(45)]

Midplane

• When plies of fabric are used in a laminate. The angle of the fabric warp is used as the ply direction angle. The fabric angle is enclosed in parentheses

[(45)/0(-45)/90]

Fabrics

g g pto identify the ply as a fabric ply.

• When the laminate is composed of both fabric and tape plies (a hybrid laminate). The parentheses around the fabric plies will distinguish the fabric

Midplane

p gplies from the tape plies.

• When the laminate is symmetrical and has an odd number of plies, the center ply is overlined to indicate that it is the midplane.

Tapes & Fabrics


p

Fatigue Performance of Composites Exceeds That of Metals

(Reference only)1.00

Maximum

25/50/25/ Gr/Ep0.75

cyclic stress/ultimate stress

0.50

Room temperature

0.25

7075-T6 aluminum

temperature, dry• R = -1.0• K1 = 3.0

0102 103 104 105 106 107


Cycles to failure

Reduced Corrosion Problems WithAdvanced Composites

• Advanced composites do not corrode like metals—the combination of corrosion and fatigue cracking g gis a significant problem for aluminum commercial fuselage structure.


Corrosion Case History – Aloha Airlines

• Low time airframe (but many Ground-Air-Ground cycles, 89,090 compression and decompression pressurization cycles from short hops)


compression and decompression pressurization cycles from short hops)

• Operated in moist, warm environment (chemical processes exponential with temperature)

767 Exterior Composite Parts


Honeycomb Usage


Summary—Advantages and Disadvantages of Composite Materials

Advantages Disadvantages

• Weight reduction(approximately 20-50%)

• Some higher recurring costs

• Higher nonrecurring costs• Corrosion resistance

• Fatigue resistance• Higher material costs

• Nonvisible impact damage• Tailorable mechanical

properties

S l th h ff t

• Repairs are different than those to metal structure

• Sales through offset

• Lower assembly costs (fewer fasteners, etc.)

• Isolation needed to prevent adjacent aluminum part galvanic corrosion


( , )

Material and Process Specifications

Material specifications

Process specifications

• Supplier qualification• Fiber requirements

P i t

• Storage and handling• Cure cycle

L d b i• Prepreg requirements– Fiber volume– Resin chemistry– Mechanical properties

• Layup and bagging procedures

• In-process quality control• Postprocess quality control– Mechanical properties

– Forms (tape, fabric)– Cure cycle– Quality controls

• Postprocess quality control• Acceptable anomalies• Splicing

– Manufacturing characteristics• Incoming and receiving tests


Building Block Approach

ElementsJoints

Coupons

Environment

RT/Ambient(Th d ) Small Panels

FullAirplaneStructure

Subcomponents

(Thousands)

(Hundreds)

(Dozens)

Large Panels

Components

Structure

Coupons and Elements

• Mechanical properties• Interlaminar properties

St t ti

Large Panels and Test Boxes• Validate design concepts• Verify analysis methods• Stress concentrations

• Durability• Bolted Joints• Impact damage characterization

E i t l f t

• Verify analysis methods• Provide substantiating data for

material design values• Demonstrate compliance with criteria• Demonstrate ability of finite element

MaterialsThe effects of temperature and moisture

t d f i d i l d

AnalysisThermal and moisture strains calculatedusing finite element model for each

• Environmental factors • Demonstrate ability of finite elementmodels to predict strain values


are accounted for in design values andstrength properties.

using finite element model for eachcritical condition.

FAA/JAA Requirements for Material Allowables

• FAR 25.613, “Material Strength PropertiesFAR 25.613, Material Strength Properties

– Statistical basis

– Environmental effects accounted for

– MIL-H-17B

• FAR 25.615, “Design Properties”, g p

– “A” basis for single load path

– “B” basis for redundant structure

• FAA AC 20-107A

• JAR 25.613, 25.615, and 25.603 similar to


, ,FAA regulations

FAA/JAA Regulations That GovernStructural Materials

• FAR 25.603, “Materials”,– Suitability and durability established by tests

– Conform to specifications that ensure strength

– Takes into account environmental conditions

• FAR 25.605, “Fabrication Methods”Fabrication methods must produce consistently– Fabrication methods must produce consistently sound structure (repeatability)

– New methods must be substantiated by tests

• FAR 25.609, “Protection of Structure”– Protected against deterioration or loss of strength

• JAR 25 603 25 605 and 25 609 similar to FAA


JAR 25.603, 25.605, and 25.609 similar to FAA regulations

FAA/JAA Advisories That GovernComposite Materials

• FAA AC 20-107A, “Composite Aircraft Structure”, p

– Presents an acceptable—but not the only—means for certifying advanced composite structure

• FAA AC 21-26, “Quality Control for the Manufacture of Composite Structure”

– Presents an acceptable—but not the only—means for complying with the quality control requirement ofFAR 21

• JAA ACJ 25.603, “Composite Aircraft Structure”


• Similar to FAA AC 20-107A

Strength Reduction of Advanced Composite Materials

Pristine Materials

R d iProcessing anomalies• Surface irregularities• Splicing

Reduction of the allowable stress

• Waviness• Inclusions• Voids

DamageStress

stress

Damage• Visible damage• Nonvisible damage• Repair (holes, etc.)D i

Allowable design Design

• Environment

Allowable strain reduction

design region

Strain


reductionS a

777 Composite Primary Structure Certification

Sequence Load Description Sequence Load Description

1 Limit proof Load 4 Strain surveypa. Up bendingb. Up bending/unsymmetricc. Down bendingd. Down bending/

567

yFatigue spectrumStrain surveyUltimate load strain survey

a. Stall buffet

2

gUnsymmetric

e. Stall buffet (unsymmetric)

Strain survey 8

b. Up bendingc. Down bending

Destruction test -d b di


Fatigue spectrum3 down bending

787 AirplaneApproximately 50% of the airframe is made from composites; a

very bold move in the commercial aircraft industry




Boeing 787 Dreamliner Logistics


Summary

• Composite parts used for aircraft applications are defined by– Material, process, and manufacturing specifications.

– Material allowable (engineering definition).

• All of these have a basis in regulatory requirements.• Most efficient use of advanced composites in aircraft• Most efficient use of advanced composites in aircraft

structure is in applications with– Highly loaded parts with thick gages.

– High fatigue loads (fuselage and wing structure, etc).

– Areas susceptible to corrosion (fuselage, etc).

Critical weight reduction (empennage wings fuselage etc)– Critical weight reduction (empennage, wings, fuselage, etc).

• Use must be justified by weighing benefits against costs.
