Composite MATERIALS

SCOPE• COMPOSITES & THEIR IMPORTANCE

– FIBERS– MATRIX

• ADVANTAGES

• DISADVANTAGES

• HANDLING

• DEFECTS & CAUSES

• HEALTH ISSUES

Weight breakdown

– Structure 30%

– Power plant 8%

– Rest is payload, fuel, fixed equipment

Light weight materials e.g. composite can contribute to the efficiency. However, there are complex issues associated with certification and maintenance and repair

STRUCTURAL WEIGHT• EVERY ENGINEER SHOULD CONCERN ABOUT WEIGHT

OTHERWISE THE COMPANY WILL FIND IT DIFFICULT TO MEET THE COMPETITION TO PRODUCE PLANES WITH GOOD PERFORMANCE

• A VERY SMALL MARGIN OF WEIGHT DETERMINES THE DIFFERENCE BETWEEN EXCELLENT AND POOR PERFORMANCE OF AIRCRAFT

• 5% INCREASE IN WEIGHT MAY RENDER A HIGHLY SUCCESSFUL MODEL TOTALLY UNACCEPTABLE

• WEIGHT OF AIRCRAFT STRUCTURE IS ABOUT 20 TO 40% OF TAKE OFF WEIGHT.

• ONE 1KG EXCESS WEIGHT IN STRUCTURE OR SYSTEM LEADS TO 10 KG INCREASE IN ALL UP WEIGHT

WHICH GIVES LIGHTER STRUCTURE ? Al ALLOY OR STEEL

TREND IN COMPOSITE USAGE

COMPOSITES IN BOEING 787

COMPOSITE VS METALLIC STRUCTURES

• BUILD UP SHAPE & PROPERTIES

• LAMINATED– INCLUSIONS– POOR BONDING– VOIDS

• PRESHABLE & ANISOTROPIC UNITS (PREPREGS)

• HIGHLY SENSITIVE TO ENVIRONMENT & PROCESS PARAMETERS

• COMPLEX QC PROCESS

• MACHINED DOWN – SHAPE

• SOLID– DEFECTS OF RAW

MATERIALS

• MOSTLY UNPERISHABLE AND ISOTROPIC

• RELATIVELY INSENSITIVE

• RELATIVELY SIMPLE QC PROCESS

COMPOSITE MATERIALS

• Two or more materials combined on a macroscopic

scale to form a useful material

• Ideal for structural applications where high strength to weight and stiffness-to-weight ratios are required

• Conventional composites limited to in-plane

distributed loads

Composite materials- constituents• Reinforcement

– Strength & Modulus

– Main load bearing member

– Decides the mechanical performance

• Matrix– Protect the reinforcement

– Gives shape to the component

– Local load transfer

– Decides the manufacturing process

Classification of Composites

REINFORCEMENT

Particulate Fiber

continuous DiscontinuousLargeParticle

DispersionStrengthened

Aligned RandomUnidirectionalBi-directional

TYPES OF COMPOSITES

ADVANCED COMPOSITES

• FIBER REINFORCED• FIBERS

– CARBON– KEVELAR– GLASS

• MATRIX– EPOXY– POLYIMIDE– POLYESTER

WHY FIBERS?

TENSILE STRAIN %

TE

NS

ILE

ST

RE

SS

MP

a

1 2 3 4

500

1000

1500

2000

2500

IM C

AR

BO

N

HS

CA

RB

ON

ARAMID

S GLASS

E GLASS

COMPRESSIVE STRAIN %

CO

MP

RE

SS

IVE

S

TR

ES

S M

Pa

0 1 2 3 4

500

1000

1500

2000

2500

IM C

AR

BO

N

HS CARBO

NARAMID

S GLASS

E GLASS

FIBERS FOR ADVANCED COMPOSITE MATERIALS - COMPARISON

REINFORCEMENT FORMS

UD TAPES

WOVEN FABRICS

REINFORCEMENTS WITH THE RESIN SYSTEM ALREADY IMPREGNATED; MATRIX IS LEFT IN B-STAGE CURING IS ARRESTED THROUGH LOW TEMPERATURES

A-STAGE: RESIN IS NOT CROSS-LINKED AT ALL

B-STAGE: LIGHTLY CROSS-LINKED, PARTIALLY CURED

C-STAGE: FULLY CROSS-LINKED

PREIMPREGNATED REINFORCEMENT (Prepreg)

All the filaments are oriented in one direction. The tape is fabricated in width ranging from 3 to 60 inches and is supplied in rolls.

Unidirectional tape works well when maximum performance is required in one direction. Tapes are made by careful alignment of side-by-side yarns; usually of 1420 or greater denier.

Tapes are usually impregnated with resin and are available from many prepreg suppliers.

Unidirectional Tape Prepreg

Unidirectional Weave Cloth (95% - 0°, 5% - 90°) This cloth has 95% of its filaments in the warp direction (length direction) and 5% in the fill direction to facilitate material handling. Its strength is approximately equal to unidirectional tape. It is fabricated and available up to 72 inches in width.This weave has the general characteristics: 1) maximum strength in one direction and 2) minimum strength in the transverse direction.

Unidirectional Weave

The oldest and most common basic textile weave in which one warp end (lengthwise thread) weaves over and then under one filling pick (crosswise thread). This weave has the general characteristics:

a. Firmest and most stable of the industrial weaves.b. Affords fair porosity with minimum yarn slippage.c. Uniform strength pattern in all surface directions.d. Affords ease of air removal in hand layup or

molding.

Plain Weave

This weave is similar to a plain weave, but it has two or more warp ends weaving as one end over and under two or more filling picks weaving as one pick. This weave has the general characteristics:

a. Less stable than a plain weave.b. More pliable than a plain weave.c. Flatter and stronger than an equivalent weight and

count of plain weave.

Basket Weave

This weave is constructed with one warp end weaving over three and under one filling pick. It has the general characteristics:

a. More pliable than either a plain weave or a basket weave.

b. Specially designed to conform closely to complex orcompound curved surfaces.

c. Makes possible the weaving of higher counts than plain or basket weaves.

Crowfoot Satin or 4-Harness Satin

A long shaft satin construction has one warp end weaving over four or more and under one filling pick. This weave has the general characteristics:

a. Most pliable and conforms readily to compound curves.b. Produces laminates and reinforced moldings with high

strength in all directions.c. Can be woven in the highest constructions or density.d. Less open than other weaves.

Long Shaft Satin

OTHER FORMS

CLASSIFICATION OF COMPOSITE MATERIALS- MATRIX

COMPOSITES

METAL CERAMIC POLYMER

THERMOSET THERMOPLASTIC

PHENOLIC

EPOXY

POLYIMIDES

PEEK

PPS

Polymer matrix• Thermoset

– Epoxy– Polyester– Phenolics– Polyimide

• Thermoplastic– PEEK– PES

Desired Characteristics of Matrix Resins

Mechanical & Thermal• High strength• High elastic elongation• High shear strength• High modulus• High heat distortion temp.• Low creep at use temp.• High toughness/impact strength• Thermal expansion near fiber• Resistance to thermal degradation• Low thermal conductivity


Processing Characteristics• Low enough melt or solution viscosity• and surface tension to permit thorough• fiber wet-out• Good flow characteristics• Rapid cure or solidification• Suitable for pre-coated reinforcement• Cure temp. not greatly above use temp.• Low shrinkage during and after molding• Long shelf life and pot life


• Chemical Properties:– Good bond to fiber (directly or– with coupling agent)– Resistance to solvents & chemicals– Low moisture absorption

• Other Factors:– Low cost– Low density– Low dielectric constant

EPOXY RESINS

• GOOD MECHANICAL PROPERTIES

• UP TO 150 O C SERVICE

• BONDS TO ALMOST ALL SURFACES

PHENOLIC RESINS

• EXCELLENT FIRE RESISTANT

• LOW SMOKE EMISSION

• EASY PROCESSING

• AIRCRAFT INTERIOR COMPONENTS.

BISMALEIMIDE RESINS

• EXCELLENT RESISTANCE TO HIGH TEMPERATURE

• GOOD MECHANICAL PROPERTIES

• AERO-ENGINE COMPONENTS

MATRIX MATERIALS FOR COMPOSITES

ADVANTAGES COMPOSITES • HIGHER SPECIFIC STRENGTH & MODULUS

– LIGHT WEIGHT– PERFORMANCE– FUEL EFFICIENT

• BETTER FATIGUE PERFORMANCE– RELIABILITY– LIFE– DOWN TIME

• TAILARABILITY / ANISOTROPIC– OPTIMUM WEIGHT & PERFORMANCE

• EASY MANUFACTURING– COST

• FREE FROM CORROSION• PART INTEGRATION

– LESS PART COUNT– ASSEMBLY TIME– WEIGHT (FASTENER)

QUASI ISOTROPIC

CFC

ALUMINIUM ALLOY

450 450 170 90

450 250 400 200

Strength MPa

TE

NS

ILE

FA

TIG

UE

107 cycles to failure

0%- 80%

- 45%- 55%

COMPARISON OF Al AND CFC IN TENSION

100 95

15%

55%

35%

35%

50%

10%

A

B

C

Material

Part Fabrication

Assembly

MR

TA

LL

IC C

ON

STR

UC

TIO

N

CO

MP

OSI

TE

CO

NST

RU

CT

ION

COST COMPARISON FOR A310 VERTICAL TAIL

CONCERNS• BRITTLENESS

– POOR IMPACT PERFORMANCE– STRESS CONCENTRATION

• LIMITED LIFE OF RAW MATERIALS– DETERIORATE IN STORAGE– SHELF & OUT LIFE– SPECIAL STORAGE

• PROCESS SENSITIVE– SENSITIVE TO PROCESS PARAMETERS– VARIATION / SCATTER

• LAMINATED STRUCTURE / DELAMINATION• Tg / ENVIRONMENTAL EFFECTS

– EFFECT OF MOISTURE & TEMPERATURE

• COST

HANDLING OF PREPREGS & RESINS

TRANSPORTATION OF PREPREGS

EPOXY RESINS ARE PERISHABLE

SHELF LIFE SHOP LIFE

STORAGE & HANDLING OF PREPREGS / ADHESIVES

AVOID CONDENSATION OF MOISTURE

RESIN – HARDENER MIXING RATIO

EFFECT OF ACCELERATOR & TEMPERATURE

LAMINATED STRUCTURES

SOME FACTS & TERMINOLOGIES

LAMINATED STRUCTURE

EFFECT OF FIBER MISALIGNMENT ON STRENGTH AND STIFFNESS

FAILURE MODE & ANGLE OF ORIENTATION

FIBER MISALIGNMENT & REDUCTION IN STRENGTH

2O 20% 4O 45% 6O 66% 10O 80%

THE LAMINA IS HIGHLY ANISOTROPIC

EFFECT OF LAY UP AND LAYUP SEQUENCE

STRETCHING – BENDING COUPLING

FIBERS TEND TO ALIGN TO DIRECTION OF THE LOAD

STRETCHING – SHEAR COUPLING

STRETCHING – TWISTING COUPLING

EFFECT OF SYMMETRY

IMPORTENCE OF LAYUP SEQUENCE

BALANCED & SYMMETRIC LAYUPS

HANDLING OF CURED COMPONENTS

HANDLING & STORAGE OF CURED COMPOSITES

• BRITTLE – IMPACT

• ABSORB MOISTURE – Tg & SERVICE TEMPERATURE

• DRILLING – DELAMINATION

• CONTAMINATION – SECONDARY BONDING & PAINTING

• PERSONAL SAFETY

IMPACT DAMAGE

• TOOL DROP

• WHILE TRANSPORTING & MOVING

• HAIL STROM

• RUNWAY DEBRIS

DELAMINATION

DELAMINATION

LOCAL FIBER BREAK

BACK SIDE FIBER BREAKAGE

PYRAMID TYPE MATRIX CRACKS

LOCAL CRUSHING / DENT

DRILLING – INDUCED DEFECTS

BACK SUPPORT

GLASS PREPREG

DRILLING DELAMINATION MECHANISM

PREPREG – MOST COMMON FORM

APPLICATIONS OF PREPREGS

SCHEMATIC OF FABRICATION PROCESS

CURE PARAMETERS

DE BULKINGLarge quantities of air are inevitably trapped between each prepreg layer and can be removed by covering the prepreg with a release film, a breather layer and applying a vacuum bag. The vacuum should be applied for 10-15 minutes at Room Temperature. The first ply attached to the tool face is generally debulking and this can be repeated after every 3 or 5 layers depending on the prepreg thickness and component shape. Debulking can be carried out overnight or during a natural break in the lay-up process.

Temperature

The oven/autoclave, component and tooling, should all reach and remain above the minimum cure temperature throughout the cure cycle.

Thermocouples used to monitor the temperature should be placed carefully to ensure accurate information is received for the whole system and to operate at the cure temperature ± 5 ºC.

Cure time

Each prepreg has a recommended cure time which starts when the lowest thermocouple reading reaches the minimum cure temperature.

Extended cure times at the recommended cure temperature do not normally have an adverse effect on the component quality.

Heat up rate

The matrix, viscosity, flow, reaction rates and component surface quality are all effected by the chosen heat up rates.

Generally, fast heating rates are possible for thin components and slow heating rates are used for large and thick components.

The heat up rate selected should avoid large temperature differentials between the component and the heat source.

Cooling rates

Cooling cycles should be controlled to avoid a sudden Temperature drop which may induce high thermal stresses in the component.

Pressure and/or vacuum should be maintained throughout the cooling period.

Vacuum

Used to remove air from the prepreg lay-up and provide a consolidating pressure for oven curing.

It is common practice in autoclave cure cycles to reduce the applied vacuum to a low level.

PRESSURE

• CONSOLIDATION OF LAYERS

• FLOW OF RESIN IN TO VOIDS & GAPS

• CONTROLS THE VOID GROWTH

COMMON DEFECTS IN COMPOSITES

DEFECTS AND POSSIBLE CAUSES

WAVINESS IN PREPREG TO BE AVOIDED

DELAMINATION

FRACTURE

MATRIX MICRO CRACK

SURFACE RESIN STARVATION

RESIN RICH POCKETS

IMPACT DAMAGE & DELAMINATION

EDGE DELAMINATION

TYPES OF COMPOSITE STRUCTURES

• MONOLITHIC– CO CURED – BONDED– COBONDED

• SANDWICH– CO CURED– BONDED– COBONDED

BONDING

SANDWICH STRUCTURES

• VERY EFFICIENT IN RESISTING BENDING LOADS

• LIGHT IN WEIGHT

• LIMITED BY SHEAR DEFORMATION

DEFECTS IN SANDWICH PANELS

DELAMINATION

CORE CRUSH

MOISTURE ABSORPTION BY CORES

MOISTURE

Epoxy based composite absorbs 0.2 wt % moisture in laboratory environment (i.e. 23 °C and 50% RH within 2 to 4 weeks. The presence of moisture in the composite can adversely affect the properties of the adhesive during the cure process, and as a result the joint strength may be compromised. Moisture released from the composite substrate during cure reduces the glass transition temperature Tg by as much as 20 °C, and lower the fracture toughness Gc of a rubber toughened epoxy adhesive by a factor of 10. Adherents (pre-dried) should therefore be stored in a dry area (i.e. desiccators or sealed container with a suitable desiccant. It is recommended that polymer composites be pre-dried in an oven

EFFECT OF MOISTURE - BONDING

EFFECT OF TEMPERATURE ON COMPRESSION STRENGTH

Avoid removal of adhesive spew from the ends of joints after cure, as there is the possibility of damaging the joint. Work on the spew to form a continuous FILLETExcessive spews should be removed before curing.

Importance of adhesive fillet

BONDING FIXTURE

It should be noted that the thicker the bond-line the higher

the risk of incorporating a high level of voids.

In addition, stresses at the corners of the joint tend to be

larger as it is difficult to maintain axial loading with a very

thick bond-line.

Thick adhesive layers can change the cure

properties producing internal stresses, thereby reducing short

and long-term performance.

Conversely too thin a bond-line can result in adhesive

starvation and debonding.

Optimum bond thickness will depend on the type of adhesive

used.

BOND LINE THICKNESS

HEALTH ISSUES

• SKIN CONTACT– CURED RESIN– UNCURED RESIN & HARDENER– FIBERS – SOLVENTS (ACETONE & MEK)

• INHALATION– HARDENER– DUSTS (DRILLING& TRIMMING)

PREVENTION OF EXPOSURE

IMPORTANCE OF GLOVES

• Prepregs can be difficult to handle with gloves, but don't give in to the urge to work bare-handed.

• Although the focus of this discussion has been on contact hazards, adequate ventilation should also be provided to minimize respiratory risks.

THANK YOU

Unidirectional Tape Prepreg All the filaments are oriented in one direction. The tape is fabricated in width ranging from 3 to 60 inches and is supplied in rolls.

Unidirectional tape works well when maximum performance is required in one direction. Tapes are made by careful alignment of side-by-side yarns; usually of 1420 or greater denier.

Tapes are usually impregnated with resin and are available from many prepreg suppliers.

Unidirectional Weave Cloth Prepreg (95% - 0°, 5% - 90°) This cloth has 95% of its filaments in the warp direction (length direction) and 5% in the fill direction to facilitate material handling. Its strength is approximately equal to unidirectional tape. It is fabricated and available up to 72 inches in width.

A greater number of relatively strong warp yarns and fewer, and generally weaker, filling yarns give this type of reinforcing fabric maximum strength in the warp direction only. This weave has the general characteristics: 1) maximum strength in one direction and 2) minimum strength in the transverse direction.

Bidirectional Weave Cloth Prepreg This cloth has close-to-equal proportions of filaments in the warp direction (length) and fill direction (width). Note that in satin weaves, the warp filaments are predominantly on one side and the fill is predominantly on the other.

Hence, the cloth is not thermally balanced within itself and in thin laminates it may be necessary to specify on which side of the cloth the warp should be to prevent twisting of the laminates after curing.

The cloth is fabricated in widths up to 72 inches.

S/N DESCRIPTION DESIGNATION

1 CARBON PRE-PREG 913-40%-G801-1020

2 CARBON PRE-PREG 913-40%-G802 NT-1000


4 CARBON UD TAPENCHR 913-35%-132-T300


6 GLASS PRE-PREG 913-37%-120-1270

7 GLASS PRE-PREG 913-37%-7781-1270


8 KEVLAR PRE-PREG 913-50%-K285-1200

9 KEVLAR PRE-PREG 913-54%-1226-1200

10 COPPER MESH913-COPPER MESH-40%-W 610 MM

11 PEEL PLY 913-54%-7849-1150

12 R-GLASS PRE-PREG913 G-20982-34+/-3%-W 1200

13 R-GLASS UD TAPE913 G-R-7-33%-W 300 MM

14 SINGLE TOW MR 913-28%-1XR1600


15 GLASS UD NVE 913-28%-192-EC 9756

16GLASS SINGLE TOW ME 913-28%-1XEC 9756

17 KEVLAR PRE-PREG914 K-285-50+/-3.0%-W 1200 MM

18 GLASS PRE-PREG914 G-120-45+/-5.0%-W 1270 MM

19 GLASS PRE-PREG914 G-7781-37+/-3.0%-W 1270 MM

20 ADHESIVE FILM FM 73

21FOAMING ADHESIVE FM 490A

ASYMMETRY IN SATIN WAVES

Composite MATERIALS

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