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
Desired Characteristics of Matrix Resins
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
Desired Characteristics of Matrix Resins
• 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
DEFECTS AND POSSIBLE CAUSES
DEFECTS AND POSSIBLE CAUSES
DEFECTS AND POSSIBLE CAUSES
WAVINESS IN PREPREG TO BE AVOIDED
DELAMINATION
FRACTURE
MATRIX MICRO CRACK
VOIDS
SURFACE RESIN STARVATION
RESIN RICH POCKETS
IMPACT DAMAGE & DELAMINATION
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
3 CARBON PRE-PREG 913-40%-G815-1070
4 CARBON UD TAPENCHR 913-35%-132-T300
5 CARBON PRE-PREG 913-40%-G833-1000
6 GLASS PRE-PREG 913-37%-120-1270
7 GLASS PRE-PREG 913-37%-7781-1270
S/N DESCRIPTION DESIGNATION
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
S/N DESCRIPTION DESIGNATION
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
Top Related