DESIGN IN COMPOSITES BASICS

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DESIGN IN COMPOSITES BASICS CASE STUDIES

• Prof S C Lakkad
• Dept of Aerospace Engineering
• Indian Institute of Technology Bombay
• Mumbai 400 076

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INTRODUCTION - 1
THE TWO KEY WORDS IN THE TITLE NAMELY DESIGN
COMPOSITES NEED TO BE DEFINED FOR THIS
PRESENTATION AS THEY OFTEN MEAN DIFFERENT THINGS
TO DIFFERENT PEOPLE
LET US CONSIDER COMPOSITES FIRST SINCE THERE IS
MORE UNIFORMITY IN ITS COMMON USAGE
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INTRODUCTION-1

• Composites are heterogeneous materials, defined
  as, Change of Properties w.r.t. Fixed Axes in
  Space (includes polycrystalline aggregate) ?
• Multiphase systems (includes particulate
  composites)?
• Fibre Reinforced Composites (FRC), with 5µm to
  100 µm dia (includes MMC Ceramic MC) ?
• Fibre Reinforced Plastics (FRP) Bulk of the
  commercial applications

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INTRODUCTION-2
COMPOSITES IN THE BROAD SENCE OF THE DEFINITION
ARE ABUNDANTLY FOUND IN NATURE (VEGETATION
ANIMAL KINGDOM, OR THE NATURALLY OCCURING
OBJECTS) BECAUSE COMBINED MATERIALS ARE MORE
STABLE /OR PROVIDE OPTIMAL PROPERTIES.
WHAT MAKES COMPOSITES INDUSTRIALLY POPULAR NOW?
IT IS THE COMBINATION OF INVENTION OF HIGH
STRENGTH/LOW DENSITY MATERIALS IN FIBROUS FORM
AND LOW DENSITY POLYMERIC MATRIX (WITH GOOD
ADHESIVE PROPERTIES)
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REINFORCEMENT -1
TENSILE STRENGTH MODULII OF SOME REPRESENTATIVE
MATERIALS
Fifth to tenth row represents modern manmade
fibres having high intrinsic and specific
strengths and modulii
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Specific Tensile Modulus v/s Specific Tensile
Strength
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REINFORCEMENT -2
DIFFERENT FORMS OF REINFORCEMENT
The basic reinforcing consist of about 10 µm dia
fibrils in the form of a bundle called tows Tows
are invariably coated with suitable material
called coupling agent. - (silanes for glass
fibers) for good bond with a
class of matrices and - epoxy resin for carbon
fibres The reinforcement has very limited use in
the form of continuous tows (e.g., filament
winding process, pultrusion).
The tows are converted to different form to meet
the requirements of fabrication process and in
the design of final product.
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DIFFERENT FORMS OF REINFORCEMENTS-2
The common forms are CHOPPED STRAND MAT (CSM) -
chopped fibers (50 mm long) held together by a
binder. (CFM) WOVEN FABRIC OR ROVINGS (WR) -
continuous fiber woven together in different
weaves in warp weft direction.
Preforms. PRE-PREGS - tows held together by
partly cured thermoset resin The above products
are further identified by DENSITY PER UNIT AREA
NATURE OF WEAVE - Plain, Satin, Twill, Number of
ends in warp weft SURFACE TREATED FOR
COMPATIBILITY WITH A CLASS OF MATRICES
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MATRIX -1

• THE FUNCTION OF THE MATRIX IS TO HOLD THE
  REINFORCING FIBRES TOGETHER i.e. GOOD
  ADHESION TO FIBRES
• SUITABLE MODULUS ELONGATION VALUES FOR
  EFFECTIVE USE OF FIBRE PROPERTIES
• MUST NOT REACT WITH THE REINFORCEMENT DURING MFG
  PROCESS TO AVOID DEGRADATION
• LOW DENSITY TO MAKE THE COMPOSITE WEIGHT
  EFFECTIVE
• POLYMERS, METALS CERAMICS HAVE BEEN TRIED AS
  MATRIX MATERIALS BUT POLYMERS MOSTLY THERMOSETS
  BUT ALSO THERMOPLASTICS - REMAIN ALL TIME POPULAR
  FOR THE FOLLOWING REASONS

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MATRIX -2 Advantages of Polymers

• They have low density (the range of specific
  gravity being 0.8 to 2.2). This makes overall
  density of the composite low.
• Good adhesion to reinforcement, resulting in good
  bond between the reinforcement and the matrix.
  (It is true mostly for thermosets).
• Good dielectric/insulation properties.
• Excellent corrosion resistance to a wide range of
  chemicals.
• Easy processibility at low temperature.

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MATRIX -3 Disadvantages of Polymers

• Susceptibility to organic solvents.
• Environmental degradation through the volume.
• Instability at high temperature. Use is normally
  restricted to below 150o C in most of the
  cases.
• Poor wear resistance in case of thermoset resins.

CONSIDERING REINFORCEMENT AND MATRIX TOGETHER THE
ADVANTAGES AND DISADVANTAGES OF COMPOSITES ARE
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ADVANTAGES OF COMPOSITES

• EXCELLENT MECHANICAL PROPERTIES - Not only
  intrinsic strength and rigidity values are
  high and the specific value are still
  better.
• GOOD CORROSION RESISTANCE
• EASY PROCESSIBILITY - Leading to a fewer
  components, particularly true with thermoset
  matrices are used.
• 4. FLEXIBILITY OF SHAPE AT LOW COST - Any
  odd shape can be provided when using
  thermoset resin as it is in liquid state
  at time of forming.

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ADVANTAGES OF COMPOSTIES-2
5. CONTINOUS CONTROL OVER PROPERTIES IN
DIFFERENT DIRECTION - The
properties in the different direction
can be varied by changing orientation
of fiber's continuously. One can orient
the fibers in the direction where strength
requirements are higher. 6. ELASTIC
FAILURE WITHOUT YEILDING - Hence no
dents (again for thermoset). This is also a
disadvantage as the failure may be
sudden.
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DISADVANTAGES OF COMPOSITES

• MOST OF THE DISADVANTAGES ARE DUE TO POLYMER
  MATRICES. For example poor thermo-mechanical
  properties, poor resistance to organic solvents,
  Low life due to environmental degradation. Low
  abrasion resistance.
• Additional disadvantages to microstructure are
• 2. RELATIVELY LOW COMPRESSIVE STRENGTH -
  Conventional materials have higher compressive
  strength than tensile but composites may have
  lower.

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DISADVANTAGES OF COMPOSITES-2
3. WEAKER STRENGTH IN SOME DIRECTION - Strength
across the direction of the fibers is very low,
similarly shear strength between the laminates
(Interlaminar shear) is low. 4. ANALYSIS IS MORE
COMPLICATED HAS TO BE DONE CAREFULLY BECAUSE OF
THE DIRECTIONAL PROPERTIES.
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DESIGN
MEANS DIFFERENT THINGS TO DIFFERENT PEOPLE AND
COVERS A WIDE RANGE FROM FASHION DESIGN TO
AIRCRAFT DESIGN
IN THE NOUN/VERB FORM THE OXFORD DICTIONARY
GIVES PRELIMINARY PLAN OR SKETCH FOR MAKING
SOMETHING, PLAN PURPOSE OR INTENTION
WE CAN PERHAPS DEFINE IT AS A SCHEME OR PLAN OF
GIVING PALPABLE SHAPE TO A SET OF IDEAS TO
PRODUCE AN ENTITY TO MEET PREDETEMINED
REQUIREMENT(S) FOR GIVEN SPECIFICATIONS AND
CONSTRAINTS
FOR STRUCTURAL DESIGN THE PROCESS OF DESIGN WORKS
OUT TO
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STRUCTURAL DESIGN
It consists of SPECIFICATION of
1. LOADS/FUNCTIONS/ENVIRONMENT e.g., Wing
Loads, Operating temperature range, Life 2.
SKELETAL GEOMETRY , e.g., Airfoil shape
distribution, planform
And INTERACTION/ITERATION amongst
3. CHOICE OF MATERIAL(S) 4. DETAILED
GEOMETRY 5. ANALYSIS
Continuous for Composites
Descrete
Only provides Shape
Not only provides shape but
material is also fabricated
6. PRODUCTION PROCESSES 7.
EVALUATION CERTIFICATION
Limited Experience of
the material
Well understood
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Product Design Development in Composites is
challenging because of

• Manufacturing process sensitivity variability
  Material is being simultaneously created.
• High anisotropy of the material
• Possibilities in cost optimization by product
  design and component integration

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MANUFACTURING PROCESSES
COMPOSITE PRODUCTS ARE EXTREMELY SENSITIVE TO
MANFACTURING PROCESSES SINCE NOT ONLY THE SHAPE
IS BEING GIVEN BUT THE MATERIAL IS ALSO BEING
CREATED SIMULTANEOUSLY IN MOST CASES
IT HAS LARGE VARIETY AND IS RESTRAINED ONLY BY
IMAGINATION. IT DEPENDS ON SHAPE, NUMBER OF
PIECES, REINFORCEMENT CONTENT REQUIRED,SURFACE
QUALITY, ETC.
SOME PROCESSES ARE INDICATED IN THE FOLLOWING
SLIDES
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SOME FABRICATION PROCESSES FOR FRP COMPONENTS
Hand lay-up process
Filament winding process
Pultrusion
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SOME FABRICATION PROCESSES FOR FRP COMPONENTS-2
Autoclave/Vacuum Bag Moulding
Compression Moulding
Resin Transfer Moulding
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CASE STUDIES
THE CASE STUDIES HAVE CHOSEN FROM THE DESIGNS
CARRIED OUT ON THE BASIS OF DIVERSITY AND THE
CHALLENGES THEY POSED. THE PRODUCTS ALSO INDICATE
WHY THEY ARE SUCCESSES ONLY IN COMPOSITES
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CASE STUDIES

• VENTRAL DIVE BRAKE FOR MiG-21
• FLOOR REACTION ORTHOSIS
• MODULAR TOILET
• ARCH ANTENNA
• SKYBUS COACH

AEROSPACE BIOMECHANICAL RAILWAY
INTERIOR ELECTRICAL/CONSTRUCTION URBAN TRANSPORT
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VENTRAL DIVE-BREAK-1 Existing Conventional
Al-Steel
EXISTING CONSTRUTION - ALUMINIUM PANELS - TWO
HIGH STRENGTH STEEL BEAMS -
HINGED IN THE FORE REGION -
HYDRAULIC JACK AT THE CENTRE -
AERODYNAMIC LOAD TRANSFERRED
FROM DUAL PANELS TO BEAMS
AERODYNAMIC LOAD 40,000 N/m2
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VENTRAL DIVE-BREAK-2 - Redesigned in CFRP
-PANEL RIBS CHANGED TO CFRP -BEAMS TO
STEEL/CFRP, -BRACKET RETAINED IN STEEL -WEIGHT
SAVING 12 -GROUND TESTED.
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VENTRAL DIVE-BREAK-Comparison Team
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FLOOR REACTION ORTHOSIS FOR POLIO AFFECTED
PERSONS
Floor reaction orthosis is a device used by polio
patients with unstable knee
Leg Muscles acts as actuators with joints at
ankle and knee
In polio patients the actuation is lost due to
paralysis as motor nerves are affected.
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FLOOR REACTION ORTHOSIS FOR POLIO AFFECTED
PERSONS - 2
Stabilising the joint by external clamping
Concept
Device based on the concept
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FLOOR REACTION ORTHOSIS FOR POLIO AFFECTED
PERSONS - 3
Alternatively deliberately force a toe contact
with ground, such that the ground reaction
results in a stabilising moment about the knee
hinge
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FLOOR REACTION ORTHOSIS FOR POLIO AFFECTED
PERSONS - 4
Device fabricated based on previous concept using
CFRP
Mass of this device is 300 grams compared to
conventional 1200 grams
The device and its variants used on more than
2000 patients
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FEM ANALYSIS OF FLOOR REACTION ORTHOSIS - 5
Co-ordinate measuring set-up
FEM analysis of FRO
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TOILET MODULE FOR RAILWAY COACHES-1
THE MAIN PROBLEM WITH EXISTING TOILETS IS MASSIVE
CORROSION UNDERNEATH AND AESTHETICS
To design and fabricate toilet module within an
envelope of Size 1.2m x 1.2m base x 2.0m
height Made in four parts which can be taken
through existing doors for easy retrofitting
inside the coach
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TOILET MODULE FOR RAILWAY COACHES-2
Made in GRP initially by contact molding
technique Use of GRP leads to easy forming of
shapes and corner contouring integrating
components
Interior view of the module
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The module is made of four components as shown in
the following drawings
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• The module components-2

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FRP ARCH ANTENNA-1

• DIMENSIONS 25M RADIUS, 75o ARCH
• IT IS USED FOR MICROWAVE RESEARCH. GFRP IS USED
  TO AVOID INTERFERENCE OF SECONDARY RADIATION
• BASE 4.5m X 4.5m TIP 2.0m X 2.0m

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FRP ARCH ANTENNA-2

• STRINGENT DEFLECTION REQUIREMENTS 25mm TIP
  DEFLECTION AT 50km/hr and 200kg LOAD WITHOUT SELF
  LOAD
• MUST NOT FAILUNDER 200 km/hr WIND CONDITIONS

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SKYBUS COACH
CONCEPT THE RAIL TRACK IS MOUNTED ON PILLARS
ABOUT 18 M HIGH THE BOGEY RUNS ON THE RAIL AS
OTHER RAIL SYSTEM BUT THE COACH IS NOT MOUNTED ON
BOGEY BUT SUSPENDED FROM THE BOGEY
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LOADS

• The critical load parameters are
• Floor Load 8 persons/m2 with average weight
  of 68kg 5340 N/m2
• Roof Load 1472 N/m2
• Breaking and acceleration 2.5m/sec2
• Wind velocity 200 kmph any direction
• Load on the side walls 675 N/m2

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DESIGN-Choice of Materials 1

• It was decided to design the coach with
• stainless steel skeletal structure and FRP
• walls and panels for the primarily for
• following reasons
• Stainless steel (SS) will not get corroded in
  costal environments and hence the structure shall
  be maintenance from this point.
• It was considered preferable to use a proven
  material for critical application

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DESIGN-Choice of Materials 2
Glass Fibre Reinforced Plastic (GFRP) was chosen
for walls and panelling for the following reasons

• It has low density(lt1.8) with good
  strength(gt100MPa for the type of GFRP used) and
  rigidity(E10000MPa)
• Good corrosion resistance
• Ability of to provide any shape at low cost
• Component integration is easy
• Improved aesthetics can easily incorporated

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There are basically two concepts of transferring
the platform load to the suspenders
The first is a cradle load transfer is by
tensile forces (considered more efficient) The
second is a portal or a box load transfer by
Bending moment The third can considered as a
combination Present Design uses the first and
combination
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DESIGN Critical Loads
The most critical design condition for the coach
is asymmetric load at the maximum intensity
This causes maximum bending moment and torsion at
the suspender inner locations putting severe
demand on the design of suspenders, attachments
and the transverse cradle beams
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STRUCTURAL LAY-OUT

• The structural lay-out consists of
• Four suspender assemblies-inner most 4.8m apart
• Two inner combination frames
• Two outer cradle frames and
• Structural members integrating with the frames
• Floor, roof and the walls made of FRP panels

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The arrangement looks as shown in the following
figure
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A VIEW OF THE STRUCTURE
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THE SKYBUS
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SKYBUS - 2
THANKS FOR PATIENT HEARING