Transcript Title

Composites:
basics and terminology
John Summerscales
Reading for a degree
Each lecture has:
• PowerPoint slides on extranet
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these need JS “soundtrack” (i.e. lectures)
• individual lecture webpages on extranet
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also read these to reinforce your learning
… and to really understand the topic
follow up the references and/or review papers
Support materials for module
• Home page on Extranet
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MATS231: http://www.tech.plym.ac.uk/sme/mats231/
MATS324: http://www.tech.plym.ac.uk/sme/mats324/
• Lecture schedule, notes and PowerPoint:
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http://www.tech.plym.ac.uk/sme/mats324/PowerPoint
• Home page also includes:
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subject index
map of local composites companies
links to Library Reading Lists
and many other useful resources ;-)
• see MooDLE student portal for assessments
Support materials
http://www.tech.plym.ac.uk/sme/mats231
Lecture & practical schedule
Free e-books
Review papers
Subject index
Practical
• manufacture and test of a composite plate
• attendance at Health and Safety lecture is
an essential prerequisite for coursework
list of attendees circulated for signature
o if your name is not on the list,
you will not be allowed to do the practical
o if you do not do the practical you will fail the
coursework element and hence the module.
o
Outline of this lecture
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Anisotropy
Fibre volume fraction (Vf)
Areal weight of fabric (WF)
Basic rule-of-mixtures
Glass transition temperature (Tg)
Crystalline melting point (Tm)
Stacking sequence notation
Anisotropy
Degree of Principal
anisotropy axes
Properties
Example
Isotropic
Orthogonal
Constant regardless of direction
Metals
Square
symmetric
Orthogonal
Two different principal axes
Unidirectional
fibres or woven
cloth
Orthotropic
Orthogonal
Three different principal axes
Unidirectional
weave with light
weft
Anisotropic
Any angle
Constant relative to axes
Filament wound
tube or many
crystals
Aeolotropic
Any angle
May change with position
Timber
Fibre volume fraction (Vf)
• n = the number of layers
• AF = the areal weight of the fabric
• ρf = density of the fibre, and
• t = the thickness of the laminate.
nAF
Vf 
ft
Basic rule-of-mixtures 1
• Elastic properties (e.g. density or modulus)
of composite calculated by rule-of-mixtures
EC = κ . ηd . ηL . ηO . Vf . Ef + Vm . Em
• if the first term of the equation is large,
the second term can be neglected
Basic rule-of-mixtures 2a
The parameters are:
• EC = modulus of composite
• Vx = volume fraction of component x
• Ex = modulus of component x
• subscripts f and m are
fibre and matrix respectively
Basic rule-of-mixtures 2b
• κ = fibre area correction factor*
• ηd = fibre “diameter” distribution factor*
• ηL = fibre length distribution factor
• ηO = fibre orientation distribution factor
*
these two factors are set to unity for man-made fibres
(but see lecture A9 on natural fibres)
Basic rule-of-mixtures 3
ηL = fibre length distribution factor
• 1 for continuous fibres
• fractional for long fibres
• 0 if fibre below a “critical length”
Basic rule-of-mixtures 4
ηO = fibre orientation distribution factor
• a weighted function of fibre alignment,
essentially cos4θ:
1 for unidirectional
o 1/2 for biaxial aligned with the stress
o 3/8 for random in-plane
o 1/4 for biaxial fabric on the bias angle
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Basic rule-of-mixtures 5
• Vf = fibre volume fraction
o 0.1-0.3
for random
o 0.3-0.6 for fabrics
o 0.5-0.8 for unidirectional
• consolidation pressure:
o no
pressure gives the lower value
o Vf increases with pressure
Basic rule-of-mixtures 6
• Ef = elastic modulus of fibre
o glass
= ~70 GPa
(equivalent to aluminium)
o aramid = ~140 GPa
o carbon = ~210 GPa
(equivalent to steel)
• figures above are lowest values
i.e. for standard fibres
Transition temperatures
in ascending order
• Tg = glass transition temperature
• Tc = peak crystallisation temperature
• Tm = crystalline melting point
typically Tm = Tg + 200±50°C
nb: no melting point in amorphous materials
• Tp = processing temperature
typically Tp = Tm + ~30°C for “semi”-crystalline polymers
Tg follows cure temperature in thermosets
• Td = degradation/decomposition temperature
may limit Tp (especially for PVC)
Glass transition temperature (Tg)
• Temperature at which
segmental motion of the chain is frozen out
below Tg polymer is elastic/brittle
o above Tg polymer is viscoelastic/tough
o more rigorous than heat distortion temperature
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• Tg for thermoplastics = Tm - ~200°C
• Tg for thermosets follows cure temp.
Crystalline melting point (Tm)
• all polymers have a Tg
• only some polymers have a Tm
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they must be able to form crystals
normally a regular repeating structure
 rarely 100% crystalline
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• polymers may degrade before melting

usually the case for thermoset
Composites
How fibres can be arranged
in order of increasing stiffness and strength:
• 3-D random
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e.g. injection moulding grades.
• planar random
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e.g. moulding compounds, chop strand mat, random swirl.
• quasi-isotropic (QI)
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e.g. continuous fibres oriented at 0°/-45°/90°/+45° or 0°/60°/120°.
• bidirectional
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e.g. woven fabrics or cross-plied UD laminates at 0 °/90 °.
• unidirectional (UD)
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e.g. pultrusions and aligned monolithic fibre composites.
Four types of
fibre-reinforced composite
• Monolithic (material)
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all layers aligned parallel
• laminate (structure - see next slides)
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orientation changes between layers
• hybrid (structure – MATS324 lecture A6)
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more than one type of fibre (e.g. carbon/glass)
• Sandwich (structure – MATS320)
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composite skins and lightweight core
Laminate stacking sequence notation
• typical laminate stacking sequence is:
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[0º/+45º/-45º/90º]ns
• where the subscripts are:
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n is the number of repeats of the sequence
Q indicates antisymmetric laminate
s means the laminate is symmetric
T is the total number of plies
overbar denotes that the laminate is
symmetric about the mid-plane of the ply
• Thus for n = 2 above, the sequence will be:
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0º/+45º/-45º/90º/0º/+45º/-45º/90º*90º/-45º/+45º/0º/90º/-45º/+45º/0º
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with * denoting the line of symmetry.
I-beam vs stacking sequence
Beam stiffness reduces from left to right:
Laminated composite plate:
0° layer or 90° layer
Equivalent beam: high EI vs low EI segments
Key points of this lecture
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resources on Student Portal and Extranet
anisotropy
fibre volume fraction (Vf)
areal weight of fabric (AF … sometimes WF)
basic rule-of-mixtures
glass transition temperature (Tg)
crystalline melting point (Tm)
stacking sequence notation