Exam (elaborations)
CDM Design
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- BIOLOGY PAPER 2 Solutions
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- BIOLOGY PAPER 2 Solutions
Exam of 23 pages for the course BIOLOGY PAPER 2 Solutions at BIOLOGY PAPER 2 Solutions (CDM Design)
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CDM DesignList three advatanges of composites - correct answer-Design: Lighter, stiffer,
stronger, more corrosion resistant
Manufacture: fewer components, fewer fasteners and fwer processes required
How can high material and manufacturing costs be overcome by design and
manufacture? - correct answer-Use of composites reduces components, fasteners
and manufacturing processes, therefore a well designed uses less materials and
thus reduced components/fasteners/labour costs
Suggest three type of form of material and section configuration examples illustrated
in introduction notes - correct answer-De haviland abatross (1937) - wodden
composite structure
Mosuqiteo (1940) - wooden laminated skin sandiwch with balsawood core and male
contrete tooling
Spitfire (1940s) - coton/flax phenolic composite to create spitfire demonstrator
Harrier GRS: BAE model with monolithic carbon fibre/epoxy wings by co-bonding
and co-curing
Gerhard Waibel ASW 22B: glider w/ hybrid glass/carbon fibre epoxy composite wing
and fuselage
Westland Augusta EH101: helicopter tailored carbon fibre eppxy BERP w/ metal
mould
Wing turbines: hybrid of glass and carbon fibre epoxy laminates manufacturing in
open moulds
Blank - correct answer-Blank
Name 5 typical consitutents of composite materials - correct answer-Fibre
Matrix
Interface
Core
Adhesive
What arrangement and form of fibre is needed for advanced composite materials? -
correct answer-Aligned, continuous fibre reinforcement
,What is a tow? - correct answer-A bundle of strands where a strand is a bundle of
filaments (a filament is a fibre)
Name three types of carbon fibre - correct answer-High modulus
Intermediate modulus
High strength
State the main attributes of carbon, kevlar and glass fibres - correct answer-Carbon:
graphic type crystals, typically high strength and high stiffness, brittle
Kevlar: aromatic polymer fibre, high tensile strength, high stiffness, fibrillation under
compression, exhibit more necking than others thus tougher characteristics
Glass: amorphouse structure, high strength, moderate stiffness, strain to failure of
2%
State main limiting properties of carbon, kevlar and glass - correct answer-Carbon:
low strain to failure (1 - 1.5%), brittle
Kevlar: moisture ingress, fibrillation under high compression
Glass: moderate stiffness and higher density than carbon
Choose either carbon, glass or kevlar for:
Impact
Specific stiffness/strength
Low cost - correct answer-Impact: Kevlar
specific: carbon
low cost: glass
Name two main types of polymer matrices and give examples of each - correct
answer-Thermoset: epoxies
Thermoplastic: PEEK
State three main differences between thermoset and thermoplastic composites -
correct answer-Thermoset: cross linked, chemical reaction occurs, cannot be
re-softened
Thermoplastic: not all of the above
State three advantages of thermoset composites - correct answer-Commonly used in
composite aerospace structures as easier to manufacturing
General mechanical properties are better than thermoplastics (i.e. stronger)
, Generally inexpensive as they don't need as much heat/pressure
State three advantages of thermoplastic composite - correct answer-Inifite shelf life
Can be re-softened (recycling/scrapping is much easier)
Little or no volatile organic compounds and no cure time needed
State three main limiting performances of thermoset matrix composites - correct
answer-Temeprature (max T of 150)
Toughness (epoxies are relative brittle w/ low strain-to-failures)
Moisure (epoxies can absorb up to 2% water and it plasticises the material)
State three main limiting performances of thermoplastic matrix composites - correct
answer-Difficult to bond due to low surface energy
Difficult to process (high manufacturing temperatures and high pressures needed for
impregration of fibres)
Expensive material and ancillaries
Choose either epoxy, phenolic, polyimide or PEEK for:
High temperature application
General mechanical performance
Toughness - correct answer-High T: phenolic/polyimide
General mechnical performance: epoxy
Toughness: toughened epoxy/thermoplastic
Why is the interface between fibres and matrix so critical? - correct answer-It
controls the properties of composite materials: if it is too weak the strength and
stiffness will be low (unable to transfer stress from matrix to fibres) if it is too strong
the toughness will be low
What is a sizing agent and what are its functions? - correct answer-A sizing agent is
used to protect the fibre surface, to aid wetting of matrix by increasing surface
energy and act as a coupling agent for chemical bonding.
Name and describe sandwich cores and state their attributes - correct
answer-Honeycomb: corrugated sheets bonded together at alternating positions to
form cells (hexagonal or rectangular). E.g. Metal: anodised aluminium sheets
Foam: polymeric foams used as core material. Closed cells are achireved by
restricting the foam to ensure foaming bubbles don't burst. E.g. Rohacell: PMMA
closed cell foam
Syntatic: resins bulked by the inclusion of lighweight fillers: e.g. glass micro-balloons
Choose either aluminium/nomex honeycomb/foam/syntatic cores for:
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