Course work from edX MOOC covering Composite Materials

1. Components not suitable for manufacture from composite materials
Due to the relatively high cost of the materials, their application to replace low cost metallic
components where weight, stiffness, strength, fatigue life, thermal expansion, corrosion resistance, isn't
an issue would not be justified from the economic point of view.
Manufacturing complexity also introduces another consideration where for example, Cables for the
bike's brake system, designed and manufactured from composite materials may require such an
investment that there would be no positive return when compared with continuing with the current
metallic solution; This could of course all change should new innovative methods of manufacture as
well as composite materials be introduced. The relative increases in the price of raw metals compared
to the price of composite materials could also impact a future decision.
The suggested "Takeaway" here is that the use of composites in lieu of metals must be justified through
the consideration of the business case as it applies to the scope of their adoption within the
organization, as well as with respect to other influencing factors such as trends in the market (what the
competition is doing) and environmental pressures likely to be on everyone's minds during the fully life
cycle of the product (meaning how the raw materials are gathered, how much energy is used to make
the finished product and how that product will be disposed of at the end of its useful life).

2. End of useful life considerations for composite material selection
Maria's concerns are quite valid, what can we do when it comes to disposal of the scrap material and
what will happen to the product once it has come to the end of it's useful life ?
Addressing the scrap and the end of life cycle issues:
In both the case of Thermosetting plastic materials and Thermo plastic materials (used in carbon fibre
reinforced or glass fibre reinforced composites), it currently isn't easily possible to separate them out for
reuse when applied for use as constituents in composite materials - as one might be able to do with
metals through melting and recasting.
On their own however, Thermoplastics can be heated and reshaped for alternative use, for example, re-
moulded to form components cosmetic in nature (inserts to close access holes, sleeves, pegs, etc.).
Thermosetting plastics however, will simple burn and cannot be reshaped for reuse with the application
of heat. This is due to the strong cross linking of the molecules associated with Thermosetting plastics
as opposed to the weaker molecular links inherent in thermo plastics
From a recycle or a disposal point of view, Maria's views on the use of Thermo plastics in lieu of
Thermosetting plastics is largely true and worth considering. There are however options for
Thermosetting plastic disposal are on the horizon :-
http://theconversation.com/recycling-the-unrecyclable-a-new-class-of-thermoset-plastics-26594
Addressing the Design Requirements issue:
However, from the design point of view, where we are interested in such material properties as
strength, durability, stiffness, thermal stability over a wide range of temperature, etc., the use of
Thermosetting plastics is the preferred choice due to their superior properties as a direct result of their
stronger inter molecular bonds.
Being a 'composites' parts manufacturer, we (probably) make use of CFRP / GFRP and as such, superior
properties are what we are (likely) concerned with and thus have to use as the guiding factor in our
selection for the appropriate base constituents in or product.

3. Composites in the Construction Industry - Buildings, Roads & Bridges
Composite materials and methods for producing buildings, Roads & Bridges are being applied to the
Construction Industry more and more but not in the conventional sense as for the Industries of
Aerospace, Consumer Goods, Energy, etc.
In the case of the latter Industries highlighted above and during this course, the desirable properties
which drive the selection of composite materials for the task, are typically strength, stiffness, weight,
thermal stability, resistance to fatigue and corrosion resistance. While the cost of the material is high
when compared to metals, the amount of material used to manufacture the final product is far less
than what would be required to construct build large scale buildings, roads and bridges.
In fact the construction of buildings, roads and bridges as well as other typical construction structures
(tunnels, etc.) rarely require simultaneously, all of the properties which the use of typical CFRP & GFRP
composite materials affords.
However different constituent materials are being put together to form composites which provide
superior properties to the individual constituents. In some cases, this has been a long standing practice
in the construction industry, for example the use of reinforcement bar(Rebar) in concrete structures, or
even the constituents which facilitate the use of medium density fibreboard (MDF) in the home
construction industry.
Traditional CFRP and GFRP are now showing up in the construction Industry when it comes to smaller
and also more complex components, where the economics and design benefits make sense. This is
largely possible through economies of scale allowing the price of their adoption to be significantly
lowered. Typically examples for the home construction industry sector would be for fixtures and
fittings, including doors and window systems which now make use of chopped unidirectional fibre
reinforced plastics.
Companies are often sometimes slow to adopt new technologies because of the huge investment
associated with the switch over to using the new materials, processes as well as because of the
different knowledge & expertise being required, unless there is a significant strategic reason for so
doing. Competition and 'the bottom line' largely tend to drive such decisions and the business case for
supporting any change over must be clear, even compelling.

4. Combining different grades of Aluminum to simulate
inhomogenous properties in an anisotropic metallic composite
As we are an Aluminum manufacturer and Aluminum is isotropic in nature, our best option when it
comes to tailoring a composite version of our product, whether it be to lower weight while maintaining
strength (effectively increasing the strength to weight ratio of the product) or reducing the cost per unit
of measure, is to :-
(1) - make use of different grades of our product in the form of thin sheet bonded together using a
compatible adhesive or bonding agent as the matrix. For example, we could make use of the cheaper
and less dense 2024 Al Alloy combined with the more expensive and stronger 7050 Al Alloy, to produce
stock of a desired cross section size dimensionally with lower weight per linear dimension but at the
desired strength and stiffness.
(2) - make use of weight lessening techniques such as by removing material from within some of the
sheets of Aluminum which make up our composite material raw stock. The modified sheet serves only
as spacers or fillers within the overall composite material stock to help build up dimensions. The
different sheets to be bonded together with a structural or non structural adhesive or bonding agent -
selected as desired for the advertised application - and which will constitute the matrix.
In both of our offerings, we are providing a new material which essentially has different properties
within its cross-section even though the material may be isotropic. In one case we are using different
isotropic 'plies' or sheets of material and in the other case we are reducing the density of some of the
'plies' or sheet.
We also envisage the opportunity to use other compatible materials in sheet form to create a sandwich
of materials which provide unique properties for the resulting composite material, such as those not
possible when it comes to GFRP and CFRP composites.
Making use of the thermal expansion and thermal conductivity of metals as well as their electrical
properties could allow for the creation of embedded sensors and circuitry within the stock metallic
composite product.

5. Designing for 'real world' loads vs predictions based on assumptions.
The following two considerations immediately come to mind :-
The first thing we should always appreciate is that predictions, the more complex the basis for them,
the greater the probability that there will be exceptions to their outcomes or error associated with their
derivation.
The second thing is that there are no perfect measurements nor perfect parts, meaning that tolerances
associated with any measurement or part will result in variation from the ideal.
Keeping the above two points in mind, we apply safety factors when designing for given loads thus
negating in some way, our efforts to fine tune to the optimum degree our solutions.
There is an age old design principle, "KISS" (Keep It Simple Stupid) and it is worth paying attention to at
all times during the design cycle. We should never attempt to design something to be more
complicated than it absolutely needs to be.
The predicted properties for our materials will be based on known averages. The loads applied will be
estimates and the derived stresses and deflections based on assumptions regarding the load cases to be
considered and boundary conditions assumed. All of the associated uncertainty occurring before parts
are even manufactured.
It should be remember that 'loads follow the stiffest path' and thus in the context of composite
materials, understanding the variation in properties of any resulting material, based on its make up, is
paramount.
Testing is the ultimate method to be used to verify predictions and substantiate any design solution but
prior to that, employing a conservative approach towards development of a design solution, is the best
way to ensure the occurrence of unwanted surprises does not happen.
The "takeaway" being that the method chosen should reflect the level of risk to be tolerated, the
desired benefits and ultimately the associated costs.

6. 150 Kg payload VTOL UAS - Metals or Composites ?
This project looks at the requirement for the design of a UAS to
operate from a remotely located docking station. The payload is to be
150 Kg, the range 150 nm and the endurance 12 hours;
This greatly challenges the abilities of VTOL offerings currently on the
market for the desired size, all up weight and cost.
One option being considered is to re-engineer the following UAS in
order to replace 70% or higher of the metallic components with
tailored composites :-
The above UAS comes up short on range and endurance and was not
designed to operate from remote docking stations where it would be
fueled and maintained by the docking station's robots.

7. From hereon we'll take a look at the issues which need to be addressed in order to achieve the desired
performance and cost goals.
The six typical factors which tend to drive the selection of composites over metals are :-
Strength
Stiffness
Lower comparable Weight
Greater Fatigue Endurance
Thermal Stability
Corrosion Resistance
On the other hand the following factors tend to make adoption of Composite Material for use less
desirable :-
Raw Material Cost per pound in weight
Damage Tolerance mitigation penalties
Susceptibility to moisture absorption
UV Radiation susceptibility
Cost and time to inspect and repair
(1) The current design makes use of a Glass Fibre Re-enforced plastic (GFRP) composite but we are
considering changing the material to CFRP in order to improve strength and stiffness.
(2) The Rotor blades are currently made of Aluminum and use a simple Aerofoil shape. We intend
to replace the simple aerofoil shape with a more complex Fan Blade which would significantly
increase the thrust produced. Application of CFRP composite material is anticipated to enable
us to achieve this goal which is not achievable with the use of current metals without negatively
impacting the weight of the UAS.
(3) We intend to do away with the current mechanical transmission which modifies the output
from the Gas Generator's turbine (40,000 RPM plus) down to the 2000 - 3000 RPM range for
the Fan. This is to be achieved by using an electric generator coupled directly to the gas
generator and using the electricity to power an electric motor which will drive the Fan as well as
power all of the avionics and payload instrumentation and other ancillary electrically powered
devices.
We also wish to reduce the weight of the engine (gas Turbine) by making use of composite
materials wherever it makes sense to do so. We plan to use composite materials in the
construction of the electrical generator and in the construction of the electrical motor in order
to reduce part counts as well as reduce weight.

8. We will now look at our design goals in the context of whether it makes sense to use metals or tailored
materials by considering the relative advantages and disadvantages outlined in the earlier section.
(1) The issue associated with this goal isn't a comparison between metals and composite materials
but rather one of one type of composite versus another. We have to weight the cost increase
against the gain in strength and likely four fold increase in stiffness.
We wish to deploy these UASs in remote locations (from Polar regions to Marine, Jungle and
Desert environments) for long periods at a time without manned attendance and hence see
strength and stiffness as being properties necessary to increase durability. The marginal cost
increase associated with the change from GFRP to CFRP is not considered prohibitive.
(2) The complexity in shape of our new Fan Blades (to replace the open Rotor Blades) is particularly
challenging to accomplish with a metal structure because of the desired compound curvature
and nacelle clearance we wish to employ near to the tips.
Metal fatigue for the Polar deployed units is of a concern and so is thermal expansion for the
Desert deployed units. Use of composite materials such as CFRP, on the other has its issues
when it comes to deployment in hot humid Jungle environments. Either choice, metals or
composite materials could adequately be protected against the detrimental effects - associated
with Marine environments - through the application of appropriate coatings and paints.
While the cost of materials for the newly desired Fan Blades would be higher if composite
materials were employed, the cost of machining and of assembly of the metallic version would
be expected to be significant when compared to the cost of making the composite material Fan
Blades.
Concerns about weight and the desire for thermal stability and maximum fatigue endurance
would thus drive our choice toward the use of CFRP in lieu of Aluminum. These would outweigh
concerns with respect to moisture absorption in hot humid climates or the effects of UV
radiation in Polar and Desert environments, as they could largely be mitigated through the use
of special coatings.
(3) Our use of composite materials in the case of the electrical generator and electric motor - which
replace the metal components (gears & shafts, etc.) of the mechanical transmission - would be
aimed primarily at reducing weight while avoiding any significant increase in cost. Cost
reductions as a result of a decrease in overall part counts for the new units would be welcomed.
We intend to locate our electrical generator at the front end of the gas generator (the so called '
cold ' section) where the incoming airflow would be utilized to assist in cooling it and thus do
not anticipate any thermal challenges during operation however, heat 'soak back' on shut down
in hot desert environments may require a special automated shut down procedure.
Therefore it is unlikely that there will be any significant advantage to using composite materials
apart from for the housings of the generator and the electric motor in order to save weight.
We do not envisage any significant advantage to the adoption of ceramic composites for the
generator's rotating components nor GFRP or other for the rotating components of the electric
motor. 'Cost for reliability' will be the decision driving metric.

9. Composite materials used in automobiles
Just looking around the interior of one's vehicle can reveal a whole host of engineered composite
materials specifically tailored to suit the requirements associated with their use.
Composite materials can be strong, stiff and thus structural or soft, strong and thus durable, all
depending on the choice of the fibre / matrix & interface combination
From simulated rich wood trim, to the centre console unit body, to seat structures, to the main
dashboard and the various instrument panel instrument housings, even parts of the steering wheel and
column, all use various types of composite materials suited for their application.
If your daily commute to work, school, or just
to meet with friends, involves using an
automobile, you likely come into contact with
several different types of composite materials,
directly or indirectly, during that time.

10. Composite materials due to their higher cost, tend to be found more readily in higher end vehicles.
The various types of composite materials used include :-
• CFRP (structural applications where strength and stiffness matter)
• GFRP (for lower cost parts of complex shapes including ducting)
• Natural Fibre composites (for semi rigid headliners and pillar trim)
• Wood Fibre composites (for wood trim fascia)
Both Thermosetting plastics and thermo plastics are used as the matrix for composite materials used in
the automotive industry depending on the desired material properties {Hardness, Rigidity, Toughness,
Durability, Thermal Stability, Corrosion Resistance, etc.}, The type of fibre and layup also serves to
satisfy for a wide variety of applications, both internal and external to the vehicle.

11. Growth in the use of Composite Materials for Commercial Aircraft manufacture
My personal observations related to the use of Composite materials in Aircraft manufacture,
particularly fibre reinforced Thermo plastics and fibre reinforced Thermosetting plastics, go back some
25 years.
Initially, so called 'wet lay-ups' were adopted for manufacture of covers and shrouds and these typically
made use of Glass fibres in a Thermosetting plastic matrix. Application was limited to non-structural
uses.
As carbon fibre became more widespread in its availability, Carbon fibre reinforced composites (of the
Thermosetting type utilizing an epoxy matrix) began to be adopted for use in secondary structural
applications, such as for the manufacture of aerodynamic fairings.
CFRP usage escalated and the introduction of larger autoclaves to allow for co-curing of 'pre-preg' and
cured assemblies to produce larger and even more complex structural components increased.
By the Mid 1990s, CFRP was being used to the manufacture the Wing-to-Body fairings, the Main
Landing Gear stowage Wheel Bins and other large secondary structural components as well as the
newly introduced aerodynamic efficiency improving Wing-lets, all making up the Regional Jet family of
aircraft.

12. The introduction of the Global Express lineage of Business Jets saw accelerated adoption of composite
materials for use in aircraft interiors. Flammability requirements arising out of new airworthiness
regulations lead to the use of phenolic plastics as the matrix of choice for many new composites being
used to manufacture the decorative trim for interior monuments such Credenzas, Decorative Bulkheads,
tables & Side Consoles, Galleys and lavatories

13. Greater adoption of CFRP replaced more traditional composite materials such as Sandwich panels
comprising of honeycomb Aluminum cores, used for aircraft floor boards. The CFRP panels provided for
lower weight and are thinner in cross section height thus reducing the volume they take up below floor
level.
Use of composite material ducts for both Cold and Hot fluid applications also increased.
For the Q400 program as with other aircraft, GFRP (with S-2 Glass fibre) is used for manufacturing the
aircraft's Radome.
Kavlar (Aramid fibre) is used for the leading edges of the wing, horizontal & vertical stabilizers.

14. The CSeries makes use of composite materials for primary wing structure, including CFRP for the wing
box and portions of the wing spars and ribs. Electrical wiring also makes use of fibre reinforced thermo
plastics for protection and in several areas fibre reinforced thermo plastic brackets and clips are used to
support and secure wiring, tubing and other components
These are just some of the many areas where composite materials have established themselves as being
the materials of choice because of their unique properties and the great benefits which come as a result
from their adoption for use.
Other programs such as Diamond Aircraft's D-Jet and Learjet's Lear-85 made far greater use of
composite materials for primary structure however both programs were shelved before entry into
service.

15. Fluid Mechanics - Viscosity, Laminar & Turbulent flow and the Boundary Layer
Unless we are dealing with introducing a Resin in vapour form to provide a matrix for the composite, I'd
look towards Fluid Mechanics - and in particular the issue of a fluid's viscosity - in order to derive
principles which may be applied to the manufacture of composite materials with regards to resin flow.
When it comes to the manufacture of composite materials comprising of a fibre and a thermoplastic or
thermosetting plastic matrix, we must focus on two key issues to obtain the desired properties.
• Achieving full wetting of the fibres along the interface with the matrix
• Avoiding the creation of void spaces within the composite
Consider a fluid flow past a surface on which there are obstacles
Although the above greatly exaggerates the distance between Tows or Yarns and certainly does not
represent the distances between individual fibres (filaments), one can appreciate the effect such
roughness would have on the flow of a fluid flowing over the surface.
Introducing the resin such that it flows parallel to the length of the fibres, whether they are in the form
of a weave or a braid as well as Rovings made of Yarns and Tows, will assist to avoid turbulence and
thus voids. It should also facilitate faster resin flow rates to speed up the infusion process.

16. Growth of the Boundary Layer within a fluid flowing over a flat plate
For large components one might become concerned with the size of the boundary layer as the fluid
flows, if this was to affect the rate at which reaction within the matrix were to take place.
If the resin is however drawn (Vacuum) or pushed (positive pressure) through the layup, one would not
anticipate any Boundary Layer impact.
To overcome restriction to the flow of the resin, methods similar to those used in aerodynamics might
be considered.
This might be accomplished through careful channeling of the flow and which may involve the use of
spacers & 'flow straighteners' within the layup itself.
Judicious placement of vacuum ports or pressure supply ports- entry and exit locations - can also serve
to 're-energize' the fluid as it flows through the layup and thus help to ensure that the fibres are well
welted and the occurrence of void spaces prevented.

17. The reality however, is that the resin is already impregnated within the layers of plies in a viscous form
and then when heated and under pressure, is forced to flow in a less viscous form, so that it distributes
evenly through the layup. It is thus not as simple a situation as the flow of a fluid over a flat surface
though it is a case of flowing a fluid along surfaces which have obstructions in the flow path.
To compel the fluid to flow , we need to apply an external force (pressure) and rely on the shear stress
developed within the fluid to cause it to flow through the layup.
The relationship with fluid mechanics can be made in that the Shear Stress within the fluid can be said
to be :-
.
The ' Takeaway'
This Shear Stress must equal the external forces per unit area causing the fluid to flow and therefore
equals the external applied pressure. We could then establish a relationship between the external
applied pressure and the velocity of the fluid (thus its flow rate) and its viscosity.

18. The Business of making world class Kayaks
Not your Grand Daddy's Kayak any more
In our quest to break into the world of high performance white water Kayaking, we're setting out by
defining the following requirements for our new product line:-
- Tough & Stiff
- Rugged & Durable
- Light Weight & Priced Competitively
- Innovative in Design
What we aim to achieve :-
Tough = able to withstand the typical impacts associated with the sport
Stiff = maintains shape for optimum hydrodynamic performance under extreme loads
Rugged = requires little maintenance
Durable = maintains high levels of performance over time
Light weight = as light as or lighter than competitors' products
Priced competitively = not amongst the most expensive in class
Innovative in Design = Introduces the latest high performance features

19. The competition's high end product
How we plan to do it :-
Toughness - To provide superior impact damage resistance we intend to make use of Toughened Epoxy
as the Thermosetting plastic of choice for the matrix used in the production of the composite material
which will make up the Kayak's Hull.
Stiffness - We intend to depart from the traditional Glass fibre and make use of Carbon Fibre as our fibre
of choice in order to improve upon the strength and stiffness of the Kayak's hull and other primary
structure
Ruggedness - Through tailoring our ply layup & fibre volume fraction as well as making use of the co-
curing of laminates of different properties, we aim to mitigate wear and the need for frequent repair in
high risk areas
Durability - Choice of a fibre dominated lay up in key areas as well as through other features selected to
accomplish goals for Toughness, Stiffness and Ruggedness, should all serve to improve the Durability of
our product. The fibre dominated lay up with 0 degrees plies outermost at the 'A' surface, together with
application of performance paints and coatings, is intended to address susceptibility to water
absorption and UV radiation degradation of the matrix

20. Light weight - The use of CFRP and through employing careful tailoring, is anticipated to assist us in
achieving amongst the highest strength to ratios for craft in the high performance market segment
Competitively Priced - By making use of lay up by hand and a VARTM process, We intend to minimize
the high cost of tooling. We also plan to use a knitting strategy whereby plies and other layup material
are supplied to dimension by the supplier. We plan to achieve this by making use of Computer Aided
Design & Manufacture 3D modeling software. This will enable us to provide our material supplier with
the desired dimensions for each ply as per their sequence in the lay up. It will also allow us to reduce
waste and inventory
Innovation in Design - Using our 3D modeling capabilities coupled with our ability to use composite
tooling with the vacuum bag process and through our sponsorship of elite athletes in the sport
contracted to help us test prototypes in the off season, we plan to continuously innovate and
incorporate those innovations which enhance performance into our newest models ahead of our
competition.

21. Designing an Aircraft wing made from Composite Materials
The typical approach employed when setting out to design the wing of an aircraft may follow :-

22. Fig. 1 above shows the typical components which make up the structure of a wing. Components may be
made of metal alloys or composite materials or a combination of both.
Whichever material is chosen, the various loads applied to the structure will give rise to stresses with
the material and how the material will behave is determined by the material's characteristics and the
size and geometry of the component.
Two types of Aeroelastic loading command one's focus
----------------------------------------------------------------
Static Loads which can give rise to :-
- Load redistribution
- Divergence
- Control reversal
Dynamic loads which can give rise to :-
- Flutter
- Buffeting
- Dynamic response
These loads cause Bending and Torsional effects and can lead to tensile, compressive and shear stressed
within the material where its deformation is resisted.
To avoid certain undesirable behaviours by the wing under some of the aforementioned Aeroelastic load
cases, stiffness (Bending and Torsional) of the structure of the wing is the prime concern while for
others, its strength (ability of the material to withstand the stresses without permanent deformation or
failure) is the key objective.

23. The above sketch represents a wind turbine blade however, it could just as well represent a wing or a
helicopter rotor or a propeller with some minor changes to the detail.
When designing the spar(s) of an aircraft's wing, we thus need to be primarily concerned with its ability
to withstand both direct and shear stresses as a result of Bending loads. Torsional loads, on the other
hand, will also give rise to shear stresses in both the spars and the wing's skin but it is the wing's skin
which provides the greatest resistance to torsional loads
The web of the spar provides us with the desired resistance to bending (EI) in the direction of the lift
vector. The spar caps serve to prevent buckling of the spar's web and to attach the wing skins to the
spar.
For the web of the spar, having the fibres of plies aligned with the span of the wing will put them in
tension - if they are below the neutral axis of the web's vertical cross section - when the wing bends
upward. The opposite will occur if the wing bends downward. Additional plies (in the form of woven
fabric)oriented at 45 degrees and -45 degrees serve to transfer any shear loads. Plies oriented vertically
(at 90 degrees) increase stiffness the web in that direction but may be optional
In the case of the spar caps, having the fibres aligned parallel with the span of the wing will also serve
to provide the best orientation for resistance to bending in the forward - aft direction.
The wing's skin is subject to pressure loads. Having the plies oriented parallel to the wing's span (0
degrees), parallel to the wing's chord (90 degrees) and also at 45 degrees and -45 degrees, provides for
the best choice lay up and the laminates should be balanced as needed.
The ply lay up for both spars and the wing's skin should be tailored in order to address the stress
distributions throughout the structure, keeping the magnitude of local stress with in the elastic region
for the composite material.

24. It is thus with this in mind that in order to save weight and minimize cost, a graphite fibre reinforced
thermoset epoxy composite material should be limited in use to locations where stresses are predicted
to be very high. Carbon fibre reinforced thermoset epoxy composite material could be used elsewhere in
areas predicted to experience medium stresses. Finally, Glass fibre reinforced thermoset epoxy
composite material can be used for non structural parts such as fuel tank access panels in the underside
of the wing.
In terms of manufacturing processes for the wing skins, the use of 'prepreg' fabric and employing a
hand layup technique for a VARTM process (making use of vacuum and a single sided mold) should
suffice for small and medium size structures. The spars however may require use of a more expensive
pair of dies and require application of positive pressure in lieu of vacuum during the curing cycle within
an autoclave.
It should be appreciated that most of the failure modes associated with the primary structure of the wing
as a unit are in relation to stiffness.

25. Complex Laminate lay ups
It is conceivable that the suggested lay up is based on the result of an optimization which takes into
account the loads applied to the part and the resulting stresses which arise as a result of the geometry
of the part
Typically, one would want to align the fibres with the direction of loading however, for complex shapes
with compound curves and tight bends, the use of a bi-direction weave (cloth) as opposed to a
unidirectional roving (tape) may better facilitate draping over such surfaces.
The choice of angles (0,5,10,30,40,45,50,60,80,85,90) suggest that the laminate is being optimized for
loads which act along the 5 degree, 30 degree, 45 degree, 60 degree and 85 degree directions, if one
considers that the material properties associated with a given ply, may be reduced by as much as 10
percent if the fibres are misaligned with the axis of loading by 5 degrees.
The diagram below shows the reduction in Tensile Strength as a result of the misalignment between the
fibres and the direction of the applied load
. . .

26. . . .
Stiffness is also affected by the mismatch between the fibre orientation and the direction of loading
. . .
. . .
To assess the practicality of adopting such a lay up, one would first have to obtain an understand of the
magnitude of the loads in the different directions and the rate of 'drop off' of material properties for the
given composite material plies being considered for use.
Where the magnitude of the anticipated load did not give rise to stresses which exceed the properties
for a standard ply orientation, one would suggest that the standard orientation be adopted and possibly
the number of such plies increased locally, if that would not lead to a significant increase in weight.
The reasoning behind the recommendation - if it was appropriate given the loading and geometry of
the part - would be that a limited number of orientations of Uni-Directional plies would facilitate easier
hand lay up and thus lower overall cost; the recommendation being a reduction from 11 different
orientations down to just 5 different ones. (symmetry requirements not included)

27. Composite materials for a remotely stationed VTOL UAS.
The goal being to determine if we can employ the use of Composite Materials to increase the Range and
Endurance of the VTOL UAS as well as its MTBF & MBTUR.
To reduce the basic Empty weight of the vehicle so that its fuel capacity can be increased, I'd propose
looking into the adoption of Composite materials with high strength to weight ratios to :-
1 - replace the existing Glass Fibre reinforced plastic outer shell of the unit
2 - replace the aluminum Rotor Blades and landing Struts
3 - replace the metal chassis, brackets, equipment housings and support structure
4 - replace the metal turbine disc containment ring

28. 1 - The original Glass Fibre reinforced plastic outer shell was expected to provide for as much as 40%
reduction in weight when compared with Aluminum, in most part due to a doubling of the relative
strength with respect to density ratio. Carbon Fibre reinforced Thermoset plastic has the potential to
even further improve on weight reduction due to its much superior relative strength with respect to
density ratio; when compared with the Glass Fibre reinforced Thermoplastic currently being used. To
mitigate the damage tolerance drawbacks, a toughened epoxy would be employed for the Thermoset
matrix.
The outer shell being exposed to the environment and to the airstream during flight, the loads and
moments to be considered for the outer shell would arise from Inertial, Aerodynamic, Thermal and
Moisture diffusion considerations. Any combination of three out of the four could apply in supposition at
any time; landing inertial loads and aerodynamic loads being mutually exclusive.
2 - Application of CFRP for use in the manufacture of the Rotor blades would provide for a much more
aerodynamically efficient Blade design, improved corrosion resistance, fatigue life and of course
reduction in weight. Dimensional stability would be a key issue to maintain the efficiency of the aerofoil
and of the Rotor blade in general and CFRP offers superior performance in this respect. Again, a
toughened epoxy would be required to provide the leading edge of the blade with the impact resistance
desired.
Aerodynamic loads & induced moments , Inertial loads and induced moments and possibly thermal
loads and built up moments as a result would need to be taken into accounts. Moisture loading would
not be anticipated to be a significant issue due to the fact that moisture may not have the opportunity
to diffuse into the blade during operation or when the unit is stowed.
The landing Struts would also benefit from an upgrade to CFRP. Increased stiffness, reduced weight,
better impact performance and increased dimensional stability along with reduced thermal expansion,
all serve to justify adoption of the new material.
Inertial loads and moments (Impact on landing), Thermal loads and associated moments as well as
Moisture loads and associated moments, the latter two due to environmental exposure, would all be
taken into account.
3 - To eliminate the need for use of permanent fasteners, co-cured or co-bonded composite structure
could include structural attachment provisions built in to the chassis itself. The superior stiffness,
dimensional stability and low thermal expansion would make this adoption of CFRP a very attractive
proposition for manufacture of a new integrated structure for the unit's chassis. Some access covers and
equipment housings could continue to be made from less expensive GFRPs and where exposure to high
temperature is unavoidable, Metals or if appropriate, Aramid Fibre reinforced plastics could be made
use of.
For these components, Static & Inertial loads and moments and in some cases, Thermal Loads and
moments would have to be considered. Aerodynamic loads would be transferred to the Chassis as
inertial and static loads and corresponding moments.

29. 4 - If it is to be installed, a Kevlar containment ring could be employed surrounding the Turbine's rotor
discs; to mitigate failure of the discs while operating at high speed. While this would provide for
excellent impact resistance through energy absorption, there is the issue of the environmental effect of
moisture diffusion.
Inertial loads, Thermal loads (some sort of intermediary heat protection would be required) and their
induced moments, as well as Moisture loading and any induced moments would all have to be
considered.

30. So called 'Black Aluminum" - making use of Quasi-isotropic laminates
Referring back to our UAS redesign project, of the four main components targeted for redesign :-
1 - Outer shell
2 - Rotor Blades and landing Struts
3 - Chassis and equipment housings & support structure
4 - Turbine disc containment ring
It is the outer shell which is likely to experience the most variety and uncertainty in terms of load path.
For this reason, a Quasi-isotropic laminate design would be best employed when developing the lay up
for the outer shell panels.
The Rotor blades would be designed for the Lift and Drag forces they generate and the moments
caused. Unidirectional fibre placement being the most likely solution. to provide resistance to bending.
In the case of the struts, again resistance to bending can be achieved through adoption of unidirectional
fibre placement. However to prevent buckling, it is very likely that an enhanced number of plies - beyond
that required to resist bending or compressive loads - will be necessary; greater material cross section
thickness or greater cross sectional area.
The lay up for the chassis and support attachments can be tailored to suit the desired load predicted
paths and thus these structural components need not necessarily be quasi-isotropic laminates.
The Turbine containment ring, on the other hand, would benefit from a lay up which included
[0, 45, -45, 90]s plies, that is to say balanced and symmetrical to avoid warping as it is manufactured
and as it is subjected to inertial loads.

31. Best Inspection strategy and most suitable technique
From the described event and conditions, one would first have to define a strategy in order to choose
the most ideally suited technique.
Having obtained from the person who best witnessed the event up close, the intensity of the impact and
their confidence level regarding their assessment, I would first order a visual inspection in situ.
If the inspection detected any form of conclusive visual damage {BVID, VID, Through Impact Damage},
I'd order the aircraft back to the hangar for repairs to be carried out.
If no conclusive visual evidence of damage {NVID} could be detected and considering the environmental
conditions (weather and visibility), I'd request a tap test be carried out; intended to identify any large
impact damage below the surface and not visible to the naked eye.
Bearing in mind that the tap test could also be rendered inconclusive as a result of certain weather
conditions, I would only dispatch the aircraft if I had a high level of confidence that there was no or
insignificant damage as a result of the impact, taking all of the information into consideration {witness
report, result of the visual inspection, result of the tap test, conditions under which all inspections were
carried out}
I would request that a manual Thermography inspection - with a hand held FLIR type camera - be
carried out immediately when the aircraft landed at its next destination. Any damage should show up
as the composite structure warms up more quickly once the aircraft is on the ground when compared to
any voids, disbonds or water ingressed areas. Any evidence of such would lead to the aircraft being
taken out of service and sent to a hangar for an Ultrasonic inspection of the vertical tail.

32. Racing Kayak damage repair
The most effective and efficient technique for repairing the type of damage shown in the images below
involves a wet lay up technique.
One must choose repair material which is the same as the original composite material { fibre & resin }
• For surface dents, it may be appropriate to seal and build up the area using solely resin.
• However for substantial cracks, it is recommend that a full repair be undertaken and this is best
accomplished using a simple staggered lay up or even a scarf joint.
This video walks us through a typical repair procedure