UWE Bristol Engineering showcase 2015

Adam Caldwell
BEng (Hons) Mechanical Engineering
Project Supervisor
Dr. David Richardson
The Structural Optimisation of Carbon Fibre Composites and Interfaces
Introduction
Hollow tubular composites can be found
across a wide array of sporting
applications. The most prominent example
of this manufacture can be seen in the
mass production of carbon fibre road bike
frames for both professional cyclists and
fans alike. Although an expensive
alternative to its metallic counterpart,
composites offer superior strength and
stiffness capabilities. These factors,
twinned with the component being very
low in weight, make the use of composites
a tantalising proposition for designers and
engineers.
In this investigation
multiple T-section
handlebar
components
(example shown in
Figure 1) and
footplate prototypes
have been produced
using bladder
inflation moulding
(BIM). Having
developed the
design of the
footplate a wet
layup vacuum
technique was then
also employed.
Figure 1 – Carbon,
Aluminum & Steel
handlebars
Handlebar Manufacture & Testing
A total of six handlebars were produced over
the course of the project, with three of
those being used for testing. The ply
orientation and material layup were driven
by the differing forces acting on various
areas of the component (bars, T-Section and
stem) during use. Following completion of the layup
the part was left to cure for 2 hours at a temperature
of 180°C . One bend test (see Fig 2a and 2b) and two
compression tests served to inform future
production and anaylsed each of the components
mechanical capability compared to calculated values
for maximum stress and deflection.
Figure 2a & 2b – Stem bend test setup on Instron 4204
Various issues were encountered and overcome
during manufacturing e.g. material pinching within
tool, air leakages. Testing on the fourth handlebar
showed each of the bars themselves could
withstand a maximum force of 924.5N, equating to a
weight of approximately 94kg per bar.
Finite Element Analysis (FEA)
Using Abaqus/CAE software regions of the handlebar
were modelled to investigate areas of high stress
concentration and measure deflective behaviour (Fig
3). These values were then validated against
Figure 3 – Stress Contour Plot from LH handlebar in Torsion
theoretical calculations and studied alongside the
testing data. Through collation of this information it
was then possible to optimise the design of the
component and ensure maximum performance.
Footplate Manufacture & Testing
A prototype scooter footplate was initially
manufactured by means of BIM using glass fibre
(GFRP)and incorporated a polystyrene foam core in its
neck (See Fig 3a and 3b). Although this did result in
excellent axial stiffness, issues with the air bladder
meant consolidation of the deck was difficult and
another less complicated concept was pursued.
Figure 3a & 3b – GFRP neck section and core cut out
The second footplate prototype omitted the integrated
metal headset and instead featured a swept neck (See
Fig 4) with a PVC foam core running the length of the
component. A hollow composite headset was later
glued to the part using an aircraft grade structural
adhesive. With two layers of 0/90 weave carbon fabric
either side of the core, the cured component exhibited
excellent flexural stiffness – reaching a maximum load
of 1429.27N during a 3-point bend test (shown below).
Figure 4 – 3-point bend test on scooter deck
Project summary
The primary aim of this investigation was to
structurally enhance and optimise the design of an
existing micro scooter handlebar. Following a
focused design, build and test campaign of the
composite handlebars, a secondary study was then
undertaken to evaluate and develop the
manufacturing method utilised to produce scooter
footplate components.
Project Objectives
• Structural optimisation of the composite layup for
scooter handlebars.
• Undertake Finite Element Analysis study
• Manufacture a optimised handlebar component
• Develop practical laboratory skill
• Validate optimisation through testing
• Evaluate the embodiment of a headset within the
scooter footplate (through research and
manufacturing trials)
• Enhanced design and manufacture of scooter
footplate
Project Conclusion
All project goals have been successfully achieved,
including the principal objective of producing a
structurally optimised handlebar component that is
also aesthetically pleasing. After undertaking a
research study and various manufacturing trials, an
alternative footplate design and manufacturing
process was implemented. Although exhibiting
excellent mechanical characteristics and surface
finish in the deck section , the footplate lacks the
necessary stiffness and strength in the neck region –
thus highlighting this as a key area for improvement
with any further investigations. A study aimed at
combining the two components into one scooter
assembly is also highly recommended.