UWE Bristol Engineering showcase 2015

Research
Research was carried out into the previous
investigations in this area conducted by students at
the University. Although previous reports had
discussed the potential for the testing rig to influence
the outcome of the tests, none had focused on
benchmark testing prior to conducting the strain rate
tests. The first part of this report concentrated on
obtaining optimum design parameters to ensure that
the apparatus used to conduct the strain rate tests
would have little or no effect on the fabric testing.
The second part focused on the manufacture and
assemble of a bespoke rig capable of delivering strain
rates beyond the capabilities of the Instron 3367
machine (500mm/min crosshead velocity). Previous
electron microscope analysis suggested the fibres
were melting at the point of fracture and so the use
of a thermal imaging camera during testing would
help corroborate this hypothesis.
Benchmark Testing
The initial set of tests were designed to setup the test
rig (An Instron 3367 Tensile testing machine) to
establish the optimum testing parameters for the
fabric . For this benchmark testing, a range of torque
(60Nm – 160Nm) was applied to the clamps to
establish a clear understanding of the effects of the
varying torque on the test specimens. At varying
torque values, the fabric suffered from varying failure
modes. The ideal failure mode was where the
specimen failed away from the clamp points and
uniformly across its surface. A specimen that failed
at the clamp’s edge was believed to have been as a
result of the stress concentration points produced
and a specimen that failed in a diagonal fashion could
be due to a misalignment between the top and
bottom clamps. It was assumed that the lower torque
figure applied to the clamp would result in the fabric
slipping from the clamps and the higher torque
would yield a break close to the clamps.
David Whale
MEng Aerospace Manufacturing Engineering
Effect of Strain Rate on the Tensile Properties of Nylon Fabrics
From previous studies, Ashley Hudson noted in his
findings that a torque of below 80Nm appeared to
show the fabric slipping from the clamps .
Extensive testing at the range of torques outlined
above proved that this was not the case and that a
torque of 140Nm provided the optimum testing
clamp torque.
It was assumed that the lower torque figure
applied to the clamp would result in the fabric
slipping from the clamps and the higher torque
would yield a break close to the clamps. From
previous studies, Ashley Hudson noted in his
findings that a torque of below 80Nm appeared to
show the fabric slipping from the clamps .
Extensive testing at the range of torques outlined
above proved that this was not the case and that a
torque of 140Nm provided the optimum testing
clamp torque.
Bespoke Rig
A new rig was manufactured at the university in
order to carry out the high strain rates required.
An Instron 8033 machine was used to provide the
hydraulic supply to the actuator in the rig
This allowed the strain rate to increase to
20 000mm/min.
Results
The results contradict previous findings in that the
breaking load capabilities of the fabric increases
with strain rate. A more important note is the
continuous appearance of sinusoidal behaviour at
smaller intervals across 3 separate tests and on
both rigs
Load (N)
Average Maximum Load per Strain Rate
3,760.00
3,740.00
3,720.00
3,700.00
3,680.00
3,660.00
3,640.00
3,620.00
3,600.00
3,580.00
3,560.00
3,540.00
0.00 100.00 200.00 300.00 400.00 500.00 600.00
Strain Rate mm/min
Thermal imaging results showed that the material
underwent fracture at the glass transition
temperature and not at the melting point of the
Nylon.
Project Supervisor
Dr. John Kamalu
Project summary
This report encompasses tests undertaken for Invista
Textiles into the behaviour of Nylon 6 6 when
subjected to an increasing strain rate. Low strain rate
testing, defined as being up to 500mm/min, has been
carried out using an Instron 3367 machine whilst
higher strain rate testing , 500mm/min+, was carried
out on a bespoke test rig manufactured at the
University of the West of England and powered using
an Instron 8803 and two dual acting actuators
connected via hydraulic hose. Thermal Imaging tests
have been conducted to determine the temperature
behaviour of the fabric when undergoing increasing
strain rates.
Project Objectives
• Carry out benchmarking tests to achieve optimum
testing parameters for the nylon fabric
• Analyse the statistical reliability of the data by
using randomised testing using lower and higher
strain rates.
• Manufacture and assemble a new test rig to
produce high strain rates not achievable via Instron
3367
• Test fabric with respect to high strain rates,
observe and record the change in tensile
properties of the fabric.
• Analyse fibres under Thermal Imaging to
determine the micro behaviour of the pieces
tested.
Project Conclusion
Optimum testing parameters have been
obtained and the fabric appears to undergo a
sinusoidal behaviour at 100mm/min
displacement increments. The fabric also
undergoes fracture at the glass transition
temperature of the Nylon at approximately
50°C