Fluid Structure Interactions
Research Group
Synchronised IRT and DIC capture to measure the strain rate
dependency of fibre reinforced composites
Duncan A. Crump1, Janice M. Dulieu-Barton1 and Steve W. Boyd1
Faculty of Engineering and the Environment, University of Southampton, UK.
dac400@soton.ac.uk
Motivation
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Objectives
The military use composite materials in land,
sea and air vehicles in high performance
applications, to assist with speed and
maneuverability.
Collisions or blast loads (Figures 1 and 2) cause
high strain rate events to occur, that may cause
the composite structure to fail completely or to Figure 1: Bird strike on aircraft nose
suffer damage that reduce service life
To reduce the risk of catastrophic failure after a
high strain rate event it is important to fully
understand the structural performance of
polymer composite materials and structures
under such loading.
It is known that the behaviour of composite
materials is dependent upon the strain rate, and
that during the formation of damage a
temperature change occurs within the material. Figure 2: Slamming on RNLI lifeboat
Intermediate strain rate – VHS Instron machine
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%
x- strain
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GFRP crossply with 0° and 90° surface
plies with wasted section to ensure
failure capture
High speed images at 5 kHz over 512 x
256 pixels
IR images at 15 kHz over 64 x 12 pixels
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(b)
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Figure 5: (a) 0° surface, (b) 90° surface ply
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Figure 6: Split Hopkinson pressure bar rig
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Southampton.
To develop digital image correlation (DIC) procedures for
capturing deformations at high velocity based.
To obtain a full field picture of the temperature evolution
during the high strain event using infra-red thermography
(IRT).
Develop the use of simultaneous IRT and DIC at high
framing rates.
To provide a thermomechanical characterisation of the
material performance using experimental data to validate
existing measured data and models.
To use full-field techniques to assess the performance and
damage tolerance of materials after experiencing high strain
rate events.
High strain rate – Split Hopkinson pressure bar
Tensile coupons up to 20 m/s
Strain rates up to 102 s-1
Test times between 1 – 15 ms
Load recorded using 80 kN
Kistler load cell
Inertia removed using slack
adaptor designed in-house
Enlarged protective enclosure
allows several optical systems to
be used simultaneously
All optical and data acquisition
systems triggered by central pulse
Figure 3: VHS Instron test machine
1. Develop high strain rate testing facilities at University of
Figure 4: Example results from
crossply GFRP specimen, DIC green box and IRT - red box
Figure 4 shows high speed
image of 0° specimen, with
DIC and IRT data at 20 ms
(14 kN) superimposed.
Figure 5 plots DIC strain and
IRT temperature vs stress at
the image mid-point.
DIC strain show linear
relationship to stress for
both specimens.
IRT
temperature
both
indicate an initial drop
Towards failure temperature
is higher for 90° specimen
Five
CFRP
crossply
specimens (10 x 10 mm)
tested at ~13.5 m/s
Strain rate of ~ 1000 s-1
achieved
Using the Hopkinson
analysis on signals from
strain gauges mounted
on the incident and
transmission bars the
stress/strain curves in
Figure 7 were obtained.
Striker velocity
up to 30 m/s
Strain rates in
the 103 s-1
Designed
around
composites
Strain
gauge
signal captured
by Picoscope at
20 MHz.
Figure 7: CFRP crossply at ~ 1000 s-1, inset is an
example of high speed image of speckled surface
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Figure 8: Example of incident, reflected and
transmission pulses together with timing of DIC data
Figure 8 demonstrates
the ability to trigger high
speed camera adequately
to obtain DIC aligned
temporally with testing
pulse.
Further work to improve
specimen alignment and
hence test consistency
Extend the SHPB to soft
materials such as foam
with
polymeric
and
hollow transmission bars
FSI Away Day 2012
Acknowledgement: This project is supported by funds from the
Engineering and Physical Sciences Research Council
and Defence Science and Technology Laboratory