Institute for Carbon Composites donated by
High strain rate characterisation of composites using split-Hopkinson bar method
Peter Kuhn / Dr. Hannes Körber
„A Comprehensive Approach to Carbon Composites Technology“Symposium on the occasion of the 5 th anniversary of the Institute for Carbon Composites
Research Campus Garching, September 11th - 12th 2014
2
Conclusion5
Test Example with Tension Bar Setup4
Test Example with Compression Bar Setup3
Introduction of Split-Hopkinson Bar test method2
Motivation1
Agenda
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
3
Conclusion5
Test Example with Tension Bar Setup4
Test Example with Compression Bar Setup3
Introduction of Split-Hopkinson Bar test method2
Motivation1
Agenda
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
4
Increased applications in which fiber reinforced polymer matrix composites are loaded dynamically
For FE-simulations, models capturing high-rate material response are required
High-rate-loading experiments provide data to validate and further develop composite constitutive models
and failure criteria
Motivation
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Side impact pole test [1] Foreign object damage [2]
5
Conclusion5
Test Example with Tension Bar Setup4
Test Example with Compression Bar Setup3
Introduction of Split-Hopkinson Bar test method2
Motivation1
Agenda
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
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Strain rate regimes and associated testing methods
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
10510-1 104102 10310110010-210-310-410-5Strain rate [1/s]
Creep
10-6
Quasi-static Intermediate High rate Impact
Inertia forces neglected Inertia forces important
Conventional load frames(hydraulic, electro mechanical)
Special servo-hydraulic frames
Hopkinson Bars and
Drop Tower
Taylor Impact Test, Expanding
Ring,…
Isothermal Adiabatic
Strain rate regimes and associated testing methods (adapted from [3])
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The striker-bar impacts the free end of the incident-bar
A longitudinal elastic compressive strain pulse is created, which propagates along the incident-bar
The pulse is partly reflected at the incident-bar/specimen interface due to change of mechanical impedance
The ratio of reflected to transmitted pulse defines the relative motion of the bar endfaces
LCC-Setup: Ø 16, 18, 25 mm steel bars & Ø 16 mm aluminium bars
Classical Split-Hopkinson Bar Setup
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Compression (SHPB)
SHPB Setup [4] Propagation of strain pulse
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In principle, very similar to Split-Hopkinson Bar for compression
Differences in loading mechanism
Differences in specimen gripping methods
LCC-Setup: Ø 16, 20, 25 mm titanium bars
Split-Hopkinson Bar Setup
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Tension (SHTB)
SHTB Setup [5]
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SH
PB
AR
aw d
ata
Classical Analysis (SHPBA)
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Procedure
incident-bar strain gauge transmission-bar strain gauge
Shifted strain waves
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IdealInhomogeneous
specimen deformationNon-planar
interface deformation
Classical Analysis (SHPBA)
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Limitation
Correct calculation of specimen strain and strain rate not always possible using SHPBA
Direct stain measurement on specimen is more accurate for composites
Strain gauges on specimen
Optical methods
[4] [6]
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Contactless measuring technique
Full 2d strain field ���, ���, ����
Verification of uniform specimen deformation and strain distribution
High speed photography reveals deformation and failure mechanisms
Strain Measurement
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Digital Image Correlation (DIC)
Setup for Optical Strain Measurement [4]
Digital Image CorrelationSoftware (GOM ARAMIS)
Principle of Digital Image Correlation (adapted from [7])
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SH
PB
AR
aw d
ata
Combined Analysis
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Procedure
Raw
dat
aD
IC
Synchronization
εS, ��S,F, σS
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Conclusion5
Test Example with Tension Bar Setup4
Test Example with Compression Bar Setup3
Introduction of Split-Hopkinson Bar test method2
Motivation1
Agenda
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
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Specimens are clamped between incident- and transmission-bar
Bar-end surfaces are covered with MoS2
Same specimen types are used for quasi-static reference tests and dynamic SHPB tests to ensure
comparability of results
Already tested at LCC: UD-CFRP, 5HS CFRP, Plain-Weave GFRP, neat resin
Setup for compression tests
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Specimen geometry and fixation
Specimen geometry Specimen fixation at SHPB Specimen fixation at electro-mechanical machine
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HR110 HR21010
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Material:
5-harness-satin carbon-epoxy
Tested in 15°-, 30°-, 45°-off-axis and weft direction (video: 45°)
SHTB test setup:
Steel bars, Ø 16 mm
Two strain rates investigated
Photron SA5 high speed camera
QS reference test setup:
Electro-mechanical testing machine
Velocity: 0,5 mm/min
3D ARAMIS system
Dynamic compression test
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Videos
Video sequence captured with high speed camera
Axial strain field determined with ARAMIS DIC system
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Compression test
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Comparison of quasi-static and dynamic material behaviou r
Specimens were tested in 15°-, 30°-, 45°-off-axis and weft direction
Strength components are transformed from loading coordinate system in material coordinate system
A maximum stress failure criterion is well suited to approximate the failure envelop
Failure envelope in � � stress spaceAxial stress-strain curves at different strain rates fo r45°-specimens (failure points marked)
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Conclusion5
Test Example with Tension Bar Setup4
Test Example with Compression Bar Setup3
Introduction of Split-Hopkinson Bar test method2
Motivation1
Agenda
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
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Specimens are glued into slotted endcaps
Threaded endcaps are screwed into bars
Same specimen types are used for quasi-static reference tests and dynamic SHTB tests to ensure
comparability of results
Already tested at LCC: UD-CFRP, Plain-Weave GFRP, FML, neat resin
Setup for tension tests
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Specimen geometry and fixation
Specimen geometry Specimen fixation at SHTB Specimen fixation at electro-mechanical machine
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Material:
Plain-Weave E-glass-epoxy
Tested in 0°-direction
SHTB test setup:
Titanium bars, Ø 16 mm
Impact velocity: about 9 m/s
Photron SA5 high speed camera (100.000 fps, 384x168 pixel²)
QS reference test setup:
Electro-mechanical testing machine
Velocity: 0,5 mm/min
3D ARAMIS system
Dynamic tension test
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Videos
Video sequence captured with high speed camera
Axial strain field determined with ARAMIS DIC system
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Tension test
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
Comparison of quasi-static and dynamic material behaviou r
All specimen failed at free length at the transition from gauge section to radius
At strain rate 170 1/s, axial strength is 50,4% higher than under quasi-static conditions
plain-weave E-glass-epoxy
Tested specimens (quasi-static) Tested specimens (hi gh rate)
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Conclusion5
Test Example with Tension Bar Setup4
Test Example with Compression Bar Setup3
Introduction of Split-Hopkinson Bar test method2
Motivation1
Agenda
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
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Conclusion
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
The Split-Hopkinson bar method is ideally suited for dynamic material characterisation of composites in the
strain rate range of 10² - 10³ 1/s
Optical strain measurement techniques, such as Digital Image Correlation (DIC), are ideally suited to obtain
all strain components of orthotropic materials and are further useful to evaluate the uniformity of the
specimen deformation
Reliable results can be achieved by using a combined analysis procedure, consisting of classical Split-
Hopkinson Bar Analysis (SHPBA) and Digital Image Correlation (DIC)
High speed photography reveals specimen deformation and failure mechanisms
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Technische Universität MünchenInstitute for Carbon CompositesBoltzmannstraße 1585748 Garchingwww.lcc.mw.tum.de
Contact
Address
FaxEmail
TelRoom
+49 89 /+49 89 /
Institute for Carbon Composites donated by
Peter Kuhn
289 - 150965504.01.438
289 - [email protected]
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Literature
09/11/2014 | Kuhn | LCC-Symposium | High strain rate characterisation of composites using split-Hopkinson bar method
[1] http://www.bmwblog.com/2013/11/29/bmw-i3-earns-4-stars-euro-ncap-crash-tests-led/
[2] http://aviatic-world.blogspot.de/2010/11/flug-qf32-die-beinahekatastrophe-das.html
[3] Nemat-Nasser S., ASM Handbook Vol 8 Mechanical Testing and Evaluation, ch. Introduction to High Strain Rate Testing, ASM Int, 2000
[4] Koerber H., Mechanical Response of Advanced Composites under High Strain Rates (PhD) 2010.
[5] Koerber H., Vogler M., Kuhn P., Camanho P.P., Experimental Characterisation and Modelling of non-linear stress-strain behaviour and strain rate effects for unidirectional carbon epoxy, ECCM16, 2014
[6] Gama B.A., Lopatnikov S.L., Gillespie J.W., Hopkinson bar experimental technique: A critical review, Applied Mechanics Reviews, vol. 57, no. 4, pp. 223-250, 2004
[7] Pan B., Qian K., Xie H., Asundi A., Two-dimensional digital image correlation for in-plane displacement and strain measurement: a review, Measurement Science and Technology, vol. 20, no. 6, p. 062001 (17pp), 2009
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