This work was supported by the DOE/NNSA Grant No. DE-NA0002007
Nathan Briggs
University of Utah
Your Title
Advised by Dr. J. L. Ding
School of Mechanical and Materials Engineering
Microstructure Analysis To gain some insights on the deformation and fracture mechanisms,
microstructure analyses using Scanning Electron Microscope or SEM
were also conducted for both untested and tested samples. Samples
of the images are shown in Figures 7 and 8.
Figure 7. Reinforced HDPE tensile test specimens:(a) .066/s (b) 1000/s
(c) 2000/s (d) 4000/s
Figure 8. Reinforced HDPE compression test specimens: (a) .066/s
(b) 1000/s (c) 2000/s (d) 4000/s
Higher strain rate samples have smoother fracture surfaces, this
supports the experimental result that higher strain rates result in lower
total strain.
Conclusions • The material response is strongly rate dependent.
• Materials exhibit different properties and behavior under
compression and tension loadings.
• The strength and ductility are higher under compression than
tension.
Numerical Modeling and Future Work To gain further insights on the material behavior particularly on the
interaction between the reinforcements and matrix, finite element
simulations will also be conducted. A nonlinear viscoelastic model [4]
is used for the matrix material. This work is ongoing.
Acknowledgements I would like to thank the Institute for Shock Physics and Dr. Ding for
setting up and advising the project. In addition I was helped greatly
and advised by Yueqi Hu, Yuanyuan Liu, and Nandita Biswas.
References [1] Hu, Y., Liu, T., Ding, J. L., and Zhong, W. H., 2013, “Deformation Behavior of
High Density Polyethylene and Its Nanocomposites under Static and Dynamic
Compression Loadings,” Polymer Composites, 34(3), 417-425.
[2] Tian Liu, Yu Want, Allen Eyler, Wei-hong Zhong, 2014, “Synergistic effects of
hybrid graphitic nanofillers on simultaneously enhanced wear and mechanical
properties of polymer nanocomposites”, European Polymer Journal, Vol. 55, pp
210-221.
[3] Ramesh, K.T. 2008, “High Strain Rate and Impact Experiments”, Springer
Handbook of Experimental Solid Mechanics, Part D|33.
[4] Pedro Areias, Karel Matous, 2007, “Finite Element Formulation for Modeling
Nonlinear Viscoelastic Elastomers”, Computational Methods in Applied Mechanics
and Engineering, 197(2008) 4702-4717.
Background and Introduction High Density Polyethylene or HDPE and other polymers have been widely
used in many industrial purposes due to its high strength to weight ratio.
Carbon nanofibers (CNF’s) and graphene platelet (GNP’s) and their
combination presents a potentially cost effective way to improve the
strength of the material without significant impact on the weight.
The mechanical behavior of HDPE composites under compressive loading
has been studied previously [1]. The aim of this study is to characterize
mechanical behavior of HDPE nanocomposites under dynamic tension
loading, and compare the results to the compression case. In particular this
study focuses on the materials response under dynamic loading with strain
rates of 1000/s, 2000/s, and 4000/s. Characterization of the material
response under these types of loading conditions allows us to better
understand the material response under impact loading such as that
encountered in a car crash.
Experimental Setup and the Operation
Principle of SHPB (Split Hopkinson
Pressure Bar)
Figure 1:Split Hopkinson Pressure Bar (SHPB) setup
Figure 2: SHPB schematic. Top: compression; Bottom: tension.
Compressed gas is used to propel a striker. When the striker impacts the
incident bar, a stress pulse is generated. The pulse travels into the sample
where some of the stress wave is reflected back into the incident bar and
the rest is transmitted through the sample into the transmitter bar. Strain
gauges on the incident and transmitter bars record the strains generated by
the stress pulse as they travel down the bars. These strain gauge data can
then be used to calculate the stress and strain characteristics of the sample.
A solid cylinder is used as a striker in the compression test, and a tube is
used in the tension test.
Materials and Test Samples HDPEs reinforced with 3% wt CNF’s and GNP’s were used in in this study.
Processing of materials was done in Dr. Zhong’s lab at WSU [2]. The
dimensions of the samples are shown in Figure 3.
Figure 3: Schematics of test specimens
Experimental Characterization and Numerical
Modeling of the Carbon Nanofiber Reinforced High
Density Polyethylene under Dynamic Compression
and Tension Loadings
a
g
Strain Gauge Data and Analysis Samples of strain gauge data from compression and tension test are shown in
Figure 4.
Figure 4: Strain gauge data are shown for compression (left) and tension (right).
Tension data has more noise than the compression data. The noise may be
attributed to more complicated geometry for the tension experimental setup
including the specimen fixture.
This data can be used to extract stress strain relations through the following
relations [3]:
𝜀 𝑒 = −2𝑐𝑏𝑙0
𝜀𝑅 , 𝜀𝑒 = 𝜀 𝑒 𝜏
𝑡
0
𝑑𝜏, 𝜎𝑒 =𝐸𝑏𝐴𝑏𝐴𝑠
𝜀𝑇𝑟
𝜀𝑡 = −𝑙𝑛 1 − 𝜀𝑠 , 𝜀 𝑡 =𝜀 𝑒
1 − 𝜀𝑒, 𝜎𝑡 = 𝜎𝑒 1 − 𝜀𝑒
where 𝜀𝑒 , 𝜎𝑒 are the engineering stress and strain, 𝜀𝑡 , 𝜎𝑡 are the true stress and
strain, 𝜀𝑇𝑟 , 𝜀𝑅 are the reflected and transmitted strains, 𝐴𝑠, 𝑙0 are the initial length
and cross sectional area of the specimen, and 𝐸𝑏 , 𝐴𝑏 are the young's modulus
and cross sectional area of the transmitted and incident bars.
Experimental Results on Macroscopic
Behavior The stress-strain curves for 3% wt CNF/GNP samples under tension and
compression loadings at different strain rates are shown in Figure 5. Pictures of
the tested samples are shown in Figure 6.
Figure 5: Comparison of 3% wt CNF/GNP samples at different strain rates under
tension (left), and compression (right).
Figure 6: Left, Tension samples arranged from .66/s(top) to 4000/s(bottom).
Right, compression samples arranged from .66/s(left) to 4000/s(right).
Some major observations are listed below.
• Material response depends on the imposed strain rate.
• Higher stiffness is seen at higher strain rates
• Lower total strain to fracture at higher strain rates indicates a decrease in
ductility.
• Material exhibits lower strength and toughness under tension compared to
compression loading.
• Material necking during tension is more pronounced for quasi-static loading,
but less visible for high strain rate loadings.
This work was supported by the DOE/NNSA Grant No. DE-NA0002007
Advised by Dr. Y. Toyoda
and Dr. Y. M. Gupta
Using Laser Interferometry to
Measure the Shock Wave Response
of 1050 Aluminum David Mildebrath
The University of Alabama
Results and Discussion • Two experiments were performed at
different impact velocities
• As expected, the final velocities were
consistent with the independently
measured impact velocity
• The difference in wave structures
suggested shock wave response of 1050
Al depends on the impact stress
Objective • 1050 aluminum is commonly used in shock
wave experiments as an impactor and a
buffer
• Knowing its shock wave response is useful
• Laser interferometry measures the shock
response wave
30 mm bore powder gun used in the
experiments
Schematic view of the experimental setup. The 1050 Al
impactor was mounted on a polycarbonate projectile
1050 aluminum – 14 GPa
Velocity profile of 1050 aluminum at 14 GPA stress
Impact Velocity = 1.61 mm/µs
1050 aluminum – 11 GPa
Velocity profile of 1050 aluminum at 11 GPA stress. Note the
two-wave structure (inset)
Impact Velocity = 1.29 mm/µs
Experimental Details • A 1050 aluminum disk was accelerated
using a powder gun and impacted on
another 1050 aluminum target
• The back surface motion of the target was
monitored using laser interferometry
Laser Interferometry • Doppler-shifted light from the back surface
is split into two legs
• An etalon delays one leg by a short time
(~0.4 ns)
• When the beams are recombined, they
generate interference fringes
• By counting fringes, the rear surface
velocity can be calculated
• The wave plate and polarizing beam
splitters shift the four signals 90o out of
phase with each other
• A beam intensity monitor is used for
diagnostic purposes
Raw detector signals from the 11 GPa shot
Schematic of the laser interferometry system
Detector 1
Detector 2
Detector 3
Detector 4
Polarizing
Beam
Splitter Beam
Intensity
Monitor
(BIM)
Primary Beam
Splitter
Mirror
Mirror
Etalon
1/8 Wave
Plate
Polarizing
Beam
Splitter
Input
Light
From
Target
Acknowledgments I would like to thanks Drs. Yoshi Toyoda, Yogendra Gupta and
Nicholas Sinclair for their help and insight, as well the entire
engineering staff at the Institute for Shock Physics
This work was supported by the DOE/NNSA Grant No. DE-NA0002007
Advised by Dr. M. D. McCluskey Department of Physics and Astronomy
Results
Mineral Oil and Pressure
Two major absorption peaks from mineral oil were observed in the frequency range of 4250-4450 cm-1. These mineral oil absorption peaks were found to linearly increase in frequency with respect to pressure. Selenium Dioxide Changes in the selenium dioxide sample may have occurred due to exposure to the FTIR vacuum chamber, affecting the color of the selenium dioxide and the IR transmission. The sample remained colorless under vacuum, but turned orange when re-exposed to air. Its shade was darker the longer it spent under vacuum. Additionally, the red selenium dioxide transformed back to its original white color when pressure was applied to it.
Conclusion
Due to the relationship between its absorption peaks and pressure, FTIR of mineral oil can potentially be used for as a method of pressure calibration. Further research should seek to determine the physical properties of selenium dioxide under vacuum and high pressures.
Sonal Nanda
Infrared Spectroscopy of Selenium Dioxide and Mineral Oil under Pressure
Overview
Previous studies, using synchrotron radiation, indicated a phase change of selenium dioxide may occur between 0.4 GPa and 0.7 GPa. We investigated selenium dioxide and mineral oil with Fourier Transform Infrared Spectroscopy (FTIR) in order to explore phase changes of selenium dioxide. We also monitored the effect of pressure on mineral oil infrared (IR) spectra. Experimental Approach
Diamond Anvil Cell
Pressure was applied to selenium dioxide and mineral oil in a diamond anvil cell (DAC), ranging from 0.1 GPa to 8.0 GPa. Ruby microspheres were included in the DAC for calibrating the pressure. Fourier Transform Infrared Spectrometer
An interferogram of the sample is taken while it is under vacuum. A Fourier transform is preformed on the raw data to obtain the transmission spectrum.
Diamond
Gasket
Sample
Fig. 1. Diagram of diamond anvil cell (DAC)
Inte
nsity
(arb
. uni
ts)
Wavelength (nm)
Ambient 2.2 GPa 3.9 GPa
Fig. 2. Ruby Fluorescence Spectra
IR Source
Adjustable Holder
DAC
Detector
Fig. 3. Setup in FTIR vacuum chamber
Wav
enum
ber (
cm-1
)
Pressure (GPa)
Peak 1
Peak 2
Fig. 5. Mineral oil absorption peak wavenumbers versus pressure
Fig. 6. Selenium dioxide pellets. Left image shows sample before being placed in FTIR vacuum chamber. Right image is of sample after 2 days
in FTIR vacuum chamber.
Fig. 4. Transmission spectra of mineral oil under various pressures.
Tran
smis
sion
(arb
. uni
ts)
Wavenumber (cm-1)
Peak 1
Peak 2 4.9 GPa
0.8 GPa
This work was supported by the DOE/NNSA Grant No. DE-NA0002007
Advised by Dr. Z. A. Dreger
Raman Shift (cm-1
)
800 820 840 860 880 900
Ra
ma
n I
nte
ns
ity (
a.
u.)
x2
x5
x50
x50
x50
x50
x50
x50
1 atm
2.3
3.9
7.2
9.3
12.1
13.2
17.0
20.2
Ring breathing
C-H)
Pressure (GPa)
0 5 10 15 20
Ra
ma
n S
hif
t (c
m-1
)
700
750
800
850
900 Ringbreathing
C-H)
(C-H)
Comb./Overt.
x10
3200 3400
Raman Shift (cm-1
)
200 400 600 800 1000 1200 1400 1600
Ram
an
In
ten
sit
y (
a.
u.)
1 atm (Rec.)
1 atmRingbreathing
(NH2)
Lattice
(C-H) + (C-NH2)
(C-H)
(C-H)
Wavenumber (cm-1
)
600 800 1000 1200 1400 1600 18003000 3200 3400
FT
IR I
nte
ns
ity (
a.
u.)
1 atm (Rec.)
1 atm
(NH2)
(C-H)
(C-C) + (NH2)
(C-C) + (NO2)
(C-H)(C-H)
(C-H)(NO2)
Raman Shift (cm-1
)
3100 3200 3300 3400
Ram
an
In
ten
sit
y (
a. u
.)
1 atm
0.6
1.4
2.3
3.9
4.7 GPa
x2
x2
x2
x2
x2
(NH2)
(C-H)
Pressure (GPa)
0 1 2 3 4
Ram
an
Sh
ift
(cm
-1)
3050
3100
3150
3200
3250
3300
3350
(NH2)
(C-H)
Hydrogen Bonding: Pressure Effect on
the N-H & C-H Stretching Vibrations
DAC • Pressure up to 20
GPa in a diamond
anvil cell (DAC)
Paul Somers
Missouri University of Science and Technology
High Pressure Stability of Para-nitroaniline:
Role of Hydrogen Bonding
Background
• Hydrogen bonding (HB) plays a key role in
defining the structures and, thus, the properties
of molecular systems
• Para-nitroaniline (PNA) is a monoclinic crystal
with space group P21/n; molecules connected
through extensive HB network
• High pressure is an important tool for under-
standing the strength and stability of HB
Objectives
• Determine changes in HB under high
pressure through monitoring the N-H
stretching vibrations
• Examine changes in vibrational, molecular,
and crystal structures under high pressure
• Investigate reversibility of pressure induced
effects
Experimental Approach
Laser (532 nm)
Recorded
Spectrum
Spectrometer
CCD Camera
DAC
• Raman and Fourier Transform Infrared (FTIR)
spectroscopy
Results
Irreversibility: Raman and FTIR Spectra
Before and After Compression
Raman Shift (cm-1
)
20 40 60 80 100 120
Ram
an
In
ten
sit
y (
a. u
.)
1 atm
2.3
3.9
4.7
5.9
9.3
12.1
13.2
20.2 GPa
x5
x50
x50
x50
x50
x50
x50
x50
Pressure (GPa)
0 5 10 15 20
Ram
an
Sh
ift
(cm
-1)
0
100
200
300
(NH2)
Pressure Effect on the Lattice Vibrations
Pressure Effect on the C-H and Ring Bending
Conclusions
• Red shift, below 3.9 GPa, and
disappearance of NH2 stretching
vibrations at higher pressures may imply
strengthening of HB due to delocalization
of hydrogen
• Disappearance and formation of peaks
above 3.9 and 9.3 GPa indicate possible
structural phase transitions
• Changes in the lattice vibrations and
retaining of phenyl ring vibrations at
higher pressure suggest possible
polymerization
• Despite the partial irreversibility of the
spectra, there was no measureable
indication of new compound formation
Ambient
PNA Ruby
References
1. S. Block and G. J. Piermarini, SPIE 878, 21 (1988).
2. E. Kavitha, N. Sundaraganesan, and S. Sebastian, Ind. J. Pure
App. Phys. 48, 20 (2010).
3. K. N. Trueblood, E. Goldish, and J. Donohue, Acta Cryst. 14, 1009
(1961).
4. M. Harrand, J. Raman Spectrosc. 2, 15 (1974).
Ruby Fluorescence and Optical Imaging
3.9 9.3 13.2 1 atm (Rec.) 1.4 GPa
Raman System