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