MSE 235 Fall 2014
School of Materials Engineering
Purdue University
Tensile Testing of Nanoscale and Macroscale Metal Samples
Instructions: Group 1 or 3 will start with the Mechanical Testing Lab in ARMS 2191.
Group 2 or 4 will start with the NanoHUB Simulation Lab in ARMS 2114.
This laboratory activity consists of a 1.5 hour physical lab and a 1.5 hour simulation lab, which
may be completed in any order. Your instructor will determine the sequence for your group.
Proper lab attire is required to complete the physical lab: You need to wear long pants, closetoed shoes and safety glasses. There will be no exceptions made for inadequate attire. Please
bring a calculator, and a flash drive for data collection and sharing.
Background: Callister, Chps. 6.1 – 6.10; 7.1-7.6, and 7.10; lecture notes from Prof. Coughlan.
Mechanical behavior is a generic term for the response of a material to applied force. This
response is measured by shape changes that the material undergoes as force is applied. The
simplest means for quantitatively measuring mechanical response is a tensile test. Force is
applied to a test specimen of cylindrical geometry. As force increases, the specimen changes
shape - first elastically and then, in addition, either plastically or the material fractures. Elastic
shape change is recoverable; the specimen returns to its original dimensions once force is
removed. Plastic shape change, by contrast, is permanent, and takes place through redistribution
of atoms. Atom movement is facilitated in crystalline materials by dislocation motion, which
occurs along slip directions, within slip planes. Materials which undergo extensive plastic flow
before they break are termed ductile. Materials that fracture with little overall shape change are
deemed brittle. The tensile test is the single most widely used experiment for characterizing the
plastic flow behavior of ductile materials.
Objectives: In the physical lab, you will learn how to mechanically test macroscale samples
of different types of metals by performing both tensile and hardness tests. From the data you
collect, you will be able to determine the yield strength, ultimate tensile strength, 0.2% offset
yield strength, % elongation at failure, and average hardness values. In the simulation lab you
will also learn how to mechanically test nanoscale samples of a metal by performing atomic
simulations located on www.nanoHUB.org to determine the yield stress of the nanowire
samples. By observing the changes in the positions of atoms as the nanowire undergoes elastic
and plastic deformation, you will see how atoms respond in the elastic region, and you will also
observe the development of slip bands when plastic deformation begins to occur. You will
compare the mechanical behavior of the macroscopic metal sample to the single crystal nanowire
by constructing stress-strain curves for each.
The learning objectives are as follows:
 Graph stress-strain curves given force vs. elongation (or time) data for a tensile test
 Determine the characteristic features of stress-strain curves (i.e., elastic region, plastic region,
Young’s modulus (E), yield strength (y), ultimate tensile strength (UTS)).
 Explain plastic deformation at the atomic level in terms of dislocation motion and slip.
 Differentiate plastic deformation for macro- versus nano-sized metals. Explain reasons for
differences in yield strength between defect free nanoscale single crystals and macroscale
polycrystalline samples
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MSE 235 Fall 2014
School of Materials Engineering
Purdue University
Physical Lab Instructions: Macroscale Mechanical Testing and Hardness
Testing
Materials: Safety attire, calculator, calipers, copper and brass tensile bars, MTS SINTECH load
frame, extensometer, Rockwell hardness testers
Figure 1 is a schematic of a typical mechanical testing load frame configured for tensile
testing. The gripping system holds the tensile samples in place while a crosshead moving at a
constant rate is used to apply a known load. The load cell is an electronic device that measures
the force (typically in Newtons, N) being applied to the sample. Knowing the sample crosssection dimensions allows one to convert from applied force to applied stress. Sample strain is
not based directly on the movement of the crosshead. For example slack in the grips, grip
slippage, and any displacement of the load frame itself (imagine the load frame is made of rubber
instead of steel) would lead to inaccurate measurements. These errors are particularly
pronounced for measurements performed at small strains such as Young’s modulus and the yield
stress.
Therefore, an extensometer –
a device that accurately
measures small displacements
– is attached directly to the
sample to measure sample
displacement.
Normalizing
the measured displacement by
the initial span of the
extensometer allows one to
determine the sample strain.
For large strain measurements
such as % elongation, simply
measuring the gauge length of Figure 1: (a) Schematic of a mechanical testing load frame and (b)
the sample before and after schematic of a "dog-bone" sample for tensile testing.
testing is sufficient to produce
an accurate result.
Physical Lab Section Instructions:
Overview:
Each lab section will measure the mechanical properties of samples of copper and brass
using the mechanical testing machine. Tensile tests will result in a force-displacement curve for
each sample being tested. Following the tensile tests, Rockwell hardness measurements will be
collected for each sample. Finally, you will analyze the tensile data and calculate the relevant
mechanical properties.
Tensile Testing:
To begin, samples of brass and copper will be handed out. Each sample should be
labeled with a number (using the permanent marker provided). For each sample, the initial gauge
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MSE 235 Fall 2014
School of Materials Engineering
Purdue University
length and gauge cross-sectional area should be measured and recorded. This information should
be copied into the Excel workbook on the PC in the back of the room.
Next, each sample will be mechanically tested using the SINTECH load frame with the
aid of the instructions detailed below. Save the resulting data file as “Sample <<name>>” and
import the data into the Excel workbook on the PC in the back of the room (create a new tab in
the workbook for each sample). Make sure to include all the relevant information about the test
in the tensile testing spreadsheet for your sample (ex, sample name, crosshead speed, initial
cross-sectional area, initial gauge length, and final gauge length).
Instructions for using the SINTECH mechanical testing machine
1. With your TA, review the method of operation for the SINTECH machine.
2. For your sample (copper and brass), make necessary measurements to calculate the crosssectional area.
3. Estimate the applied force needed to reach the ultimate tensile strength using the sample
dimensions and property values in Appendix B of Callister (assume your brass sample is made
from copper alloy C36000). Check your answer with the TA. Your TA will select the appropriate
crosshead speed.
4. Mark the initial gauge length on the sample and measure the length using your calipers.
5. Load the sample into the grips and attach the extensometer. Why is the extensometer used?
6. Start the test, and at some point past yielding (your TA will tell you when), pause the test and
remove the extensometer. Why do we need to remove the extensometer?
7. Restart the test without the extensometer and test to failure.
8. After removing your sample, measure the final gauge length using your calipers.
9. For each sample that you test, please make sure you have recorded the following data:
a. Crosshead speed (mm/mm)
b. Initial gauge length (mm)
c. Final gauge length (mm)
d. Initial cross-sectional area (mm2)
Rockwell Hardness Testing:
After completing tensile testing of each sample, perform hardness measurements on both
the gauge and grip sections of each sample, using the Rockwell Hardness testers and the
instructions provided below. Record all measurements in the Excel workbook on the PC on a tab
called “Hardness Measurements”.
Instructions for using the Rockwell Hardness tester
1. The TA will demonstrate the method of operation for the Rockwell Hardness tester.
2. Using the Rockwell-B scale (HRB), measure and record the hardness of each tensile
sample:
a. Take at least 5 hardness measurements from the grip region of the sample.
b. Take at least 5 hardness measurements from the gauge region of the sample.
3. Record your measurements and compile the values using the available PC.
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MSE 235 Fall 2014
School of Materials Engineering
Purdue University
In-Lab Data Analysis (if time allows)
For at least one of the samples that you tested in tension, calculate the following from the
engineering stress-strain curve obtained during the tensile test:
(a) Young’s modulus (only for tests that used an extensometer).
(b) Tensile strength or Ultimate Tensile Strength (UTS).
(c) 0.2% offset yield strength (σy)
(d) % elongation at fracture
When processing your data, note the following: extensometer displacement is given in mm. To
convert to strain, you need to divide by the extensometer initial gauge length of 50 mm. Also, be
sure not to mix units. Stress is measured in N/m2, the MTS software dimensions are in mm, and
the calipers measure in mm or cm. Compare your calculated values of mechanical properties
with reference values from the Tables in Appendix B of Callister. Your values may differ from
the reference values by 10 - 20% (or even 30-50% for Young’s modulus). However, if your
values are different by more than a factor of ten there is a good chance that there were problems
with either the data acquisition or your calculations. Now is the time to sort these issues out, not
when you are preparing your final lab report.
From your hardness data, find average hardness values for the copper and brass grip and
gauge regions. Discuss with your TA why the hardness values are different in the grip and gauge
region and between copper and brass.
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MSE 235 Fall 2014
School of Materials Engineering
Purdue University
Simulation Lab: Nanoscale Mechanical Testing by NanoHUB Simulation
Molecular dynamics (MD) is a popular modeling and simulation technique used in
materials science. The method involves calculating the forces acting on atoms and then solving
Newton’s equations of motion to obtain the time evolution of the atomic positions and velocities,
from which materials properties can be obtained. If accurate interatomic potentials are used, a
simulation can provide an accurate description of real materials and be a valuable research tool.
The challenge is that these interatomic potentials are not simple and are not directly measurable.
Researchers are currently working on developing increasingly accurate interatomic potentials to
better describe and predict the properties of materials.
We will use an MD simulation tool developed by Professor Alejandro Strachan to access
research-grade simulation codes on nanoHUB.org. Professor Strachan teaches an on-line course
on molecular dynamics that can be viewed at https://nanohub.org/resources/5838; the first lecture
provides an overview of how the method works.
In this section of the lab, we will perform a “tensile test” on a single crystal nanowire.
Since a physical specimen of a copper nanowire would oxidize leaving little metal to test, we
will use a platinum nanowire. In FCC metals, such as Cu and Pt, slip occurs on the closed
packed {111} planes along the close packed directions <110> in the slip plane. Using the MD
simulations, you will be able to observe the formation of slip bands in the platinum nanowire.
Your teaching assistant will first guide you through a simple tensile test (simulation) of a
platinum nanowire to acquaint you with the usage of the tools on nanoHUB. You then will
conduct a more involved test to collect data to be used in your report.
Procedure for running a MD simulation on nanoHUB:
We will first use a prebuilt nanowire with a tensile axis along <110> and test that during the
laboratory period. Your TA will guide you through the use of the nanoMATERALS simulation
toolkit and will help you visualize and save your results. During this time you are to complete
the “In-Lab Worksheet” for the MD simulations. Discuss your results with your classmates.
Complete the following steps to test an <110> oriented platinum nanowire:
Step 1:
Input Model
Input Model: Pt_nanowire_r13
Create Supercell:
a direction = 1
b direction = 2
c direction = 1
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MSE 235 Fall 2014
School of Materials Engineering
Purdue University
Step 2:
Energy Expression
Interatomic Potential = Default
Step 3:
Driver Specifications
Ensemble = NVE
MD time step = 0.004ps
Number of time steps = 4000
Temperature = 300 K
“Strain per MD step:”
Y direction = 0.00003
Periodic Tasks:
Write Energy File (steps) = 5
Write to trajectory (steps) = 500
Atomic Structural Analysis = yes
Use the “trajectory animation” under the “Results” tab to visualize your results in the form of a short
movie.
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MSE 235 Fall 2014
School of Materials Engineering
Purdue University
Creating your own <110> nanowire with a rectangular base
These instructions will guide you through the procedure to create a cylindrical nanowire with one
of three different crystallographic orientations to the tensile axis (the <110> orientation is listed
here and the <100> and <112> orientations are listed in the appendix). These nanowires can
then be tested to explore the effect of crystalline orientation on slip during the tensile test.
When rotating or viewing a cylindrical specimen from different directions, it is difficult to
identify the crystallographic axes. In order to more easily determine the orientation of the
specimen, a rectangular portion, whose crystalline faces have known indices, is left at the base of
the nanowire.
Furthermore, movement of the atoms on the surface of the wire during the MD simulations can
make identifying the crystallographic planes and directions difficult. In order to easily identify
the arrangement of atoms in the planes and along the directions related to slip, an image of the
simulation domain is saved before creating and testing the nanowire.
The procedure for defining the simulation domain, saving images of the crystal structure before
testing, and defining and testing a nanowire are described in the following text.
1) Input Model: First select the unit cell to use. We will use the Pt_111_unit cell. Note if
you hover the mouse over the input some background information is displayed. The lattice
parameter of Pt is a=0.3925 nm. The Pt_111_unit cell is predefined in simulation as:
x = a/2[11̅2] = 0.4807 nm; y = a/2[110] = 0.2775 nm; and z = a[1̅11]=0.6798 nm.
By stacking these Pt_111_unit cells, a larger crystal is created as shown the next step.
2) Create a Supercell: Create a supercell by repeating the unit cell along the a, b, and c
directions using a=10, b=32, and c=10. This is our single crystal (or simulation domain)
from which we will create the [110] nanowire.
b
8.880 nm
a
c
Note using the Pt_111 unit cell:
a= (10)(0.4807) = 4.807nm
b= (32)(0.2775) = 8.880nm
c=(10)(0.6798) = 6.798nm
The orientation of the a, b , and c axes
corresponds to the orientation of the initial
output images from the MD simulations.
3) Capture the atomic arrangement of the faces of the supercell:
Before creating a nanowire, take snapshots of each of the faces so that you will be able to
recognize the atomic arrangement of the(11̅2), (110), and (1̅11) planes. To do this, define
the following Driver Specifications:
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MSE 235 Fall 2014
School of Materials Engineering
Purdue University
“Driver Specifications:” Ensemble = NVE
Number of steps = 5
Write to trajectory (steps) = 2
Simulate the structure, then increase the sphere size representing the atoms to produce a nice
looking image. Rotate the supercell to obtain views normal to each of the three faces, and
save an image of each face. Save an image of each face and include the name of the face and
plane in the file name.
Example output showing
the single crystal Pt and
the atomic arrangement
̅ 11) face.
on the (1
4) Create a nanowire along [110] with a radius of 1.4nm and “test” it: You will define the
nanowire under the “Advanced Options” tab. An explanation of the commands are given in
the appendix. Clear your results and use the following simulation parameters:
“Input Model:”
Pt_111_unitcell.bgf
a=10; b=32; and c=10
“Driver Specifications:”
Ensemble = NVE
MD time step = 0.004ps
Number of time steps = 4000
“Strain per MD step:”
Y direction = 0.00003
“Periodic Tasks:
Write Energy File (steps) = 5
Write to trajectory (steps) = 500
Atomic Structural Analysis = yes
“Thermalization steps”
Thermalize system before MD run? Yes
Ensemble = NVT
Number of thermalization steps=1000
“Advanced Options”
Enter the following text after the comments. Do not
use “#” as these are for comments. See Appendix I
for meaning of these commands.
SELECT/Y_REGION 11.10 88.80
SELECT/INV
SELECT/CYL_CTR 1 3 14 24.035 33.99
SELECT/INV
SELECT/DEL
(5) Run the simulation: This may take some time so you may need to check your results after
the lab period.
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MSE 235 Fall 2014
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6) Save your results: You will need the following data to complete your report.
(i) The yy-stress-component vs time saved as a spreadsheet file.
(ii) Snapshots of the structure before and after yield.
7) Analysis of stress and strain: The stress results from the MD simulations have not
incorporated the size of the computational domain or the cross-sectional area of the
nanowire. To make this correction, the stress values should be multiplied by the crosssectional area of the computational domain then divided by the cross-sectional area of the
nanowire.
Correction factor =
(4.807𝑛𝑚)(6.798𝑛𝑚)
𝜋(1.4𝑛𝑚)2
= 5.31.
Thus multiply your stress values in the spreadsheet by 5.31. You can also calculate the strain
by using the imposed strain rate. The strain rate is the strain per step divided by the MD time
step.
𝜀̇ =
𝑠𝑡𝑎𝑖𝑛 𝑝𝑒𝑟 𝑀𝐷 𝑡𝑖𝑚𝑒𝑠𝑡𝑒𝑝
𝑀𝐷 𝑡𝑖𝑚𝑒𝑠𝑡𝑒𝑝
Using the time values in the spreadsheet calculate the corresponding strain, 𝜺 = 𝜺̇ 𝒕
From this data you can plot the stress-stain curve for the nanowire.
LAB REPORT INSTRUCTIONS
To prepare your lab report, use the “Tensile Testing of Nanoscale and Macroscale Metal
Samples Report Template” which will be available on Blackboard.
Your lab report should consist of the following items:
Tensile tests of copper and brass

From the macroscale mechanical testing results from the copper and brass samples
(compiled in Excel workbook available on Blackboard), complete the following data
tables and include these in your lab report. Report average values ± standard deviations
whenever possible. Be wary of using too many significant figures. Be sure to include
table labels and descriptive captions.
Metal
Initial
crosssectional
area (m2)
Initial
gauge
length
(mm)
Final
gauge
length
(mm)
Young’s
Modulus,
E
(GPa)
0.2%
offset
yield
stress
(σy)
Ultimate
tensile
stress
(σUTS)
%
elongation
at failure
(%)
Copper
Brass
Metal
Hardness Value (RH-B),
Grip Region
Hardness Value (RH-B),
Gauge Region
Copper
Brass
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MSE 235 Fall 2014
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Purdue University

Immediately following your data tables, compose a short paragraph that references and
describes both tables (like what you might find in a results and discussion section of a
technical report), being sure to describe “the what” and “the so what” of each table. In
your discussion, it is suggested that you compare the brass and copper mechanical
properties to values found in Appendix B of Callister. How does the yield stress of brass
compare to the yield stress of copper? What causes the difference in strength? Can this
difference be detected at the local level (and how)?

Create a figure that displays representative mechanical testing stress-strain results from a
macroscale copper and brass metal sample being deformed in tension. The figure should
include a plot of the full deformation response and a separate plot highlighting the elastic
deformation region. Be sure to include a figure label and descriptive caption. You may
also wish to label features of interest directly on the plots. Ensure the stress-strain results
are presented using the computer program ‘Origin’.

Following the figure, compose a short paragraph that references and describes the figure
(like what you might find in a results and discussion section of a technical report), being
sure to describe “the what” and “the so what” of the figure. Make sure you discuss all
important features of the stress-strain curve. It is suggested that you compare the brass
and copper features to each other.
Tensile test simulation of platinum nanowire
Results:
 Create a figure that displays the stress-strain curve from the platinum nanowire. You will
need to use the corrected stress values based on the size of your nanowire. Since the
strain rate is also known, the strain values can be calculated. Estimate Young’s modulus
from the stress-curve (ignore the oscillations). Also report the values of yield stress and
ultimate tensile strength.

Create a figure showing the images saved from your simulation of the (110), (1̅11), and
(11̅2) planes of the platinum single crystal (supercell).
o For the (110) plane, clearly mark and label the [1̅11] and [11̅1] directions paying
attention to the atomic arrangement of atoms in that plane.
o For the (1̅11) plane (11̅2) planes, clearly mark and label the [110] direction.

Using snapshots of the nanowire taken from simulation, create a figure that displays
representative results of the platinum nanowire being deformed in tension. Be sure to
include a figure label and descriptive caption. The figure should include images of the
nanowire both before and after plastic deformation. Label the orientation of the active
slip planes in your figure.
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MSE 235 Fall 2014
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Discussion:
Following the figures, compose a paragraph that references and describes the figures. You
should answer the following questions within your text:

Use your textbook and look up the value for Young’s Modulus for Pt. Similarly look up
the value for the yield stress and ultimate tensile strength. How do these values compare
with those from the nanowire stress-strain curve? Explain.

Discussion of single crystal slip: Slip in FCC metals occurs on {111} planes along the
<110> directions in the slip plane. There are 4 possible {111} sets planes on which slip
may occur and these are (111), (1̅11), (11̅1), 𝑎𝑛𝑑 (111̅). For the nanowire simulation
with the loading axis along [110] does slip occur on all 4 sets of {111} planes? Which
sets of {111} planes did slip occur? Why did slip not occur on the other sets of {111}
planes? Be specific in your reasoning (Hint, refer to your figures to help identify the
orientation of the different {111} planes in the nanowire).
.
Comparison of nanoscale and macroscale results: In one final short summary paragraph,
compare your nanoscale and macroscale results and observations to each other, directly
highlighting the similarities and differences. Compare values for E and y. For the same metal,
are the values of Young’s modulus similar or drastically different? For the same metal, are the
values of y similar or drastically different? Using the content and theory from your class notes
and reading assignments, explain reasons for the observed behavior.
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MSE 235 Fall 2014
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Pre-Lab Questions (to be answered before coming to lab):
1. What equations are used to calculate engr. stress and engr. strain? Define each parameter and
include units.
2. What equation is used to calculate % elongation at failure? Define each parameter and
include units.
3. Draw an example stress-strain curve for copper alloy C26000 (also known as cartridge brass)
that was cold worked (H04 temper). Label the axes with approximate values and units. Also
label the regimes of elastic and plastic deformation and the 0.2% offset yield stress.
Appendix B in Callister will be helpful for this question.
4. Using the stress-strain curve in Question 3, illustrate how you would calculate the Young’s
Modulus of the copper alloy above.
5. An FCC single crystal tested in tension along the [001] direction is shown to the rights. For a
(111) slip plane, give [hkl] values for the three possible slip directions. Circle the direction
for which the resolved shear stress is zero. Explain your answer.
____________
________
__________
6. A schematic of a dislocation moving through a crystal is shown below. Why is the shape of
the columns of atoms marked A, B, C, and D curved in Figures (a) and (b) but not in (c)?
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In-Lab worksheet for the nanoHUB simulations (will be answered in-lab):
1. Do you observe dislocations in the nanowire? Would you expect the presence of dislocations
in a macroscale metal sample?
2. Sketch the stress-strain curve for a nanoscale nanowire and that of a macroscale metal
sample. Label the elastic region, yield stress, and ultimate tensile stress.
Nanoscale Sample
Macroscale (Bulk) Sample
(Ignore the oscillations and
sketch a smooth curve)




3. For the curves drawn in Question 2, what are approximate values for Young’s modulus (E),
the yield stress (y), and the ultimate tensile strength (UTS) of the nanowire and macroscale
(bulk) sample.
Nanowire Sample
E=
Yield stress =
UTS =
Macroscale (Bulk) Sample
E=
Yield stress =
UTS =
4. Consider a tensile sample and three different sets of planes (shown below). For the same
applied normal stress, which set of planes experiences the highest shear stress (circle it)?
Explain your answer.
5. The figure on the right shows the atomic configuration of
a fictitious nanowire. Assume the nanowire is deformed
plastically in tension. If the empty circles represent
possible atom positions, fill in circles to show the shape of
the nanowire after slip has occurred throughout one plane.
Show the slip plane as a line.
Before
After
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Appendix I: Comments on the script commands to produce a <110> nanowire
with a rectangular base
“Advanced Options”
SELECT/Y_REGION 11.10 88.80
88.80 Å
y
x
Selects the region of the computational cell
from 11.10 Å to the top
11.10 Å
48.07 Å
SELECT/INV
88.80 Å
Inverts the selection from the bottom of the
computational cell to 11.10 Å to the top
11.10 Å
48.07 Å
SELECT/CYL_CTR 1 3 14 24.035 33.99
88.80 Å
Create a cylinder with the axis in the 1-3 (x-z)
plane having a radius of 14Å and centered at
24.035 and 33.99 Å.
11.10 Å
24.035 Å
SELECT/DEL
SELECT/INV
88.80 Å
14 Å
Invert the selection and delete it to
create the nanowire and base.
11.10 Å
24.035 Å
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Appendix II: Creating an <112> oriented nanowire
An alternate testing orientation that you can try on your own. Note you are creating the
nanowire along the x-direction of the supercell. Thus from the results use the
xx_stress_tensor_component versus time for calculating the stress strain curve.
Part 2: Creating your own nanowire
1) First define your simulation cell. We will use the Pt_111_unit cell. The lattice parameter of
Pt is a=0.3925 nm and the cell consists of:
y
Coordinate system
x = a/2[11̅2] = 0.4807 nm;
x
used for simulation
y = a/2[110] = 0.2775 nm; and
and graphical output.
̅
z = a[111] =0.6798 nm.
z
2) Create a supercell (input model) using a=20, b=14, and c=7. Thus our simulation cell as
aligned along the x-direction.
3) Before creating a nanowire, save the crystallographic information containing the atomic
arrangement on the (11̅2), (110), and (1̅11) planes. To do this, define the following:
“Driver Specifications:”
Ensemble = NVE
Number of steps = 5
Write to trajectory (steps) = 2
Use the default values for the other options and then select “Simulate.” View the results and
increase the atomic radius to produce a nice looking image. Next, save an image of each plane.
4) Create a nanowire along [110] with a radius of 1.4 nm and “test” it. We will keep the
rectangular base to aid in determining the crystallographic orientation. Clear your results and
use the following simulation parameters:
“Driver Specifications:”
Ensemble = NVE
MD time step = 0.004ps
Number of time steps = 4000
“Strain per MD step:”
X direction = 0.00003
“Periodic Tasks:
Write Energy File (steps) = 5
Write to trajectory (steps) = 1000
Atomic Structural Analysis = yes
“Thermalization steps”
Thermalize system before MD run? Yes
Ensemble = NVT
Number of thermalization steps=1000
“Input Model:”
Pt_111_unitcell.bgf
a=20; b=14; and c=7
“Advanced Options”
SELECT/X_REGION 19.228 96.14
SELECT/INV
SELECT/CYL_CTR 2 3 14 19.425 23.793
SELECT/INV
SELECT/DEL
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Appendix III: Creating an <100> oriented nanowire
An alternate testing orientation that you can try on your own. The orientation here may be easier
to visual as the standard 001 unit cell is used.
Part 2: Creating your own nanowire
1) First define your simulation cell. We will use the Pt_unit cell.
y
The lattice parameter of Pt is a = 0.3925 nm.
This is a 4 atom FCC unit cell with the axes aligned
along <100>.
x
Coordinate system
used for simulation
and graphical output.
z
2) Create a supercell (input model) using a=10, b=23, and c=10. Thus our simulation cell as
aligned along the y-direction.
3) Before creating a nanowire, save the crystallographic information containing the atomic
arrangement on the {100} planes. To do this, define the following:
“Driver Specifications:”
Ensemble = NVE
Number of steps = 5
Write to trajectory (steps) = 2
Use the default values for the other options and then select “Simulate.” View the results and
increase the atomic radius to produce a nice looking image. Next, save an image of each plane.
4) Create a nanowire along [010] with a radius of 1.4 nm and “test” it. We will keep the
rectangular base to aid in determining the crystallographic orientation. Clear your results
and use the following simulation parameters:
“Driver Specifications:”
Ensemble = NVE
MD time step = 0.004ps
Number of time steps = 4000
“Strain per MD step:”
Y direction = 0.00003
“Periodic Tasks:
Write Energy File (steps) = 5
Write to trajectory (steps) = 1000
Atomic Structural Analysis = yes
“Thermalization steps”
Thermalize system before MD run? Yes
Ensemble = NVT
Number of thermalization steps=1000
“Input Model:”
Pt_unitcell.bgf
a=10; b=23; and c=10
“Advanced Options”
SELECT/Y_REGION 19.228 96.14
SELECT/INV
SELECT/CYL_CTR 1 3 14 19.625 19.625
SELECT/INV
SELECT/DEL
16
MSE 235 Fall 2014
School of Materials Engineering
Purdue University
Appendix IV: Structure of bulk polycrystalline Pt vs single crystal nanowire
Additional background material:
Consider a tensile specimen made from a polycrystalline platinum with the
microstructure shown below. Platinum is FCC and each grain represents a crystal of a different
orientation. If the bar has a 1 cm diameter, how many grains would the cross-sectional area of
the bar contain?
Now consider a platinum nanowire with the dimensions shown below. Clearly the size of the
wire is much smaller than the grain size of the polycrystalline sample. The nanowire here
consists of a perfect FCC single crystal containing no dislocations before testing.
The question is which will have the higher yield stress and why?
Diameter: 2.6 nm
Microstructure of an as-cast polycrystalline Pt
alloy. Note the average grain size.
Ref: Paolo Battaini, Platinum Metals Rev. 55
(2011) 74-83.
Periodic length: 4.1 nm
Structure Pt nanowire
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