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Experimental Results
To investigate the effects of CNT sheet scrolled fibers on
composite mechanical properties, such as compressive
strength and interfacial shear strength, through
nanoscale simulations
 The high tensile strength of polymer matrix composites
(PMC) is derived primarily from the high strength of the
carbon fibers embedded in the polymer matrix. However,
their compressive strength is generally much lower due
to the fact that under compression, the fibers tend to fail
through micro-buckling (or kinking) .
 Further, the mechanical load transfer in carbon fiber
composites is often limited by the shear strength of the
interface between fiber and matrix.
 Our preliminary tests on the spiral-wrapped CNT sheets
around a fiber, which is then embedded in a polymer
matrix, indicate that a significant improvement (~80%)
in compressive properties (78%) is feasible using the
proposed approach.
Objective
Background
Project Overview
Pruthul Kokkada, Samit Roy, Hongbing Lu
A Molecular Dynamics Study of Carbon Nanotube Sheet Scrolled
Fiber Composite for Enhanced Interfacial Mechanical Properties
Compressive Strength Comparison
a) Case I: Transfer Shear with CNT parallel to fiber
direction ( 0 degree case)
b) Case II: Transfer Shear with CNT at 90 degrees to
fiber direction
Study of Overwrap Bias Angle
Conclusions
 This project has been funded by the Low Density Materials
Program at AFOSR
Acknowledgement
 In order to understand the effect of CNT sheet orientation
on composite compressive strength, an atomistic model was
developed to study the interphase region between the epoxy
(Epon-862), carbon fiber and the scrolled MWNT sheets
 The predicted compressive strength from the MD results for
baseline Epoxy/Carbon Fiber interface does not agree well
with the experimental results for Graphite /Epoxy. This
could be attributed to the fact that the applied strain rate of
4.25 x 1011 sec-1 used in the MD simulations is much higher
than the actual strain rate used in the experiments.
 We can state qualitatively that the introduction of 4 wt% of
MWNT to the Epoxy/Carbon Fiber interphase leads to an
improvement of 25% in compressive strength over baseline
data for 0o bias angle, and 22% when for 90o bias angle to
the direction of the carbon fiber
Advanced Materials Processing Laboratory,
Department of Aerospace Engineering and Mechanics,
The University of Alabama, Tuscaloosa, AL
Strain Rate Comparison
Results
Future Work
 Work is underway to study the effect of strain rate on
compressive strength prediction.
 FEA Simulation of Nanoindentation using Cohesive Layer
 Multiscale integration of the nano, micro and macro sale
models in an analysis software
Nanoindentations tests by 3 m flat punch (performed
at UT-Dallas)
MD - Modeling
 Potential style = ReaxFF
 Temperature = 300 K
 Periodic boundary condition in the x and z direction, and
Fixed boundary condition in the y direction.
 Dimensions:
oEPON 862: 13.5nm x 10.3nm x 6.8nm
oCarbon Fiber: 13.5nm x 6.8nm (3 Sheets)
oCNT-1 : Chirality: (5,5); Diameter: 0.67 nm; Length: 6.8 nm
oCNT-2 : Chirality: (10,10); Diameter: 1.34 nm; Length: 6.8
nm
Modified Argon Formula And Virial
Stress Computation by LAMMPS
12
0
1
c
c
Y
G



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12
12
12
cG



I J I J
N N
k k k k kk k
IJ
m v v r f
P
V V
 
 
Case 0: Transverse Shear of Epoxy/Carbon Fiber
(Baseline) Interphase at 300 K
Case I: Transverse Shear with MWNT parallel to
fiber direction (0 degree case) at 300 K
Case II: Transverse Shear with MWNT at 90 degree
to fiber direction at 300 K
Y
(MPa)
𝛄 𝐘
𝐆 𝟏𝟐𝐜
(MPa)
o
(rad)
c
(MPa)
%
Change
in c
A. Graphite-
Epoxy
(Published data)
- - 2680 - 690 -
B. Baseline
Epon862/Carbon
Fiber (MD result)
155 0.0004 387500 0.1 1544 -
C.Epon862/MWN
T/Carbon Fiber
with 0 bias angle
(MD result)
196 0.0012 163333 0.1 1936 25 %
D.Epon862/MWN
T/Carbon Fiber
with 90 bias angle
(MD result)
192 0.0016 120000 0.1 1889 22%