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1For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Nanoscience and Nanotechnology at Virginia Tech
Applications of Cellulose Nanocrystals and Carbon Nanotubes in Hybrid Nanofibers for Improving Damage
Tolerance and Damage Detection in Aerospace Composites
Gary Seidel, Rakesh Kapania, and Michael PhilenAerospace and Ocean Engineering
Barry Goodell and Scott RenneckarDepartment of Sustainable Biomaterials
NIA Workshop on Nanomaterials for Aerospace
February 21st 2014
2For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Conventional Z-pinning in Aerospace Composites
Z-pins are small carbon-composite or metal pins that are inserted in the Z-direction in polymer matrix composites to increase: 1) delamination fracture toughness, 2) impact damage resistance, and 3) ultimate strength of joints through the development of a crack bridging mechanism. Carbon fiber (Z-Fiber) pins are most commonly used in aerospace composite applications. Currently there is expanding use of Z-pinning in several military aircraft including the FA-18 Superhornet and C17-Globemaster III heavy-lift transporter.
Mouritz, A., Chang, P., and Isa, M. (2011). ”Z-Pin Composites: Aerospace Structural Design Considerations.” J. Aerosp. Eng., 24(4), 425–432
3For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Durability of conventional Z-pinned composites
Greenhalgh, E., et al., Evaluation of toughening concepts at structural features in CFRP--Part I: Stiffener pull-off. Composites Part A: Applied Science and Manufacturing, 2006. 37 (10): p. 1521-1535
A.P. Mouritz / Environmental durability of z-pinned carbon fibre–epoxy laminate exposed to water. Composites Science and Technology 72 (2012) 1568–1574
The stiffness of the Z-pins and incompatible bonding systems can result in interfacial crack development, and ultimate failure with pull-out of the Z-pins. Ideally failure would occur at a higher loading, with failure in the pins or fabric.
4For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
A syringe will deliver a liquid suspension of CNF sol, which transforms into a high strength micro-strand (consisting of nanofibers) when delivered to the fabric layers.
Syringe, filled with cellulose nanofibers(CNFs – shown in green)
Multilayer fabric mat (glass, carbon, aramid)
The syringe plunger is depressed on the “up-stroke” using a controlled flow rate to deliver a single 50µm micro-strand of the CNFs (with each micro-strand containing many nanofibers).
Theoretically, the CNF needle extruded CNFs will have a tensile modulus capacity of about 20 GPa, and strength of 320 MPa. Ideally with enhanced bonding capacity compared to Z-pins.
Goodell, Renneckar, Kapania, Philen. 2013
Proposed Virginia Tech Experimental Process: “Discontinuous wet stitching” DWS method using cellulose nanofibers (CNFs)
5For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Cellulose in nature is always found as a bundle “Microfibril”
[Microfibril portion of this figure adapted from J. K. C. Rose and A. B. Bennett, “Cooperative Disassembly of the Cellulose-Xyloglucan Network of Plant Cell Walls: Parallels Between Cell Expansion and Fruit Ripening,” Trends Plant Sci. 4, 176–83 (1999).]
Existence (cell wall, secondary cell wall for wood 40~50%)Functionality (main structural component)
6For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Nanocellulose is derived from the microfibrils that compose plant cell walls through modification and homogenization
7For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Properties
Published in: Tsuguyuki Saito; Ryota Kuramae; JakobWohlert; Lars A. Berglund; Akira Isogai; Biomacromolecules DOI: 10.1021/bm301674e
Elastic moduli of single fibrils prepd. by TEMPO-oxidation or acid hydrolysis were 145.2 ± 31.3 and 150.7 ± 28.8 GPa, resp. Iwamoto, S.; Isogai, A.; Iwata, T.; Cellulose Communications (2010), 17(3), 111-115
Films are transparent
Strength of fibril Nanocellulose: high aspect ratio~400
Diameter – 1nm to 15nmLength- 200nm to 2000nm
Width depends upon starting material and treatment conditions
Length depends upon “degree of polymerization” of cellulose and severity of homogenization
8For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Multifunctional Cellulose Nanofibers
Structural Level Response
Global-Local Modeling of Hybrid Z-Pinned Laminates
Disperse Carbon Nanotubes liquid suspension of CNF sol, which transforms into a high strength multifunctional hybrid micro-strand when delivered to the fabric layers.
Syringe, filled with cellulose nanofibers and CNTs (Hybrid sol – shown in purple)
CNTs have high electrical conductivity, are inherently piezoresistive, and can form conductive networks through electron hopping.
Li et al. (2007)Simmons (1963)
T. Komedaet al 2011
Simulation of HOMO
Ren and Seidel 2013
Chaurasia and Seidel 2014
Thus CNTs can impart piezoresistive response to hybrid micro-strand allowing deformation and damage sensing.
9For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Multiscale Modeling and Characterization of the Effects of Damage Evolution on the Multifunctional Properties of Polymer Nanocomposites
Participants:
Objective:• Understand how nanoscale effects between
individual nanotubes become macroscale measurable quantities within the composite.
• Develop concurrent multiscale model which transitions electromechanical and damage effects from nano- to macroscale
Why It Matters:• Transition from scheduled maintenance or post-flight
NDE to on-board structural health monitoring through design, integration, and interpretation of CNT nanocomposite deformation/damage detection in composites and apply towards updated envelope and remaining life prediction.
Recent Accomplishments• Electromechanical nanoscale interface cohesive zone
approach demonstrates increased gage factor indicating ability to distinguish deformation and damage state/evolution
• Effective gage factors demonstrate tension-compression asymmetry, optimum concentration (near percolation), CNT dispersion and orientation sensitivities and magnitudes as observed in experiments
• Nanoscale Interface Load Transfer: Sensitive to polymer chain entanglement and cross-linking, interface functionalization, and temperature
Clients• AFOSR
• Virginia Tech – Gary Seidel• UDRI – K. LafdiSpecial Equipment:• Dielectrophoretic alignment & microtensile optical
microscopy technologies
App33ε
EffectiveG33
-40-20020406080100120
-100
10203040506070
0 100 200 300 400
Res
ista
nce
(ohm
s)
lbs.
Time (sec)
LoadR-Ro
Cyclic loading MicrotensilePiezoresistive Testing
Macroscale Gage Factor
10For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Nanoscale RVE with cyclic loading Cyclic tests performed on nanoscale RVE to study the effect of damage accumulation on the effective piezoresistiveresponse. Damage accumulation leads to higher gauge factors on load reversal and reloading.
)/(ˆ 22 mSVJ
)/(ˆ22 mSΣ
A
B
C
D
A
B
C
D
0
5
10
15
20
25
0.00E+00
1.00E+02
2.00E+02
3.00E+02
4.00E+02
5.00E+02
6.00E+02
-0.05 0 0.05 0.1 0.15 0.2App22ε
Eff22Σ EffG22
Loading/Unloading CycleA-B-C-D-A-D-C
Chaurasia and Seidel 2014
11For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Multiscale Piezoresistive Modeling
0.0
5.0
10.0
15.0
20.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0%
Stress for element 58 Stress for element 111
Resistivity for element 58 Resistivity for element 111
Macroscale Applied Strain
Nor
mal
ized
Cha
nge
in R
esis
tivity
Nor
mal
ized
axia
l str
ess
Nanoscale Young’s modulus: Nanoscale resistivity:
Element 58 (Tip) Element 58 (Tip)
Macroscale Response
Macroscale resistivity Macroscale stress
Comparison between the response at the tip (Element 58) and at the base (Element 111):
12For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Testing and Evaluation in LaboratoryObjectives:• Determine piezoelectric and piezoresistive
coefficient properties of hybrid nanofibers• Evaluate hybrid nanofibers in composites for
energy harvesting under vibratory conditions• Evaluate composites for structural health
monitoring using impedance-based methodsMethods:• Short circuit and open circuit natural
frequencies yield piezoelectric coupling coefficient.
• Energy harvesting capabilities are quantified by measuring the output power over a broad spectrum of vibratory loads and frequencies.
• Change in mechanical impedance results in change of electrical impedance using piezoelectric coupling →can indicate presence of local damage.
0
0.2
0.4
0.6
1 100 100001000000
Pow
er R
MS
(μW
)
Load Resistance (Ohms)
0.00001
0.0001
0.001
0.01
0.1
130 130 230 330
FRF
Frequency (Hz)
OpenClosed
13For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Alignment of CNTs and Characterization of CNT Nanocomposites
0
200
400
600
800
1000
1200
1400
1560 1570 1580 1590 1600 1610 1620
0 deg
15 deg
30 deg
45 deg
60 deg
75 deg
90 deg
103
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10-11
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10-5
Frequency(Hz)
Con
duct
ivity
(S/c
m)
Pure Acrylate PolymerRandom (EAC=0)
1 kHz 30 mins Parallel1 kHz 30 mins Perpendicular10 kHz 30 mins Parallel10 kHz 30 mins Perpendicular
Assessing Aligned CNT Filament Thickness
Assessing Electrical Conductivity in CNT Filament Alignment and Transverse Directions
Dielectrophoretic alignment of nanotubes in polymer matrix – Can be extended to hybrid micro-fibers
Carbon nanotube –polymer nanocomposite fracture toughness
Assessing CNT Alignment via Raman Spectroscopy
Digital Image Correlation
Fractured Sample
14For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Conductive Polymer Nanocomposites as Large Strain Sensors Rakesh K. Kapania, Mohammed R. Sunny
Objective:• To investigate the feasibility of using
conductive polymers nanocomposites as large strain sensors
Experimental Setup
Motivation:• It is difficult to measure large strain (>10%) as there
is no suitable sensor material to best of our knowledge.
• Conductive polymers can be stretched like rubber (upto ~200%) and have high conductivity (sheet resistance ~100 Ohm/sq.).
• A promising sensor material for large strain applications
Accomplishments• Experimentally studied the variation of electrical
resistance with cyclic strain for different strain rates.• Observed the phenomena of hysteresis and
relaxation in the experimental data.• Developed a modified fractional calculus model and
a modified dynamic Preisach model to model the hysteresis and relaxation.
• Developed a compensator to remove the effect of hysteresis and relaxation from the data for sensor calibration.
Equipment:
1. Sunny, M. R., and Kapania, R. K., “Artificial neural network based identification of a modified dynamic Preisach model,” International Journal for Computational Methods in Engineering Science and Mechanics, 15(1), 2014, pp. 45-53
2. Sunny, M.R., and Kapania, R.K. “Modified dynamic Preisach model for hysteresis”, AIAA Journal, 48(7), 2010, pp. 1523-1530
3. Sunny, M.R., Kapania, R.K., Moffitt, R., Mishra, A., and Goulbourne, N., “A modified fractional calculus approach to model hysteresis”, Journal of Applied Mechanics, 77(3), 2010, pp. 031004-1 - 031004-8
References:Linear Stage NLS4-10-25 by Newmark Systems Inc.
15For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Curvilinearly Stiffened Panel and Wing with Additive Manufacturing Rakesh K. Kapania, Sameer B. Mulani
Objective:• Optimization of curvilineary stiffened panels
and wings manufactured using 3D printingMotivation:• Expanding the design space to minimize the weight of
the stiffened panel/wing while satisfying the constraints• Changing the mode shapes, frequencies of the
structure apart from the load paths• Bringing medium fidelity FEM tools much earlier in
design phase to increase the confidence• Impact NASA goals• Affecting the coupling between bending and torsion• Multi-objective optimization where sound power and
mass are goals
Accomplishments:• Stiffened Panel Structural and Vibro-acoustic
Optimization with Curvilinear Blade or T Stiffener, Reliability Calculation and Reliability-Based-Design Optimization, Surrogate Modeling
• Four Panels Experimentally Validated• Up to 20% Weight Savings and 8 dB Reduction in
Maximum Sound Pressure Level• Optimized Commercial Wings and Weight Saving is
more than 17%
1. Mulani, S. B., Slemp, W. C. H., and Kapania, R. K., “EBF3PanelOpt: An Optimization Framework for Curvilinear Blade-Stiffened Panels”, Thin-Walled Structures, 63, 2013, pp. 13-26
2. Locatelli, D., Mulani, S. B., and Kapania, R. K., “Wing Box Weight Optimization Using Curvilinear Spars and Ribs (SpaRibs)”, Journal of Aircraft, 48(5), 2011, pp. 1671-1684.
3. Islam, M. M. and Kapania, R. K., “Global–Local Finite Element Analysis of Adhesive Joints and Crack Propagation”, Journal of Aircraft, 2014.
4. Mulani, S. B., Duggirala, V., and Kapania, R. K., “Curvilinearly T-Stiffened Panel Optimization Framework under Multiple Load Cases Using Parallel Processing”, Journal of Aircraft, 50(5), 2013, pp. 1540-1554
References:Global Analysis Local Analysis
VM Stress
16For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Example Projects: Active/morphing control of airfoil – spoiler
and aileron surfaces Damage detection using MFC phased array
for guided wave beamsteering Damage classification in structural systems
using machine learning algorithms Variable stiffness structures for shape
holding and vibration control Nanocomposite fabrication and
characterization of multifunctional properties Advanced curvilinear-stiffened unitized
structures
1200 ft2 facility in Randolph Hall hosting state-of-the-art-equipment necessary for system identification, material and structural system testing, real-time control system implementation, ultrasonic displacement, strain, and velocity measurement. Examples: Polytec laser vibrometer, 3D Digital Image Correlation (DIC), multiple dSpace control systems, several NI DAQ systems (100 MS/s and 24 bit resolution), fiber optic strain and displacement sensors, testing frames, dynamic spectrum analyzers, resistivity measurement cell, precision LCR meter, scanning electron microscope, optical microscopes, fumehood, sonicator, variety of shakers and dynamic testing equipment for performing modal testing and general vibration testing, and unique I-Beam wall for mounting large structures (e.g. airfoils, blades).
Aerospace Structures and Materials Laboratory
http://www.asml.aoe.vt.edu/
17For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at gary.seidel@vt.edu
Acknowledgements
Rakesh KapaniaNorris and Laura
Mitchell Professor of Aerospace Engineering
(540) 231-4881 rkapania@vt.edu
Michael Keith PhilenAssociate Professor
Aerospace and Ocean Engr. (540) 231-2548 mphilen@vt.edu
Gary D SeidelAssistant Professor
Aerospace and Ocean Engr. (540) 231-9897
gary.seidel@vt.edu
Barry GoodellProfessor, Department of Sustainable Biomaterials
540-231-8854 goodell@vt.edu
Scott RenneckarAssociate Professor
Department of Sustainable Biomaterials 540-231-7100
srenneck@vt.edu
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