nanoscience and nanotechnology at virginia tech · nanoscience and nanotechnology at virginia tech....

1For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at [email protected]

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

mailto:[email protected]


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



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.



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)



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)



Nanocellulose is derived from the microfibrils that compose plant cell walls through modification and homogenization



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



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.



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

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ista

nce

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Cyclic loading MicrotensilePiezoresistive Testing

Macroscale Gage Factor



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

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0.00E+00

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-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



Multiscale Piezoresistive Modeling

0.0

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Stress for element 58 Stress for element 111

Resistivity for element 58 Resistivity for element 111

Macroscale Applied Strain

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mal

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in R

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tivity

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axia

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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):



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

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1 100 100001000000

Pow

er R

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Alignment of CNTs and Characterization of CNT Nanocomposites

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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



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.



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



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/


http://www.asml.aoe.vt.edu/


Acknowledgements

Rakesh KapaniaNorris and Laura

Mitchell Professor of Aerospace Engineering

(540) 231-4881 [email protected]

Michael Keith PhilenAssociate Professor

Aerospace and Ocean Engr. (540) 231-2548 [email protected]

Gary D SeidelAssistant Professor

Aerospace and Ocean Engr. (540) 231-9897

[email protected]

Barry GoodellProfessor, Department of Sustainable Biomaterials

540-231-8854 [email protected]

Scott RenneckarAssociate Professor

Department of Sustainable Biomaterials 540-231-7100

[email protected]


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