1 For 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 Philen Aerospace and Ocean Engineering Barry Goodell and Scott Renneckar Department of Sustainable Biomaterials NIA Workshop on Nanomaterials for Aerospace February 21 st 2014
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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
2For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at [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
3For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at [email protected]
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 [email protected]
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 [email protected]
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)
7For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at [email protected]
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 [email protected]
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 [email protected]
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
10For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at [email protected]
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.
14For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at [email protected]
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 [email protected]
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
16For More information, please contact Drs. B. Goodell, R. Kapania, S. Renneckar, G. Seidel, and M. Philen at [email protected]
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).