Multi-fidelity Modeling of Interfacial Micromechanics for Off-Aligned Polymer/Carbon Nanotube Nanocomposites - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Multi-fidelity Modeling of Interfacial Micromechanics for Off-Aligned Polymer/Carbon Nanotube Nanocomposites write by Reed Kopp. This book was released on 2016. Multi-fidelity Modeling of Interfacial Micromechanics for Off-Aligned Polymer/Carbon Nanotube Nanocomposites available in PDF, EPUB and Kindle. Recent initiatives to stimulate development of next-generation rotorcraft featuring leap-ahead improvements in speed, payload, range, and durability, such as Clean Sky and Future Vertical Lift, have revitalized research efforts directed toward advanced, unconventional designs that emphasize lower operations and sustainment costs. Accordingly, soft-inplane damperless bearingless and hingeless rotor concepts have garnered significant interest. However, soft-inplane designs are susceptible to aeromechanical instabilities, such as air and ground resonance, which can potentially induce catastrophic blade vibrations without sufficient blade damping. To ensure stability, current composite blades typically require auxiliary damping sources that incur weight, volume, complexity, and maintenance penalties. Alternatively, one promising approach for achieving new lightweight, low vibration rotorcraft structures is passive damping engineered intrinsically into a structure via polymeric nanocomposites.In this study, a multi-fidelity modeling effort is employed to investigate the interfacial load transfer micromechanics, including strain energy storage and dissipation, of an off-aligned discontinuously-reinforced polymer/carbon nanotube nanocomposite. The effects of off-alignment angle on nanocomposite mechanical properties is of primary interest. The methodology in this study is separated into two independent modeling tracks: a simplified analytical micromechanics model and a high-fidelity 3D finite element model. Both model types explore transverse fixed and transverse free boundary conditions applied to the representative volume element, which correspond to applied strain and applied stress external loading conditions, respectively. Each model accounts for interfacial shear stress variations along the azimuthal direction of the nano-inclusion surface that are a result of nonzero and non-right alignment angles with respect to the applied loading. The analytical micromechanics models examine non-embedded fiber conditions, for which matrix end material effects are neglected, in the preslip and postslip regimes and embedded fiber conditions, for which matrix end material effects are included, in the preslip regime. The non-embedded micromechanics model is based on principles from an extended Cox model for discontinuous fiber reinforcement and generalized shear lag analysis for off-aligned discontinuous fibers; furthermore, the energy dissipation, which is based on principles of a simple amplitude-dependent friction damper, is assumed to be caused only by interfacial slip friction between constituents and is functionally dependent on the interfacial shear force acting over slipped portions of the matrix/nano-inclusion interface. In order to isolate the effects of azimuthal interfacial shear stress variation, a comparison of the current non-embedded model with an alternative non-embedded analytical model that employs an interfacial shear magnitude approach is performed. The embedded analytical micromechanics model is based on principles from a modified Cox model that extends the non-embedded approach to account for finite matrix end material and nonzero fiber end normal stress. The finite element model is implemented in the preslip regime for an embedded fiber with limited off-alignment angle range.The material properties employed by each model reflect those of a realistic multi-walled carbon nanotube/poly-ether-ether-ketone nanocomposite architecture. In the preslip regime, the FEM and analytical model predictions for interfacial shear and nano-inclusion normal stress distributions generally display good agreement, which is improved by including inclusion end stress effects in the analytical models. For the transverse fixed boundary condition, the non-embedded analytical model predicts reduced interfacial slip damping capacity as off-alignment increases, with initiation of slip becoming impossible at relatively high off-alignment angles. However, for the transverse free boundary condition, the non-embedded analytical model predicts that zero interfacial slip damping occurs comparatively at more moderate off-alignment angles, with nonzero damping occurring at both lower and higher off-alignment angles. The phenomena of extrema in interfacial slip damping with respect to alignment angle is due to the relative strain behavior between nanocomposite constituents caused by elastic stiffness mismatch. The alternative azimuthal magnitude non-embedded analytical model generally underpredicts storage modulus and greatly overpredicts loss modulus (for nonzero and non-right off-alignments) compared with the corresponding properties predicted by the current non-embedded analytical model because the alternative azimuthal magnitude approach assumes a greater interfacial slip surface area for a given off-alignment angle and strain magnitude compared to the current approach. Overall, the results demonstrate that nano-inclusion alignment angle substantially affects nanocomposite stiffness and interfacial damping and that azimuthal variation of the interfacial shear is a critical feature of nanocomposite mechanics. The outcome of this multi-fidelity modeling study is an array of qualified nanocomposite mechanical property prediction methods spanning a wide range of practical off-alignment angles, applied dynamic strain amplitudes and static strain magnitudes, loading and fiber embedment conditions, and nano-inclusion geometries and concentrations.
Mechanics of Composite, Hybrid and Multifunctional Materials, Volume 5
Mechanics of Composite, Hybrid and Multifunctional Materials, Volume 5 - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Mechanics of Composite, Hybrid and Multifunctional Materials, Volume 5 write by Piyush R. Thakre. This book was released on 2018-10-15. Mechanics of Composite, Hybrid and Multifunctional Materials, Volume 5 available in PDF, EPUB and Kindle. Mechanics of Composite, Hybrid, and Multifunctional Materials, Volume 5 of the Proceedings of the 2018 SEM Annual Conference & Exposition on Experimental and Applied Mechanics, the fifth volume of eight from the Conference, brings together contributions to this important area of research and engineering. The collection presents early findings and case studies on a wide range of areas, including: Recycled Constituent Composites Nanocomposites Mechanics of Composites Fracture & Fatigue of Composites Multifunctional Materials Damage Detection & Non-destructive Evaluation Composites for Wind Energy & Aerospace Applications Computed Tomography of Composites Manufacturing & Joining of Composites Novel Developments in Composites
Micromechanics Modeling of the Multifunctional Nature of Carbon Nanotube-polymer Nanocomposites
Micromechanics Modeling of the Multifunctional Nature of Carbon Nanotube-polymer Nanocomposites - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Micromechanics Modeling of the Multifunctional Nature of Carbon Nanotube-polymer Nanocomposites write by Gary Don Seidel. This book was released on 2010. Micromechanics Modeling of the Multifunctional Nature of Carbon Nanotube-polymer Nanocomposites available in PDF, EPUB and Kindle. The present work provides a micromechanics approach based on the generalized self-consistent composite cylinders method as a non-Eshelby approach towards for assessing the impact of carbon nanotubes on the multi-functional nature of nanocom-posites in which they are a constituent. Emphasis is placed on the effective elastic properties as well as electrical and thermal conductivities of nanocomposites con-sisting of randomly oriented single walled carbon nanotubes in epoxy. The effective elastic properties of aligned, as well as clustered and well-dispersed nanotubes in epoxy are discussed in the context of nanotube bundles using both the generalized self-consistent composite cylinders method as well as using computational microme-chanics techniques. In addition, interphase regions are introduced into the composite cylinders assemblages to account for the varying degrees of load transfer between nanotubes and the epoxy as a result of functionalization or lack thereof. Model pre-dictions for randomly oriented nanotubes both with and without interphase regions are compared to measured data from the literature with emphasis placed on assessing the bounds of the effective nanocomposite properties based on the uncertainty in the model input parameters. The generalized self-consistent composite cylinders model is also applied to model the electrical and thermal conductivity of carbon nanotube-epoxy nanocomposites. Recent experimental observations of the electrical conductivity of carbon nanotube polymer composites have identifed extremely low percolation limits as well as a per-ceived double percolation behavior. Explanations for the extremely low percolation limit for the electrical conductivity of these nanocomposites have included both the creation of conductive networks of nanotubes within the matrix and quantum effects such as electron hopping or tunneling. Measurements of the thermal conductivity have also shown a strong dependence on nanoscale effects. However, in contrast, these nanoscale effects strongly limit the ability of the nanotubes to increase the thermal conductivity of the nanocomposite due to the formation of an interfacial thermal resistance layer between the nanotubes and the surrounding polymer. As such, emphasis is placed here on the incorporation of nanoscale effects, such as elec-tron hopping and interfacial thermal resistance, into the generalized self-consistent composite cylinder micromechanics model.
Analytic and Computational Micromechanics of Clustering and Interphase Effects in Carbon Nanotube Composites
Analytic and Computational Micromechanics of Clustering and Interphase Effects in Carbon Nanotube Composites - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Analytic and Computational Micromechanics of Clustering and Interphase Effects in Carbon Nanotube Composites write by Daniel Carl Hammerand. This book was released on 2006. Analytic and Computational Micromechanics of Clustering and Interphase Effects in Carbon Nanotube Composites available in PDF, EPUB and Kindle. Effective elastic properties for carbon nanotube reinforced composites are obtained through a variety of micromechanics techniques. Using the in-plane elastic properties of graphene, the effective properties of carbon nanotubes are calculated utilizing a composite cylinders micromechanics technique as a first step in a two-step process. These effective properties are then used in the self-consistent and Mori-Tanaka methods to obtain effective elastic properties of composites consisting of aligned single or multi-walled carbon nanotubes embedded in a polymer matrix. Effective composite properties from these averaging methods are compared to a direct composite cylinders approach extended from the work of Hashin and Rosen (1964) and Christensen and Lo (1979). Comparisons with finite element simulations are also performed. The effects of an interphase layer between the nanotubes and the polymer matrix as result of functionalization is also investigated using a multi-layer composite cylinders approach. Finally, the modeling of the clustering of nanotubes into bundles due to interatomic forces is accomplished herein using a tessellation method in conjunction with a multi-phase Mori-Tanaka technique. In addition to aligned nanotube composites, modeling of the effective elastic properties of randomly dispersed nanotubes into a matrix is performed using the Mori-Tanaka method, and comparisons with experimental data are made. Computational micromechanical analysis of high-stiffness hollow fiber nanocomposites is performed using the finite element method. The high-stiffness hollow fibers are modeled either directly as isotropic hollow tubes or equivalent transversely isotropic effective solid cylinders with properties computed using a micromechanics based composite cylinders method. Using a representative volume element for clustered high-stiffness hollow fibers embedded in a compliant matrix with the appropriate periodic boundary conditions, the effective elastic properties are obtained from the finite element results. These effective elastic properties are compared to approximate analytical results found using micromechanics methods. The effects of an interphase layer between the high-stiffness hollow fibers and matrix to simulate imperfect load transfer and/or functionalization of the hollow fibers is also investigated and compared to a multi-layer composite cylinders approach. Finally the combined effects of clustering with fiber-matrix interphase regions are studied. The parametric studies performed herein were motivated by and used properties for single-walled carbon nanotubes embedded in an epoxy matrix, and as such are intended to serve as a guide for continuum level representations of such nanocomposites in a multi-scale modeling approach.
Multiscale Modeling of Multifunctional Carbon Nanotube Reinforced Polymer Composites
Multiscale Modeling of Multifunctional Carbon Nanotube Reinforced Polymer Composites - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Multiscale Modeling of Multifunctional Carbon Nanotube Reinforced Polymer Composites write by AHMED ROWAEY Rowaey Abdelazeam ALIAN. This book was released on 2018. Multiscale Modeling of Multifunctional Carbon Nanotube Reinforced Polymer Composites available in PDF, EPUB and Kindle. In this thesis, novel multiscale modeling techniques have been successfully developed to study multifunctional nanocomposite polymeric materials. Interfacial, mechanical, electrical, and piezoresistive properties of carbon nanotube (CNT)-reinforced polymer composites were investigated using molecular dynamics (MD), micromechanics, and coupled electromechanical modeling techniques. Additionally, scanning electron microscopy was used to determine the morphology and dispersion state of a typical CNT-epoxy composite. Based on these measurements, realistic nanocomposite structures were modeled using representative volume elements (RVEs) reinforced by CNTs with different aspect ratios, curvatures, orientations, alignment angles, and bundle sizes. At the nanoscale level, the interfacial shear strength was determined via pull-out MD simulations. Additionally, the stiffness constants of a pure polymer, pristine and defective CNTs, and an effective fiber consisting of a CNT and a surrounding layer of polymeric chains were determined using the constant-strain energy minimization method. The obtained atomistic mechanical properties of the composite constituents were then scaled up using Mori-Tanaka micromechanical scheme. Monte Carlo simulations were conducted to determine the percolation and electrical conductivity of RVEs containing randomly dispersed CNTs. An advanced search algorithm was developed to identify percolating CNT networks and transform them into an equivalent electrical circuit formed from intrinsic and tunneling resistances. A solver based on the modified nodal analysis technique was then developed to calculate the effective conductivity of the RVE. Finally, the electrical model was coupled with a three-dimensional finite element model of the RVE to determine the coupled electromechanical behavior of the composite under tensile, compressive, and shear loads from the resistance-strain relationship. The outcome of the developed modeling approach revealed that: the elastic modulus of a nanocomposite reinforced with well-dispersed straight CNTs was found to increase almost linearly with the increase of their volume fraction and double at CNT volume fraction of 5.0 %; the combined effect of CNT waviness and agglomeration results in a significant reduction in the bulk properties of the nanocomposite; CNTs with grain boundaries perpendicular to the tube axis experience 60% reduction in its mechanical strength; and the nanocomposite gauge factor can reach up to 3.95 and is sensitive to loading direction and CNT concentration.
