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  • 1
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    Predicting the Influence of Nano-Scale Material Structure on the In-Plane Buckling of Orthotropic Plates (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A multi-scale analysis of the structural stability of a carbon nanotube-polymer composite material is developed. The influence of intrinsic molecular structure, such as nanotube length, volume fraction, orientation and chemical functionalization, is investigated by assessing the relative change in critical, in-plane buckling loads. The analysis method relies on elastic properties predicted using the hierarchical, constitutive equations developed from the equivalent-continuum modeling technique applied to the buckling analysis of an orthotropic plate. The results indicate that for the specific composite materials considered in this study, a composite with randomly orientated carbon nanotubes consistently provides the highest values of critical buckling load and that for low volume fraction composites, the non-functionalized nanotube material provides an increase in critical buckling stability with respect to the functionalized system.
    Keywords: Mechanical Engineering
    Type: AIAA Paper 2004-1607 , 45th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamic, and Materials Conference; Apr 19, 2004 - Apr 22, 2004; Palm Springs, CA; United States
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  • 2
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    Micromechanics Modeling of Functionally Graded Interphase Regions in Carbon Nanotube-Polymer Composites (2006)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The effective elastic properties of a unidirectional carbon fiber/epoxy lamina in which the carbon fibers are coated with single-walled carbon nanotubes are modeled herein through the use of a multi-scale method involving the molecular dynamics/equivalent continuum and micromechanics methods. The specific lamina representative volume element studied consists of a carbon fiber surrounded by a region of epoxy containing a radially varying concentration of carbon nanotubes which is then embedded in the pure epoxy matrix. The variable concentration of carbon nanotubes surrounding the carbon fiber results in a functionally graded interphase region as the properties of the interphase region vary according to the carbon nanotube volume fraction. Molecular dynamics and equivalent continuum methods are used to assess the local effective properties of the carbon nanotube/epoxy comprising the interphase region. Micromechanics in the form of the Mori-Tanaka method are then applied to obtain the global effective properties of the graded interphase region wherein the carbon nanotubes are randomly oriented. Finally, the multi-layer composite cylinders micromechanics approach is used to obtain the effective lamina properties from the lamina representative volume element. It was found that even very small quantities of carbon nanotubes (0.36% of lamina by volume) coating the surface of the carbon fibers in the lamina can have a significant effect (8% increase) on the transverse properties of the lamina (E22, k23, G23 and G12) with almost no affect on the lamina properties in the fiber direction (E11 and v12).
    Keywords: Composite Materials
    Type: AIAA Paper 2006-1678 , 47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference; May 01, 2006 - May 04, 2006; Newport, RI; United States
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  • 3
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    Molecular Dynamics Simulations of Adhesion at Epoxy Interfaces (2008)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The effect of moisture on adhesives used in aerospace applications can be modeled with chemically specific techniques such as molecular dynamics simulation. In the present study, the surface energy and work of adhesion are calculated for epoxy surfaces and interfaces, respectively, by using molecular dynamics simulation. Modifications are made to current theory to calculate the work of adhesion at the epoxy-epoxy interface with and without water. Quantitative agreement with experimental values is obtained for the surface energy and work of adhesion at the interface without water. The work of adhesion agrees qualitatively with the experimental values for the interface with water: the magnitude is reduced 15% with respect to the value for the interface without water. A variation of 26% in the magnitude is observed depending on the water configuration at a concentration of 1.6 wt%. The methods and modifications to the method that are employed to obtain these values are expected to be applicable for other epoxy adhesives to determine the effects of moisture uptake on their work of adhesion.
    Keywords: Nonmetallic Materials
    Type: American Society for Composites 23rd Annual Technical Conference; Sep 09, 2008 - Sep 11, 2008; Memphis, TN; United States
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  • 4
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    Deformation and Failure of a Multi-Wall Carbon Nanotube Yarn Composite (2008)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Forests of multi-walled carbon nanotubes can be twisted and manipulated into continuous fibers or yarns that exhibit many of the characteristics of traditional textiles. Macro-scale analysis and test may provide strength and stiffness predictions for a composite composed of a polymer matrix and low-volume fraction yarns. However, due to the nano-scale of the carbon nanotubes, it is desirable to use atomistic calculations to consider tube-tube interactions and the influence of simulated twist on the effective friction coefficient. This paper reports laboratory test data on the mechanical response of a multi-walled, carbon nanotube yarn/polymer composite from both dynamic and quasi-static tensile tests. Macroscale and nano-scale analysis methods are explored and used to define some of the key structure-property relationships. The measured influence of hot-wet aging on the tensile properties is also reported.
    Keywords: Composite Materials
    Type: 49th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference; Apr 07, 2008 - Apr 10, 2008; Schaumburg, IL; United States
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  • 5
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    Elastic Response and Failure Studies of Multi-Wall Carbon Nanotube Twisted Yarns (2007)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Experimental data on the stress-strain behavior of a polymer multiwall carbon nanotube (MWCNT) yarn composite are used to motivate an initial study in multi-scale modeling of strength and stiffness. Atomistic and continuum length scale modeling methods are outlined to illustrate the range of parameters required to accurately model behavior. The carbon nanotubes yarns are four-ply, twisted, and combined with an elastomer to form a single-layer, unidirectional composite. Due to this textile structure, the yarn is a complicated system of unique geometric relationships subjected to combined loads. Experimental data illustrate the local failure modes induced by static, tensile tests. Key structure-property relationships are highlighted at each length scale indicating opportunities for parametric studies to assist the selection of advantageous material development and manufacturing methods.
    Keywords: Composite Materials
    Type: 22nd Annual Technical Conference of the American Society for Composites; Sep 17, 2007 - Sep 19, 2007; Seattle, WA; United States
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  • 6
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    Cross-Linked Nanotube Materials with Variable Stiffness Tethers (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The constitutive properties of a cross-linked single-walled carbon nanotube material are predicted with a multi-scale model. The material is modeled as a transversely isotropic solid using concepts from equivalent-continuum modeling. The elastic constants are determined using molecular dynamics simulation. Some parameters of the molecular force field are determined specifically for the cross-linker from ab initio calculations. A demonstration of how the cross-linked nanotubes may affect the properties of a nanotube/polyimide composite is included using a micromechanical analysis.
    Keywords: Nonmetallic Materials
    Type: ASC/ASTM-D30 Joint 19th Annual Technical Conference; Oct 17, 2004 - Oct 20, 2004; Atlanta, GA; United States
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  • 7
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    Multiscale Modeling of Thermal Conductivity of Polymer/Carbon Nanocomposites (2010)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Molecular dynamics simulation was used to estimate the interfacial thermal (Kapitza) resistance between nanoparticles and amorphous and crystalline polymer matrices. Bulk thermal conductivities of the nanocomposites were then estimated using an established effective medium approach. To study functionalization, oligomeric ethylene-vinyl alcohol copolymers were chemically bonded to a single wall carbon nanotube. The results, in a poly(ethylene-vinyl acetate) matrix, are similar to those obtained previously for grafted linear hydrocarbon chains. To study the effect of noncovalent functionalization, two types of polyethylene matrices. -- aligned (extended-chain crystalline) vs. amorphous (random coils) were modeled. Both matrices produced the same interfacial thermal resistance values. Finally, functionalization of edges and faces of plate-like graphite nanoparticles was found to be only modestly effective in reducing the interfacial thermal resistance and improving the composite thermal conductivity
    Keywords: Composite Materials
    Type: LF99-8623
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  • 8
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    Multi-scale Rule-of-Mixtures Model of Carbon Nanotube/Carbon Fiber/Epoxy Lamina (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A unidirectional carbon fiber/epoxy lamina in which the carbon fibers are coated with single-walled carbon nanotubes is modeled with a multi-scale method, the atomistically informed rule-of-mixtures. This multi-scale model is designed to include the effect of the carbon nanotubes on the constitutive properties of the lamina. It included concepts from the molecular dynamics/equivalent continuum methods, micromechanics, and the strength of materials. Within the model both the nanotube volume fraction and nanotube distribution were varied. It was found that for a lamina with 60% carbon fiber volume fraction, the Young's modulus in the fiber direction varied with changes in the nanotube distribution, from 138.8 to 140 GPa with nanotube volume fractions ranging from 0.0001 to 0.0125. The presence of nanotube near the surface of the carbon fiber is therefore expected to have a small, but positive, effect on the constitutive properties of the lamina.
    Keywords: Composite Materials
    Type: 2005 MRS Fall Meeting; Nov 28, 2005 - Dec 02, 2005; Boston, MA; United States
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