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A three-dimensional model for the mechanics of elastic/hyperelastic materials reinforced with bidirectional fibers is presented in finite elastostatics. This includes the constitutive formulation of matrix–fiber composite system and the derivation of the corresponding Euler equilibrium equation. The responses of the matrix material and reinforcing fibers are characterized, respectively, via the Neo-Hookean model and quadratic strain energy potential of the Green–Lagrange type. These are further refined by the Mooney–Rivlin strain energy model and the high-order polynomial energy potential of fibers to incorporate the nonlinear behaviors of the matrix material and fibers. Within the framework of differential geometry and strain-gradient elasticity, the general kinematics of bidirectional fibers, including the three-dimensional bending of a fiber and twist between the two adjoining fibers, are formulated, and subsequently integrated into the model of continuum deformation. The admissible boundary conditions are also derived by virtue of variational principles and virtual work statement. In particular, a dimension reduction process is applied to the resulting three-dimensional model through which a compatible two-dimensional model describing both the in-plane and out-of-plane deformations of thin elastic films reinforced with fiber mesh is obtained. To this end, model implementation and comparison with the experimental results are performed, indicating that the proposed model successfully predicts key design considerations of fiber mesh reinforced composite films including stress–strain responses, deformation profiles, shear strain distributions and local structure (a unit fiber mesh) deformations. The proposed model is unique in that it is formulated within the framework of differential geometry of surface to accommodate the three-dimensional kinematics of the composite, yet the resulting equations are reframed in the orthonormal basis for enhanced practical unitality and mathematical tractability. Hence, the resulting model may also serve as an alternative Cosserat theory of plates and shells arising in two-dimensional nonlinear elasticity. [ABSTRACT FROM AUTHOR]

Stretchable composites have drawn the significant focus of researchers due to their necessity and importance in advanced technical areas. In this paper, we prepared the multiwall carbon nanotube (MWCNTs)/thermoplastic polyurethane (TPU) composites with excellent dispersion using the double extrusion followed by solvent casting techniques. These techniques enhanced the interaction between the MWCNTs and TPU. The electrical properties, electromagnetic interference (EMI) shielding and dynamic mechanical analysis of the prepared MWCNTs/TPU composites are analyzed. The EMI shielding performance at different phr of MWCNTs reinforced TPU composites is determined in the X-band frequency range. The 20 phr MWCNTs reinforced TPU composite having a thickness of 0.15 mm showed a total shielding effectiveness of ∼ 37.4 dB, which is much higher as compared to pure TPU. The improvement in electrical properties is well supported by scanning electron microscopy (SEM) images and Raman spectroscopic analysis. SEM is used to analyze the dispersion of MWCNTs within the TPU matrix. The morphology showed that MWCNTs are well dispersed in the TPU matrix with the addition of 5phr MWCNTs. It was found that 5phr MWCNTs reinforced TPU composites have an excellent value of storage modulus, loss modulus and tan δ which exhibit better properties as compared to the other MWCNTs reinforced TPU composites. The enhancement in DMA properties is due to the strong interfacial interaction between the fillers and matrix. These stretchable and light weight MWCNTs/TPU composites act as excellent EMI shielding materials, especially in next-generation defense and electronic devices industries. [ABSTRACT FROM AUTHOR]

The mechanics of fiber-reinforced composite materials is presented within the framework of the second strain gradient theory. As such, a continuum-based model is developed for the analysis of elastic materials reinforced with bidirectional fibers and subjected to finite plane deformations. The obtained model is subsequently applied to the cases of the unidirectional fiber composites for the purpose of model implementation. The Euler equilibrium equations and the associated boundary conditions are obtained via the variational principle and iterative integration by parts. In particular, we formulate the complete expressions of Piola-type triple stress and its coupled triple force arising in the third gradient of continuum deformations, which, in turn, yield the unique deformation maps in the presence of admissible boundary conditions of higher order. The solutions of the resulting systems of differential equations are obtained via the custom-built numerical scheme from which smooth and dilatational shear angle distributions are predicted throughout the entire domain of interest. It is also observed that the third gradient constitutive parameter is associated with the volume dilatation of third-gradient continua, which may be appeared in the form of shear band inclination angle. [ABSTRACT FROM AUTHOR]

A molecular dynamics simulation study was conducted to identify the contributions of polyoligosilsesquioxane (POSS) nanoparticles to the thermoelastic behaviors of cross-linked epoxy nanocomposites. POSS nanoparticles functionalized using pre-cured epoxy were first embedded in an epoxy matrix and the resulting nanocomposites were then cured to a conversion ratio of 87 %. According to the volume fraction of the functionalized POSS nanoparticles, the stress-strain curves, coefficients of thermal expansion (CTEs), and glass transition temperatures of the nanocomposites were determined using a classical molecular potential model. Based on the efficient interfacial load transfer through the epoxy-functionalized structures at the interfaces between the POSS particles and epoxy matrices, the Young's moduli and volumetric CTEs of the nanocomposites were effectively improved. Additionally, no clear reinforcing effects of the POSS nanoparticles were observed in the glass transition behaviors. Using the multi-inclusion model, the thermoelastic properties of effective POSS nanoparticle were determined from inverse micromechanical method. [ABSTRACT FROM AUTHOR]

Hygroscopic aging causes swelling, degradation of mechanical and interfacial properties in thermosetting epoxy polymers, which eventually lead to a fast fracture at the interface in nanocomposite. Since the epoxy is a widely used high performance thermoset polymer for aerospace structures, durability analysis is necessary for the sake of maintenance and stability of the structures. In this study, the hygroelastic behavior of pure epoxy and epoxy/graphene nanocomposite is investigated through atomistic molecular dynamics (MD) simulation. To determine the hygroelastic behavior of epoxy materials, amorphous molecular unit cells of pure epoxy and epoxy/graphene nanocomposites with its highest possible cross-linking ratio and moisture contents of 0 and 2 wt% are considered. Through the classical ensemble simulations, diffusion coefficient of water in matrix, coefficient of moisture expansion (CME) and elastic modulus of pure epoxy and epoxy/graphene nanocomposites are determined. [ABSTRACT FROM AUTHOR]

The mechanical behavior of oxygen functionalized single layer graphene (graphene oxide, GO)/polyethylene (PE) nanocomposites is studied by all atom-based molecular dynamics (MD) simulation and finite element analysis (FEA). To account for the effect of the oxygen functional group, both pristine and 15 hydroxyl functionalized graphene embedded into the transversely isotropic nanocomposites unit cell models are considered. Using the classical ensemble simulations at 200K and at atmospheric pressure, the transversely isotropic elastic constants of the nanocomposites molecular unit cell structures are determined from uniaxial tension and shear tests. To evaluate the effect of the addressed oxygen functional groups on elastic constants of the nanocomposites, periodic FEA models with the perfect interface condition between the graphene and PP matrix are constructed. Due to the degradation of the graphene by the oxidation, the longitudinal Young's modulus and the in-plane shear modulus of the nanocomposites determined from the MD simulation and FEA are found to be degraded by the oxygen functional groups. According to the MD simulation results, however, the longitudinal shear modulus of the nanocomposites is improved by the oxygen functional groups compared with the pristine graphene. On the other hand, FEA analysis of the longitudinal shear modulus is overestimated unless the oxygen functional group-dependent cohesive interface law between the graphene and PP matrix is addressed. [ABSTRACT FROM AUTHOR]

While poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane, pV3D3) is a promising dielectric material, synthesized from an iCVD process, the physical properties of pV3D3 film have yet to be studied in detail. In this study, the thermoelastic properties of pV3D3 are investigated by molecular dynamics simulations. An amorphous molecular unit cell of pV3D3 is modeled with periodic boundary conditions. The PCFF force field is applied to describe all the inter- and intramolecular interactions. Through classical ensemble simulations, the mechanical properties including the stress-strain curves in tension and compression are determined. The glass transition temperature and the coefficient of thermal expansion are determined from the simulation of cooling-down from an elevated temperature. The simulation results show that the pV3D3 is in an almost rubbery state near room temperature. Moreover, a clear hydrostatic pressure effect is observed in the compressive loading condition of pV3D3 and its elastic modulus is within the range of typical thermoplastic. [ABSTRACT FROM AUTHOR]