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In this work, the effect of carbon nanotube (CNT) size on the effective elastic properties of a hybrid composite reinforced by fuzzy fiber is investigated using a unit cell-based micromechanical approach. This hybrid nanocomposite is composed of the CNT, carbon fiber, polymer matrix and interphase created due to the non-bonded van der Waals interactions between the CNTs and polymer. The novel constructional feature of this hybrid nanocomposite is that the uniformly aligned CNTs are radially grown on the surface of the horizontal carbon fibers. The CNT and carbon fiber are modeled as a transverse isotropic solid, while the interphase and polymer matrix are assumed to be isotropic. The influence of CNT size on the overall behavior of polymer matrix nanocomposite (PMNC), composite fuzzy fiber (CFF) and hybrid composite reinforced with fuzzy fiber is examined. Results show that size of CNT is more significant for the transverse effective properties of the hybrid nanocomposites reinforced with fuzzy fiber. It has been found that the transverse effective properties of hybrid nanocomposite are improved with increasing the CNT size. The micromechanical model is also used to examine the influence of interphase on the overall behavior of the PMNC, CFF and hybrid composite reinforced with fuzzy fiber. The effective elastic properties of the hybrid composite obtained by the present micromechanical model demonstrate very good agreement with those predicted by the other researches.

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In this work, an elastoplastic constitutive model is planned to analyze the effects of adding silica nanoparticles on the overall elastic-plastic stress-strain curves of the polymer matrix nanocomposites. The elastic modulus of the nanocomposites are evaluated by the combination of the Mori-Tanaka and Eshelby micromechanical models considering interphase region formed due to the interaction between silica nanoparticles and the polymer matrix. Then, the elastic-plastic stress-strain curves of nanocomposites are extracted by employing a micromechanics-based ensemble-volume averaged homogenization procedure. To prove the validity of the developed method, the predictions are compared to the experimental data existing in the literature. The effects of volume fraction and diameter of silica nanoparticles, thickness and adhesion exponent of the interphase on the polymeric nanocomposite elastic-plastic stress-strain curves are extensively examined. Stiffer elastoplastic behavior is found in the presence of interphase region. The results clearly indicate that the strengthening of the silica nanoparticle-reinforced polymer nanocomposites is improved with (1) increasing nanoparticle volume fraction, (2), decreasing the nanoparticle diameter, (3) increasing the interphase thickness and (4) decreasing the interphase adhesion exponent. Finally, the elastic-plastic stress-strain curves of silica nanoparticle/polymer nanocomposites under biaxial loading is achieved.

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In this research, an analytical method is presented for predicting the viscoelastic and dynamic behavior of polymer nanocomposite. The analytical model is achieved by coupling the SUC micromechanical model with standard linear solid model. Boltzmann superposition principle is used to develop the constitutive equations. First, the strain associated with a relaxation experiment is considered, and then by using the idea of linearity as embodied in the Boltzmann superposition principle, the resulting stress history is predicted. Eventually, the creep function corresponding to the relaxation modulus is obtained and the hysteresis loop for nanocomposite material is represented. Creep response is sinusoidal in time and a function of stress history. Loss and storage modulus and material behavior in Laplace domain are obtained using standard linear solid model and SUC micromechanical model, respectively. Standard linear solid model is achieved by paralleling the Kelvin model with Maxwell model. The model is validated with experimental results. Effects of different interphase thickness, CNT volume fraction and phase angle on hysteresis loop is studied. Obtained results reveal that increasing the CNT volume fraction and phase angle leads to decreasing and increasing the nanocomposite hysteresis loop area, respectively. Also, Interphase thickness contains considerable effects on the nanocomposite dynamic behavior.