Chuang Feng

Investigation of uniaxial stretching effects on the electrical conductivity of CNT-polymer nanocomposites

A theoretical study is carried out to investigate the effects of uniaxial stretching on the electrical conductivity of carbon nanotube (CNT)–polymer composites using a mixed micromechanics model, which incorporates two conductivity mechanisms: electron hopping and conductive networks. The uniaxial stretching induces volume expansion of the composites, re-orientation of CNTs and a change in conductive networks, which are characterized by the variation of the CNT concentration, the CNT orientation distribution function and the percolation threshold, respectively. Modelling results demonstrate that stretching decreases the electrical conductivity of the composite in both the longitudinal and transverse directions. It is also observed that stretching has more significant effects on the electrical conductivity of the composites with a lower CNT volume fraction. Furthermore, the effects of Poissons ratio on the electrical conductivity are also investigated. Possible reasons for the observed phenomena are interpreted. This work can be claimed to provide a theoretical prediction on the trend of the stretching effects on the electrical properties of CNT–polymer composites.

Micromechanics Modeling of Bi-Axial Stretching Effects on the Electrical Conductivity of CNT-Polymer Composites

In this paper, the bi-axial stretching effects on the electrical conductivity of carbon nanotube (CNT)-polymer composites are studied by a mixed micromechanics model with the consideration of the electrical conductive mechanisms. The bi-axial stretching effects are characterized by volume expansion of composite, re-orientation of CNTs and change of conductive networks. Simulation results demonstrate that the bi-axial stretching decreases the electrical conductivity of the composites due to the dominant role of the stretching-induced change in conductive networks, i.e., the increase in the percolation threshold, the separation distance among CNTs and the breakdown of the networks. It is also found that the bi-axial stretching enhances the decreasing rate of the electrical conductivity and increases the distribution randomness of the CNTs in the bi-axial stretching plane, as compared to a uni-axial stretching case. Furthermore, the dependency of the variation of electrical conductivity on the CNT concentration and sizes is also investigated. Possible reasons for the variation trends are interpreted. The study in this paper is expected to provide an increased understanding on the stretching effects upon the electrical conductivity of CNT-polymer composites.

Dynamic characteristics of a dielectric elastomer-based microbeam resonator with small vibration amplitude

An analytical model is developed in the current work to analyze the dynamic characteristics of a dielectric elastomer (DE)-based microbeam resonator. The ambient pressure effect is taken into account by using the squeeze-film theory. Based on the Euler–Bernoulli beam model, approximate analytical solutions for the quality factor (Q-factor) and the resonant frequencies of the resonator have been derived using Raleighs method for small amplitude vibration. The results indicate that the ambient pressure has significant effects on the Q-factor and the resonant frequency shift ratio, which represent the dynamic performance of the resonator. The active frequency tuning for such a resonator becomes feasible by changing the applied electrical voltage. It is found that high voltage is beneficial for improving the sensitivity of the resonator. However, high voltage may put the resonator at the risk of mechanical instability. The cut-off voltage for buckling has also been studied to predict the mechanical integrity of the resonator. This study is expected to be useful for design and applications of DE-based microresonators.

Dynamic Buckling of Thermo-Electro-Mechanically Loaded FG-CNTRC Beams

Functionally graded carbon nanotube reinforced nanocomposites have drawn great attention in both research and engineering communities. The weak interfacial bonding between carbon nanotubes and the matrix, which traditionally hinders the application of carbon nanotube reinforced nanocomposites, can be remarkably improved through the graded distribution of carbon nanotubes in the matrix. Within the framework of classical beam theory, this paper investigates the dynamic buckling behavior of functionally graded nanocomposite beams reinforced by single-walled carbon nanotubes and integrated with two surface bonded piezoelectric layers. The governing equations of the beam subjected to an applied voltage, a uniform temperature and an axial periodic force are derived by applying Hamiltons principle. Numerical results are presented for beams with different distribution patterns and volume fractions of carbon nanotubes and end support conditions. The influences of the beam geometry, temperature change, applied voltage, static axial force component, boundary condition, carbon nanotube volume fraction and its distribution on the unstable regions of FG-CNTRC piezoelectric beams are discussed in detail.

Buckling of graphene platelet reinforced composite cylindrical shell with cutout

This paper investigates the buckling behavior of graphene platelets (GPL) reinforced composite cylindrical shells with cutouts via finite element method (FEM) simulation. Youngs modulus of the composites is determined by the modified Halpin-Tsai micromechanics model while the mass density and Poissons ratio of the composites are approximated by the rule of mixture. Comprehensive parametric study is conducted to investigate the effects of the weight fraction and the shape of GPL fillers, the geometry of the shell and the position and orientation of the cutout on the buckling behaviors of the cylindrical structures. The results demonstrate that the addition of GPLs can significantly increase the load bearing capacity of the cylindrical shells. Larger sized GPLs with fewer single graphene layers are favorable reinforcing fillers in enhancing the buckling performances of the structures. The buckling load is sensitive to the location of the cutout with larger aspect ratio. Moreover, the orientation of the cutout is found to have significant effects on the buckling load when the orientation angle (Formula presented.) is falling within the ranges - (Formula presented.)/2 (Formula presented.) - (Formula presented.)/4 and (Formula presented.)/4 (Formula presented.)/2.

Nonlinear Vibration Analysis of a Dielectric Elastomer Based Microbeam Resonator

Dynamic characteristics of a dielectric elastomer based micro beam resonator are investigated by taking into consideration of squeeze-film damping, large deformation and electrical voltage. The analysis shows that the resonant frequency of the resonator can be tuned through changing applied electrical voltage. It is observed that the natural frequency of the resonator increases with the increase of the vibration amplitude. In addition, the ambient pressure can significantly alter the resonant frequency of the resonator. The analysis is envisaged to provide qualitative predictions and guidelines for design and application of DE-based micro resonators.