CNT Waviness Research Articles

Numerical analysis of elastic–plastic properties of polymer composite reinforced by wavy and random CNTs

A geometric generation algorithm is proposed to produce the 3D finite element model to analyze the polymeric composite with randomly dispersed and wavy CNTs, typical in CNT/polymer composite. Considering the model randomness, the statistical criterion has been employed to determine the sample capacity, and then the critical size of FE models has been determined based on the degree of departure from isotropy and the statistical inhomogeneity. Moreover, a comparison is conducted among five types of FE models when CNT distribution is completely random; the differences are not evident among their predictions. However, when predicting the micro-field distribution inside materials, the beam models present a huge difference to the solid models. Furthermore, we explore the effect of the CNT length, orientation and waviness on the elastic–plastic properties of composite by using the FE model describing CNTs as effective continuum solid fibers, and then compare the FE predictions with experimental data.

Mechanical testing and modelling of a vertically aligned carbon nanotube composite structure

Abstract Recent advances have shown effective reinforcement of a polymer matrix using vertically aligned carbon nanotube (VACNT) forests grown using chemical vapour deposition (CVD). Such structures are known to wet readily through capillary interactions to form fully wetted composites that retain the dispersion and alignment of the CNT within the matrix thus overcoming two major problems in CNT composite production. So far VACNT composite fabrication has been limited by available forest size and as a result mechanical characterisation of such materials has been restricted and has generally been conducted using nanoindentation techniques. In this work VACNT composite samples are produced that are of a sufficiently large size to conduct Dynamic Mechanical Thermal Analysis (DMTA) in single cantilever mode allowing macroscale testing of the complete composite sample. Results from experiments are compared to current VACNT composite modelling techniques that consider CNT waviness which is known to exist within such composite samples. Previously the effects of as grown VACNT waviness have been considered detrimental to the overall mechanical properties of these novel composites as analysis has typically been conducted in the axial direction where applied load and VACNT axis are parallel. In this work a positive effect on sample modulus resulting from VACNT waviness has been found in the transverse plane, perpendicular to the CNT axis. Specifically an increase in modulus of over 20% is observed with only a 2 vol.% CNT loading and is in agreement with wavy CNT composite modelling.

The effect of interfacial shear strength on damping behavior of carbon nanotube reinforced composites

The effect of interfacial shear strength (ISS) on the mechanical and damping properties of carbon nanotube reinforced composites (CNT-RCs) is investigated in the present study using a multiscale simulation. The atomic lattice of CNTs is modeled with the modified molecular structural mechanics (MMSM) approach and reduced to an equivalent beam element (EBE) which is used as the basic building block for the construction of full length CNTs embedded in the polymer. Linear material properties are assigned to the EBEs, while a Maxwell–Wiechert material model is used for modeling the viscoelastic behavior of the polymer. The interfacial load transfer mechanism between the lateral surface of the carbon nanotube and the surrounding matrix is taken into account with a nonlinear bond-slip friction-type model. Finite element models of representative volume elements (RVEs) are constructed comprised of two independent meshes: a structured with solid elements for the matrix and a series of embedded EBEs for the full length CNTs inside the matrix. Straight as well as wavy CNTs are considered. In the case of wavy CNTs, random CNT geometries are generated using the spectral representation method with evolutionary power spectra (EPS) which are derived from processing scanning electron microscope (SEM) images. Stochastic average properties were derived with Monte Carlo simulation. The mechanical and damping properties of the CNT-RCs are assessed on the basis of sensitivity analyses with respect to various weight fractions and interfacial shear strength (ISS) values. Numerical results are presented, showing the significant effect of the ISS as well as the influence of CNT waviness on the damping behavior of CNT-RCs.