T.C. Theodosiou

Numerical Simulations Using a Molecular Mechanics-based Finite Element Approach: Application on Boron-Nitride Armchair Nanotubes

Boron-nitride nanotubes can be thought of as rolled sheets of plane hexagonal boron-nitride. In this paper a computationally efficient modeling approach is pursued. The honeycomb-like structure of the lattice is exploited and a special finite element is developed based on this hexagonal pattern. The internal energy is calculated using semi-empirical molecular mechanics functions and energy minimization algorithms are applied in order to obtain the equilibrium state under various loading conditions. Results are found to be in agreement with data found in the open literature. The introduced modeling approach provides a computationally efficient way to analyze nanotubes without the need of large-scale simulations, while it does not require lattice periodicity and structural perfection.

Piezoresistive behavior of CNT nanocomposites using atomistic and micromechanics models

In carbon nanotube (CNT) polymer nanocomposites (PNC), the formation of conductive CNT networks results in electrical conductance and piezoresistive behavior. The latter occurs as applied strain affects the electric properties of the nanotubes. Modeling of piezoresistive behavior is investigated in two discrete scales. At the nanoscale, where for the prediction of the CNT piezoresistive behavior the Tight-Binding approximation is employed together with the Miller- Good approximation. At the microscale where percolation is studied using both two- and three- dimensional models and as well as the differences in resultant predictions. Numerical results at both scales are presented.

Molecular mechanics simulations of graphene using finite elements

This paper demonstrates a modelling approach for graphene and related nanostructures by embedding molecular mechanics equations into finite element codes. Atomistic interactions are modelled using specialty finite elements, based on analytical expressions of molecular mechanics equations. The major advantages of the proposed approach can be summarised as: (i) direct integration into well-established software; (ii) more realistic representation than other similar approaches; and (iii) user-friendly way to create an atomistic structure. Examples of incorporating the developed finite elements into Abaqus are also demonstrated. The introduced approach does not claim to replace other well-established molecular mechanics/dynamics software, but to provide a more intuitive structural modelling approach for graphene.

An Explicit Time Domain Spectral Finite Element for Guided Wave SHM in Composite Plate Strips with Physically Modelled Active Piezoelectric Sensors

A novel explicit time domain spectral finite element is developed which enhances the simulation accuracy and efficiency of active guided wave based SHM systems for laminated composite strips, in three distinct ways. A new generalized theoretical framework is formulated for piezolaminates which captures symmetric and antisymmetric Lamb waves by employing third-order Hermite polynomials in the approximation of displacements and electric potential through the thickness. The physical presence of piezoelectric actuators and sensors is encompassed in the governing equations. Stiffness, mass, piezoelectric and electric permittivity matrices are assembled, and the coupled transient electromechanical response is predicted by a properly formulated explicit time integration scheme. The excellent accuracy and computational efficiency of the developed FE is first validated against reported numerical results. Additional correlations are presented with measured Lamb wave responses generated by PZT active sensor pairs on carbon/epoxy plate strips. doi: 10.12783/SHM2015/106

A Finite Wavelet Domain Method for the Rapid Simulation of Wave SHM Systems in Composite Plate Strips for Impact and Damage Detection

A computationally efficient numerical method is developed for the prediction of transient response phenomena in composite structures including guided wave propagation and impact. The method takes advantage of the outstanding properties of compactly supported Daubechies wavelet scaling functions and their capability to provide global-local spatial approximations of displacements in specified finite domains of the structure, hence is termed Finite Wavelet Domain method. The theoretical background and numerical formulation are summarized. Its advantages are outlined, including the capability to provide consistent diagonal mass matrices. Formulations for the simulation of impact events and active guided wave generation are presented. Numerical results are shown for two distinct cases of transient dynamic problems: anti-symmetric and symmetric straight-crested wave (S and A ) propagation in composite plate structures generated by piezoelectric actuators; and simulation of impact events and impact detection. Comparisons against traditional finite elements quantify the benefits in computational time, convergence rate and accuracy of the new method. doi: 10.12783/SHM2015/222

Investigation of the Electromechanical Sensory Potential of CNT-Polymer Nanocomposites Using Nano- and Micro-Scale Models

This paper presents a modeling framework, in the context of which the electric conductance of a CNT-Polymer nanocomposite subjected to known mechanical loads can be modeled. Both nano- and micro- scale models are implemented in order to study the various phenomena, that take place; CNT properties are predicted using atomistic and subatomic models, while composite properties and percolation eects are investigated using micromechanics. Results show a great potential for the CNTs to be used as sensory devices.