Showing papers by "S. P. Harsha published in 2012"

Effect of carbon nanotube orientation on the mechanical properties of nanocomposites

Abstract: Carbon nanotubes (CNTs) have been regarded as ideal reinforcements of high-performance composites with enormous applications. In this paper, nano-structure is modeled as a linearly elastic composite medium, which consists of a homogeneous matrix having hexagonal representative volume elements (RVEs) and homogeneous cylindrical nanotubes with various inclination angles. Effects of inclined carbon nanotubes on mechanical properties are investigated for nano-composites using 3-D hexagonal representative volume element (RVE) with short and straight CNTs. The CNT is modeled as a continuum hollow cylindrical shape elastic material with different angles. The effect of the inclination of the CNT and its parameters is studied. Numerical equations are used to extract the effective material properties for the hexagonal RVE under axial as well as lateral loading conditions. The computational results indicated that elastic modulus of nano-composite is remarkably dependent on the orientation of the dispersed SWNTs. It is observed that the inclination significantly reduces the effective Young’s modulus of elasticity under an axial stretch. When compared with lateral loading case, effective reinforcement is found better in axial loading case. The effective moduli are very sensitive to the inclination and this sensitivity decreases with the increase of the waviness. In the case of short CNTs, increasing trend is observed up to a specific value of waviness index. It is also found from the simulation results that geometry of RVE does not have much significance on stiffness of nano-structures. The results obtained for straight CNTs are consistent with ERM results for hexagonal RVEs, which validate the proposed model results.

Vibration based performance prediction of ball bearings caused by localized defects

Abstract: This paper is focused on accurate performance prediction due to localized defects (like spalls) of microns level on the bearing components, which is essential to the design for high performance. In the mathematical formulation, the contacts between the rolling elements and the races are considered as nonlinear springs, whose stiffnesses are obtained by using Hertzian contact deformation theory. The formulation predicts the discrete spectra with the characteristic defect frequencies and their harmonics, which is helpful in prediction of system stability and to avoid severe (chaotic) vibrations in a rotor bearing system. The results are presented in the form of bifurcation diagrams, Fast Fourier Transformation (FFT) and Poincare maps for individual defects of bearing components. The system also shows the three different categories of system behavior under nonlinear dynamic conditions.

Vibration-based fault diagnosis of a rotor bearing system using artificial neural network and support vector machine

Abstract: This paper presents the vibration analysis of the healthy and cracked rotor supported on various faulty bearings. In rotating machines, one of the main causes of breakdown is faults in ball bearings. This study is mainly focused on fault diagnosis of rotor bearing system using artificial neural network (ANN) and support vector machine (SVM). The vibration response is obtained and analysed for the healthy and cracked rotor with the various defects of ball bearings. The specific defects considered on bearings are: crack in outer race, inner race with spall and corrosion pitting in balls. Statistical methods are used to extract features and to reduce the dimensionality of original vibration features. A comparative experimental study of the effectiveness of ANN and SVM is carried out. The results show that for this study, ANN is a better classifier than SVM.

Ann based fault diagnosis of rolling element bearing using time-frequency domain feature

Abstract: This paper presents a methodology for an automation of fault diagnosis of ball bearings having localized defects (spalls) on the various bearing components. The system uses the wavelet packet decomposition using ‘rbio5.5’ real mother wavelet function for feature extraction from the vibration signal, recorded for various bearing fault conditions. The decomposition level is determined by the sampling frequency and characteristic defect frequency. Maximum energy to minimum Shannon entropy ratio criteria is used for selection of best node of wavelet packet tree. The two features kurtosis and energy are extracted from the wavelet packet coefficient for selected node of WPT. The total 10 data sets at five different speeds corresponding to each bearing condition are recorded for fault classification. Thus, extracted features are used to train and test neural network with multi layer perceptron to classify the rolling element bearing condition as HB, ORD, IRD, BD and CD. The proposed artificial neural network with multi layer perceptron classifier has overall fault classification rate of 97 %.

Chaotic response analysis of single-walled carbon nanotube due to surface deviations

Abstract: Nonlinear vibrational behavior of a single-walled carbon nanotube based mass sensors is considered The modeling involves stretching of the mid plane and damping The equation of motion involves two nonlinear terms due to the curved geometry and the stretching of the central plane due to the bridged boundary conditions The manifestation of instability and chaos in the dynamic response is observed The regions of periodic, sub-harmonic and chaotic behavior are clearly seen to be dependent on added mass and the surface deviations Poincare maps and frequency spectra are used to explicate and demonstrate the miscellany of the system behavior

Mass detection using single walled boron nitride nanotube as a nanomechanical resonator

Abstract: The feasibility of the Boron Nitride Nanotubes (BNNTs) as nanomechanical resonators, using continuum mechanics based approach and finite element method (FEM) is illustrated in this paper. Two types of end constraints of single walled boron nitride nanotubes (SWBNNTs), namely cantilevered and bridged are assumed. Analytical formulas based on continuum mechanics are used to examine the mass sensitivity of SWBNNTs considering as a thin wall tubes for both types of end constraints for different lengths and different diameters. The FEM analysis, considering SWBNNT as a transversely anisotropic material is performed and results are compared with the continuum mechanics based approach. The results indicated that the mass sensitivity of SWBNNT-based nanomechanical resonators can reach 10-8 fg and a logarithmically linear relationship exists between the resonant frequency and the attached mass, when mass is larger than 10-7 fg. The sensitivity of resonant frequency shift to both tube length and diameter has also been demonstrated. It is clear that the change in resonant frequency shift to tube length is more significant than that with the tube diameter and mass sensitivity increases when smaller size nanotube resonators are used in mass sensors. The simulation results based on present FEM found in good agreement with the analytical approach.

A multiscale approach for estimating the chirality effects in carbon nanotube reinforced composites

Abstract: In this paper, the multiscale representative volume element approach is proposed for modeling the elastic behavior of carbon nanotubes reinforced composites. The representative volume element incorporates the continuum approach, while carbon nanotube characterizes the atomistic approach. Space frame structure similar to three dimensional beams and point masses are employed to simulate the discrete geometrical constitution of the single walled carbon nanotube. The covalent bonds between carbon atoms found in the hexagonal lattices are assigned elastic properties using beam elements. The point masses applied on each node are coinciding with the carbon atoms work as mass of beam elements. The matrix phase is modeled as a continuum medium using solid elements. These two regions are interconnected by interfacial zone using beam elements. Analysis of nanocomposites having single walled carbon nanotube with different chiralities is performed, using an atomistic finite element model based on a molecular structural mechanics approach. Using the proposed multi scale model, the deformations obtained from the simulations are used to predict the elastic and shear moduli of the nanocomposites. A significant enhancement in the stiffness of the nanocomposites is observed. The effects of interfacial shear strength, stiffness, tensile strength, chirality, length of carbon nanotube, material of matrix, types of representative volume elements and types of loading conditions on the mechanical behavior of the nanocomposites are estimated. The finite element results are compared with the rule of mixtures using formulae. It is found that the results offered by proposed model, are in close proximity with those obtained by the rule of mixtures.

Dynamic analysis of fixed-free single-walled carbon nanotube-based bio-sensors because of various viruses

Abstract: In the present study, the vibrations of the fixed-free single-walled carbon nanotube (SWCNT) with attached bacterium/virus on the tip have been investigated. To explore the suitability of the SWCNT as a bacterium/virus detector device, first the various types of virus have been taken for the study and then the resonant frequencies of fixed-free SWCNT with attachment of those viruses have been simulated. These resonant frequencies are compared with the published analytical data, and it is shown that the finite element method (FEM) simulation results are in good agreement with the analytical data. The results showed the sensitivity and suitability of the SWCNT having different length and different masses (attached at the tip SWCNT) to identify the bacterium or virus.

Energy optimal trajectory planning of an underwater robot using a genetic algorithm

Abstract: This paper presents optimal trajectory planning for an autonomous underwater robot. The optimization parameter is taken as the energy consumed by the robot to traverse its arm tip from a predefined...

Interference in Reading E-Paper under Whole- Body Vibration Exposure with Subject Posture

Abstract: There is increasing use of laptop computer in rail vehicles for performing various sedentary activities such as reading and typing. The vibration is a major factor influencing the reading performance during the journey. Therefore, an experimental study was conducted to investigate the extent of interference perceived in reading an e-paper in two seated postures (backrest support and leaning over the table) under random vibration. The study involved 30 healthy male subjects who were excited with vibration acceleration in mono-, dual, and multi-axes in 1–20 Hz at 0.4, 0.8, and 1.2 m/s amplitudes. The task consisted of reading the given paragraph of an e-paper under various vibration stimuli, and it was evaluated by time taken to complete the task and subjective evaluation of reading difficulty. The subjective evaluation showed that the reading difficulty increased with vibration stimuli for both the subject postures. The subjects perceived higher difficulty and degradation in reading performance for vibration in dual and multi-axes, which was comparable to that for lateral and vertical directions also. The perceived difficulty and impairment in reading performance was greater while reading with the laptop on their lap for vibration in the x-axis, while the effect was just the reverse for other axes.

Geometric non-linear analysis of thin flat membrane

Abstract: This paper present the model analysis for the predicating the behaviour of inflatable membrane structure of general L-shape with a thickness in millimetre using the various smart material which optimally within structural member subjected to prestressed rather than bending or moments. A numerical solution for membranes may also be found using the finite element method. In this paper flat thin membrane choose to analysis the behavioural effect of the membranes using the properties of different smart material and compare their results in terms of frequency and generalized mass with mode shape. This analysis makes more effective to selects the smart material in the space technology. Geometrically nonlinear Vibration analysis of arbitrary L-shape membrane is also done using a finite element package, ABAQUS. The analysis shows good agreement between finite element and analytical solutions.

Wrinkling Dynamics of Membrane Based on User Defined Wrinkle Pattern

Abstract: In this paper, a wrinkling algorithm is described to simulate realistic wrinkles on the membrane for large computational overheads. The membrane has very little in-plane deformations and most of the deformations come from buckling. The formulation of the deformed area due to symmetric loading uses the modulated method to ensure or characterize the user defined wrinkle pattern which is based on deformation of individual triangle. The methodology facilitates the use of small in-plane deformation stiffness's and a coarse mesh for the numerical simulation. This approach has been validated using the numerical simulation considering the different symmetric loading condition on the particular triangular shaped element. Moreover, the ability to design wrinkles (even on generalized deformable models) makes this method more versatile.