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PERCOLATION STUDY OF NANO-COMPOSITE CONDUCTIVITY USING MONTE CARLO SIMULATIONPERCOLATION
Title
PERCOLATION STUDY OF NANO-COMPOSITE CONDUCTIVITY USING MONTE CARLO SIMULATIONPERCOLATION.
Creator
Bai, Jing, Lin, Kuo-Chi, University of Central Florida
Abstract / Description
A Monte Carlo model is developed for predicting electrical conductivity of carbon nanofiber composite materials. The conductive nanofibers are models as both 2D and 3D network of finite sites that are randomly distributed. The percolation behavior of the network is studied using the Monte Carlo method, which leads to the determination of the percolation threshold. The effect of the nanofiber aspect ratio on the critical nanofiber volume rate is investigated in the current model, each of the...
Show moreA Monte Carlo model is developed for predicting electrical conductivity of carbon nanofiber composite materials. The conductive nanofibers are models as both 2D and 3D network of finite sites that are randomly distributed. The percolation behavior of the network is studied using the Monte Carlo method, which leads to the determination of the percolation threshold. The effect of the nanofiber aspect ratio on the critical nanofiber volume rate is investigated in the current model, each of the nanofibers needs five independent geometrical parameters (i.e., three coordinates in space and two orientation angles) for its identification. There are three controlling parameters for each nanofiber, which includes the nanofiber length, the nanofiber diameter, and the nanofiber aspect ratio. The simulation results reveal a relationship between the fiber aspect ratio and the percolation threshold: the higher the aspect ratio, the lower the threshold. With the simulation results obtained from the Monte Carlo model, the effective electrical conductivity of the composite is then determined by assuming the conductivity is proportional to the ratio of the number of nanofibers forming the largest cluster to the total number of nanofibers. The numerical results indicate that as the volume rate reaches a critical value, the conductivity starts to rise sharply. These obtained simulation results agree fairly with experimental and numerical data published earlier by others. In addition, we investigate the convergence of the current percolation model. We also find the tunneling effect does not affect the critical volume rate greatly. We propose that the percolation model is not scalable as well.
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Date Issued
2009
Identifier
CFE0002644, ucf:48230
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002644
NONDESTRUCTIVE TESTING METHODS AIDED VIA NUMERICAL COMPUTATION MODELS FOR VARIOUS CRITICAL AEROSPACE AND POWER GENERATION SYSTEMS
Title
NONDESTRUCTIVE TESTING METHODS AIDED VIA NUMERICAL COMPUTATION MODELS FOR VARIOUS CRITICAL AEROSPACE AND POWER GENERATION SYSTEMS.
Creator
Warren, Peter, Ghosh, Ranajay, Raghavan, Seetha, Gou, Jihua, University of Central Florida
Abstract / Description
A current critical necessity for all industries which utilize various equipment that operates in hightemperature and extreme environments, is the ability to collect and analyze data via non destructivetesting (NDT) methods. Operational conditions and material health must be constantly monitoredif components are to be implemented precisely to increase the overall performance and efficiencyof the process. Currently in both aerospace and power generation systems there are many methodsthat are...
Show moreA current critical necessity for all industries which utilize various equipment that operates in hightemperature and extreme environments, is the ability to collect and analyze data via non destructivetesting (NDT) methods. Operational conditions and material health must be constantly monitoredif components are to be implemented precisely to increase the overall performance and efficiencyof the process. Currently in both aerospace and power generation systems there are many methodsthat are being employed to gather several necessary properties and parameters of a given system.This work will focus primarly on two of these NDT methods, with the ultimate goal of contributingto not only the method itself, but also the role of numerical computation to increase the resolutionof a given technique. Numerical computation can attribute knowledge onto the governing mechanicsof these NDT methods, many of which are currently being utilized in industry. An increase inthe accuracy of the data gathered from NDT methods will ultimately lead to an increase in operationalefficiency of a given system.The first method to be analyzed is a non destructive emmision technique widely referred to asaccoustic ultrasonic thermography. This work will investigate the mechanism of heat generationin acoustic thermography using a combination of numerical computational analysis and physicalexperimentation. Many of the challenges typical of this type of system are addressed in this work.The principal challenges among them are crack detection threshold, signature quality and the effectof defect interactions. Experiments and finite element based numerical simulations are employed,in order to evaluate the proposed method, as well as draw conclusions on the viability for futureextension and integration with other digital technologies for health monitoring. A method to determinethe magnitude of the different sources of heat generation during an acoustic excitation isalso achieved in this work. Defects formed through industrial operation as well as defects formedthrough artificial manufacturing methods were analyzed and compared.The second method is a photoluminescence piezospectroscopic (PLPS) for composite materials.The composite studied in this work has one host material which does not illuminate or have photoluminescenceproperties, the second material provides the luminescence properties, as well asadditional overall strength to the composite material. Understanding load transfer between the reinforcementsand matrix materials that constitute these composites hold the key to elucidating theirmechanical properties and consequent behavior in operation. Finite element simulations of loadingeffects on representative embedded alumina particles in a matrix were investigated and comparedwith experimental results. The alumina particles were doped with chromium in order to achieveluminscence capability, and therefore take advantage of the piezospectrscopic measurement technique.Mechanical loading effects on alumina nanoparticle composites can be captured with Photostimulated luminescent spectroscopy, where spectral shifts from the particles are monitored withload. The resulting piezospectroscopic (PS) coefficients are then used to calculate load transferbetween the matrix and particle. The results from the simulation and experiments are shown tobe in general agreement of increase in load transferred with increasing particle volume fractiondue to contact stresses that are dominant at these higher volume fractions. Results from this workpresent a combination of analytical and experimental insight into the effect of particle volume fractionon load transfer in ceramic composites that can serve to determine properties and eventuallyoptimize various parameters such as particle shape, size and dispersion that govern the design ofthese composites prior to manufacture and testing.
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Date Issued
2018
Identifier
CFE0007262, ucf:52203
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007262