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VIBRATION ANALYSIS OF CARBON NANOTUBE USING CONTINUUM MODEL AND FINITE ELEMENT MODEL
Title
VIBRATION ANALYSIS OF CARBON NANOTUBE USING CONTINUUM MODEL AND FINITE ELEMENT MODEL.
Creator
Subramaniam , Hari, Wang, Quan, University of Central Florida
Abstract / Description
The main objective of the thesis is to propose the methods of determining vibration behavior of carbon nanotubes (CNTs) using continuum models and finite element models. Secondary objective is to find the effect of van der Waals force on vibration of multiwalled carbon nanotubes . The study of vibration behavior of CNTs is important because of their potential engineering applications such as nano-mechanical resonators and tips of scanning probe instruments where they are subjected to...
Show moreThe main objective of the thesis is to propose the methods of determining vibration behavior of carbon nanotubes (CNTs) using continuum models and finite element models. Secondary objective is to find the effect of van der Waals force on vibration of multiwalled carbon nanotubes . The study of vibration behavior of CNTs is important because of their potential engineering applications such as nano-mechanical resonators and tips of scanning probe instruments where they are subjected to mechanical vibrations. Continuum modeling is based on an elastic beam model. The interlayer van der Waals interactions are represented by Lennard-Jones potential. In finite element modeling, single walled nanotubes (SWNTs) are modeled as finite beam elements and multi-walled nanotubes (MWNTs) as finite solid elements. The interlayer van der Waals interactions are simulated by distributed springs. The proposed finite element approach and continuum approach for vibration analysis of CNTs are verified by comparing the results with experimental and analytical results available in the literature. The results from both continuum and finite element modeling show that the effect of van der Waals force on vibration of MWNTs are high for smaller aspect ratios irrespective of boundary conditions and number of layers; fixed nanotube than cantilever nanotube for the same dimensions ; five-walled nanotube than a double walled nanotube for the same aspect ratio.
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Date Issued
2005
Identifier
CFE0000735, ucf:46555
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000735
FINITE ELEMENT SIMULATION OF REPAIR OF DELAMINATED COMPOSITE STRUCTURES USING PIEZOELECTRIC LAYERS
Title
FINITE ELEMENT SIMULATION OF REPAIR OF DELAMINATED COMPOSITE STRUCTURES USING PIEZOELECTRIC LAYERS.
Creator
Navale, Kunal, Wang, Quan, University of Central Florida
Abstract / Description
Damage in composite material fabricated aerospace, aeronautical, mechanical, civil and offshore structures often results from factors such as fatigue, corrosion and accidents. Such damage when left unattended can grow at an alarming rate due to the singularity of the stress and strain in the vicinity of the damage. It can lead to increase in the vibration level, reduction in the load carrying capacity, deterioration in the normal performance of the component and even catastrophic failure. In...
Show moreDamage in composite material fabricated aerospace, aeronautical, mechanical, civil and offshore structures often results from factors such as fatigue, corrosion and accidents. Such damage when left unattended can grow at an alarming rate due to the singularity of the stress and strain in the vicinity of the damage. It can lead to increase in the vibration level, reduction in the load carrying capacity, deterioration in the normal performance of the component and even catastrophic failure. In most conditions, the service life of damaged components is extended with repair instead of immediate replacement. Effective repair of structural damage is therefore an important and practical topic. Repair can extend the service life and can be a cost efficient alternative to immediate replacement of the damaged component. Most conventional repair methods involve welding, riveting or mounting additional patches on the parent structure without removing the damaged portion. These methods tend to be passive and inflexible, faced with the limitations of adjusting the repair to the changes in external loads.Besides, in certain cases these methods may lead to additional damage to the structure. For example, the in-situ drilling required in some cases can cause damage to items such as hidden or exposed hydraulic lines and electrical cables. Welding or bonding patches can cause significant stress alterations and serious stress corrosion problems, apart from burdening the weight sensitive structures. Above all, effective repair applying conventional analytical methods hinges on calculation of the singularity of stress and strain in the vicinity of the damage, which is be a difficult as only approximate solutions are available. Thus, a need is felt to update the repair methods with the advancement in fields of materials, sensing and actuating. This can make the repair more effective and efficient than conventional repair methodology. Current research proposes the use of piezoelectric materials in repair of delaminated composite structures. A detailed mechanics analysis of the delaminated beams, subjected to concentrated static loads and axial compressive loads, is presented. The discontinuity of shear stresses induced at delamination tips due to bending of the beams, under action of concentrated static load and axially compressive load, is studied. This discontinuity of the shear stresses normally leads to the sliding mode of fracture of the beam structures. In order to ensure proper functioning of these beam structures, electromechanical characteristics of piezoelectric materials are employed for their repair. Numerical simulations are conducted to calculate the repair voltage to be applied to the piezoelectric patches to erase the discontinuity of horizontal shear stress at the delamination tips and thus, render the beam repaired. The variation of repair voltage with location and size of the delamination is considered. FE simulations are performed to validate the numerically calculated voltage values. The research presented serves to provide information on the design of piezoelectric materials for the repair of delaminated composite structures.
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Date Issued
2005
Identifier
CFE0000873, ucf:46662
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000873