A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering 25 May 2017 / Two of the main contributors to high voltage insulation failure are thermal and electrical stresses. The failures may be mitigated by using nanodielectrics. The enhanced effect of nanoparticles in nanodielectrics is attributed to an interaction zone/interphase around each individual nanoparticle between the nanoparticle and host polymer. However, particle clumping or agglomerates are a major challenge in nanodielectric technology. In this work mitigation of the clumping challenges was explored through Rheology in determining optimal particle loading levels. The nanodielectrics studies were Boron Nitride and Carbon Nanospheres in Araldite Epoxy. The rheology results indicated an optimal loading level of 1.09 vol % to 1.35 vol% for Boron Nitride in Epoxy and 0.33 vol% for Carbon Nanospheres in Epoxy. Microscopy, dielectric spectroscopy, electrical tree characterisation, thermal expansion and laser flash analysis were used to validate the efficacy of the rheology results. The results indicated improved properties of the resultant dielectric such as; increased mechanical stiffness, increased electrical resistance and the percolation threshold, partial discharge suppression and increased thermal conductivity at the glass transition temperature. This study has established a rheology-based technique incorporated in the manufacturing process to determine the optimal filler loading of C/Epoxy and BN/Epoxy nanodielectrics. Future work is recommended as investigating either new particle types such as Sulphur hexafluoride in Carbon Nanospheres or mixtures of Carbon Nanospheres and Boron Nitiride. / MT 2017

In this investigation, polymer precursor of syntactic foam has been reinforced with SiC nanoparticles to enhance mechanical and fracture properties. Derakane 8084 vinyl ester resin was first dispersed with 1.0 wt% of SiC particles using a sonic cavitation technique. In the next step, 30.0 wt% of microspheres (3M hollow glass borosilicate, S-series) were mechanically mixed with the nanophased vinyl ester resin, and cast into rectangular molds. A small amount of styrene was used as dilutant to facilitate mixing of microspheres. The size of microspheres and SiC nanoparticles were 20-30 um and 30-50 nm, respectively. Tension, compression, and flexure tests were conducted following ASTM standards and a consistent improvement in strength and modulus within 20-35% range was observed. Fracture toughness parameters such as KIC and GIC were also determined using ASTM E-399. An improvement of about 11-15% was observed. Samples were also subjected to various environmental conditions and degradation in material properties is reported. / by Debdutta Das. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

In this work, epoxy resins were modeled using all atom representations in nanoscale simulation boxes. Tetrafunctional epoxy and corresponding multifunctional amine were chosen as model materials. Algorithms of constructing interconnected network structures were invented developed to properly account for the chemical structures and computational cost. Monomers were generated in diamond lattice and crosslinked to model complex epoxy multifunctional network. The initial configurations were relaxed and equilibrated using molecular dynamics and suitable force field. Physical, thermal and mechanical properties resulting from equilibrated simulation box are in good agreement with experimental results. Possible impact of chemical degradation was studied by adopting oxidation and hydrolysis algorithms. Mechanism of degradation was based on bonds reaction probability and chemical structures of epoxies. Both oxidation and hydrolysis were found to decrease materials performances by reducing number of crosslinking points. Elastic modulus of materials was directly related to crosslinking density. Interfaces between two types of epoxies were constructed to study interactions at interfaces. Covalent bonds linking two components play an important role in interfacial strength. Free volume calculation helps to identify and monitor nucleation of crazes and voids within materials. It was found voids and cracks prefer to initiate and grow at 2 interfaces and lead to failures. Additional compatibilizer layers can improve overall composite performances by preventing void growth at interfaces. Diffusion pattern of water in epoxy resins was studied by tracking displacement of single molecules during certain time intervals. The characteristic of water diffusion in epoxies was interpreted by free volume theory. Reactive force field was introduced to study thermal degradation behavior of epoxy resins. Number of molecules and variation of different types of covalent bonds during heating processes were tracked and analyzed to uncover the degradation mechanism of epoxy resins.

Thesis (M.S.)--Mississippi State University. Department of Chemical Engineering. / Title from title screen. Includes bibliographical references.

M. Tech. Engineering: Chemical. / Aims to establish the cure kinetics of the thermosetting systems through the use of rheology and differential scanning calorimetry. Dynamic mechanical and thermal mechanical analyses will be used to ascertain the mechanical properties. The resistance to thermal degradation will be determined by thermogravimetric analysis.

No description available.

The application of laser generated ultrasonics was first demonstrated in the mid-seventies and has shown good potential when applied to isotropic materials. However, its use with composite materials is still in the early stages of development. This study explores the potential for application of laser generated Rayleigh and Lamb waves in graphite/epoxy composites. Numerical results are obtained by the solution of the wave equations using assumed solutions, and enforcing the boundary conditions. Experimentally, Rayleigh and Lamb waves were generated by a Q-switched ruby laser in the ablation regime and detected by piezoelectric pinducers which permitted accurate phase velocity measurements. The Rayleigh wave velocity was measured at various directions relative to the fiber direction and results were found to agree closely with numerical predictions. The increase of surface wave velocity using thin plates could be useful for the application of delamination detection in thick composites and an increase of Rayleigh wave attenuation could indicate damages caused by impact. Also, surface waves can reflect from small surface cracks. Therefore, laser generated surface waves, particularly along the fiber direction, have high potential for application in non-destructive testing. Lamb wave experiments were conducted in aluminum plates and gave distinctive signals, but there were some difficulties in detecting the precise arrival of each Lamb wave mode for the graphite/epoxy composite plates. / Graduation date: 1992

Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Engineering, 2007. / "May, 2007." Title from electronic dissertation title page (viewed 04/07/2008) Advisor, Erol Sancaktar; Committee members, Avraam I. Isayev, Sadhan C. Jana, Darrell H. Reneker, Shing-Chung Wong; Department Chair, Sadhan C. Jana; Dean of the College, George R. Newkome; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Thesis (M.Eng.). / Written for the Dept. of Civil Engineering and Applied Mechanics. Title from title page of PDF (viewed 2008/05/13). Includes bibliographical references.

Thesis (M.S.)--University of Michigan, 1986.