Nandagopal Bhowmik

Micromechanical and Nanoscratch Behavior of SiCp Dispersed Metal Matrix Composites

Micromechanical response of silicon carbide particle dispersed Al/Mg/Ti/Cu composite, synthesized by powder metallurgy technique was investigated. A correlation between their microhardness and nanomechanical properties at submicron length scale was established. Hardening effect of SiC particles on the hardness, elastic modulus, recovery index, and plastic energy of the matrices was prominent and may be due to the interactions between geometrically necessary and statistically stored dislocations along with their impediment with dispersoids-matrix interface. The elastic recovery obtained from nanoscratch measurement was also correlated with the recovery parameter, which was derived from the nanoindentation of the composite compacts.

Effect of Space Charge Density and High Voltage Breakdown of Surface Modified Alumina Reinforced Epoxy Composites

The incorporation of 90 nm alumina particles into an epoxy matrix to form a composite microstructure is described in present study. It is shown that the use of ultrafine particles results in a substantial change in the behavior of the composite, which can be traced to the mitigation of internal charges when a comparison is made with conventional fillers. A variety of diagnostic techniques have been used to augment pulsed electro-acoustic space charge measurement to provide a basis for understanding the underlying physics of the phenomenon. It would appear that, when the size of the inclusions becomes small enough, they act cooperatively with the host structure and cease to exhibit interfacial properties. It is postulated that the particles are surrounded by high charge concentrations. Since particles have very high specific areas, these regions allow limited charge percolation through filled dielectrics. The practical consequences of this have also been explored in terms of the electric strength exhibited. It would appear that there was a window in which real advantages accumulated from the nano-formulated material. An optimum filler loading of about 0.5 wt.% was indicated.

Electromagnetic Interference Reflectivity of Nanostructured Manganese Ferrite Reinforced Polypyrrole Composites

Nano-size manganese ferrite reinforced conductive polypyrrole composites reveal a core-shell structure by in situ polymerization, in the presence of dodecyl benzene sulfonic acid as the surfactant and dopant, and iron chloride as the oxidant. The structure and magnetic properties of manganese ferrite nano-fillers were measured, by using X-ray diffraction and vibrating sample magnetometer. The morphology, microstructure, and conductivity of the composite were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, and four-wire technique. The microwave-absorbing properties of composites reinforcement dispersed in resin coating with the coating thickness of 1.2 nm were investigated, by using vector network analyzers, in the frequency range of 8~12 GHz. A reflection loss of -8 dB was observed at 10.5 GHz.