Papers by Keyword: Pinholes

Abstract: Various defects on the CNT wall have been reported, which are formed during the synthesizing process. CNTs have superior properties compared to the traditional engineering materials. However, these properties hold only for the ideal case of carbon nanotubes, where these are made of perfect hexagonal graphite honeycomb lattice of mono-atomic layer thickness. The advantages or disadvantages of the presence of defects in carbon nanotubes depend on their applications. Structural defects may increase the adhesion of other atoms and molecules to carbon nanotubes. It has also been found that the defects in CNT do cause a change in its resonant frequency as compared to that of a non-defective CNT. The defects that have been considered for the purpose of analysis in this research includes defects in the carbon nanotubes likewise Waviness, Vacancy Defect, Pinhole Defect, Fracture and Stone Wales Defect. It has been observed that with the increase in the number of defects in CNT, a reduction in the fundamental frequency is observed.

Abstract: This study investigates the shape evolution of the pinholes on the bloom surfaces, which are originated from the continuous casting process, during multi-pass hot bar rolling. It is important to track the shape evolution of the pinholes since they can be formed as the sharp surface cracks after hot bar rolling and can initiate the surface bursts in the cold forging process. It is very hard to track the deformation behavior of the pinholes with detection tools during hot rolling, so the numerical simulations can be properly utilized. In general, the size of the pinholes in the bloom surface is order of micrometer although the bloom size is order of millimeter. This size discrepancy between them makes it difficult to discretize the domain including the pinholes for the finite element (FE) simulations. To overcome this limitation of the conventional FE simulation, multi-scale technique coupling the macro and micro models was developed in current study. This technique was implemented into the commercial simulation code, DEFORM-3D. The developed multi-scale simulation technique was capable of simulating the shape evolution of the pinholes through multi-pass hot bar rolling successfully. It is concluded that aspect ratio of the initial pinhole should be larger than 2.0 approximately to prevent it folded.