Effect of SEBS on water treeing behaviors of cross-linked polyethylene
We investigated the effect of an aromatic polymer, styrene-(co-ethylene-butadiene)-styrene (SEBS), on water tree resistance of cross-linked polyethylene (XLPE). The XLPE/SEBS samples were characterized by means of gel content determination, different scanning calorimetry (DSC), scanning electron microscopy (SEM) and the accelerated water treeing experiment. Our results clearly indicated that the samples with SEBS showed improved water tree resistance in comparison to blank samples. It was also found that the blends had excellent dielectric property form the viewpoint of practical application.
Electrical properties of chemically modified polyethylenes
This report describes electrical properties such as space charge distribution, water treeing characteristics and ac breakdown strength in PE (polyethylene) modified by grafting and blending techniques. A control PE shows heterocharge. In AA (acrylic acid)-grafted PE (LDPE-g-AA), the heterocharge observed in PE decreases at low AA contents and homocharge is observed at high AA contents. In NBA (n-butyl acrylate)-grafted PE (LDPE-g-NBA), on the other hand, this heterocharge gets larger at all graft ratios to 0.12%. However, these components decrease the water tree length measured under specific conditions and increase ac breakdown strength. Details of the results are described and their origins are discussed. The results obtained with the LDPE-g-NBA are compared with those of PE/ethylene NBA copolymer blends.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME