Non contact wear measurement on pneumatic seals
Abstract An experimental methodology aimed at the evaluation of wear in pneumatic seals is presented. New equipment was designed and manufactured in order to measure the radial thickness of worn material on the sealing edge both axially and circumferentially, by means of a laser sensor, as well as to avoid the necessity of disassembling the seals. The methodology is intended as an instrument for a quick comparison of seal prototypes and is proposed as an alternative to those methods that globally quantify the wear of samples by measuring their loss of weight or volume. Results obtained on a NBR commercial lip seal are presented.
Tribological testing of peroxide-cured EPDM rubbers with different carbon black contents under dry sliding conditions against steel
The friction and sliding wear behaviors of peroxide-cured ethylene/propylene/diene rubbers (EPDM) were studied against steel counterparts under dry conditions. The carbon black (CB; N347 type) content of the EPDM rubbers was varied between 0 and 60 parts per hundred parts rubber (phr). For their tribotesting, different test configurations, viz. pin(steel)-on-plate(rubber) (POP) and roller(steel)-on-plate(rubber) (ROP), were used and their oscillation wear behavior (fretting) studied, too. The EPDM rubbers were characterized using dynamic-mechanical thermal analysis (DMTA), hardness, tensile and tear tests. The coefficient of friction (COF), volume loss and specific wear rate of the EPDM rubbers were determined. It was found that with increasing CB content all above characteristics were reduced. However, the COF and wear parameters strongly depended on the related test configuration. The wear mechanisms were concluded by inspecting the worn surfaces in scanning electron microscope (SEM) and discussed.
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