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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

An investigation of friction and wear mechanisms in selected thermoplastics

Potter, Joseph R. January 1983 (has links)
These studies developed from Scanning Electron Microscope (SEM) observations of abrasive wear of a polymer disk sliding against metal asperity models. The investigator was unable to observe actual particle formation but did identify elastic and plastic deformation of the polymer, and a debris buildup and extrusion process occurring at the leading edge of the asperity. On the assumption that this process could lead to a surface fatigue condition, pin-on-disk wear trials were completed using a spherical steel ball sliding on polycarbonate, rigid PVC, and ultra-high molecular weight polyethylene specimens in dry and lubricated conditions. A delay in debris formation was observed in the rigid PVC and polycarbonate dry sliding trials. In each case a higher rate of friction force increase coincided with debris formation. No debris was produced in the ultra-high molecular weight polyethylene dry sliding trials, and the friction force trace was flat. An SEM analysis of the polycarbonate and rigid PVC wear tracks revealed pitting consistent with the Delamination Theory of wear. The effect of the lubricants was to significantly alter the form of the friction force traces, but not to eliminate wear in rigid PVC and polycarbonate. The results of the investigation, particularly the delay in wear debris generation, indicated that a fatigue wear mechanism appeared to exist in dry metal pin-on-polymer disk sliding systems. A qualitative wear model was developed to relate the in-situ SEM observations and the results of the pin-on-disk trials. / M.S.
2

Nondestructive inspection of load induced damage in fiber reinforced polyphenylene sulfide

Fields, Richard Elliot January 1982 (has links)
The present work presents the results of an investigation of properties of polyphenylene sulfide (PPS) reinforced with random, continuous glass fibers, approximately 30% by weight. The investigation included both characterization of the mechanical properties and nondestructive inspection of the material. The objectives of the nondestructive inspection program were twofold: i) to determine nondestructive testing techniques were most responsive to developing damage and ii) to identify the damage modes using the nondestructive testing methods. The mechanical testing program involved the study of three types of specimens: straight sided tensile coupon, dogbone, and streamline. The streamline specimen typically fails in the narrow region and therefore appears to be relatively unaffected by stress concentrations induced by the specimen geometry. Results are given for all three specimen types and comparisons made for the measured mechanical properties. Several nondestructive testing methods, including C-scan, ultrasonic attenuation, acoustic emission, X-ray radiography, and edge replication, were applied to study the damage developed under quasi-static tension loading of this material. The C-scan, edge replication, and X-ray radiography tests were performed both initially and after intermediate stages of loading. These three tests appear to be unresponsive to the developing damage. That is, these techniques were unable to detect any distinctive patterns around the regions of final failure. The most responsive NDT techniques are ultrasonic attenuation and acoustic emission. Both of these methods yield quite distinct changes with increasing load. The acoustic emission tests, for example, show an extremely rapid rise in count rate at loads of about two-thirds of ultimate. The ultrasonic attenuation measurements display maxima and minima when taken in real-time as the specimen is loaded. In an effort to determine the damage mechanisms in the material and to understand the results of the NDE tests, virgin and damaged specimens were destructively examined with the aid of a scanning electron microscope (SEM). The SEM appears to show that the acoustic emission production is corning from cracking of the transverse glass fibers. The results of all tests to date are presented together with recommendations and conclusions for the application of nondestructive test methods to PPS. / Master of Science

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