No abstract

Stand-alone plasma-sprayed tubes of 7 wt% Y 2 O 3 -ZrO 2 made from the same starting powder but at two different sites were subject to stress-relaxation testing in axial compression at temperatures of 251, 10001, 10501, 11001, and 12001C and at an initial stress of 10-80 MPa. A time-dependent stress response was observed for both coatings at all temperatures. For example, a 20 MPa stress applied at 10501C relaxed to B3 MPa in 180 min. When the same initial stress was applied at 12001C, the coating fully relaxed in 32 min. For all experimental conditions evaluated, an initial fast stress-relaxation regime was observed (o10 min), followed by a slower second stress-relaxation regime at later times (410 min). Coatings with higher as-sprayed densities exhibited a lengthened fast relaxation regime as compared with less dense coatings. A Maxwell model was modified in order to provide an accurate fit to the experimental stress-relaxation curves. From scanning electron microscopy experiments and mechanical data, the mechanism for stress relaxation from 251C through 12001C, particularly during fast relaxation, was proposed to be the formation of cracks parallel with respect to the applied load. In addition to this mechanism, stress relaxation that occurred in specimens tested at 10001C through 12001C was proposed to be due to partial or complete closure of cracks oriented perpendicular to the applied stress.

This paper discusses tool geometry, the reliability of surface measuring equipment in respect to feed/cutoff ratios and the relationship of fatigue and surface finish and other aspects of a surface which are not defined by B.S. 1134.

A plasma-sprayed 7-wt%-yttria-stabilized zirconia standalone tube was incrementally loaded in uniaxial compression inside a scanning electron microscope. Micrographs taken at each increment showed cracks perpendicular to the applied load to have partially closed and cracks parallel to the applied load to have opened. New cracks were observed to nucleate and then propagate in a direction parallel to the applied load.

Results are presented of a study of a fiber reflection Mach-Zehnder interferometer that is based on identical couplers. It has been found that, for couplers having splitting ratios within a certain range, it is always possible to switch all the light between transmission and reflection by varying the interferometer phase difference. Outside of this range, the device reflects only a small portion of the incoming light. Devices based on couplers with various splitting ratios are shown to be potentially suitable for a range of applications.