Tetsuya Kuwano

Effect of Gas Environment on Friction Behavior and Tribofilm Formation of PEEK/Carbon Fiber Composite

This study investigated the friction and wear behaviors of polyetheretherketone composites containing carbon fibers (PEEK-CF) sliding against stainless steel in terms of their dependencies on gas environments. Sliding tests with a block-on-ring apparatus were conducted in humid/dry air and dry nitrogen at normal temperature and nitrogen at cryogenic temperature of 113 K. Friction and wear significantly decreased when sliding occurred in low-humidity, low-oxygen, and low-temperature environments. The friction coefficient, initially 0.25 in ambient humid air, decreased to below 0.10 in the dry nitrogen environment and 0.03 in nitrogen at 113 K. Microscopic observations, surface roughness measurements, and surface composition analysis of worn surfaces were conducted after the sliding tests. After sliding in humid air, the surface roughness of the PEEK-CF block was increased from its initial value by adhesions of large wear particles. However, the surface roughness of the block decreased due to the formations of tribofilms that were micrometers thick and composed of fine wear particles of polymer and carbon fibers after sliding in dry nitrogen. X-ray photoelectron spectroscopy analysis and the Raman spectroscopy analysis indicated increased carbon content with graphite structures on the worn surface after sliding in dry nitrogen. Consequently, it was considered that PEEK-CF changed its wear process in the dry nitrogen environment and formed a smooth surface with carbon particles containing graphite, which is thought to be advantageous in reducing friction.

Natural Frequencies of Centrifugal Compressor Impellers for High Density Gas Applications

Characteristics of natural frequencies of an impeller and an equivalent disc were investigated in high-density gas to develop a method for predicting natural frequencies of centrifugal compressor impellers for high-density gas applications. The equivalent disc had outer and inner diameters equal to those of the impeller. We expected that natural frequencies would decrease with increasing the gas density because of the added-mass effect. However, we found experimentally that some natural frequencies of the impeller and the disc in high-density gas decreased but others increased. Moreover, we observed, under high-density condition, some resonance frequencies that we did not observe under low-density condition. These experimental results cannot be explained by only the added-mass effect. For simplicity, we focused on the disc to understand the mechanism of the behavior of natural frequencies. We developed a theoretical analysis of fluid-structure interaction considering not only the mass but also stiffness of gas. The analysis gave a qualitative explanation of the experimental results. In addition, we carried out a fluid-structure interaction analysis using the finite element method. The behavior of natural frequencies of the disc in high-density gas was predicted with errors less than 6%.Copyright

Use of Design-by-Analysis for Designing Shear Key Structure

In many vessels with container, such as those involving rotating machinery, barrel casings are closed with disc shaped end covers on both axial sides. The end covers are fixed to the barrel casing with bolted joints or retaining devices. A shear key structure is often applied to pressurized vessels as a retaining device, because it can endure higher pressure than bolted joints can. Stress distribution in the shear key and the casing depends on the contact condition between the shear key and the casing. Thus, it is difficult to design a shear key structure merely by using Design-by-Formula procedures. We designed the shear key structure according to Design-by-Analysis procedures based on finite element (FE) analysis. By taking the contact condition between shear key and casing into consideration in an FE model and carrying out elastic and inelastic analyses, we developed a new shear key structure configuration. We will confirm the validity of the new shear key structure by means of pressure tests that will be conducted in May of 2009.Copyright