Fracture mechanics approach to fretting fatigue and problems to be solved

A large number of research works have been devoted to fretting fatigue from both mechanical and metallurgical viewpoints. In the present paper, fracture mechanical approaches for evaluating fretting fatigue life and strength have been briefly reviewed. Furthermore, a new approach based on a singular stress field near the contact edge and on fracture mechanics has been proposed. The directions of crack initiation and propagation as well as fretting fatigue life, which have coincided with the experimental results, could be estimated according to the new approach, in which singular stress near the contact edge and mixed mode crack growth have been taken into consideration. In the application of the new method to predict the fretting fatigue behavior, there are still several problems to be clarified, which have also been discussed in detail.     

Effect of processing conditions on the characteristics of pores in hot isostatically pressed alumina

Effect of processing conditions on the characteristics of residual pores was studied with an optical microscope in hot isostatically pressed translucent alumina ceramics. Green bodies formed by isostatic pressing were sintered at 1300, 1400 and 1600°C and then hot isostatically pressed at a temperature 50°C below the respective sintering temperature for 1 h at 100 MPa. All specimens were fully dense within experimental accuracy (±0.1%), and the grain size increased with increasing sintering/hot isostatic pressing temperatures. A variety of pores were found in all specimens. The distribution of pores was uniform at various locations within the specimen. The pore population decreased with increasing pore size, but was finite in the size range exceeding 84 m. The pores in this range increased with increasing sintering/hot isostatic pressing temperature. Except for these large pores, the pore population was similar under all processing conditions.     

Inverse interactorizing and triangularizing with an arbitrary poleassignment using the state feedback

A simple method is presented on how to generate the state feedback which makes the closed-loop transfer matrix the inverse of the interactor matrix. This can be regarded as a generalization of decoupling control using state feedback. An arbitrary pole assignment which preserves the lower left triangular form of the inverse of the interactor matrix is also considered     

Loop diuretics act directly on adenylate cyclase in rat renal tubular basolateral membranes

We have reported previously that loop diuretics, especially azosemide and ethacrynic acid, may act not only on the AVP receptor site, but also on the post-AVP receptor site in rat renal tubular basolateral membranes. The purpose of this study was to examine whether loop diuretics (furosemide, azosemide, ethacrynic acid) affect the post-AVP receptor components, using GTP-gamma S, forskolin and cholera toxin as tools acting distal to the receptor. Adenylate cyclase activity stimulated by 10(-9)M AVP was inhibited more potently by azosemide and ethacrynic acid than by furosemide at the concentration of 10(-3) M. Azosemide and ethacrynic acid at concentrations above 10(-4) M also significantly decreased the enzyme activity that was stimulated by 10(-7) M GTP-gamma S and 10(-5)M forskolin, while significant inhibition by furosemide was observed only at 10(-3)M. In addition, the inhibitory effect of these loop diuretics on cholera toxin-stimulated enzyme activity was almost similar to the results observed in AVP-, GTP-gamma S- or forskolin-stimulated the enzyme activity. From these results, we conclude that loop diuretics, especially azosemide and ethacrynic acid, directly affect adenylate cyclase in part as well as the AVP receptor site.     

A 30 frames/s 2/3-in 1.3 M-pixel progressive scan IT-CCD imagesensor

A 30 frames/s 2/3-in 1.3 M-pixel progressive scan interline-transfer charge-coupled device (IT-CCD) image sensor has been developed for video and digital still-camera applications. To obtain high frame-rate images, a 49-MHz driving horizontal CCD (H-CCD) was developed. An 8-phase drive for vertical CCDs (V-CCDs) makes it possible to operate in a variety of modes, such as 1050 line progressive scan mode and 1049 line wide dynamic range interlaced scan mode. For digital still camera use, removing residual charges stored in the V-CCDs before exposure is essential, therefore new narrow-channel barrier over-flow drain (NCB-OFD) attached under the H-CCD was developed. The NCB-OFD automatically drains out extra charges and has the advantages of requiring neither an over-flow control gate nor any additional masks     

A 1-V high-speed MTCMOS circuit scheme for power-down applicationcircuits

This paper proposes a new multithreshold-voltage CMOS circuit (MTCMOS) concept aimed at achieving high-speed, ultralow-power large-scale integrators (LSI's) for battery-driven portable equipment. The “balloon” circuit scheme based on this concept preserves data during the power-down period in which the power supply to the circuit is cut off in order to reduce the standby power. Low-power, high-speed performance is achieved by the small preserving circuit which can be separated from the critical path of the logic circuit. This preserving circuit is not only three times faster than a conventional MTCMOS one, but it consumes half the power and takes up half the area. Using this scheme for an LSI chip, 20-MHz operation at 1.0 V and only a few nA standby current was achieved with 0.5-μm CMOS technology. Moreover, this scheme is effective for high speed and low-power operation in quarter-micrometer and finer devices     

Oxidation behavior and mechanical properties of low-oxygen SiC fibers prepared by vacuum heat-treatment of electron-beam-cured poly(carbosilane) precursor

EB-cured PCS fibers were heat-treated at 1273–1673 K under a reduced pressure of 1.33 Pa, and subsequently they were exposed to 1773 K in air. The thermal stability and oxidation resistance of the fibers were investigated through TG, XRD analysis, specific resistivity measurement, SEM observation and tensile tests. The oxidation rates at initial stage are thought to be strongly dependent upon the microstructure of the fibers in the as-heat treated state and the presence of water vapor. Incomplete ceramization and the occurrence of active-oxidation during heat-treatment yielded poor oxidation resistance to the fibers. The oxidation caused the grain growth of SiC, drop of resistivity and degradation of strength. The oxidation of the fibers was retarded at later stage. The fibers heat-treated at 1573 K had high strength and high oxidation resistance.     

Flexural strength,fracture toughness and fatigue crack growth behaviour of chromium alloyed γ-base TiAl

Mechanical properties of -base titanium aluminides strongly depend on microstructural parameters. Flexural strength, fracture toughness and fatigue crack growth properties were estimated for the cast and heat-treated (HT-TiAlCr) and cast, heat treated and isothermal forged (ITF-TiAlCr) chromium alloyed -base titanium aluminides at room temperature. HT-TiAlCr possessed superior fracture properties compared to ITF-TiAlCr. Toughening due to microcracks, and crack bridging by uncracked ligaments were observed in the test materials. Presence of lamellar grains in HT-TiAlCr increased the crack growth resistance and contributed positively to fracture properties. The coarse grain size promoted large crack deflection and fracture surface mismatch and caused high levels of crack closure in HT-TiAlCr. Combined crack-tip blunting and bridging by ductile -phase was significant in the case of ITF-TiAlCr. Fracture mechanisms of test materials were investigated and correlated to the fracture properties.     

FRETTING FATIGUE OF AN AUSTENITIC STAINLESS STEEL IN SEAWATER

Abstract— Fretting fatigue tests of an austenitic stainless steel used for a propeller tail shaft were carried out in seawater and in air. In seawater, fretting significantly reduced the fatigue strength, however, the fretting fatigue lives at higher levels of stress were longer than those in air. The tangential force coefficient (defined as the ratio of the frictional force amplitude and the contact load) in seawater was much lower than that in air and varied in the range from 0.3 to 0.5 during the fretting fatigue tests. The lower tangential force coefficient in seawater seems to be the main reason for the longer fretting fatigue life in seawater. The prediction of fretting fatigue life was made on the basis of elastic-plastic fracture mechanics, where the frictional force between the specimen and the contact pad was taken into consideration. The predicted fatigue lives agreed well with the experimental results in both air and seawater.     

A simple derivation of the interactor matrix and its applications

An interactor matrix plays several important roles in the control system theory. In this article, we present a simple method to derive a special interactor matrix using Moore–Penrose pseudoinverse. The interactor by the proposed method has all its zeros at the origin, and has the all-pass property in the discrete-time. A systematic procedure to obtain an identity interactor, which has an lower triangular structure or has arbitrarily prespecified zeros, is also shown.