Stress distribution in a segmented coating film on metal fibre under tensile loading

When a coating film on a metal fibre or wire is brittle, it exhibits multiple-fracture under loading. In order to describe the exerted tensile stress on the segments of a coating film as a function of the distance from the end of the segments and as a function of applied stress, a new approximate calculation method is presented, assuming that the interfacial bonding strength is high enough and no interfacial debonding occurs. Using the present calculation method, effects of geometrical factors such as fibre diameter, thickness of coating film and length of segment as well as those of mechanical factors such as Young's modulus, shear modulus and the yield stress of the fibre and the coating film on the exerted tensile stress on the segments and also on the exerted shear stress at the interface are described in a quantitative manner.     

High-Temperature oxidation of cathodically hydrogen-charged two-phase (Ti3Al,TiAl) titanium aluminides

Ti-42A1, Ti-45A1, and Ti-5OA1 (at. pct) titanium aluminides, which were cathodically hydrogen charged in a 5 pct H₂SO₄ solution for charging times between 1.8 ks (0.5 hours) and 14.4 ks (4 hours), were oxidized in a static air under atmospheric pressure at temperatures between 1170 K (897 °C) and 1350 K (1077 °C). All the hydrogen-charged alloys, as well as alloys without hydrogen charging, followed parabolic oxidation kinetics. The weight gains of the alloys after hydrogen charging for normally less than 3.6 ks (1 hour) were 20 to 30 pct less than those without hydrogen charging. In the alloys charged with hydrogen for more than 7.2 ks (2 hours), the weight gains increased with increasing the charging time. The activation energies of oxidation indicated that the oxidation-controlling factor would change after a charging time of 7.2 ks (2 hours) in all the alloys. The decrease in the activation energies with charging time was more drastic in the Ti-5OA1 alloy, which suggested that hydrogen damage, such as cracking, was more severe in the Ti-50Al alloy than in the Ti-42A1 or Ti-45A1 alloys. The formation of cracks during hydrogen charging provides titanium-diffusion paths and accelerates formation of rutile (TiO₂) scale on the surface of the alloys. The TiO₂ on the alloys after hydrogen charging formed at a comparatively lower temperature than that on the alloys without charging.     

Growth and coarsening of g. p. Zones in Al- Zn alloys

The structural changes during the precipitation of G. P. zones in Al-Zn binary alloys have been investigated by means of anin situ small-angle scattering technique using synchrotron radiation. Defining a specific time, normalized by the half-completion time, the time-dependent evolution of the precipitation process can be divided into three periods, independent of alloy composition and quench-ing conditions. The structural and kinetic features of the first two periods have been analyzed in detail. The first stage represents a growing process of clusters with diffuse interface into the well-defined G. P. zones. The average size of these clusters increases, and the density decreases. The second stage corresponds to the Ostwald ripening process. This mechanism is described by utilizing a modified Lifshitz-Slyozov-Wagner theory.     

A computer simulation on tensile strength of surface-Damaged fibers

The strength of surface-damaged fibers was studied by means of a computer simulation experiment based on the Monte-Carlo method using a simple model which assumes that the surface flaws can be regarded as mode I notches on fiber surfaces, the strength of undamaged fibers obeys the Weibull distribution function, and the largest flaw determines the strength of damaged fibers. Normal and exponential distribution functions were taken as the flaw size distribution function. By employing the present simulation method, the effects of average flaw size, coefficient of variation of flaw size, density of flaws, and gage length on average strength and its coefficient of variation were studied. It was found that the surface-damaged fibers can retain their full strength only when the average flaw size is small, the coefficient of variation of flaw size is small, density of flaw size is low, and gage length is short. Otherwise the average strength of damaged fibers was reduced seriously. It was emphasized that the scatter of size of flaws and density of flaws strongly affect the strength of fibers as well as flaw size and gage length.     

Still life, a protein in synaptic terminals of Drosophila homologous to GDP-GTP exchangers

The morphology of axon terminals changes with differentiation into mature synapses. A molecule that might regulate this process was identified by a screen of Drosophila mutants for abnormal motor activities. The still life (sif) gene encodes a protein homologous to guanine nucleotide exchange factors, which convert Rho-like guanosine triphosphatases (GTPases) from a guanosine diphosphate-bound inactive state to a guanosine triphosphate-bound active state. The SIF proteins are found adjacent to the plasma membrane of synaptic terminals. Expression of a truncated SIF protein resulted in defects in neuronal morphology and induced membrane ruffling with altered actin localization in human KB cells. Thus, SIF proteins may regulate synaptic differentiation through the organization of the actin cytoskeleton by activating Rho-like GTPases.     

Tensile strength of fibre-reinforced metal matrix composites with non-uniform fibre spacing

The influence of non-uniform fibre spacing on the strength of unidirectional fibre-reinforced metal matrix composites was studied by means of a Monte-Carlo computer simulation experiment. The influence of yield stress of the matrix and scatter of the fibre strength on the strength of composites were also studied for both uniform and non-uniform fibre spacings. It was demonstrated that (1) the strength of composites with non-uniform fibre spacing is lower than that with uniform spacing due to the high stress concentration arising from the breakage of fibres, and (2) the reduction in strength of composites due to the non-uniformity increases with increasing scatter of fibre strength. For both cases of uniform and non-uniform spacings, the following tendencies were observed : (a) the strength of composites increases but then decreases with increasing yield stress of matrix, (b) it is very sensitive to yield stress of the matrix when the scatter of fibre strength is large but not when it is small, and (c) it decreases but then increases with increasing scatter of fibre strength when the yield stress of the matrix is high, while it decreases monotonically with increasing scatter of fibre strength when the yield stress is low.     

Electron microscopic study on the oxidation ofβ-tin irradiated by electron beam

Effects of electron beam irradiation to-tin thin foils have been studied using high-resolution electron microscopy. By the beam irradiation, the-tin crystal at the extreme-thin foil region disappear, and amorphous oxide films covering the-tin crystal are converted into SnO₂ micro-crystallites of about 5 to 10 nm in diameter. The present study also shows that the causes for the development of SnO₂ are not due to the increment in the temperature of amorphous and-tin regions resulting from the electron irradiation. It seems that the conversion into SnO₂ is caused by the ionization action of electron beam to atom species.     

Studies on syntheses and permeabilities of special polymer membranes. X. Effects of conditions of membrane preparation on permeation characteristics of cellulose acetate membranes in separation of aqueous polymer solutions

The effects of casting solvents, dissolution temperature of casting solution, and pH and temperature of gelation solution, etc. on the permeation characteristics of cellulose acetate membranes in the separation of polymers from their aqueous solutions were investigated, using aqueous solutions of poly(ethylene glycol) and poly(vinyl alcohol) as feed. The permeation characteristics were influenced significantly by the conditions of membrane preparation and of the permeation. It was found that a concentration polarization at the membrane surface occurred with poly(vinyl alcohol) molecules, but it was very small with poly(ethylene glycol). The above results were discussed in detail from points of view of structure of the resulting membranes and the interactions between the solvent, the solute in the feed and the cellulose acetate molecules.     

Hydrogenolysis products of pyridine extract of a Japanese lignite

Petroleum ether insoluble fractions of a pyridine extract of a Japanese lignite were pyrolysed with tetralin. The chain length of alkyl groups bonded to aromatic rings and the average chemical structure of aromatic compounds in the lignite were obtained from analyses of hydrogenolysis products. Gas Chromatographic analyses of fractions eluted by cyclohexane showed the presence of C₁₅ to C₃₄ straight-chain alkanes. The chemical structures of the other fractions were analysed quantitatively by a combination of ¹³C and ¹H n.m.r. The unit structure of petroleum ether insoluble fractions in the lignite consists of one to three aromatic rings with straight-chain alkyl groups, some of which are about 25–30 carbon atoms long.