A new experimental method for measuring life time and crack growth of materials under multi-stage and random loadings

The experimental equipment and method of operation of a special computer-controlled fatigue testing machine is described. This resonance testing machine, operating at ultrasonic frequencies (20 kHz), performs one-step, multistage, and random fatigue tests with the aid of a computerized control system in very short testing times. Differences between this method and testing procedure at conventional frequencies are pointed out. However, it is emphasized that the high frequency tests have practical merit aside from lower energy cost and testing times. Initial results of two-stage fatigue experiments are reported.     

A convergent Pd-catalyzed asymmetric allylic alkylation of dl- and meso-divinylethylene carbonate: enantioselective synthesis of (+)-australine hydrochloride and formal synthesis of isoaltholactone

The use of a mixture of dl- and meso-divinylethylene carbonate as an electrophile in palladium-catalyzed asymmetric allylic alkylation reactions is reported. From the diastereomeric mixture of meso and chiral racemic starting materials, a single product is obtained in high optical purity employing either oxygen or nitrogen nucleophiles. The resulting dienes have proven to be versatile synthetic intermediates as each carbon is functionalized for further transformation and differentiated by virtue of the reaction. A mechanism for this intriguing transformation is proposed and a concise enantioselective total synthesis of (+)-australine hydrochloride is reported as well as a formal synthesis of isoaltholactone.     

Effect of substitution of Ce on superconducting properties of Bi1.7Pb0.3Sr2Ca2−x Ce x Cu3O10+δ system

We have investigated the superconducting properties of the Bi_1.7 Pb_0.3Sr₂Ca_2−xCe _x Cu₃O_10+δ system with x=0.00, 0.02, 0.04, 0.08 and 0.1 by X-ray diffraction and magnetic susceptibility. The substitution of Ce for Ca has been found to drastically change the superconducting properties of the system. X-ray diffraction studies on these compounds indicate decrease in the c-parameter with increased substitution of Ce at Ca site and volume fraction of high T _c (2 : 2 : 2 : 3) phase decreases and low T _c phase increases. The magnetic susceptibility of this compound shows that the diamagnetic on set superconducting transition temperature (onset) varies from 109 K to 51 K for x=0.00, 0.02, 0.04, 0.08 and 0.1. These results suggest the possible existence of Ce in a tetravalent state rather than a trivalent state in this system; that is, Ca²⁺ → Ce⁴⁺ replacement changes the hole carrier concentration. Hole filling is the cause of lowering T _c of the system.     

Self-assembled growth of nanostructural Ge islands on bromine-passivated Si(111) surfaces at room temperature

We have deposited relatively thick (∼60 nm) Ge layers on Br-passivated Si(111) substrates by thermal evaporation under high vacuum conditions at room temperature. Ge has grown in a layer-plus-island mode although it is different from the Stranski-Krastanov growth mode observed in epitaxial growth. Both the islands and the layer are nanocrystalline. This appears to be a consequence of reduction of surface free energy of the Si(111) substrate by Br-passivation. The size distribution of the Ge nanoislands has been determined. The Br-Si(111) substrates were prepared by a liquid treatment, which may not produce exactly reproducible surfaces. Nevertheless, some basic features of the nanostructural island growth are reasonably reproducible, while there are variations in the details of the island size distribution.     

The distribution of plastic deformation during 21 kHz fatigue of copper samples

A new method of investigating the portion of plastic deformation during fatigue tests of copper samples has been developed. Until now plastic deformation could only be estimated as opposed to being directly measured. Cholesteric li-crystals were applied to the sample surfaces before the fatique test and the temperature distribution during deformation was measured by the change in colour of these crystals. This then allows the distribution of the plastic deformation along the sample to be calculated. Film recordings of the colour, and hence the temperature change showed that plastic deformation is spread along the sample in a manner similar to that predicted by theory; plastic deformation is not mainly concentrated in the middle of a specimen.