SMALL FATIGUE CRACK GROWTH BEHAVIOUR UNDER TWO STRESS LEVEL MULTIPLE LOADING

Small fatigue crack growth behaviour in a low alloy steel was investigated under two stress step multiple loading in which the secondary stress was below the fatigue limit. Crack growth rates were presented in terms of a stress intensity factor and compared with data obtained under constant amplitude loading. In the higher ΔK region, crack growth rates increased monotonously with increasing ΔK even though the stress level was below the fatigue limit, and tended to be lower than those for constant amplitude loading. In the lower ΔK region, cracks showed a complicated behaviour, that is, an initial high growth rate was observed followed by an arrest or a drop to a minimum value and then a gradual increase. The average crack growth rates per cycle at both primary and secondary stresses in each block were approximately consistent with the da/dn-ΔK relation for constant amplitude loading. A suggestion for the prediction of crack growth life is given.     

Development of Aluminum Titanate-Mullite Composite Having High Thermal Shock Resistance

Thermomechanical properties of aluminum titanate-mullite composites were studied for a wide composition range to develop material having high thermal shock resistance. The thermal shock resistance tended to increase with increasing aluminum titanate content. Composite having 82 vol% aluminum titanate can withstand water quench from above 1200°C and has a room-temperature strength of 60 MPa. Composite with less aluminum titanate has lower thermal shock resistance but has higher strength. The relation between thermal shock resistance and strength, Young's modulus, and thermal expansion coefficient is discussed.     

Influence of crystal orientation on the processing of copper single crystals by ECAP

Single crystals of high-purity copper, having two different orientations, were pressed through one pass in equal-channel angular pressing (ECAP) at room temperature and then examined using several different analytical techniques. For both orientations, it is shown that elongated arrays of cells or subgrains are formed in the first pass with their long axes aligned parallel to the primary slip system. The average width of these subgrains was measured as ∼0.2 μm which is similar to the equilibrium grain size reported in polycrystalline Cu after processing by ECAP. These results confirm earlier observations using an aluminum single crystal except only that the subgrain width in copper is significantly smaller. This difference is attributed to the lower stacking-fault energy in copper and the consequent low rate of recovery.     

Copper(I)‐Catalyzed Allylic Substitution of Silyl Nucleophiles through Si?Si Bond Activation

We report the first copper(I)‐catalyzed reaction between a disilane and allylic carbonates to produce allylsilanes. The silyl nucleophilic substitution proceeded primarily in a S_N2 fashion whereas S_N2′ products were also obtained through σ‐π‐σ isomerization of the copper(III) intermediate depending on the substrate’s steric bulk.