We report angle-resolved photoemission (ARPES) measurements, density functional and model tight-binding calculations on Ba 2 IrO 4 (Ba-214), an antiferromagnetic (T N = 230 K) insulator. Ba-214 does not exhibit the rotational distortion of the IrO 6 octahedra that is present in its sister compound Sr 2 IrO 4 (Sr-214), and is therefore an attractive reference material to study the electronic structure of layered iridates. We find that the band structures of Ba-214 and Sr-214 are qualitatively similar, hinting at the predominant role of the spin-orbit interaction in these materials. Temperature-dependent ARPES data show that the energy gap persists well above T N , and favor a Mott over a Slater scenario for this compound.

A B S T R A C TThe ratcheting behaviour of Inconel 718 was investigated at 649 • C under uniaxial cyclic loading. Stress-control tests have been conducted at various combinations of stress amplitude and mean stress. The ratcheting strain at failure increases with increasing mean stress for a given stress amplitude and with decreasing stress amplitude for a given mean stress. Fatigue lives were correlated using three mean stress models: the Goodman equation, the Smith-Watson-Topper (SWT) parameter and the Walker parameter. It has been shown that the Goodman equation and the SWT parameter do not correlate life data, while the Walker parameter yields acceptable correlation. The SWT parameter was modified to incorporate the ratcheting effect. The new parameter is found to yield correlation similar to that of the Walker parameter.Keywords Goodman equation; mean stress effect; ratcheting strain; SWT parameter; uniaxial fatigue; Walker parameter. N O M E N C L A T U R Eσ a = stress amplitude σ m = mean stress σ eq a = equivalent stress amplitude σ max = maximum stress R = stress ratio (R = σ min /σ max ) ε r = ratcheting strain N = number of cycles N f = number of cycles to failure σ f = fatigue strength coefficient b = fatigue strength exponent γ = Walker exponent I N T R O D U C T I O NMany engineering components are subjected to cyclic loading in which the fatigue process takes place under stress-control conditions. Fatigue cycles may not be fully reversed. In these circumstances, the mean stress effect has to be taken into account in fatigue life prediction. A phenomenon that occurs in the presence of mean stress in the low-cycle fatigue regime is ratcheting, which results from the accumulation of plastic strain. Ratcheting causes fatigue damage of the material and shortens the life of engineering components significantly, unless a shakedown state is reached in the early stage of life. Naturally, this important phenomenon has received the attention of many researchers, and numerous studies have been carried out on the deformation aspect of the phenomenon. The Armstrong-Frederick nonlinear kinematic hardening rule 1 is widely used in ratcheting analysis. The decomposed model by Chaboche 2 and the multilinear model by Ohno and Wang 3 belong to this category. These models have been successful for predicting uniaxial ratcheting, but they tend to overpredict ratcheting under multiaxial loading. Despite many modified models suggested 4,5 to resolve the shortcomings, the prediction of ratcheting strain under multiaxial loading still remains a challenging problem. Not only that, there are many other variables influencing ratcheting behaviour which need to be further investigated. For all these and other reasons, the 1076

Multiaxial fatigue under variable amplitude loading is investigated using Kandil et al.’s parameter, rainflow cycle counting on the shear strain history, and the Miner-Palmgren damage rule. Fatigue data are obtained on tubular specimens of S45C steel under proportional and nonproportional tension-torsion loading. The approaches using the maximum shear strain range (Δγmax) plane and the maximum damage (Dmax) plane as the critical plane are investigated. The damage is computed for each reversal or for each cycle. The results show that both Δγmax and Dmax approaches yield acceptable fatigue lives irrespective of the damage computation method. Damage computation for each reversal tends to shift fatigue life toward the nonconservative side for some nonproportional loading. It is concluded that the overall procedure used in this study is viable for multiaxial life prediction under variable amplitude loading for the test material.

We investigate by angle-resolved photoemission the electronic structure of in situ grown tetragonal CuO, a synthetic quasi-two-dimensional edge-sharing cuprate. We show that, in spite of the very different nature of the copper oxide layers, with twice as many Cu in the CuO layers of tetragonal CuO as compared to the CuO 2 layers of the high-T c cuprates, the low-energy electronic excitations are surprisingly similar, with a Zhang-Rice singlet dispersing on weakly coupled cupratelike sublattices. This system should thus be considered as a member of the high-T c cuprate family, with, however, interesting differences due to the intralayer coupling between the cupratelike sublattices.