The effect of the flow-forming process on the fatigue behavior of an Al-Si-Mg alloy was investigated using synchrotron X-ray microtomography. The fatigue life of the flow-formed-T6 specimen was found to be longer than that of the as-cast-T6 in all the selected stress amplitudes. The X-ray-scanned radiographs of a flow-formed-T6 specimen were reconstructed to allow three-dimensional (3-D) visualization of distribution of micropores and pore-crack interactions. Observations were performed on different tomographic slices to investigate the interaction between the micropores and the crack. Micropores have been associated with deflections of the crack path. Mode I and Mode II stress-intensity factors (SIFs) were calculated at each position along the fatigue-crack path using a micromechanics model. The SIF increased rapidly when the fatigue crack came close to a micropore. It was found that the average value of SIFs along entire crack paths was slightly higher than the remotely applied stress intensity, although the level of antishielding was pronounced in some local regions. Crystallographic texture is proposed to be the important factor for the observed higher fatigue resistance in flow-formed-T6 material.
The two-photon absorption coefficient β in InP has been measured in the wavelength range of 1640 to 1800 nm by the Z-scan technique in relatively thick materials. The values of β have been evaluated from the fit to the equation including the spatial and temporal profiles of the focused Gaussian beam. The polarization dependence of β has also been measured. The dependence has been expressed very well by the expression of β with the imaginary part of the third-order nonlinear susceptibility tensor χ (3) .
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