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Single-edge notched specimens of a unidirectional SiC long fibre reinforced titanium alloy, were fatigued under four point bending. The propagation behaviour of short fatigue cracks from a notch was observed on the basis of the effects of fibre bridging. The branched fatigue cracks were initiated from the notch root. The fatigue cracks propagated only in the matrix and without fibre breakage. The crack propagation rate decreased with crack extension due to the crack bridging by reinforced fibres. After fatigue testing the loading and residual stresses in the reinforced fibres were measured for the arrested cracks by the X-ray diffraction method. The longitudinal stresses in the reinforced fibres were measured using high spatial resolution synchrotron radiation. A stress map around the fatigue cracks was then successfully constructed. The longitudinal stress decreased linearly with increasing distance from a location adjacent to the wake of the matrix crack. This region of decreasing stress corresponded to the debonding area between the fibre and the matrix. The interfacial frictional stress between the matrix and the fibre could be determined from the fibre stresses. The bridging stress on the crack wake was also measured as a function of a distance from a notch root. The threshold stress intensity factor range, corrected on the basis of the shielding stress, was similar to the propagation behaviour of the monolithic matrix. Hence the main factor influencing the shielding effect in composites is fibre bridging. [ABSTRACT FROM AUTHOR]

Suppressing the stress corrosion cracking (SCC) by reducing the carbon content in austenitic stainless steels is apparently not effective on core shrouds used in boiling water reactors in Japan: trans-granular cracking was found in the shrouds. To clarify the mechanism of the cracking, in situ stress measurements on specimens under stretched conditions in hot water have been attempted in the present study. An in situ device for diffraction measurements at synchrotron radiation facilities has been developed, and in situ experiments have been carried out at SPring-8. The SUS316L steel specimen was solution heat-treated, surface-ground and then placed in the in situ device. Sapphire windows were used for the light path in the device. A sufficient diffracted beam intensity was obtained through two sapphire windows and water. The side-inclination method was used for measuring the stress exerted on the specimen. A 2θ–sin2ψ plot showed that a tensile stress was induced. The measured stress value is considered to be the summation of stresses owing to pre-straining, in situ loading and residual stress owing to surface grinding. [ABSTRACT FROM AUTHOR]

Fatigue tests of crack propagation from a precrack in thin-walled tubular specimens made of a medium-carbon steel were performed under cyclic torsion with and without superposed static or cyclic axial loading. The stress ratio of cyclic loading was−1. The fatigue crack-propagation path from a precrack was compared with the predictions based on the maximum tangential stress criterion. The direction of fatigue crack propagation follows the direction of the maximum of the range of the tangential stress,Δσ*θ max, near the crack tip determined from the stress intensity factor (SIF) which was calculated by considering the contacts of crack faces at the minimum load. The SIF calculated from the actual crack path by using the body force method (BFM) showed that the mode II SIF range quickly approached zero after a small amount of crack extension. The crack-propagation rate decreased first and then increased with crack extension. The initial dip of the crack-propagation rate was caused by the development of crack closure with crack extension. As cracks extended a long distance, the propagation rate was faster than the uniaxial data. This acceleration of crack propagation was caused by excessive plasticity near the crack tip. [ABSTRACT FROM AUTHOR]