Crack Orientation Dependence of Fatigue Behavior in Titanium Single Crystals by Thin Sheet Plain Bending

Abstract

Fatigue test of titanium single crystals with different crystallographic orientations has been carried. To investigate fatigue fracture behavior of small single crystals, plain bending fatigue test method for thin sheet specimen was developed. One end of the sheet specimen is fixed at a voice coil of the loudspeaker and the other end is set free. A bending mode resonance occurs in the specimen due to forced vibration at the fixed end. In A-specimen, a notch plane and the direction are (11 20) and [1100], respectively, the crack propagates parallel to {1100} plane and striation-like markings are observed on the fatigue surfaces. In B-specimen with a notch of (1100) [1120], the crack also propagates parallel to {1100} plane as similar to A-specimen. These cracks are deduced to extend by alternating shear on two intersecting prismatic slip systems at the crack tip. In F-specimen with a notch of (0001) [11 20], the crack propagates parallel to (0001) and some trace of pyramidal slip was observed on the fatigue surface. As a result, S-N curves of each specimen showed strong orientation dependence. Fatigue strength of F-specimen is higher than that of A- and B-specimen.