抄録
Pulsating tensile fatigue tests were carried out, using the CT specimens cut out from a high tensile rolled steel in three different directions. The crack length in each directional specimen was measured by an optical microscope and N-l curves were approximated by quadric curves, and then the effects of stress ratio and plate thickness on anisotropy of fatigue crack propagation were examined. The fracture surface was observed by a scanning electron microscope. The main results obtained are as follow: (1) ΔK-dl/dN relations obtained from N-l curves approximatd by the quadric curves determined from each five points of data are comparatively reasonable. (2) Anisotropy of crack propagation slightly exists in this material and the resistance for fatigue crack propagation in the smallest in the specimen whose cracks propagate along the laminated structure. (3) The effects of stress ratio and plate thickness on the anisotropy are small.
