1987 年 30 巻 270 号 p. 1898-1905
A Fatigue crack Propagation test was carried out on HT80 and mild steel, and crack through thickness behavior was examined in detail, both experimentally and analytically. The major results are as follows. 1) The fatigue crack shape before penetrating the whole thickness is almost semicircular, and the measured aspect ratio is larger than the value obtained by calculation using the K value proposed by Newman-Raju. 2) It is found that the crack growth behavior on the back surface, i.e., the growth behavior of cracks after they have run through the plate, is unique and can be divided into three stages, a, b and c. 3) The fatigue crack growth rate at the stage b is constant for a wide range and is in direct proportion to the n-th power of the range of stress, Δσ. 4) A new model has been proposed to evaluate the K value after cracking through the plate thickness. 5) The K value proposed by the authors makes it possible to explain quantitatively the particular behavior of cracks after they have run through the plate.