1977 年 26 巻 280 号 p. 80-86
The thin-walled cylindrical specimens subjected to internal pressure were fatigued in tension-compression, in order to study the fatigue behavior under the biaxial stress condition. The results are summarized as follows:
(1) The circumferential stress increases the fatigue strength, while the tensile mean stress decreases it. But the fatigue limit is nearly constant independently of the stress condition.
(2) The number of cycles to form cracks detectable at the external surface decreases with increasing tensile stress on the maximum shear stress plane. Although the specimen is approximately under the biaxial stress condition, the radial stress should be taken into consideration for the crack initiation.
(3) The fatigue crack propagation rate is expressed by a power function of the stress intensity range. But the exponent and constant vary with the stress condition.
(4) The plastic zone size ahead of the crack tip, ξ, observed with an optical microscope has a close relation with the crack propagation rate, but is independent of the stress condition and the crack length:
(5) The relation between the plastic zone size ahead of the crack tip, ξ*, obtained by the modified Dugdale's model and the crack propagation rate is given by the following function. da/dN=1.24×10-10ξ*1.88