We have investigated the effect of the notch inclination angle (φ), which is defined as the angle between the center line of a specimen and the center line of V-groove having notch opening angle of 90°, on the plane bending fatigue behavior. This study was conducted to reveal the influences of φ on the plane bending fatigue limit, the fatigue crack initiation and propagation and the behavior of non-propagating crack.
The main results obtained are as follows;
(1) The fatigue limit was increased and the fatigue life was prolonged with the increase of φ. Especially, the test specimen having the notch shape like a step (in this case, φ=45°) showed the tendency that the fatigue life is much longer than other cases (φ=0°, φ=15°, φ=30°).
(2) In case of stress level having the inflexion point in the fatigue crack growth curves, the results obtained were independent of the influence of φ. The fatigue crack growth rate (dl/dN) decreased with an increase of crack length until it reached to the inflexion point of dl/dN in the fatigue crack growth curve. Then it increased or the fatigue crack became non-propagating, depended on the level of the applied stress. The similar tendency was found in the relation between dl/dN and the stress intensity factor range (ΔK), when ΔK was taken as a parameter instead of the crack length. In the increasing range of dl/dN, the following equation was experimentally obtained between dl/dN and ΔK.
dl/dN=5.92×10^-11×ΔK^4.19
In the decreasing range of dl/dN, the relation between dl/dK and ΔK was able to be arranged using the stress concentration factor (α).