Abstract
From a review of previous reports concerning the notch effect on the fatigue strength of metals, it is understood that the damaging effect of notch is reduced at elevated temperatures in many cases. However, metallic materials are activated metallurgically at high temperature, so that many factors such as loading frequency, state of stress, grain size and atomosphere surrounding a specimen have remarkable effects on the strength of notched specimen, and, as easily understood, their influences vary according to the kind of material. Moreover, when a material is tested under a repeating load superimposed on a static load, some properties are observed characteristic to notched specimens, which are considered to be related with the well-known strengthening effect of notches under creep load.
This investigation aims to study those properties of the notched specimen of Cr-Mo-V steel, a kind of heat resistant steel, under pulsating load at 490°C. An emphasis is put on the clarification of the effect of loading frequency. The results have been discussed in comparison with those obtained from the previous experiment on the plain specimen of the same steel under similar conditions. It is concluded that, in the stress range where the repeating load is moderately small, the frequency has effects to increase the strength both for deformation and for fracture, and that the strength itself is largely increased in the notched specimen than that of the plain specimen in the same stress range. This result concides in its tendency with those of previous reports worked by several authors.
