抄録
It is generally known that the fatigue strength of the materials is increased by the workhardening of the materials before fatigue tests. Some reports, however, have recently published concerning a state that the stress of pre-loading given to mild steels which has been made just above the yield stress of the steels decreases the endurance limit of the materials.
Therefore, we made experiments to ascertain this result and further to obtain the endurance diagram of the work-hardened mild steel in the case of torsional fatigue.
The summary of the results is as follows. In case a comletely reversed alternating stress is given to the materials subjected to a pre-loading just above the yield stress, the endurance limit is reduced by about 10%. The pre-loading stress above this value hardly affects the endurance limit and it remains at nearly the some value with the non-preloaded specimens.
But in case fatigue tests where the mean stress is given to the materials subjected to a moderately high pre-loading tress, the endurance limit is increased by the pre-loading if the mean stress is applied in the same direction as the pre-loading stress, and it is almost equal to that of the non-preloaded specimens if this direction is reversed.
