Abstract
The term“Fatigue Damage”is very ambiguous and has been used as different meanings. In some cases, fatigue damage is represented by the degree of changes in physical or mechanical properties of materials due to stress reversals, such as changes of shock resistance, damping cofficient, and others. But the author believe teat these changes do not represent the true fatigue damage, because they do not always mean the decrease of fatigue life of materials. On the contrary, in some cases, they mean even the incresse of it. In such cases, these changes are training rather than damage.
In some cases, fatigue damage has been represented with the decrease of the endurance limit of materials. But the author cannot agree with this representation, because it seems to contain the following unreasonableness. The term “Fatigue Damage” is used when we consider the fatigue life of materials at the stress levels over the endurance limit. If we attempt to keep working stresses always less than endurance limit, the conception of fatigue damage is needless, because fatigue failure does not occure at the stress levels below endurance limit. Fatigue damage is the matter concerning with fatigue life and not with endurance limit. So fatigue damage should not be represented with the decrease of endurance limit.
Then the author believe that it is most reasonable to represent fatigue damage as the rate of diminution of fatigue life in future. This representation has been already adopted by many researchers. (Refer to the Notes (2), (3) at the end of the paper.) If we adopt the representation, fatigue damage cannot be decided only by the stress history in past, but must be influenced by the stress which will be applied in future. It is self-evident that the life in future depends on the stress in future. This is the so-called future effect on fatigue damage.
In this paper the future effect on fatigue damage was obtained by experiments in some cases.
