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**Published:** Jan 1971

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**Source: **STP519-EB

In the quest for a physical justification of the term “state of fatigue of materials subjected to cyclic loading,” the present paper first investigates the question what conclusions must be drawn, if states of fatigue (Ω) exist that can be characterized by a single number (0 ≤Ω ≤ 1). It was found that, if such states of fatigue do in fact exist, they can be determined experimentally, and the mathematical relationships of cumulative damage with regard to irregular loading are then fixed and can be stated: no additional model assumption, for example, the arbitrary assumption of an analytical function for Ω, will then be necessary and would be wrong.

If it is not possible for states of fatigue to be characterized by a single number, not even for a limited selection of types of loading, then it is likewise impossible to give any simple or closely accurate mathematical relationship for the actual cumulative damage. Nevertheless, it is possible in such cases to make safe life estimates, but it is only by experiment that the degree of certainty of such estimates can be determined in any particular case.

**Keywords:**

fatigue (materials), damage, predictions, sequence of cycles, crack propagation, fatigue-sensors

**Author Information:**

Burbach, J *Krupp Forschungsinstitut, Essen,*

**Committee/Subcommittee:** E08.05

**DOI:** 10.1520/STP38031S