COMPARISON OF VARIOUS RELATIONS DESCRIBING THE HAIGH FATIGUE DIAGRAM

摘要

The influence of various asymmetry of loading cycle on fatigue limit is very clearly presented by the Haigh fatigue diagram, i.e. by the dependence of stress amplitude on mean stress (sometimes minimum and maximum stresses of loading cycle are considered or the stresses are expressed relatively to UTS). This dependence is usually described by various phenomenological relations. The paper compares these relations and proposes a new dependence based on Walker's description of the influence of various loading cycle asymmetry on the position of fatigue (Woehler's or S-N) curves in high-cycle region consisting in multiplicative factor of (1 - R)~(-m) where R is the parameter of cycle asymmetry. This approach allows precise description for low values of mean stress but for high mean stresses close to UTS where R is very close to 1, unacceptable inequality σ_C(R) = σ_C(0)(1 -R)~(-m) > UTS can appear. The solution of this problem is also proposed in the paper.