Abstract
A prediction method of service loading from striations on fracture surface is proposed. Although it is well known that striation spacing corresponds to the crack growth rate da/dN, it is not possible to determine Pmax and Pmin under service loading only from s. This is because the value of s is influenced not only by ΔK but also by the stress ratio R (=Pmin/Pmax).
The new idea in this study for determination of Pmax and Pmin is based on the anticipation that the information on R must be included in the relative height of striation H to s. The results of fatigue tests on 2017-T4 Al Alloy CT specimens showed a definite correlation between H/s and R. The difficulty of the measurement of H was overcome by sectioning the specimens at an inclined angle and by measuring small distance using SEM.
Striations under R=-1 were compressed and flat, and H/s was small. With increasing R, H/s became large. Therefore, the standard laboratory test results on the relationship between s and ΔK, and also that between H/s and R enables us to predict service loading from the fatigue fracture surfaces.
