There are many fatigue test and statistical procedures to establish the life distribution function Q = Q(N) at constant stress (S) level. But the stress distribution function, Q = Q(S), at specified life (N) is more important to the designer, and it remains less developed. Generally, if the fatigue life distribution Q(N) and fatigue curve S(N) equations are defined, the fatigue strength distribution Q(S) is implied. However, it has been shown [4, 6, 7, 9] that any life distribution model Q(N) may be transformed into the complicated strength distribution function Q(S). In this study orthogonal relations have been developed in order to predict complications and to resolve the problem under certain conditions. With the aid of the orthogonal relations strength distributions Q(S) have been deduced using (1) lognormal, (2) two-parameter Weibull, and (3) three-parameter logweibull life models Q(N).