ABSTRACT
The unified equation is a neat, symmetrical, and elegant mathematical expression that, although derived for tensile rupture, is equally applicable to all long-term modes of failure. When applied to the fiber direction of unidirectional plies, the unified equation predicts the long-term safety factors to rupture. The unified equation solves all load-dependent durability issues of any laminate. The unified equation computes the infiltration, stiffness, weep, and rupture durability of any ply. The critical ply and the mode of failure depend on the intended service. The classical constant life diagrams, or Goodman diagrams, are condensed representations of the unified equation. The ply diagrams are direct competitors of the unified equation in the solution of long-term load-dependent failures. The unified equation and the Goodman diagrams have equal competence and accuracy in the analysis of time-independent failures—infiltration, stiffness and weeping. The Goodman diagrams applied to time-independent, fully cycle-dependent, long-term failures of plies is a graphical representation of the unified equation.
