Abstract: Heuristic deterministic models are often proposed to reproduce S-N and €-N fields as well as crack growth curves aiming at providing basic material characterization to be used in lifetime design. Usually, they arise from the intuition of the researchers and are supported by experimental data, sometimes being complemented by micromechanical considerations based on good knowledge of physical and metallurgical properties of the material. In spite of their utility, this procedure implies serious limitations. In this work, some new methodological suggestions are presented allowing the functional structure of the problem under consideration to be derived, in an attempt of avoiding arbitrary assumptions. The relevant variables involved in the problem are recognized from experimental evidence, a reduced set of dimensionless variables is selected using dimensional analysis, a set of compatibility conditions are established and the constraints to be fulfilled by the model considered. Such models also enable planning a meaningful testing program for reliable estimation of the parameters.

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