Multiaxial fatigue life estimation based on a piecewise ruled S–N surface

A multiaxial model for fatigue life estimation, formulated in terms of a piecewise ruled S–N surface, is proposed. The first ruled surface considers the sum of a deviatoric stress amplitude and the maximum hydrostatic stress as an exponential function of the number of cycles to failure. For small magnitudes of the hydrostatic stress, another surface is defined by considering only the effect of the deviatoric stress amplitude upon the expected fatigue life. The deviatoric stress amplitude was computed by the maximum prismatic hull concept. The model proved successful when compared with other multiaxial criteria for available data.