Using the concept of the tensile-instability mechanism which determines the ultimate strength of most of the ductile materials under uniaxial or biaxial tension conditions, two new analyses are carried out. In these are considered an effect previously neglected: Variation of Poisson’s ratio (based on total strain) with strain in the plastic range. One analysis treats a uniaxial tensile specimen, and the predicted results are generally in better agreement with experimental values for seven alloys of aerospace structural importance than the results of classical theory, in which Poisson’s ratio is assumed to remain constant at a value of 1/2 in the plastic range. The other considers a thin-walled spherical shell subject to internal pressure, and the predicted result is again closer to the experimental value than that predicted by classical theory.

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