Nonlinear analyses of structural components are normally carried out by finite element codes making Use of constitutive theories in which the material response is separated into the two important groups of phenomena known as rate‐dependent “creep” and rate‐independent “plasticity.” A number of viscoplastic constitutive theories in which creep and plasticity effects are combined into a unified plastic strain model have recently been proposed and are still undergoing active development. In this paper, the constitutive equations of the Bodner‐Partom model are used to present the time dependent, inelastic properties of Inconel 718 at 650 °C. This representation covers a wide range of loading conditions. The developed numerical technique to establish the Bodner parameters is based on simulation with fourth‐order Runge‐Kutta integration coupled to a least square measure for good curve fitting to a series of tests. To determine the eight Bodner parameters, an error function consisting of the square of the difference between experimental and model strains was minimized in the time domain by a direct search method. The specific material parameters for the Bodner model were determined to best fit sets of tensile and creep data. The parameters so obtained are in good agreement with those obtained by other investigators. The present parameters generate better response curves than those from graphical methods used in earlier investigations.


Aerospace Engineering



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