Abstract

The design and analysis of structural components to operate at elevated temperature and severe stress levels, such as a low-cycle fatigue-limited jet engine disk, require an accurate prediction of the nonlinear stress-strain . response encountered during the cyclic loading conditions. Nonlinear analysis of such components is normally carried out by a finite element code 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, an elastic-plastic finite element model incorporating the Bodner-Partom model of nonlinear time dependent material behavior is presented. The parameters in the constitutive model are numerically extracted by a least-square fit to experimental data obtained from unaxial stress-strain and creep tests at 65ifC. The finite element model of a double notched specimen is employe_d to determine the elastic-plastic strain and comparison is , made to experimental data. e The constitutive model parameters evaluated in this paper are found to be in good agreement with those obtained 'by other investigators. However, this numerical technique tends to give better agreement with the respo11Se curves than does the graphical methods used by the other investigators. The model calculated ef4$1jc-plastic strain agreed well with the experimental.

Disciplines

Aerospace Engineering

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URL: http://digitalcommons.calpoly.edu/aero_fac/91