The Yield Condition of Nodular Cast Iron Subjected to Triaxial Stresses

The yield stresses of ferritic nodular cast iron under triaxial stress states with various values of Lode's parameter over a wide range of hydrostatic stresses are obtained by operating testing apparatus under hydrostatic pressure. It is found that the yield stress is influenced by Lode's parameter and hydrostatic stress. The initial yield surface in principal stress space is derived from a model in which the stress concentration in matrix around spherical graphite nodules dispersed in the material is considered. Comparison of the experimental results with the theoretical results suggests that the initial yield surface of the material is unsymmetric with respect to the hydrostatic stress axis, swells in the negative side of the axis, and is a closed surface.