YIELD SURFACE FOR GRAY CAST-IRON UNDER BIAXIAL STRESS

Biaxial plane stress experiments have been performed on cruciform specimens made of graphite grey cast iron. Different ratios of tensile and compressive loads were applied in two perpendicular directions. The primary objective of this investigation is to determine the locus of the yield surface (yield curve) under plane stress, and to establish yield functions that could model the elastoplastic behavior of grey cast iron with reasonably good accuracy. The experiments show that a sufficiently accurate description is obtained by using the ordinary von Mises yield function in the compressive-compressive region, and elsewhere, the von Mises yield function modified with a term containing the first stress invariant. It was also found that for tensile loadings nonelastic deformations develop at low stress levels. Use of the above yield function must therefore be accompanied by a very large hardening modulus for tensile loads.