Effects of Hydrostatic Pressure on the Flow Stress of Cast Iron

A theory is developed in this paper to explain the effects of hydrostatic pressure on the deformation of cast iron. It is assumed that a graphite flake in an iron matrix acts as a penny-shaped crack. The external stresses necessary to induce a finite plastic zone near the crack tip are calculated with rough approximation. The analysis provides a qualitative explanation of the following experimental evidences : (1) Superposed hydrostatic pressure increases the flow stress of cast iron. (2) The increase of flow stress due to hydrostatic pressure is reversible with respect to the hydrostatic pressure. (3) Hydrostatic pressure decreases the anisotropy of cast iron usually observed in torsion tests.