Modeling stress development during the solidification of gray iron castings

Abstract

A method has been developed to predict stress development in gray iron foundry castings. A new yield function, based on theoretical developments by Frishmuth and McLaughlin,⁹ and on experiments by Coffin¹⁰ was implemented as a user-written element in a commercial finite element package. The yield function takes into account the strong dependence of the yield stress in cast irons on the loading path. Stresses resulting from thermal displacements in the cooling casting are computed using the new yield function in an elastic-viscoplastic stress analysis. In earlier work, techniques were developed to represent the mold in the thermal analysis by sets of boundary conditions on the surface of the part. For this work, a second user-written element was used to apply force-displacement boundary conditions on the surface of the casting to represent the mechanical constraint of the mold. The properties for this element were based on soil mechanics considerations. Example problems are given, showing a substantial difference in the computed stresses when using the present formulation, in comparison to results obtained with the more usual von Mises yield function.