Calibration of a Ductile Fracture Method for Evaluating the Effects of Indications in Cast Steel

Abstract

This thesis presents research performed toward the calibration of a ductile fracture index (DFI) used for predicting the performance of steel castings. The research is primarily analytical; however, it is based on prior supporting experimental work and is to be used for future experimental work. The analytical research involves finite-element (FE) simulations of standard pull-coupons created using the general-purpose finite-element program ANSYS. The research consists of: (1) a parameter study examining indication size, number, spacing, type, and edge effects; (2) appropriate selection of DFI input and failure criteria; and (3) a mesh sensitivity study examining indication shapes, including smooth and jagged indications. The steel evaluated is cast and comparable to steel used in construction. The indications evaluated are primarily surface indications, but internal body indications are also included. An experimental program was also designed for the purpose of verifying the results of this analytical research and can be performed by future researchers. The goal of the DFI calibration effort is the development of a reliable methodology for designers to relate casting quality to structural performance. The results presented in this thesis: (1) show the effect on structural performance of the various indication parameters; (2) provide information on the appropriate selection of parameters and failure criteria for using the DFI; and (3) appropriate mesh sizes to use, including the indication-geometries that are impacted by mesh sensitivity. Recommendations are made for use of the DFI in the future experimental research.