An Analytical Evaluation of The Effects of Idealized Macro-Indications on the Performance of Cast Steel Structural Components Under Uniaxial Tension

Abstract

This thesis presents work done to accurately model and quantify the behavior of indications in cast steel. An analytical evaluation of different indications was performed to determine how different indication characteristics affect the performance of cast steel. The end goal of this research is to create a comprehensive design guide for the use of cast steel in construction.A ductile fracture index (DFI) was calibrated based on the void growth model (VGM) and stress modified critical strain (SMCS) model. A set of coupons with different indications was modelled in the finite element (FE) software ANSYS, and matching physical specimens were tested. A modified SMCS and VGM were used to predict failure in the FE models. The predictions were compared to the peak load of the physical tests to determine their accuracy. Both the SMCS and VGM methods were found to be reasonably accurate with average errors of 16.6% and 10.2%, respectively. The modified SMCS is less computationally intensive than the VGM. Because of this, the modified SMCS is called DFI to differentiate it from the normal SMCS and is used for failure prediction in the analytical evaluation discussed in this thesis. A comprehensive study on indication characteristics and their effect on the ductility of cast steel was performed. A total of seventeen different indications were modelled using FE software with varying characteristics. Each indication was placed in a coupon of the same shape to allow each characteristic to be isolated. The indication characteristics studied were size, shape, sharpness, proximity to edges and other indications, and geometry. The size of indications and where they were in the geometry appeared to have little effect on the local ductility and performance of the cast steel. The shape, sharpness, and proximity of the indications all had marked effects on the predicted ductility and performance of the cast steel. In some cases with dramatic changes in indication geometry or two indications close together, the triaxiality was high enough to control failure. For most indications studied, however, the rate at which equivalent plastic strain increased relative to the deformation around the indication was the controlling factor in the performance of the casting. As the equivalent plastic strain increased faster, failure was predicted sooner. Thus, indications that caused the equivalent plastic strain to increase more quickly have a negative effect on the performance of cast steel. Indications that are sharper or that are closer to edges and other indications cause equivalent plastic strain to increase more quickly, which in turn causes failure to be predicted earlier. Complementary experimental verification of the analytical evaluation in this thesis has been performed and is discussed in another thesis by co-researcher, George Saphir (Saphir, 2024).