ANALYTICAL EVALUATION OF CASTING QUALITY EFFECTS ON STRUCTURAL PERFORMANCE OF CAST STEEL NODES

Abstract

This thesis presents model development and analytical studies toward the prediction of theperformance of cast components of varying quality. The modeling extends work from previous phases of the research program which demonstrated a promising failure prediction model based on the Ductile Fracture Index (DFI). In this approach, finite element analysis (FEA) is used to create representative analytical models of typical cast geometries with various imperfections (e.g. porosity, inclusions, etc.), referred to as indications. These indications are modeled discretely inside the body of the cast components in the simulation model. FEA is then used to apply structural loading to the models and interpret performance by evaluating: (1) ductility; (2) strength; and (3) failure location. In this thesis work, the DFI approach is examined in comparison to or in combination withthe Gurson-Tvergaard-Needleman (GTN) porous metal model. The GTN approach can analyze the effects of porosity within cast nodes without discrete indication modeling. The ultimate objective of the research is the evaluation of cast steel structural nodes of realistic geometry under typical engineering loading scenarios. These model representations include: (1) A planar truss assemblage in a K-shaped node configuration; and (2) a moment-frame joint assemblage in a T-Shaped node configuration. The primary focus of the thesis research is the development and evaluation of computational tools and analysis methods needed to evaluate the cast nodes. Preliminary findings are also presented. Preliminary results of the analytical models show a high stress triaxiality component in asubset of models with concentrations of severe indications in or near the geometric transitions in the T-Node Castings near the Hollow Structural Steel (HSS)-to-casting interface. This high stress triaxiality, combined with a concentration of effective plastic strain, cause early failure in such specimens. The models and approaches developed in this thesis permit subsequent research to fully evaluate the performance of realistic cast nodes of differing quality.