Analytical and Experimental Study on the Effect of Discontinuities on Cast Steel Component Performance

Abstract

An experimental and analytical study is performed to investigate the effect of different discontinuities on the yield strength, ultimate strength and ductility of steel cast components. Steel plates containing various discontinuities were cast in sand molds, cut to size, and tested in monotonic tension to fracture. Radiographic imaging was used to identify, classify, and rate discontinuities. Three different types of discontinuity and three different ASTM 2868 indication levels were tested. The discontinuities varied in size from 0.46 percent to 9.09 percent of the average gross-section area of the specimens. Specimens rated Level 2 or lower tended to fracture at the minimum section, not at the discontinuity. Specimens with Level 5 indications tended to fracture at the discontinuity. Specimens that fractured at the discontinuity had reduced ductile capacity. Elongation was reduced by Level 5 indications by between 45.7 to 70.0 percent. Ductile fracture predictive models were used in finite-element analysis to predict component performance. Models used color data from radiography for discontinuity size. Good agreement is obtained between experimental and predicted elongation at fracture. The analytical modeling methods used in this thesis allow for accessible prediction of ductile capacity of a cast component.