Master of Science (M.S.), University of Dayton, 2021, Mechanical Engineering

To numerically simulate and predict the plastic deformation of aerospace metal alloys during extreme impact events (e.g., turbine engine blade-out and rotor-burst events, and foreign object damage), accurate experimental knowledge of the metal's hardening behavior at large strains is requisite. Tensile tests on round cylindrical specimens are frequently used for this purpose, with the metal's large-strain plasticity ultimately captured by an equivalent true stress vs. equivalent true plastic strain curve. It is now well known that if axial strain is measured using an extensometer, the equivalent true stress-strain curve calculated from this measurement is valid only up to the onset of diffuse necking. That is, once the strain field heterogeneously localizes in the specimen gage (onset of necking), extensometers, which average the strain field over the gage section, are unable to capture the local strain at the site of fracture initiation. Thus, a number of approaches have been proposed and employed to correct the post-necking hardening response. One commonly-used technique is an iterative approach commonly referred to as finite-element model updating (FEMU). This approach involves inputting a suite of candidate post-necking equivalent true stress-strain curves into finite-element software. The true stress-strain curve that produces the best agreement between simulation and experiment is ultimately adopted. In this document, a novel variation of this iterative approach is presented, aimed at decreasing computational expense and iterative effort with a better first guess that bounds this fan of prospective true stress-strain curves. In particular, we use local surface true (Hencky) strain data at the fracture location in an approximate analytical formula to generate a first guess curve and upper bound on the candidate true stress-strain fan of curves. To assess its performance and robustness, the proposed approach is verified using experimental data for a menu of ae (open full item for complete abstract)

Committee: Robert Lowe Ph.D. (Advisor); Luke Sheridan Ph.D. (Committee Member); Dennis Buchanan Ph.D. (Committee Member); Jeremy Seidt Ph.D. (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Mechanical Engineering; Mechanics