A Novel, Efficient Approach for Determining the Post-Necking True Stress-Strain Response of Aerospace Metals
Yatik Rashmin Shah
To numerically simulate and predict the plastic deformation of aerospace metals and alloys during extreme impact events (e.g., turbine engine blade-out and rotor-burst events, bird strikes, and foreign object damage), accurate 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 a true stress vs. true plastic strain curve. During tensile testing, the strain field in the specimen gage section evolves from a nearly homogeneous profile prior to necking to a heterogeneous profile after the onset of necking. Concomitantly, the customary analytical relationships used to convert between engineering stress-strain and true stress-strain break down after necking, since the state of stress is no longer homogeneous or uniaxial after necking. Thus, a number of approaches have been proposed and employed to correct the post-necking hardening response. Although effective, these approaches are generally complex and/or computationally expensive, which can be particularly problematic for large experimental programs. In this talk, a novel and efficient post-necking correction method is proposed and benchmarked. Using the equivalent true strain history obtained from a digital image correlation virtual strain gage placed at the fracture location, an approximate first-order analytical approach is used to calculate the corresponding equivalent true stress. This true stress calculation is used to generate a simple post-necking hardening law, using linear interpolation between known true stress-strain states at necking and fracture. This approach is successfully benchmarked using experimental data from a suite of metals with different crystal structures and hardening behavior: Inconel 625, Inconel 718, 17-4 precipitation hardening (PH) stainless steel, and Ti-6Al-4V titanium alloy.
Primary Advisor's Department
Mechanical and Aerospace Engineering
Stander Symposium, School of Engineering
Institutional Learning Goals
Scholarship; Practical Wisdom; Vocation
"A Novel, Efficient Approach for Determining the Post-Necking True Stress-Strain Response of Aerospace Metals" (2023). Stander Symposium Projects. 3240.