Date of Award
Fall 2023
Project Type
Dissertation
Program or Major
Mechanical Engineering
Degree Name
Doctor of Philosophy
First Advisor
Brad L Kinsey
Second Advisor
Marko Knezevic
Third Advisor
John T Roth
Abstract
Stress superposition is defined as the incorporation of additional stresses into an existing manufacturing process during a single operation. In this thesis, experiments, simulations, and modeling of stress superposition in sheet metal deformation were investigated. Stress superposition can be used in manufacturing to reduce forming forces, increase material formability, and tailor the final part properties of products according to their intended applications, creating so-called functionally graded materials. Austenitic stainless steels (SS) were the focus due to their susceptibility to strain-induced phase transformation from austenite to martensite based on the stress state applied. In the first chapter, a novel cruciform specimen was designed to improve material characterization and modeling, which were essential to accurately determine how to adjust the parameters of the manufacturing processes to affect the final part properties. Next, parameters were identified for a martensitic transformation kinetics model experimentally and implemented into a single point incremental forming finite element model. The simulations were validated by experimental results for a truncated square pyramid. After that, To demonstrate the stress superposition strategy with corresponding finite element analyses, the superposition of tensile and compressive stresses into single point incremental forming was used to vary the phase transformation in the formed parts. Then, the continuous bending under tension process was used to investigate the residual stress development and phase transformation under the complex stress states inherent to the process. In future research, these results will inform further studies focused on exploiting stress superposition to improve metal forming processes, e.g., manufacturing heterogeneous trauma fixation hardware components, i.e., implants to hold fractured bones together during healing, using double-sided incremental forming as a proof-of-concept for the application of this work in industry.
Recommended Citation
Mamros, Elizabeth Marie, "Affecting Martensitic Transformation and Residual Stress Development Through Stress Superposition and Incremental Forming" (2023). Doctoral Dissertations. 2795.
https://scholars.unh.edu/dissertation/2795