Doctor of Philosophy, University of Akron, 2018, Mechanical Engineering

This dissertation aims to develop valid numerical approaches to investigate the micromechanics of ductile fracture process and predict the ductile material failure under various loading conditions. As the first portion of this work, a layered unit cell micromechanics model is proposed. This model consists of three void containing material units stacked in the direction normal to the localization plane. Localization takes place in the middle material unit while the two outer units undergo elastic recovery after failure occurs. Thus, a failure criterion is established as the material is considered failure when the macroscopic effective strain of the outer material units reaches the maximum value. Comparisons of the present model with several previous models suggest that the present model is not only easy to implement in finite element analysis but also more suitable to robustly determine the failure strain. A series of unit cell analyses are conducted for various macroscopic stress triaxialities and Lode parameters to investigate the dependency of failure strain on stress state. The analysis results also reveal the effect of the stress state on the deformed void shape within and near the localization band. Additionally, analyses are conducted to demonstrate the effect of the voids existing outside the localization band. Next, the unit cell model is utilized to investigate the effect of hydrogen on ductile fracture demonstrated by its influence on the process of void growth and coalescence. The evolution of local stress and deformation states results in hydrogen redistribution in the material, which in turn changes the material's flow property due to the hydrogen enhanced localized plasticity effect. The result shows that hydrogen reduces the ductility of the material by accelerating void growth and coalescence, and the effect of hydrogen on ductile fracture is strongly influenced by the stress state experienced by the material, as characterized by the stress tr (open full item for complete abstract)

Committee: Xiaosheng Gao Dr. (Advisor); Chang Ye Dr. (Committee Member); Gregory Morscher Dr. (Committee Member); Ernian Pan Dr. (Committee Member); Chien-Chung Chan Dr. (Committee Member) Subjects: Mechanical Engineering