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Micromechanical modeling of the ductile fracture process

Luo, Tuo
http://orcid.org/0000-0001-6921-1891
http://rave.ohiolink.edu/etdc/view?acc_num=akron153661073583016

Abstract Details

2018, Doctor of Philosophy, University of Akron, 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 triaxiality and the Lode parameter. The predicted material responses of three modified Gurson models are also investigated: GTN model, shear-modified-GTN model, and the shear-modified-GTN applied with anisotropic material model. A single material point test model equivalents to a computational cell of Gurson type models is utilized to demonstrate the effect of damage parameters and its evolution through the loading process when undergoing proportional stress loading. The shear-modified-GTN with anisotropic material model is implemented and calibrated using experimental data of commercially pure titanium, which exhibits complex plastic anisotropy and tension-compression asymmetry. The predicted results show good agreement with the experimental results obtained from various loading applications and specimen geometries. In addition, the predicted results also reveal the important effect of volumetric damage and shear damage under the influence of plastic anisotropy.
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)
180 p.
Mechanical Engineering
Ductile fracture; Plasticity; Anisotropic material; Void damage; Shear damage; Unit cell analysis; Finite element analysis; Stress triaxiality; Lode angle; Hydrogen embrittlement; Localization; Elastic unloading

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Citations

  • Luo, T. (2018). Micromechanical modeling of the ductile fracture process [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron153661073583016

    APA Style (7th edition)

  • Luo, Tuo. Micromechanical modeling of the ductile fracture process. 2018. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron153661073583016.

    MLA Style (8th edition)

  • Luo, Tuo. "Micromechanical modeling of the ductile fracture process." Doctoral dissertation, University of Akron, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron153661073583016

    Chicago Manual of Style (17th edition)

akron153661073583016
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This open access ETD is published by University of Akron and OhioLINK.