In the present thesis, fatigue behavior of nodular cast iron (NCI) is investigated using micromechanical simulations. An elastic-plastic porous material experiences an increase in a void volume fraction with each cycle of loading. This is called void ratchetting. The hypothesis of this thesis is to explain the fatigue failure of NCI using void ratchetting mechanism. The strain-life, stress-life, notch support effect, and fatigue crack growth are studied using the micromechanical simulations. In all these studies, matrix material is defined as an elastic-plastic with isotropic/kinematic hardening. No damage law is used to define material degradation. The axisymmetric cell model is developed to study strain-life and stress-life approaches for fatigue. The cell model is subjected to cyclic loading and cycle by cycle simulations are carried out until failure. The failure of the cell model is defined based on the drop in the macroscopic response of the cell model. The notch support effect is investigated using a 2D plane strain model within stress-life concept. From the simulation results, strain-life and stress-life curves are extracted, and they are in qualitative and quantitative agreement with experimental data collected from literature. The fatigue crack growth is studied using a micromechanical cell model under small scale yielding conditions. The graphite particles are considered as voids, and they are resolved discretely in fracture process zone. The region outside of the fracture process zone is considered as a homogenized medium. When positive alternating loads are applied, ligaments in the fracture process zone show ratchetting behavior, which is responsible for an effective fatigue crack growth. This mechanism is relevant for the fatigue crack growth in NCI. The 2D plane strain boundary layer model is able to predict the effect of load ratio on threshold for the fatigue crack growth and the fatigue crack growth rate. The fatigue crack growth rate curves obtained from the simulations are compared with experimental data. It is essential to note that the void ratchetting (plastic collapse of the intervoid ligaments) is a crucial mechanism in NCI and more focus should be given to this mechanism as it is simple to implement and gives satisfying simulation results.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:72791 |
| Date | 19 November 2020 |
| Creators | Lukhi, Mehul |
| Contributors | Kuna, Meinhard, Münstermann, Sebastian, Technische Universität Bergakademie Freiberg |
| Publisher | Technische Universität Bergakademie Freiberg |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 2418092-0 |
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