| タイトル | A Geometric Approach to Modeling Microstructurally Small Fatigue Crack Formation |
| 本文（外部サイト） | http://hdl.handle.net/2060/20100024243 |
| 著者（英） | Ingraffea, A. R.; Christ, Robert J., Jr.; Littlewood, David J.; Maniatty, Antionette M.; Bozek, J. E.; Veilleux, M. G.; Hochhalter, Jake D. |
| 著者所属（英） | NASA Langley Research Center |
| 発行日 | 2010-06-01 |
| 言語 | eng |
| 内容記述 | The objective of this paper is to develop further a framework for computationally modeling microstructurally small fatigue crack growth in AA 7075-T651 [1]. The focus is on the nucleation event, when a crack extends from within a second-phase particle into a surrounding grain, since this has been observed to be an initiating mechanism for fatigue crack growth in this alloy. It is hypothesized that nucleation can be predicted by computing a non-local nucleation metric near the crack front. The hypothesis is tested by employing a combination of experimentation and nite element modeling in which various slip-based and energy-based nucleation metrics are tested for validity, where each metric is derived from a continuum crystal plasticity formulation. To investigate each metric, a non-local procedure is developed for the calculation of nucleation metrics in the neighborhood of a crack front. Initially, an idealized baseline model consisting of a single grain containing a semi-ellipsoidal surface particle is studied to investigate the dependence of each nucleation metric on lattice orientation, number of load cycles, and non-local regularization method. This is followed by a comparison of experimental observations and computational results for microstructural models constructed by replicating the observed microstructural geometry near second-phase particles in fatigue specimens. It is found that orientation strongly influences the direction of slip localization and, as a result, in uences the nucleation mechanism. Also, the baseline models, replication models, and past experimental observation consistently suggest that a set of particular grain orientations is most likely to nucleate fatigue cracks. It is found that a continuum crystal plasticity model and a non-local nucleation metric can be used to predict the nucleation event in AA 7075-T651. However, nucleation metric threshold values that correspond to various nucleation governing mechanisms must be calibrated. |
| NASA分類 | Metals and Metallic Materials |
| レポートNO | LF99-9323 |
| 権利 | Copyright, Distribution under U.S. Government purpose rights |
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