Seminar

A configurational energy criterion using discrete dislocation plasticity for the prediction of fatigue crack nucleation sites in Ni superalloys

Nikoletta Prastiti

Department of Mechanical Engineering

Monday 25th February 2019
Time: 12.00pm
Venue: Room G01, Royal School of Mines, Imperial College London
Contact: Ms Hafiza Bibi
Tel: 020 7594 7252

Abstract: High-performance nickel-based superalloys commonly find application as safety critical rotatory components in the automotive, power and aerospace industries due to their exceptional mechanical properties. This kind of application involves cyclic loading and therefore, the dominating failure mechanism is fatigue. The stage of crack nucleation during fatigue may consume a considerable fraction of the life of an engineering component compared to that for crack propagation. In addition, the former is not as well understood, in the sense of obtaining useful quantitative predictions of safe component lifetimes and therefore leading to highly conservative and expensive safe-life component design. The key for accurate quantitative predictions lies in the mechanistic understanding of crack nucleation.

A new stored energy criterion [1] that has been established and used within a crystal plasticity framework to predict the location of fatigue crack nucleation sites, has been reproduced in a more fundamental way using a discrete dislocation methodology [2] that explicitly represents the dislocations and dislocation pile ups in regions that could potentially act as fatigue crack nucleation sites.  Integrated experimental, characterisation and computational crystal plasticity studies in Ni single and oligo crystals [3] were used for the critical appraisal of the new discrete dislocation approach which showed satisfactory qualitative agreement.

 

[1]  Wan, V. V. C., D. W. MacLachlan, and F. P. E. Dunne. "A stored energy criterion for fatigue crack nucleation in polycrystals." International Journal of Fatigue 68 (2014): 90-102.

[2]  Van der Giessen, Erik, and Alan Needleman. "Discrete dislocation plasticity: a simple planar model." Modelling and Simulation in Materials Science and Engineering 3.5 (1995): 689.

[3]  Chen, Bo, Jun Jiang, and Fionn PE Dunne. "Microstructurally-sensitive fatigue crack nucleation in Ni-based single and oligo crystals." Journal of the Mechanics and Physics of Solids 106 (2017): 15-33.

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