Aerospace Engineering PhD Candidate: Shardul Panwar, Dissertation Chair: Assoc. Prof. Veera Sundararaghavan

In this dissertation, we develop numerical and analytical models to primarily predict microstructural effects on fatigue crack growth and subsequent long crack growth behavior. In the macro-scale, the new contribution is a variational multiscale cohesive method (VMCM) to determine the fatigue crack growth rates in the long crack growth regime. The calibration of the macro-scale VMCM cohesive parameters, which represent the crack tip mechanics, is addressed with the development of a linear elastic fracture mechanics-based irreversible cohesive model. In the micro-scale, we develop a VMCM approach that incorporates local microstucture and predicts the microstructurally short crack growth paths through slip planes that are in multiple grains and across grain boundaries. To calibrate the cohesive parameters, a dislocation theory-based cohesive model is employed that efficiently predicts the microstructurally short fatigue crack growth rates through multiple grains. The last chapter extends a three-dimensional microstructurally short fatigue crack growth model in order to better understand the sub-surface crack interactions with multiple grain boundaries. This method is utilized to model two cases of microstructurally short fatigue crack-grain boundary interactions in magnesium WE43 alloy. Thus, the tools developed in this dissertation aid in improving our understanding of the multiscale fatigue response.


Publications

Journals

Panwar, S. and V. Sundararaghavan. On the application of the distributed dislocation technique to the Interactions of Microstructurally Short Fatigue Cracks with Grain Boundaries in Magnesium WE43 Alloy, in preparation for the International Journal of Fatigue.

Panwar, S. and V. Sundararaghavan. A Fracture Mechanics-Based Irreversible Cohesive Model for Long Fatigue Crack Growth regime, in preparation for the International Journal of Fatigue.

Panwar, S., J. Adams, J. Allison, W. Jones, and V. Sundararaghavan. A Grain Boundary Interaction Model for Microstructurally Short Fatigue Cracks, submitted as a Technical Note to the International Journal of Fatigue (2017).

Panwar, S. and V. Sundararaghavan. Dislocation Theory-Based Cohesive Model for Microstructurally Short Fatigue Crack Growth. Materials Science and Engineering: A 708 (2017): 395-404.

Panwar, S., S. Sun, and V. Sundararaghavan. Modeling Fatigue Failure using the Variational Multiscale Method. Engineering Fracture Mechanics 162 (2016): 290-308.

Conferences

Panwar, S., V Sundararaghavan, Modeling the Influence of Microstructural Features on Microstructurally Short Cracks in a Mg Alloy, Symposium MB6: Cyclic Deformation and Fracture at the Nanoscale, MRS Fall meeting and exhibit, Boston MA, Nov 27-Dec 2, 2016.

Panwar, S. and V. Sundararaghavan, Modeling Fatigue Failure using a Variational Multiscale Method, 11th World Congress on Computational Mechanics (WCCM XI), Barcelona Spain, 20-25 July 2014.

Patent

Umesh N. Gandhi, Yuyang Song, and Panwar, S., Bumper Design using Shear Thickening Fluids, U.S. Patent Application Submitted, 2017.