PhD Thesis Final Examination (Defense)
 

Jamshid Fariborz

(Advisor: Dr. Claudio Di Leo)

Numerical Framework for Understanding and Predicting Microstructural Effects on Environment-Induced Cracking of Al Alloys
 

Tuesday, August 11
9:00 a.m. 
Weber 200

Abstract: 
The presence of hydrogen along grain boundaries (GBs) in alloys significantly degrades mechanical properties by reducing both the critical strength and fracture energy of these boundaries. Understanding hydrogen transport and identifying hydrogen-concentrated regions are therefore essential for predicting material behavior and failure mechanisms. This study investigates stress-driven hydrogen diffusion in alloys undergoing large elasticplastic deformations, with the aim of identifying key factors influencing damage evolution. The developed framework models the hydrogen diffusion between the Aluminum grains and grain boundaries during deformation and inter-granular fracture that allows us to study the effects of the accumulated hydrogen in the material on damage evolution. Through a systematic 2D sensitivity analysis, we examine the effects of varying microstructure geometries, loading rates, and environmental conditions. Our model accounts for accelerated hydrogen diffusion along GBs compared to lattice diffusion within grains, as well as isotropic plastic deformation of grains connected via GBs, which are modeled using a linear traction-separation law. The coupling between hydrogen diffusion and mechanical response arises from (i) hydrogen-induced GB degradation and (ii) stress-driven diffusion in both grains and GBs. The numerical implementation of this multiphysics model is performed using the finite element software ABAQUS. Our simulations successfully capture the strain-rate-dependent transition from ductile to brittle fracture modes, providing insights into hydrogen embrittlement mechanisms.

Committee:

• Dr. Claudio Di Leo (advisor), School of Aerospace Engineering
• Dr. George A. Kardomateas, School of Aerospace Engineering 
• Dr. Graeme J. Kennedy, School of Aerospace Engineering
• Dr. Christos E. Athanasiou, School of Aerospace Engineering 
• Dr. Josh Kacher, School of Materials Science and Engineering