Crystal Plasticity Finite Element Modeling of Fatigue and Creep-Fatigue of Alloy 617 at High Temperature
U.S. Department of Energy (DoE), Nuclear Energy University Programs (NEUP) initiative.
Research Goal and Objectives
Develop novel testing and experimentally validated prediction methodologies for creep-dominated creep fatigue response of Alloy 617.
Overview of Computational Tasks:
Crystal Plasticity Theory:
Choice of Flow Rule and Evolution Equations:
- Softening is observed at the tension part of first load cycle for both fatigue and creep-fatigue tests. Similar softening is also observed in the compression part after strain hold in each cycle of creep-fatigue tests.
- Dislocation velocity increases with stress –> dislocation drag solutes hence extra resistance is produced –> dislocations accumulate enough energy to break solutes away from their equilibrium positions –> resistance drops as more and more solutes start moving together with dislocations.
- Strain hold –> dislocation velocity decreases with stress –> solutes settle down in new equilibrium positions –> softening happens when reverse loading is applied.
- In a fatigue tests, solutes do not have enough time to settle down in their new equilibrium positions as reverse loading follows immediately.
- Activation energy based flow rule for nickel-based alloy subject to cyclic loading at high temperatures (Busso):
- Slip resistance evolution (Busso): from statistically stored forest obstacles.
- Backstress evolution (Busso): from dislocations bowing between obstacles.
- New slip resistance evolution equation proposed by incorporating an static recovery which reflects the slip resistance changes caused by solute drag creep.