Creep Flashcards
What is creep?
A failure mechanism caused by prolonged constant loads at high temperatures. It is a time-independent deformation.
Can occur at stress below yield strength at elevated temperatures.
What are the 3 stages of creep?
Primary creep - deformation rate decreases due to work hardening - the slope of the curve decreases
Secondary creep - constant rate of creep - the rate of work hardening is balanced by the rate of recovery leading to stable deformation
Tertiary creep - accelerated creep rate leading to failure - associated with high stress and high temperature causing necking
What are some methods of improving creep resistance?
- High melting point
- Coarse grains (for high-temperature applications)
- Introducing stable precipitates that do not grow in grains and at grain boundaries
- Grains parallel to the load
- Low stacking fault for FCC crystals.
What is a split dislocation in FCC crystal structures?
When two partial dislocations meet in an FCC material and from a net Burgers vector. This vector isn’t part of any of the slip planes, therefore it acts like an obstacle for dislocation, hindering deformation.
What is stacking fault energy?
When layers of the structure are missing leading to the formation of a new crystal structure. This can be a consequence of dislocations moving in the lattice.
Because dislocations are far apart from each other this reduces the energy of the system
But locally the energy is increased because another crystal structure is fromed.
