1. Continuum Mechanics Mohsen Malayjerdi

2. » Strain : intensity of deformation strain = change in length/original length » Stress : intensity of force Stress = force/ area (MPa, psi) » Strain rate: rate of change in strain with time, units of time -1

3. » Creep: Time dependent deformation of a material/component under load. Original h F Compressed ∆h ∆h Time Instantaneous elastic deformation Instantaneous elastic recovery force applied force removed Elastic Materials:

4. » Creep: Time dependent deformation of a material/component under load. Viscoelastic Materials: Original h F Compressed ∆h Instantaneous elastic deformation ∆h Time force applied force removed retarded deformation (creep) Instantaneous elastic recovery retarded recovery permanent deformation

5. » Time Dependent Deformation

7. » Where Does it Occur? Combustion chambers (gas & oil fired furnaces) Pressurized piping (steam power plants, nuclear plants, heat exchangers) Blades and components in gas turbines (Jet engines, power plant turbines)

8. » Creep Curve: 1) Primary: Strain rate slow due to work hardening 2) Secondary: Strain rate constant Balance of work hardening and anealing 3) Tertiary: Strain rate constant Necking Phenomena

9. » Mechanism of Creep Deformation Creep occurs as a result of the diffusion of vacancies Thermal energy (temperature) is a catalyst for diffusion

10. » Ageing hardening: Aluminium alloys + Cu, Mg, Zn, Sc warm it to the point that all solute is solubilized Then rapid cooling (quench) In order to reduce the system energy, diffusion of atoms and vacancies occurs

11. » Creep Age forming (CAF): a process in which a part, usually an aluminium machined plate, is forming by creep on a tool at the same time that an ageing precipitation heat treatment is conducted.

12. » CAF process :