Creep Deformation

This blog page can be used for a last minute revision on the topic of 'Creep deformation' from the material science course.

Creep Deformation

- Creep Deformation is being defined as time dependent , permanent deformation and also under constant load or stress .

Examples of creep

- Sagging shelves

- Ruptured water pipe

Creep process

Part 1 : Dislocation Movement

- The low stress levels and heat energy is being applied. The dislocations in the lattice will take place slowly. Thus , the shape of the material will tend to differ slowly with time .

Part 2 : Vacancy Diffusion

- The low stress level which are less than yield strength and also heat energy is being applied. The atoms move and vacancies accumulate to form voids. Thus , the cross sectional area will decrease and  weaken the material.

- The voids are microscopic and can be detected only under a microscope. 

Creep strain vs time graph  

Creep strain vs time graph

Factors affecting the rate of the creep 

Magnitude of stress -  The greater the stress being exerted , the greater the amount of force to move the dislocations , leading to greater rate of creep.

Temperature -  When the temperature increases , the more heat energy is available for the vacancies to diffuse  , leading to a greater rate of creep .

Time -   Creep is time - dependent . The greater the amount of time  , the greater the amount of deformation.

Material Property - Creep depend on the melting point of the metal. ''T'' is the operating temperature. "T_m” . If the "T" is lower than 40% of  "T_m” ,   the creep will not occur in the metal.