As indicated in the accompanying diagram, the creep of a material can be divided into three stages. First stage, or primary creep, starts at a rapid rate and slows with time. Second stage (secondary) creep has a relatively uniform rate. Third stage (tertiary) creep has an accelerating creep rate and terminates by failure of material at time for rupture.
How to Perform a Creep Test?
To determine creep properties, a material is subjected to prolonged constant tension or compression loading at constant elevated temperature. Deformation is recorded at specified time intervals and a creep vs. time diagram is plotted. Slope of curve at any point is creep rate. If failure occurs, it terminates the test and the time for rupture is recorded. If specimen does not fracture within the test period, creep recovery may be measured.
How to Determine Stress-Relaxation?
To determine stress-relaxation of a material, the specimen is deformed a given amount and decrease in stress is recorded over prolonged period of exposure at constant elevated temperature. The stress-relaxation rate is the slope of the curve at any point.
- Metal Working
- Soldered Joints
- High-Temperature Materials