Creep Properties
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?
 Select image to enlarge
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.
Typical Applications
- Metal Working
- Springs
- Soldered Joints
- High-Temperature Materials
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