Learning topic
Elastic and Plastic Deformation
The difference between elastic and plastic deformation, unloading behavior, permanent strain, and limits of elastic models.
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According to their behavior after unloading, deformations are commonly separated into elastic and plastic components. Real material response may also depend on time, loading rate, and temperature.
Elastic deformation
Elastic deformation disappears after the load is removed: within the adopted model, the body recovers its original shape and dimensions. At sufficiently low loads many engineering materials are approximated as linearly elastic.
Plastic deformation
Plastic deformation is irreversible. After unloading, permanent deformation remains. A real deformation process may contain both elastic and plastic components.
Time-dependent behavior
Some materials do not respond independently of loading duration. Creep is the development of deformation with time under sustained loading and can be especially important at elevated temperature. Stress relaxation is a decrease in stress with time while deformation is maintained. Viscoelastic behavior combines elastic response with time dependence.
Why the distinction matters
Linear-elastic equations cannot automatically be extended into ranges of significant plastic deformation or processes in which time and temperature are important. The calculation model must match the actual material response. Detailed stress-strain behavior is considered later with mechanical properties of materials.