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Deformation

The deformation measures how much an object deforms from its original dimensions or size in a given direction. Depending on which deformation you measure, you can calculate different types of strain.

strain - definition - mechanics

A deformation is called elastic deformation if the stress is a linear function of strain. In other words, stress and strain follow Hooke’s law. Beyond the linear region, stress and strain show nonlinear behavior, and this inelastic behavior is called plastic deformation.

Hooke's lawElastic Deformation

Elastic deformation and elastic strain is a transitory dimensional change that exists only while the initiating stress is applied and disappears immediately upon removing the stress. When a metal is subjected to a load (force), it is distorted or deformed, no matter how strong the metal or light the load. This deformation may or may not be permanent. Up to limiting stress, a body will be able to recover its dimensions on the removal of the load. The applied stresses cause the atoms in a crystal to move from their equilibrium position. All the atoms are displaced the same amount and maintain their relative geometry. When the stresses are removed, all the atoms return to their original positions, and no permanent deformation occurs.

Plastic Deformation

permanent deformationPlastic deformation and plastic strain is a dimensional change that does not disappear when the initiating stress is removed. If the limiting load is exceeded, the body will experience permanent deformation on the removal of the load. Plastic deformation occurs in material bodies after stresses have attained a threshold value known as the elastic limit or yield stress and result from a slip or dislocation mechanism at the atomic level.

 

References:
Materials Science:
  1. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  2. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
  3. William D. Callister, David G. Rethwisch. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.
  4. Eberhart, Mark (2003). Why Things Break: Understanding the World by the Way It Comes Apart. Harmony. ISBN 978-1-4000-4760-4.
  5. Gaskell, David R. (1995). Introduction to the Thermodynamics of Materials (4th ed.). Taylor and Francis Publishing. ISBN 978-1-56032-992-3.
  6. González-Viñas, W. & Mancini, H.L. (2004). An Introduction to Materials Science. Princeton University Press. ISBN 978-0-691-07097-1.
  7. Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing, and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
  8. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

See above:

Strength