In every engineering application solid structures are subjected to external loading. Such loading can be broadly classified into two categories—normal load and shear load. Tensile and compressive loading are two different types of normal loading. All other types of loading such as bending, torsional, etc. are basically combination of these three basic types of loading. When sufficient external load is applied on a solid body, it undergoes deformation. The very basic mechanism of deformation is the shifting of layers of atoms from their original lattice position under the influence of external force.
When such shifting or displacement occurs in a very small length, the atoms can revert back to their corresponding lattice sites after external load is removed. Such deformation is termed as elastic deformation. Thus elastic deformation is temporary and makes no harm to the structures. However, if atoms displaced by a longer length then the deformation becomes permanent and full recovery becomes impossible. Such deformation is termed as plastic deformation and the entire structure can change its original shape and size because of it. Various similarities and differences between elastic deformation and plastic deformation are presented below in table form.
Similarities between elastic and plastic deformations
- Any type of loading (normal, shear or mixed) may result both types of deformations.
- Plastic deformation can occur only after the material is elastically deformed. So without elastic deformation, plastic deformation is not possible.
- Both elastic and plastic deformations are useful; however, based on the application.
Differences between elastic and plastic deformations
| Elastic Deformation | Plastic Deformation |
|---|---|
| Elastic deformation is a temporary deformation under the action of external loading. | Plastic deformation is the permanent deformation. |
| Once the external load is removed from an elastically deformed body, it regains its original shape. | When a body is plastically deformed, it retains its deformed shape even after the removal of external load. |
| In elastic deformation, atoms of the material are displaced temporarily from their original lattice site. They return back to their original position after the removal of external load. | In plastic deformation, atoms of the solid are displaced permanently from their original lattice site. They don’t return back to the original position even after the removal of external load. |
| Elastic deformation is characterized by the property Elasticity. By definition, elasticity is the property of the solid material by virtue of which it tends to regain its shape after the removal of external load. | Plastic deformation is characterized by the property Plasticity. By definition, plasticity is the property of the solid material by virtue of which it tends to retain its deformed shape even after the removal of external load. |
| Amount of elastic deformation is very small. | Amount of plastic deformation is quite large. |
| External force required for elastic deformation of solid is quite small. | Force required for plastic deformation is also higher. |
| Energy absorbed by the material during elastic deformation is called module of resilience. | Total energy absorbed by the material during elastic and plastic deformation region is called module of toughness. |
| Hooke’s Law of elasticity is applicable within this elastic region. | Hooke’s Law is not applicable if the material is plastically deformed. |
| Most solid materials display a linear stress-strain behavior within this elastic region. | Stress-strain curve is non-linear in plastic region. |
| Material first undergo elastic deformation under the application of external loading. | Plastic deformation occurs after it is elastically deformed due to the application of external loading. |
| Mechanical and metallurgical properties of the solid material remain unaltered when it is elastically deformed. | Many properties of the solid material change considerably for plastic deformation. |
References
- Book: Callister’s Materials Science and Engineering by R. Balasubramaniam (Wiley India). Buy this book
- Book: Introduction to Machine Design by V. B. Bhandari (McGraw Hill Education India Private Limited). Buy this book
- Book: A Textbook of Strength of Materials by R. K. Bansal (Laxmi Publications Private Limited). Buy this book
- Book: Strength of Materials by S. S. Rattan (Tata McGraw Hill Education Private Limited). Buy this book