When external load is applied on a solid material, it tends to deform. Deformation occurs due to shifting of atoms from original position to a new position. Such shifting may be temporary (elastic deformation) or permanent (plastic deformation). In elastic deformation, atoms can completely regain their original lattice position after removal of external load; while in plastic deformation, such recovery is not complete and thus material retains its deformed shape and size.
Whatever be the case, in order to make such deformation by shifting the atoms form their stable position to another new position, substantial amount of energy is required. Based on the degree of deformation, energy requirement also varies. Capability of a solid material to absorb energy during deformation is measured by two different properties, called resilience and toughness. Maximum energy that a solid material can absorb while it is elastically deformed is called resilience. Similarly, maximum energy that a solid material can absorb while it is plastically deformed is called toughness. Since area under load-elongation curve (alternate name for stress-strain curve) indicate energy (Load × Elongation => N × mm => milli-joule => Energy), so both resilience and toughness can be indicated on stress-strain curve, as depicted below. Various similarities and differences between resilience and toughness are given in the following sections.
Similarities between resilience and toughness
- Both resilience and toughness indicate capability to absorb energy during deformation; however, resilience is associated with elastic deformation only, while toughness is associated with both elastic and plastic deformations.
- Moduli of both the properties have same unit and dimension.
Differences between resilience and toughness
| Resilience | Toughness |
|---|---|
| Resilience is defined as the ability of the solid material to absorb energy when it is elastically deformed. | Toughness is defined as the ability of the solid material to absorb energy until fracture occurs. |
| Modulus of resilience is the indication of resilience property of solid material. By definition, modulus of resilience is the energy, per unit volume, required to deform a particular solid material up to its elastic limit under tensile testing. | Modulus of toughness is the indication of toughness property of solid material. By definition, modulus of toughness is the energy, per unit volume, required for breaking a particular solid material under tensile testing. |
| Modulus of resilience is the area below engineering stress-strain curve up to elastic point. | Modulus of toughness is the total area below engineering stress-strain curve. |
| Value of modulus of resilience is smaller. | Value of modulus of toughness is much larger than modulus of resilience. |
| Resilience is important property to consider when high elastic deformation is desired, such as in springs. | Toughness is important consideration for metal forming processes (forging, bending, sheet metal operations, etc.). |
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