Elasticity: Elasticity is the property of a material to regain its original shape and size after the removal of applied force. It obeys Hooke’s Law within the elastic limit.
Plasticity: Plasticity is the property of a material to undergo permanent deformation without breaking when subjected to external forces beyond the elastic limit.
Chapter 8 Mechanical Properties of Solids focuses on the behavior of solid materials under various forces. It explains stress strain elasticity plasticity and the relation between them. Key topics include Young’s modulus bulk modulus shear modulus and Poisson’s ratio. These principles are crucial for understanding material strength and real-world engineering applications.
Deforming Force: A deforming force is any force applied on the outside to change the shape or size of a material. Such forces can result in either elastic or plastic deformation depending on the intensity of the applied force and material characteristics. Deforming forces can occur from tension, compression, shear, or torsion.
Elasticity:
Elasticity refers to a material’s ability to regain its original shape and size after removal of the applied deforming force. Some materials exhibit this so that they can be deformable in a temporary manner while characteristically, stress and strain are directly proportional within the elastic limit. Restoration to the original state is made possible by interatomic forces.
Plasticity:
Plasticity is the ability of a material to undergo permanent deformation once it has been subjected to a deforming force greater than its elastic limit. Once the force is removed, the material will not return to its original shape and will have altered its structure. Plastic behavior is characterized by a lack of proportionality between stress and strain once the elastic limit has been reached.
Perfectly Elastic Bodies:
Perfectly elastic bodies are materials that can return to their original shape and size after the removal of any applied deforming force, regardless of the magnitude of the force, as long as it does not exceed the material’s elastic limit. They exhibit linear stress-strain behavior and follow Hooke’s Law throughout their entire range of deformation.
Example: An ideal rubber band behaves like a perfectly elastic body, which means it stretches and returns to its original shape once the deforming force is removed.
Perfectly Plastic Bodies:
Perfectly plastic bodies are the ones that fail to regain the shape once they lose the externally applied deforming force. Thus, they go for permanent deformation with no evidence of elastic deformation. After yield point, more stress will create only plastic deformation with no further rise in the level of stress.
Example: Modeling clay is an example of a perfectly plastic body, as it can be easily shaped and will retain the new shape after the applied force is removed.
Understanding these concepts is essential for studying material behavior under various forces and applications in engineering and materials science.