Elastic And Plastic Deformation

• Elastic and Plastic Deformation explains temporary vs permanent shape changes in materials under stress.
• Elastic and Plastic Deformation is key in material science for strength, durability, and design.
• When an external force is applied to a solid, it may change shape or size.
• This is called deformation.
• It can be elastic or plastic depending on the extent of the force and the material properties.
• Solids deform in two main ways under stress:

Elastic Deformation

• Definition: A temporary deformation. The material returns to its original shape after removal of stress.
• Cause: Stretching of interatomic bonds.
• Behavior: Linear stress-strain relationship (Hooke’s Law).
• Example in pharmaceutics: Microcrystalline cellulose exhibits predominantly elastic behavior.

Hooke’s Law:

$\sigma = E \cdot \varepsilon$

• Where:
  • E = Elastic modulus or Young’s modulus

Plastic Deformation

• Definition: A permanent deformation. The material does not return to its original shape after stress is removed.
• Cause: Irreversible movement of atoms or particles.
• Important in powder compression: Materials must undergo some plastic flow to form solid, coherent tablets.
• Example: Starch and calcium phosphate show more plastic deformation.

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