This document discusses deformation of solids under stress. It defines elastic deformation as temporary deformation that returns to the original shape when stress is removed. Plastic deformation is permanent and the material retains its deformed shape. Elastic deformation involves small amounts of strain and follows Hooke's law, while plastic deformation has larger strains and does not follow Hooke's law. The document also defines stress, strain, elastic modulus, Hooke's law, and the Heckel equation as they relate to deformation of solids.

1. DEFORMATION OF SOLID
Kiran C Rodge
Shivlingeshwar college of Pharmacy,
Almala, Tq-Ausa,Dist-
Latur,Maharashtra

2. Elastic and Plastic Deformation
O Elasticity is the measure of the amount that the object can return
to its original shape after these external forces and pressures stop.
O Plasticity is when something is stretched, and it stays stretched,
the material is said to be plastic. When energy goes into changing
the shape of some material and it stays changed, that is said to
be plastic deformation.

3. 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.
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.
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.

4. Stress
stress is defined as a force applied per unit area. It is given by the
formula
Stress = Force/Area
σ = F/A (unit is N/mm2)
σ is the stress applied
F is the force applied
A is the area of force application

5. Stress applied to a material can be of two types. They are:
● Tensile Stress:
It is the force applied per unit area which results in the increase in
length (or area) of a body. Objects under tensile stress become thinner
and longer.
● Compressive Stress:
It is the force applied per unit area which results in the decrease in
length (or area) of a body. The object under compressive
stress becomes thicker and shorter.

6. What is Strain?
According to the strain definition, it is defined as the amount of ratio
of change in dimensions due to applied stress to the original
dimensions of the body.
The relation for deformation in terms of length of a solid is given
below.
ϵ=δl / L
where,
ϵ is the strain due to stress applied
δl is the change in length
L is the original length of the material.

7. Depending on stress application, strain experienced in a body can be
of two types. They are:
● Tensile Strain: It is the change in length (or area) of a body due to
the application of tensile stress.
● Compressive Strain: It is the change in length (or area) of a body
due to the application of compressive strain

8. Elastic modulus
O Elastic modulus is defined as ratio of stress to strain of an
object..
δ = Stress / Strain

9. Specifying how stress and strain are to be measured, including
directions, allows for many types of elastic moduli to be defined. The
three primary ones are:
1.Young's modulus (E)
It is defined as the ratio of tensile stress to tensile strain. It is often
referred to simply as the elastic modulus.
2.The shear modulus or modulus of rigidity (G )
It is defined as shear stress over shear strain. The shear modulus is
part of the derivation of viscosity.
3.The bulk modulus (K)
It is defined as volumetric stress over volumetric strain, and is the
inverse of compressibility. The bulk modulus is an extension of
Young's modulus to three dimensions.

10. Hooke’s law
It states that when a material is loaded within its elastic limit, the
stress is directly proportional to the strain.
Stress α Strain
σ α e
σ = Ee
Where,
E - Young‟s modulus in N/mm2
σ - Stress
e - Strain

11. Heckel Equation…
D = Density of powder
K = constant
P = Applied pressure
A = Particle rearrangement