- Stress is defined as the resistance force acting per unit cross-section area of a body. It is calculated as the applied load divided by the cross-sectional area. - The main types of stress are normal stress, shear stress, tensile stress, and compressive stress. Tensile stress results from pulling forces, while compressive stress is from pushing forces. - Shear stress acts tangentially across a surface. Elasticity refers to a material's ability to deform under stress but return to its original shape when the stress is removed, as described by Hooke's law.

1. APPILED MECHANIC
AND SOM
BY SINY MARY LONA

2. STRESS AND STRAIN
Stress is defined as the resistance force acting per unit cross-section area of the body. It is also
defined as the ratio of applied load to the cross section area of the body.

3. UNITS OF STRESS
Since the unit of load is N and the unit of cross section area is m2 or cm2 or mm2. So the SI unit of
stress is N/m2 or N/cm2 or N/mm2. Generally in the numerical problems we
use N/ m2 or N/mm2.
Relation between units of stress:
1 MN/m2 = 106
N/m2
= 102
N/cm2

4. TYPES OF STRESS
The various types of stress in the strength of materials are:
1. Normal Stress:
the stress that acts perpendicular to the cross-section area is called normal stress.
Normal stress is further subdivided into two types
1. Tensile stress
2. Compressive stress

5. Tensile Stress:
When a body is subjected to two equal and opposite pulls, than the stress induced in the body
is called tensile stress. Tensile stress results in the increase in length and decrease in the cross
section of the area of the body.Tensile stress acts normal to area and its pull to area.
P= Full or force acting on body
A=Cross section of body
A bar subjected to a tensile load P at its end.

7. A bar is subjected to Tensile load P at its end.Consider secX-Xwhich divides bar
into 2 parts
Left part to section X-X is in equilbrium if P=R
Similarly Right part of section X-X is in equilbrium P=R
Thus resisting force per unit area is known as Stress or Intensity of stress
Thus tensile stress 𝜎= Resisting Force/Area=R/A
=Applied Load/Area=P/A

8. TENSILE STRAIN

9. Tensile Strain= Increase in length/original Length
=dL/L
Where dL=Increase In length
L=Original Length

10. Compressive Stress
When 2 equal and opposite pushing force are applied on a body stress due to this
force is known as Compressive stress

11. Stress induced in a body when subjected to equal and opposite pushes.As a result
there is decrease in length of body is known as Compressive Stress
Compressive Stress acts normal to the area and pushes the area.
Let Axial push P acting on cross section A
Compressive Stress=Resisting Force /Area
Under equilbrium load Condition
𝜎C=
R/A=P/A

12. Compressive Strain

14. Shear Stress
Define Shear Force:
Shearing is infact the slipping of one layer over another under action of
force. Chopping vegetables is by direct shear. Shaving hair is another
excellent example of shearing due to shear stress. All operations carried out
by scissors are shearing.

16. Shear Stress
Stress Stress :Stress induced in a body when subjected 2 equal and opposite
forces which are act tangentially across the resisting section as a result of which
body tends to shear off across the section known as shear Stress and
corresponding strain is known as Shear strain.

17. Shear Stress

18. Consider a rectangular block of height ‘h’ and Length ‘L’
Let bottom face AB of block be fixed to surface
Let a force ‘F’ be applied tangentially along the top surface CD of block such that
such force acts tangentially along the surface known as shear stress.
𝛕=F/A
Shear Strain=𝛥L/L

19. Elasticity:

20. Defination of Elasticity

22. Elastic Limit: It is a value beyond which material will not regian to its original
shape.

23. Hook’s Law

24. Hooks Law : When a material is loaded within elastic limit,stress is proportional
to strain produced by stress.
Ratio of Stress to corresponding strain is constant within elastic limit.This
constant is known as Modulus of Elasticity.
Hooke's law states that the strain of the material is proportional to the applied stress within
the elastic limit of that material. When the elastic materials are stretched, the atoms and
molecules deform until stress is been applied and when the stress is removed they return to
their initial state.