simple definition of stress, stain and load ... description of its types

1. STRESS, STRAIN &
LOAD

2. Load
 A load may be defined as a force tending to effect and
produce deformations, stresses or displacements in the
structure.
 Common loads in engineering applications are tension and
compression
 Tension :- Direct pull
ex :- Force present in lifting hoist
 Compression :- Direct push
ex :- Force acting on the pillar of a building
 Sign convention followed: Tensile forces are positive and
compressive negative

3. Types of load
 There are a number of different ways in which load can
be applied to a member. Typical loading types are:
(a) Dead/ Static load
(b) Live load
(c) Impact load or shock load
(d) Cyclic loads & Repeated loading

4. Dead Loads
“ Non fluctuating or static forces generally caused by
gravity and relatively constant for an extended time.”
Weight of the structure
Ex :- Floors, Beams, Roofs
Loads that are “always there”

5. Dead Loads

6. Live Loads
“ Load due to dynamic effect. This are usually
unstable or moving loads.”
Loads that may move or change mass or weight
ex: People, furniture, equipment
Load exerted by a lorry on a bridge

7. Live Loads

8. Impact loads:
Impact load is caused by vibration or impact or
acceleration.
The dynamic effect on a stationary or mobile body
as imparted by the short, forcible contact of
another moving body.
 A mass, with a known velocity, hitting an object
and thereby causing a suddenly applied impact
load.

9. Cyclic load
“A load which is applied over and over.”
Cyclic load on a structure can lead to fatigue damage
or failure. These load can be repeated loading on a
stricture or can be due to vibration.
 For example, if you twist a wire again and again
with the same effort, it breaks after a point, though
you're applying the same force.

10. Strain
When a body is subjected to some external force, there
is some change of dimension of the body. The ratio of
change of dimension of the body to its original
dimension is known as strain.
Strain is a dimensionless quantity.

11. Types of strain
a) Tensile strain
b) Compressive strain
c) Volumetric strain
d) Shear strain

12. Types Of Strain
 Tensile strain :- Ratio of increase in length to original length of
the body when it is subjected to a pull force.
 Compressive strain :- Ratio of decrease in length to original
length of the body when it is subjected to a push force.
 Volumetric strain :- Ratio of change of volume of the body to
the original volume.
 Shear strain :- Strain due to shear stress.

13. Stress
 When a material is subjected to an external force, a
resisting force is set up within the component, this
internal resistance force per unit area is called stress.
 SI unit is N/m² or Pascals
 1kPa=1000Pa, 1MPa=10 Pa, 1 Gpa=10 Pa,⁶ ⁹
1 Terra Pascal=10¹² Pa

14. Types of stress
1) Normal stress :- It is the stress which acts in direction
perpendicular to the area.
Normal stress is further classified into tensile
stress and compressive stress.
It consists ;
a. Tensile stress
b. Compressive stress
2) Shear stress

15. Tensile stress
 It is the stress induced in a body, when it is
subjected to two equal and opposite pulls
(tensile forces) as a result of which there is a
tendency in increase in length.
 It acts normal to the area and pulls on the area.

16. Tensile stress
Under tensile stress the bar suffers stretching or elongation

17. Tensile stress
Consider a uniform bar of cross sectional area A subjected to an
axial tensile force P. The stress at any section x-x normal to the line
of action of the tensile force P is specifically called tensile stress .
Since internal resistance R at x-x is equal to the applied force P.
Tensile stress=(internal resistance at x-x)/(resisting area at x-x)
=R/A =P/A.
Tensile strain (e)=Increase in length/Original length
= dL/L

18. Compressive stress
Stress induced in a body, when subjected to two
equal and opposite pushes as a result of which
there is a tendency of decrease in length of the
body.
It acts normal to the area and it pushes on the
area.

19. Compressive stress
Under compressive stress the bar suffers shortening.

20. Compressive stress
If the bar is subjected to axial compression instead of axial
tension, the stress developed at x-x is specifically called
compressive stress.
Compressive stress = R/A
= P/A.
Compressive strain= Decrease in length/ Original length
= δL/L

21. Sign convention for direct stress
and strain:-
Tensile stresses and strains are considered positive
in sense producing an increase in length.
Compressive stresses and strains are considered
negative in sense producing decrease in length

22. Shear stress
 Stress Induced in a body, when subjected to two equal
and opposite forces which are acting tangentially
across the resisting section as a result of which the
body tends to shear off across that section.

23. Shear stress
Consider the section x-x of the rivet forming joint
between two plates subjected to a tensile force P as
shown in figure.
The stresses set up at the section x-x acts along the
surface of the section, that is, along a direction
tangential to the section. It is specifically called shear
or tangential stress at the section and is denoted by σ.
σ = R/A
= P/A.

24. Elastic module
Hooke’s law states that: “When a body is loaded
within elastic limit, the stress is proportional to
strain.” or “Within the elastic limit the ratio of
stress applied to strain developed is a constant.”
The constant is known as Modulus of elasticity or
Elastic modulus or Young’s modulus.

25. Elastic module
 Mathematically within elastic limit,
E = Stress/Strain=σ/e
but, σ= P/A; e =δl/l
E=P*l/A*δl
δl=P*l/A*E
 Young's modulus (E) is generally assumed to be the
same in tension or compression and for most of
engineering applications has a high numerical value.
 Typically, E=210 x 10⁹ N/m² or E = 210 GPa for steel