3. Stress:
• Stress is defined as a force applied per unit area.
Types Of Stresses :
4. Compressive Stress:
• The stress which induced in a body when it is subjected to two
equal and opposite pushes as shown in the figure given below is
called compressive stress.
5. Tensile Stress:
• If the deforming force or applied force results in the increase in
the object’s length then the resulting stress is termed as tensile
stress.
• For example:When a rod or wire is stretched by pulling it with
equal and opposite forces (outwards) at both ends.
6. Torsional Stress:
• Torsional shear stress or Torsional stress is the
shear stress produced in the shaft due to the
twisting .
7. Shear Stress:
• The external force acting on an object or
surface parallel to the slope or plane in which
it lies; the stress tending to produce shear.
8. Normal Stress:
• The stress so produced by the perpendicular
action of a force on a given area is called
normal stress.
9. Strain:
• The ratio of change in a dimension
that takes place with a material under
stress .
10. Torsion testing involves the twisting of a sample
along an axis and is a useful test for acquiring
information like :
Torsional shear stress, maximum torque, shear
modulus, and breaking angle of a material or the
interface between two materials.
Torsion Testing
11. Torsion testing involves twisting the wire, either to failure
or to some predetermined number of twists, whereupon
inspection for surface cracking can be undertaken.
The strain of interest is the engineering shear strain, γ,
which involves displacements in the wire cross section
plane in the circumferential direction.
12. where Nt is the number of full twists and L is the length of wire twisted. The value
of Nt may be usefully expressed in terms of an angle of twist, θt, especially if Nt is small,
less than one, and so on. In that case:
13. •Toughness is resistance to fracturing
•Tough material are not easily breakable and can withsand high pressure
•Measured by
•Rockwell hardness test
•Brinell hardness test
•Knoop hardness test
•Vickers hardness test
Toughness :
14. •Stiffness is resistance to deflection.
Stiffness :
where,
F is the force on the body
δ is the displacement produced by the force along the same degree of freedom (for
instance, the change in length of a stretched spring)
In the International System of Units, stiffness is typically measured in newtons per
meter
In Imperial units, stiffness is typically measured in pounds(lbs) per inch.
S = F/δ
15. Hardness :
•Hardness is resitance to scratching and cuttting
•Hard Materials are scratch proof
•Affect the Plasticity of Material
•Examples :
•Some examples of hard materials are diamond, boron carbide,
quartz, tempered steel, ice, granite, concrete
