• The mainproblem of engineering mechanics of
material is the investigation of the internal
resistance of the body.
• The externally applied forces are termed as loads.
(1) Due to service conditions
(2) Due to environment in which the component works
(3) Through contact with other members
(4) Due to fluid pressures
(5) Due to gravity or inertia forces.
3.
As we knowthat in mechanics of deformable
solids, externally applied forces act on a
body and body suffers a deformation. From
equilibrium point of view, this action should
be opposed or reacted by internal forces which
are set up within the particles of material
due to ?????
Now stress isdefined as the force intensity or
force per unit area.
Where A is the area of the X – section
6.
• Here weare using an assumption that the
total force or total load carried by the
rectangular bar is uniformly distributed over
its cross – section.
• local regions of high stresses known as stress
concentrations.
7.
• If theforce carried by a component is not
uniformly distributed over its cross – sectional
area, A, we must consider a small area, ‘dA'
which carries a small load dP, of the total
force ‘P', Then definition of stress is ..
8.
Types of Stress
•There are 2 types of stresses
(1) Normal Stress (2) Shear Stress
• Other stresses are the composite of these 2
stresses
• Bending stress is a combination of tensile,
compressive and shear stresses.
• Torsional stress, as encountered in twisting of
a shaft is a shearing stress.
9.
Normal Stress
• Ifthe stresses are normal to the areas
concerned, then these are termed as normal
stresses.
• This is also known as uniaxial state of stress,
because the stresses acts only in one
direction.
10.
• We havebiaxial and tri-axial state of stresses
where either the two mutually perpendicular
normal stresses acts or three mutually
perpendicular normal stresses acts.
11.
Tensile & CompressiveStresses
• The normal stresses can be either tensile or
compressive whether the stresses acts out of
the area or into the area.
12.
Bearing Stress
• Whenone object presses against another, it is
referred to a bearing stress (They are in fact
the compressive stresses).
13.
Shear Stresses
• Ifdistribution of forces are parallel, rather
than normal, to the area concerned are
referred to as shear forces. The resulting force
intensities are known as shear stresses.
14.
Where P isthe total force and A the area over
which it acts.
As we know that the particular stress generally
holds good only at a point therefore we
can define shear stress at a point as mentioned
above.
