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8. What are the assumptions made in simple theory of bending?
The assumptions made in the theory of simple bending are:
> The material of the beam is homogeneous this implies that it is uniform in
density, strength and have isotropic properties meaning possessing same elastic
property in all directions.
> Even after bending the cross section of the beam remains constant.
> During the initial stages the beam is straight and unstressed.
> All the stresses in the beam are within the elastic limit of its material.
> The layers of the beam are free to contract and expand longitudinally and
laterally
> On any cross section the perpendicular resultant force of the beam is
zero.
> Compared to the cross-sectional dimension of the beam the radius of
curvature is very large.
9. Why is stress considered important in a shaft?
The following types of stresses are prevalent in shafts:
> At the outermost surface of the shaft the max shear stress occurs on the
cross-section of the shaft.
> At the surface of the shaft on the longitudinal planes through the axis of
the shaft the maximum longitudinal shear stress occurs.
> At 45 degrees to the maximum shearing stress planes at the surface of the
shafts the major principal stress occurs. It equals the max shear stress on the
cross section of the shaft.
> For certain materials where the tensile and compressive strengths are
lower in measure as compared to the shear strength, then the shaft designing
should be carried out for the lowest strengths.
> All these stresses are of significance as they play a role in governing
the failure of the shaft. All theses stresses get generated simultaneously and
hence should be considered for designing purposes
10. What do you understand by the Hooke`s Coupling what are its purposes?
The Hooke`s coupling is used to connect two shafts whose axes intersect at a
small angle. The two shafts are inclined at an angle and is constant. During
motion it varies as the movement is transferred from one shaft to another. One
of the major areas of application of this coupling is in gear boxes where the
coupling is used to drive the rear wheels of trucks and other vehicles. In such
usage scenarios two couplings are used each at the two ends of the coupling
shaft. they are also used to transfer power for multiple drilling machines. The
Hooke`s coupling is also known as the Universal coupling. The torque
transmitted by the shafts is given by :
T= (pie/16) x t x (d) cube
Where T = torque, t = shear stress for the shaft material and d the diameter of
the shaft.
11. What kind of materials should be used for shafts manufacturing?
Some of the qualities that should be present in materials for shafts are as
follows:
> The material should have a high index of strength.
> Also it should have a high level of machinability.
> The material should possess a low notch sensitivity factor.
> The material must also have wear resistant properties.
> Good heat treatment properties should also be present
The common material used to creates shafts of high strengths an alloy of steel
like nickel is used. The shafts are manufactured by hot rolling processes and
then the shaft is finished using drawing or grinding processes.
12. Why should a chain drive be used over a belt or rope driven drive? State
pro`s and con`s?
The advantages of using a chain drives are:
> In a chain drive no slip occurrence takes place.
> The chains take less space as compared to rope or belts as they are made
of metal and offer much strength.
> The chain drives can be used at both short and long ranges and they offer
a high level of transmission efficiency.
> Chain drives can transmit more load and power as compared to belts.
> A very high speed ratio can be maintained in one step of chain drives.
Some of the cons of using a chain drive are:
> The cost of producing chain drives is higher as compared to that of belts.
> The chain drives must be serviced and maintained at regular intervals and
henceforth their cost of ownership is high comparatively.
13. What are the different types of springs and explain them briefly?
Springs can be broadly classified into the following types:
> Helical Springs: These springs as their name suggests are in coil form and
are in the shape of helix. The primary purpose of such springs are to handle
compressive and tensile loads. They can be further classified into two types:
compression helical spring and tension helical spring each having their own
unique areas of application./
> Conical and volute springs: Both these spring types have specialized areas
of usage where springs with adaptable rate according to the load is required.
In case of conical springs they are wound so as to have a uniform pitch while
on the other hand volute springs are wound in a slight manner of a parabloid.
> Torsion Springs: The characteristics of such springs is that they tend to
wind up by the load. They can be either helical or spiral in shape. These types
of springs are used in circuit breaker mechanisms.
> Leaf springs: These types of springs are comprised of metal plates of
different lengths held together with the help of bolts and clamps. Commonly
seen being used as suspensions for vehicles.
> Disc Springs: As the name suggests such types of springs are comprised of
conical discs held together by a bolt or tube.
> Special Purpose Springs: These springs are all together made of different
materials such as air and water.
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