Actually, the shaft is one of the most important constituents in some engines; it is a revolving or

static component that has normally a cylindrical shape, but can be squared or cross-shaped. In
addition, they can be solid or hollow. Its main function is to convey power from one member to
another by a rotational movement. This power is supplied to the shaft over a tangential force and
then transmitted to different elements which are connected to the shaft thanks to the subsequent
torque or twisting moment. For instance, we can find gears, pulleys, cranks, and rolling-elements
attached to the shaft resulting in bending moment together with the forces applied on them. In
other words, its purpose is to transmit loads to the stationary system of the nacelle in the case of
a wind turbine. Thus, the shaft is subjected to some external forces that should be taken into
consideration while designing it.

In fact, there are many classifications for shafts based on a specific feature; for instance, there are
two types of shaft according to their usage: 1. Transmission shafts: their role is to transfer power
from the origin to the engines assimilating power that are connected to the shaft. 2. Machine
shafts: they constitute a fundamental part of a device itself Furthermore, we can also classify
shafts according to their shape as: straight, cranked, flexible, or articulated.

Since it goes through many types of loads, there should be specific materials used to produce it
with the following characteristics:

Having a great strength - Having a suitable and strong machinability - Having the smallest
possible value for notch sensitivity factor - Having appropriate heat treatment features - Having
elevated wear resistant features

In the fabrication phase, shafts are exposed to hot rolling and completed by cold drawing or
turning and grinding. Cold drawing is a method used to decrease the cross-sectional area/form of
a specific type of metal like a bar or tube by pulling it through a die to obtain an outstanding final
surface. Turning and grinding are methods, a matter elimination process, which consist of
generating turning fragments by getting rid of undesirable substances. However, grinding is used
when we have very hard materials [10]. Actually, there are three forms of stresses that are
prompted in the shafts: 1. Shear stress because of the transmission of torque. 2. Bending stress
because of the weight of the shaft itself and the forces acting on the engine’s components 3.
Stress resulting from combination of torsional and bending loads 3.3.2 Design of the main shaft:
In the design phase, there are some steps to be followed going from the broad to the narrow
information to cover all the related concerns even if there are some restrictions and challenges
that will be confronted. Overall, a wind turbine must be evaluated for the numerous loads it will
undergo all the way through its conception lifetime. A crucial objective in this concern is to
check that the turbine will be qualified to bear these weights with an appropriate security
boundary. This duty is arranged by examining the wind turbine for particular pertinent load
situations. These load states can be obtained by joining appropriate 23 design conditions for the
wind turbine with several external factors. Since, in our project we focus only on the main shaft,
thus we will examine 4 static load situations. Besides this, there are other design issues that
should be taken into consideration in case of requirements that need to be met: - Choice of
machine (upwind/ downwind and horizontal/ vertical axis) - Type of drive train (direct/ geared) -
Choice of operating speed (constant/ variable) - Weight and size - Type of material - Type of
generator (Synchronous/ asynchronous) - Power and type of current - Safety and protection -
Costs of manufacturing and maintenance 3.3.3 Materials used for the main shaft: Shafts can be
conceived depending on strength or rigidity and stiffness. However, if we are considering
rigidity and stiffness, this means that we should evaluate the characteristics of the materials that
can be employed to manufacture the main shaft. In general, one of the main concerns of
manufacturers when making a product is to select the best material that will be suitable for their
goal. They should take into consideration all the characteristics and the functions to be
accomplished by the product to be manufactured in order to pick the ideal material. Thus, there
are many things to take into account while making the main shaft such as its length, diameter,
function within the system, and the type of wind turbine in which it will be used. The industry
domain is in continuous improvement and there is always new releases of new products and
materials that are used to make the main shaft. There is a diversity of types of materials that can
be used for the main shaft, but we are 24 interested in the material that has the properties that
will match our needs. These materials are metals and we will consider four types of steel. The
most important characteristics to be considered for our application are: the ultimate tensile
strength, yield strength, young’s modulus, and the density of the material. Accordingly, we will
make a comparison between four types of steel which are: carbon steel, alloy steel, stainless
steel, and tool steel. Our selection process will be based on taking the highest values of all the
properties. The table below shows some characteristics of the four types of steel we considered at
room

3.3.4 The forces applied on the main shaft: When designing the main shaft, manufacturers should
take into consideration the worst cases relative to the loads applied on it such as the bending
moment and torsion. The bending moment represents the weight of the rotor that is composed of
the wind turbine blades and the hub. The torsion characterizes the design torque of the wind
turbine (Q) when the blades are rotating according to their normal operational conditions in
addition to the break torque which is applied when an emergency happens and thus the wind
turbine must be stopped. In order to determine the values of the bending moment and torsion
applied on the main shaft that we will be using, we have to determine the electrical consumption
of the individuals. This will enable us to find the power of the electric generator with the aim of
securing enough supply of electricity for domestic appliances to be employed either directly or
indirectly (storing electrical energy on batteries).

1. Shafts:

Input Power by AC motor = ¼ HP=188.625Watt

SHAFT STRENGTH UNDER TORSIONAL LOAD

The shafts are always subjected to fatigue load hence they must be calculated for fatigue strength
under combined bending and torsion loading. However, the initial estimate of diameter is
obtained from the torque that is transmitted by the shaft. The bending moment variation along
the length of the shaft is established after fixing some structural features like distance between
supporting bearings and distance between points of application of forces and bearings.

Following notations will be used for shaft.

d = diameter of shaft,

Mt = torque transmitted by the shaft, =25 Kgcm= 2.4516625 Nm.

W = power transmitted by the shaft (W)

N = rpm of the motor shaft = 1275 rpm

τs = permissible shearing stress,

σb = permissible bending stress, and

Mb = bending moment.

Considering only transmission of torque by a solid shaft.

The power transmitted by shaft and the torque in the shaft are related as

W= Mt* ω

If W is in Watts and Mt in Nm. ω is angular velocity in rad/s and equals 2πN/60

W=2πNMt/60

Mt= 30W/ πN……………………………..………eqn 1

The shearing stress and the torque are related as

τ = 16 Mt*103 / π*d3

If Mt is in Nm and d in mm.

Mt= π/16 (103 τ d3 ) ………………………………… eqn 2

d3 = Mt*16 /π103 τ

In Eq. (3) W is in Watt, τ in N/mm2, N in rpm and d in mm.

For calculating shaft diameter, d, we substitute the permissible value of shearing stress in place
of τ. Table below describes permissible values for steel shaft under various service conditions,
when the bending are much smaller then torsional loads.

Table: Allowable Shear Stress for Shafts

Service Condition τ s (MPa)

Heavily loaded short shafts carrying no axial 48-106
load
Multiple bearing long shafts carrying no axial 13-22
load
Axially loaded shafts (bevel gear drive or 8-10
helical gear drive couplings etc. )
Shafts working under heavy overloads (stone 4.5-5.3
crushers, etc.)

So equation 3 becomes

d3 = Mt*16 /π103 τ

Taking allowable shear stress for shafts under small loads in coupling as τ= 8 MPa = 8*106 Pa

d3 = Mt*16 /π τ 106

d3 = 2.45166*16 /π*48*106

d3= 2.6012 *10-7 m

d= 0.00638m = 6.38mm
Considering factor of safety as 1.5, the shaft size will be

D= 3*d

D= 3*6.38

D= 19.15 mm.

En8 Rounds Bright Drawn / Turned bars available sizes

Diameter 5 6 8 10 12 15 18 20
Size in
22 24 25 28 30 32 35 40
mm

Diameter 1/4 5/16 3/8 7/16 5/8 1/2 3/4 11/16

Size in
7/8 1 11/4 13/8 17/16 15/8 13/4 21/4
inches

So selected shaft diameter closest to D= 19.38 mm is = D=20 mm.

This is taken as 20 mm to add better safety and availability in market.

So we take diameter of second shaft will also be 20 mm.