Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.11, pp.1027-1039, 2011
jmmce.org Printed in the USA. All rights reserved
1027
Design of a Cantilever - Type Rotating Bending Fatigue Testing Machine
K. K. Alaneme
Department of Metallurgical and Materials Engineering
Federal University of Technology, Akure, PMB 704, Nigeria
ABSTRACT
This research is centered on the design of a low–cost cantilever loading rotating bending
fatigue testing machine using locally sourced materials. The design principle was based on
the adaptation of the technical theory of bending of elastic beams. Design drawings were
produced and components/materials selections were based on functionality, durability, cost
and local availability. The major parts of the machine: the machine main frame, the rotating
shaft, the bearing and the bearing housing, the specimen clamping system, pulleys, speed
counter, electric motor, and dead weights; were fabricated and then assembled following the
design specifications. The machine performance was evaluated using test specimens which
were machined in conformity with standard procedures. It was observed that the machine has
the potentials of generating reliable bending stress – number of cycles data; and the cost of
design (171,000 Naira) was lower in comparison to that of rotating bending machines from
abroad. Also the machine has the advantages of ease of operation and maintenance, and is
safe for use.
Keywords: Fatigue; failure analysis; machine; design
1. INTRODUCTION
Structural materials, machine components, and materials utilized in many industrial and
specialized fields such as aerospace, defense, power generation among others; are often
subjected to varied stress cycles or dynamic loading conditions during the course of their use.
It is thus not surprising that most of these materials fail primarily by fatigue while in service.
Fatigue failures are reported to account for more than 75% of documented materials failures
of which a great percent occur catastrophically [1-2]. Fatigue cracks once initiated often grow
in an insidious manner resulting in failures with serious implications. The technical problems,
economic and potential human losses which accompany fatigue failures make its
consideration during materials design of utmost importance if the challenges associated with
its occurrence are to be mitigated [3].

1028 K. K. Alaneme Vol.10, No.11
A lot of research interest has been devoted to studying the fatigue behavior of engineering
materials with a view to arriving at ways to effectively design against the failure mode [4-5].
The success of these research efforts is hinged on having a reliable means of evaluating the
fatigue properties of materials. Over the years, there have been varied testing equipments and
methods developed for fatigue evaluation [6-7]. The servo – hydraulic machines are currently
the fastest and most versatile with features that allow for a wide range of test variations to be
performed on it. The high cost of these machines is a drawback to its use especially in most
African countries where investment in research and development is still low. Also most
manufacturing companies and medium scale establishments involved in materials
development using indigenous processing equipment and techniques would find it
unaffordable. The electromechanical systems like the rotating bending fatigue machines
which are relatively cheaper are still not readily available as they would have to be imported
from abroad. This research work thus aims at addressing this problem by venturing into the
design of a low – cost rotating bending fatigue testing machine using locally sourced
materials. It is expected that on completion the machine would be found reliable and
affordable by research institutes, universities, and companies that are involved in materials
development and durability analysis.
1.1 Design Theory
The theory governing the design of the fatigue machine is the cantilever loading elastic beam
bending principle often referred to as the technical theory of bending [8]. A beam is a
relatively long member that can support loads perpendicular to its axis. It can also support
applied moments that tend to bend it resulting in the compression of the lower layers of the
beam and the extension of the upper layers of the beam. The stress on the beam as a result of
the bending is referred to as bending stresses [9]. The adaptation of this theory is applied in
the workings of the cantilever loading type of rotating bending fatigue test which consists in
the application of a known constant bending stress (due to a bending moment) to a round
specimen on one end which is not hinged while the other extreme end of the specimen is
fixed, combined with the rotation of the sample around the bending stress axis until failure
occurs (Figure 1). The rotation and simultaneous bending on which the fatigue machine
operates ensures that the bending stresses which leads to stretch the upper layers of the
specimen and compress the bottom layers as is applicable in stationary beams; is evenly
distributed around the entire circumference of the specimen.
For round specimens, the moment of resistance for circular sections is applicable [8], and is
given by:
( ) 1
yR
E
I
M
σ
==
and
( ) 2
64
4
4
mm
d
I⋅ =
π

Vol.10, No.11
Where E = Young’s Modulus; R = radius of
moment; σ = bending stress; y = distance from the neutral layer to a generic point; I = the
second moment of area of the section about the neutral axis
Figure 1:
Cantilever loading
2.
MATERIALS AND METHODS
2.1 Materials
The various materials used are:
Angle Bar, Electric Motor, Speed Counter, Pulleys, Speed
Switch,
Wire and Plug, Switch, Dead Weight, Flat Wood Plate, Plastic Clips.
2.2
Machine Design and Considerations
The main
parts of the fatigue machine
main bearings, which create the two supports;
proximity
sensor, which detects the rotation motion of the shaft and sends
counter; digital counter, which
takes
to failure of the specimen.
The various parts/components of the fatigue machine were
systematically coupled
together through the preparation of design drawings
application of the theoret
ical principles of bending which had been thoroughly studied
design drawings for the fatigue machine
2.3
Materials Selection and Application
2.3.1 Shaft
A medium carbon low alloy steel material sourced locally was
shafts of the machine. The fatigue resistance of the steel was taken into consideration before
selection. The machine design requires the use of two shafts
electric motor and links the motor to
system through the pulleys as shown in Figure 2. The function of the shaft attached to the
electric motor is to transmit torque from the motor to the second shaft that anchors the
bearings and bearing h
ousing, clamping system, and the specimen. The principal function of
the second shaft is to rotate the specimen while it is under the action of bending moments
from the dead weights applied at the left arm of the clamping system. The shaft is threaded to
a
llow for screwing of the specimen chucks.
Vol.10, No.11
Design of a Cantilever
Where E = Young’s Modulus; R = radius of
curvature of the bent beam; M = bending
= bending stress; y = distance from the neutral layer to a generic point; I = the
second moment of area of the section about the neutral axis
; d = diameter
of specimen in
Cantilever loading
type of rotating-
beam fatigue testing machines
MATERIALS AND METHODS
The various materials used are:
Chucks, Bolts and Nuts, Ball Bearings,
Flat Metal Plate,
Angle Bar, Electric Motor, Speed Counter, Pulleys, Speed
Belt, Rotating Shaft, Automatic
Wire and Plug, Switch, Dead Weight, Flat Wood Plate, Plastic Clips.
Machine Design and Considerations
parts of the fatigue machine
are: the electric motor
, which gives the rotation; three
main bearings, which create the two supports;
o
ne load bearing, where the load is applied
sensor, which detects the rotation motion of the shaft and sends
the
takes
data from the sensor and records the number of rotation
The various parts/components of the fatigue machine were
together through the preparation of design drawings
ical principles of bending which had been thoroughly studied
design drawings for the fatigue machine
are presented in Figure 2 - 3.
Materials Selection and Application
A medium carbon low alloy steel material sourced locally was
selected for the design of the
shafts of the machine. The fatigue resistance of the steel was taken into consideration before
selection. The machine design requires the use of two shafts
–
the first is connected to the
electric motor and links the motor to
the second shaft that contains the specimen clamping
system through the pulleys as shown in Figure 2. The function of the shaft attached to the
electric motor is to transmit torque from the motor to the second shaft that anchors the
ousing, clamping system, and the specimen. The principal function of
the second shaft is to rotate the specimen while it is under the action of bending moments
from the dead weights applied at the left arm of the clamping system. The shaft is threaded to
llow for screwing of the specimen chucks.
1029
curvature of the bent beam; M = bending
= bending stress; y = distance from the neutral layer to a generic point; I = the
of specimen in
mm.
beam fatigue testing machines
Flat Metal Plate,
Belt, Rotating Shaft, Automatic
, which gives the rotation; three
ne load bearing, where the load is applied
;
the
signals to the
data from the sensor and records the number of rotation
The various parts/components of the fatigue machine were
based on the
ical principles of bending which had been thoroughly studied
. The
selected for the design of the
shafts of the machine. The fatigue resistance of the steel was taken into consideration before
the first is connected to the
the second shaft that contains the specimen clamping
system through the pulleys as shown in Figure 2. The function of the shaft attached to the
electric motor is to transmit torque from the motor to the second shaft that anchors the
ousing, clamping system, and the specimen. The principal function of
the second shaft is to rotate the specimen while it is under the action of bending moments
from the dead weights applied at the left arm of the clamping system. The shaft is threaded to

1030 K. K. Alaneme Vol.10, No.11
Figure 2: Fatigue Testing Machine without Casing
Figure 3: First Angle Projection of the Fatigue Testing Machine without Covering

Vol.10, No.11 Design of a Cantilever 1031
2.3.2 Bearings and Bearing Housing
The bearings selected for the design were self sealed spherical roller bearings which have
high load carrying capacity and it can accommodate misalignment and shaft deflections
maximum of 0.5°. Bearings of 22mm bore diameter were selected for the design; it was
ensured that the bearings would allow for the mounting of all components onto the shaft
physically and that the mass of all components including the bearings was minimized.
The bearing housing is a cylindrical hollow shaped steel material possessing good strength
and toughness. The housing design was implemented by selecting dimensions that will result
in smaller minimum bending moment which is desirable or realistic shaft geometry in order
to produce the required bending moment. The housing was bored to the size of the external
diameter of the chuck which is 25mm. Two bearings were then forcefully inserted into the
housing at both ends. The housing support was fabricated and then welded to the side of the
housing so that it provides rigidity and support. The housing support on the right arm of the
clamping system was firmly held by bolts on the frame with the intension of making it fixed
so that it can only allow for rotating motion. The second housing on the left arm of the
clamping system had supports which allows for flexible movement of the housing. The
housing is held to the supports by the use of bolts and nuts in order to accommodate the
flexibility required. Figure 4 shows the manner the shaft is inserted into the bearings.
Figure 4: tightly fitted bearing in the bearing housing and the shaft connection to the bearings
2.3.3 Clamps and clamping mechanism
A three jaw drill chuck with threaded fittings was selected as the specimen clamp for the
fatigue machine (Figure 5). The drill chuck was selected because it is durable and cheap to
procure. The specimen clamp is expected to firmly grip the specimens without allowing for
extraneous bending moments during operation of the machine. Also, the specimen must not
rotate from the grip or be displaced vertically or horizontally. The clamping mechanism
allows for the specimen and chuck connection at the right arm of the shaft and bearing system
to be fixed allowing for only rotating motion while the specimen and chuck connection at the
left arm of the shaft and bearing system allows for both rotating and bending forces to act on
the specimen by making the connection flexible as shown in Figure 3.

1032 K. K. Alaneme Vol.10, No.11
Figure 5: Drill chuck
2.3.4 Proximity sensor
The proximity sensor utilized in the design is presented in Figure 6. The sensor is utilized to
detect the oscillation of nearby objects without having any physical contact with the object;
so far the objects are not more than a distance of 15mm from it. A proximity sensor often
emits an electromagnetic or electrostatic field, or a beam of electromagnetic radiation
(infrared, for instance), and looks for changes in the field or return signal. It has been found
suitable for detecting the number of revolutions of rotating materials hence it was selected to
detect the number of revolutions of the shaft under the applied bending moments leading to
fatigue failure. The sensor was placed on the end of the shaft at the left arm of the main frame
of the machine to detect every cycle the shaft rotates. The rotating motion of the shaft and
sends signal to the counter.
Figure 6: Proximity Sensor
2.3.5 Digital counter
A 6 digit digital counter was selected for recording the number of stress cycles a specimen
undergoes during testing. It was ensured that the digital counter was compatible with the
proximity sensor selected, that is, it should be able to translate the signals from the sensor to a
numerical output. The digital counter utilized can relay digital outputs, but can be
programmed to run for a specified number of cyclic revolutions utilizing an analog input
bottom incorporated into the counter (Figure 7). It can also be programmed to evaluate rate in

Vol.10, No.11 Design of a Cantilever 1033
a given time. Conventionally, an 8 – digit counter is utilized for the design of rotating
bending fatigue machines. The unavailability of the 8 – digit counter led to the use of the 6 –
digit counter which was readily available within the country.
Figure 7: 6 digit Digital Counter
2.3.6 Electric motor
An electric motor uses electrical energy to produce mechanical energy, very typically through
the interaction of magnetic fields and current-carrying conductors. The electric motor used is
a 0.75kW 1 horse power motor that is designed to rotate at 2920 revolutions per minute and
50Hz (Figure 8).
Figure 8: Electric motor
2.3.7 Frame and seat of motor
The frames were cut from angle bar of dimension 2 inch by 2 inch alloy steel of good
strength and toughness and welded together to serve as support for the whole set up. A flat
flexible metallic plate was cut and attached to a part of the frame to serve as seat for the
electric motor. The flexibility is to accommodate ease of adjustment of the electric motor and
belt transmitting motion from the electric motor to the shaft.

1034 K. K. Alaneme Vol.10, No.11
2.3.8 Electrical connections and circuit diagrams
The electrical connection is done in such a way that when the whole machine is put on, the
counter comes on and is indicated by the lighting of a bulb but the whole machine doesn’t
come on not until the second switch is put on, this is to ensure safety and to be able to control
the whole machine. The electrical connection diagram is presented in Figure 9.
No
Component
1 Bulb Indicator for Electric Motor
2 Electric Motor
3 Bulb Indicator for Speed Counter
4 Speed Counter
Figure 9: Electrical connection diagram
2.4 Assembly
The different fabricated and purchased part are then assembled together to form the required
setup as shown in the design. This starts by passing the turned shaft through the bearing in the
housing forcefully and the shaft is allowed to extend beyond the bearing housing. A pulley is
fixed to the electric motor and another to the extended shaft of the fixed bearing housing. The
electric motor is then securely fastened to its seat and properly aligned with the upper pulley.
The chuck is then screwed to the threaded mouth of the shaft and the two bearing housing are
tightly screwed to the wooden base and properly aligned with each other. Finishing operation
involves the addition of body fillers and grinding of all the parts of the machine using emery
papers to make sure the parts are smooth. Thereafter, spraying of the machine was performed
and the wooden coverings attached. The resulting work at different stages of finishing is
presented in Figures 10 – 12.

Vol.10, No.11 Design of a Cantilever 1035
Figure 10: The fatigue testing machine after coupling before finishing
Figure 11: The fatigue testing machine after coupling and finishing
Figure 12: Fatigue Testing Machine Showing Dead Weight

1036 K. K. Alaneme Vol.10, No.11
2.5 Control of the Machine
The machine is controlled by two switches; one switch turns on the whole system while the
other puts on the electric motor which eventually starts the whole experiment. The magnitude
of the load used for testing is predetermined and is applied through the loading arm of the
fatigue machine. The bending moment on the specimen and the bending stress are calculated
using the relevant relations as discussed in section 1.1. The number of cycles to achieve
failure is recorded on the digital counter. The electric motor operates at a constant speed of
2920 rev/min and a frequency of 50Hz. The revolution counting can be achieved with
precision by ensuring that the distance between the proximity sensor and the rotating shaft
does not exceed 15mm. This will imply regular check after each operation of the machine.
2.6 Testing
Mild steel of predetermined chemical composition was utilized to prepare specimens for the
fatigue test. The reason for selection of mild steel is that there are well documented stress life
fatigue data on mild steel available in literatures. The specimens were machined having a
total length of 80mm with 15mm at both ends of the specimen to be held in the chuck so that
the length experiencing tension-compression (gauge length) is 50mm. The diameter of the
specimen is 12mm while the neck diameter is 8mm. The typical fatigue specimen
configuration with dimensions is presented in Figure 13.
Figure 13: representative specimen dimensions
The machined samples were mounted on the chucks of the machine. The distance from the
neck to the specimen’s contact surface with the bearing was measured. The concrete weight
was then applied. The revolution counter was set to zero and the electric motor switch turned
on. The test terminates once the specimen fractures; after which the electric motor is witched
off.

Vol.10, No.11 Design of a Cantilever 1037
3. RESULTS AND DISCUSSION
3.1 Machine Performance
The machine enables the evaluation of the stress life fatigue behavior of the tested material
through the plotting of bending stress against number of cycles from which the fatigue
limit/fatigue strength of the test material can be determined.
The working principle of the fatigue machine is easy to learn hence the operation of the
machine does not require any specialized training. Following a few simple instructions on the
instruction manual and placing the sample in between clamps/chucks, then turning on the
switches, gets the machine running.
The duration of testing is comparable to that of conventional rotating bending fatigue
machines which have an electric motor that operates at 2920 rev/min and 50Hz.Similar
machines take approximately 56 hours to achieve 10
7
cycles. The machine during testing was
observed to be safe to operate as the whole set up was tightly secured to the base. When
testing is to be performed thorough care is taken to ensure that the specimens are tightly
clamped in the chuck to safeguard against removal of specimen when the machine is in
operation. This ensures that when fracture occurs, the specimen will still be firmly held by
the chucks of the machine. The machine was also properly earthed to prevent shock in case of
a short circuit.
The maintenance strategy to ensure that the machine performs at high efficiency is quite
simple. The wires of the machine are properly protected against mutilation by domestic
rodents. The proximity sensor is regularly checked to ensure that the maximum distance for
reliable sensing of the shaft rotation is not exceeded; also regular cleaning of the sensor
particularly if the machine has been unused for some time. In the case of machine
malfunction, all parts are easily detachable and to be repaired.
3.2 Cost Analysis
The entire materials and equipment used for the design of the fatigue machine are presented
in Table 1. The materials and equipment used in the design are locally sourced, and the
overall cost of designing the machine is approximately 171,000 Naira ($1100.00). The
machine is cheap in comparison to similar designs from abroad.

1038 K. K. Alaneme Vol.10, No.11
Table 1: Bill for Engineering Management and Evaluation
4. CONCLUSIONS
This research was centered on the design of a low–cost cantilever type rotating bending
fatigue testing machine. The design principle is based on the adaptation of the technical
theory of beam bending. On completion and testing, it was observed that the machine has the
potentials of generating reliable bending stress-number of cycles data. It was also observed
that the machine has the advantages of ease of operation and maintenance, and is safe for use.
S/N
Description (materials) Quantity
Unit Rate Amount( ₦ )
Pieces Naira
MATERIALS ACQUISITION
1 Electric motor 2 Nr 15,000 30,000
2 Proximity 1 Nr 17,200
3 Speed counter 1 Nr 17,200 24,500
4 Chucks/clamps 2 Nr 4,000
5 Bolt & nut 24,500
6 Ball bearings 4 Nr 2,400
7 Flat metal plate 20 M
2
2,000 6,000
8 Angle bar 3 IN
2
15,000
9 Pulley 2 Nr 600 2,000
10 Speed belt 2 Nr 300 1,000
11 Rotating shaft 5 M 5,000 2,500
12 Control switch 2 Nr 1,000 1,400
13 Wire & plug 500 2,500
14 Dead weight (concrete) 400 4,000
15 Wooden covering & polishing 700 7,500
16 Electrical clips 1 Nr 200
FABRICATION
17 Fabrication of various components &
assembly
200 30,000
18 ELECTRICAL
Electrical connection 5,000
19 PAINTING AND POLISHING
Auto-base spray 6,500
Miscellaneous 10,000
20 Sub total 171,000

Vol.10, No.11 Design of a Cantilever 1039
ACKNOWLEDGEMENT
The author appreciates the support of the Association of Commonwealth Universities (ACU)
for the award of its Wington Titular Fellowship in Engineering which he utilized at the
Materials Engineering Department Indian Institute of Science, Bangalore. The support
received from Prof U Ramamurty at whose laboratory the author worked with various types
of fatigue machines is immensely appreciated. The author equally recognizes the assistance
of Adesheyoju P. A., Afolabi B. M., Oguntimehin J. O and Oke S.R.; in materials sourcing
and the fabrication process.
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