FIELD OF THE INVENTION
The present invention relates to a mounting device to support and mount
traveling microscopes having flexibility to access any specimen location and
orientation to ensure an accurate crack length measurement. The present
invention further relates to process of mounting a traveling microscope on a
fatigue testing machine to accurately measure crack length of a welded
sample.
BACKGROUND OF THE INVENTION
Fatigue is the weakening of a material caused by repeatedly applied loads. It
is the progressive and localized structural damage that occurs when a
material is subjected to cyclic loading. The nominal maximum stress values
that cause such damage may be much less than the strength of the material
typically quoted as the ultimate tensile stress limit, or the yield stress limit. A
fatigue is a failure of material or machine due to the action of repeated or
fluctuating stress on a machine member for some number of times. This
failure begins with a small crack. The initial crack is so minute that it cannot
be detected by the naked eye and is even quite difficult to locate in a small
magnification. The crack will develop at a point of discontinuity in the
material such as a change in cross section, a keyway, a hole or a notch. Less
obvious points at which fatigue failure are likely to begin are inspection or
stamp marks, internal cracks or even irregularities caused by machining.
Once a crack is initiated the stress concentration effect becomes greater and
the crack progresses more rapidly. As the stressed area decreases in size, the
stress increases in magnitude until finally, the remaining area fails suddenly.
A fatigue failure therefore is characterized by two distinct regions. The first of
those is due to the progressive development of crack, while the second is due
to sudden fracture. Unlike other failures, fatigue failure gives no visible
warning in advance. It is sudden and totally dangerous. This sudden failure,

which is dangerous, and can lead to not just minor accident but fatal accident
and loss of lives triggered the quest to invent a machine that can test and
give or predict the effect of fatigue on various metals such as steels, cast-
iron, aluminium etc.
Fatigue results in the nucleation of cracks in the structure. Fatigue cracks
initiate from locations of stress concentrators and grow during cyclic loading
to cause final catastrophic fracture. Over a period of time, the sizes of these
cracks reach a critical dimension and this result into a catastrophic failure of
the structure. Hence it is necessary to replace the structure before the crack
reaches the critical value. Thus evaluation of fatigue crack growth rate and
fatigue life is necessary for safety as well as from economic point of view.
Fatigue behaviour of a welded joint is investigated by paying attention to
fatigue crack propagation. Accuracy of measurement of crack length is as
important as the measurement of crack itself. From the accurate
measurement of crack increments, it is possible to plot graphs between crack
growth rate with respect to the number of cycles and stress intensity factor
range which helps in demarcating the crack propagation region from
catastrophic failure region. In order to make accurate measurement of crack
growth, mounting the travelling microscope in right way is very important.
The conventional method of using the travelling microscope for such
application is by placing the microscope on a table placed bedside the fatigue
testing machine. The disadvantage of this arrangement is that it is never rigid
and is susceptible for any disturbances while taking measurement. Also the
minimum distance that can be maintained from the specimen to the
measuring point has a constraint as the table is placed away from the
machine base. The fabricated rail provides a flexible method to mount the
microscope, right in front of the crack to give the best view of crack head.

US patent document US 4364113 describes optical monitoring of crack. A
television camera trained on the test piece is connected to a discriminator
which converts the image points of the television image into binary pulses.
The binary pulses of the television image are stored from time to time in a
store. A comparator compares the contents of the store with the binary
pulses of a consecutive television image and ascertains deviations between
two consecutively-taken television images. The number of the non-coincident
binary pulses of the compared television images is counted and indicated.
This method of crack length measurement is expensive and require special
skill set. Our invention is different in the sense that it uses travelling
microscope which is simple and require little skill only. Also the measurement
is made in real time with reasonable accuracy not by any captured and
processed image.
US patent document US 5539656 describes an apparatus for monitoring the
growth of surface cracks in materials includes a means for applying a load to
a specimen to simulate actual use of the specimen, means for illuminating the
specimen, means for capturing images of the specimen, and means for
processing the images to monitor crack growth in the specimen. Again, our
investigation is different in the sense that it helps in making the measurement
in real time with reasonable accuracy not by any captured and processed
image. Also the crack length is not estimated through processed image, it is
measured directly.
US patent 4175447 describes an apparatus for detecting crack length of a
test piece in a fatigue test wherein crack length is automatically detected and
the tip of the crack is displayed on a monitor. The image is picked up by a
scan converter memory so as to be memorized for an extended period. The
memorized image is then introduced into an image analyser while monitored
on a monitor screen. The tip of the crack is analysed and calculated in the
image analyser and the position of the optical-scope is adjusted accordingly.

Our investigation is different in the sense that the overall system requires an
expensive mean to support the individual equipments whereas our invention
is simple, easy and rigid. Also the measurement is made in real time with
reasonable accuracy not by any captured and processed image and thereby
calculating the crack length. The optical scope is placed far from the test
piece whereas in our invention we have a close field observation.
Authors D. R. Moore, J. G. Williams and A. Pavan in the non-patent literature
entitled “Fracture Mechanics Testing Methods for Polymers, Adhesives and
Composites” that a describe low power travelling microscope can be used for
fatigue crack length measurement. The literature recommends to make a
reference mark on a specimen prior to testing in order to eliminate potential
errors due to movement of travelling microscope. But once the crack starts
propagating, there is no significance for this reference mark. Accordingly, the
disclosed arrangement is more susceptible to disturbances whereas the
proposed invention is more rigid and almost eliminates any chance for
disturbing the setup.
J. R. Mohanty, B. B. Verma and P. K. Ray et al, in the non-patent literature
entitled “Determination of Fatigue Crack Growth Rate from Experimental
data; a New Approach”, describes the use of travelling microscope with 20X
magnification. The extend of accuracy of crack length measurement is
important in deriving the crack prediction model. Our invention is different I
the sense that the microscope is placed far from the test piece whereas in
our invention we have a close field observation and flexibility to adapt to the
orientation of the specimen.
All the above prior art fail to specify as to how the travelling microscope was
indeed mounted for measuring the crack length. The general practice is to
mount the travelling microscope on a desk or table with almost the height of
the specimen placed close to the fatigue testing machine. The disadvantage

of this practice is, there is no convenience to measure the crack length, the
microscope being placed at a considerable distance from the sample, it’s not
easy to adjust with the varying height of the specimen location, etc.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a mounting device to
support and mount travelling microscopes having flexibility to access any
specimen location and orientation to ensure an accurate crack length
measurement.
A further object of the invention is to propose a process of mounting a
travelling microscope on a fatigue testing machine to accurately measure
crack length of a welded sample.
SUMMARY OF THE INVENTION
Accordingly, there is provided a mounting device to support and mount
traveling microscopes having flexibility to access any specimen location and
orientation to ensure an accurate crack length measurement. According to
the invention, the device consisting of a pair of rails welded with at least a
pair of C-clamps at either ends, the distance between the rails being
maintained to allow accurate fitting of the rails with the platform of the
traveling microscope. The C-clamp is drilled to form internal thread to fasten
the rail to a pair of hydraulic shaft of a fatigue testing machine. The clamps
are fasten the shafts of the fatigue testing machine corresponding to location
of the specimen. The clamps are fastened to each of the shafts and the rails
in arc shape connecting the two vertical shafts of the fatigue testing machine.
Also it maintains almost even distance from the specimen. The working of the
device is as follows:
placing the assembly of the rails and C-clamp (male portion) over the

hydraulic shaft of the fatigue testing machine; fastening the female portion to
the male portion of the C-clamp to hold the assembly to the shaft; placing the
travelling microscope over the mounting rail according to the orientation of
the specimen; viewing the specimen through the microscope for a first hand
check; adjusting in respect of illumination, the microscope along the rail till
the view is clear; mounting the travelling microscope over the rail, including
fine tuning the levelling screw to ensure horizontal levelling of the base of
the microscope; and adjusting the cross wire on the specimen where
measurement is to be taken.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The proposed invention will be better understood by the following description with
reference to the accompanying drawings:
> Fig 1: shows the fabricated device of the invention.
> Fig 2: C-clamp for holding the rail onto the hydraulic shaft of a fatigue
testing machine.
> Fig 3: Mounting device fixed to the fatigue testing machine.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Accordingly referring to the figure 1, 2 and 3, the invention, provide a device
consisting of a pair of rails (item 1) welded with C-clamps (item 2a) at either
ends. The male portion of the C-clamp (item 2a) is welded to the pair of rails
and the female portion (item 2b) is used to integrate it with the shaft of
fatigue testing machine. The distance between the rails are maintained
uniform so that the platform of the travelling microscope can be well fitted to
the rails and any movement along the rail will be smooth and easy. Stiffeners
(item 3) are provided to ensure the uniformity between the rails and rigidity

of the same. The C-clamps (2a) are provided with internal thread to facilitate
the fastening of the rail to the hydraulic shaft (item 4) of the fatigue testing
machine. The diameter of the C-clamps are designed to match the diameter
of the shaft of fatigue testing machine. The clamps can be fastened to the
shafts of the fatigue testing machine according to location of the specimen
(item 6) using the fastener (item 5). The clamps (2a) are fastened, to each of
the shafts to ensure more rigidity. The rail is in arc shape, with a radius of
curvature of 460 mm, to avoid any sharp edge and provide continuity in path.
The distance between the C-clamps is 790mm and the parallel distance
between the pair of rails (1) is 25 mm. Also it maintains almost even
distance from the specimen. The working is as follows: Take the assembly of
the rails and C-clamp (male portion) and place it with hydraulic shaft of the
fatigue testing machine. Fasten the female portion to the male portion of the
C-clamp to hold the assembly to the shaft. Place the travelling microscope
over the mounting rail according to the orientation of the specimen. View the
specimen through the microscope for a first hand check. If there is no proper
illumination, move the microscope slightly along the rail till the view is clear.
Mount the travelling microscope over the rail. Fine tune the leveling screw to
ensure the horizontal leveling of the base of the microscope. Adjust the cross wire
on the specimen where measurement is to be made.
Advantages:
1. The device can be adjusted according to the height of the specimen to be tested.
2. Since the rail is in arc shape, the microscope can be moved along the rail to
adjust to the any orientation of the specimen about vertical axis.
3. Device can be placed reasonably closer to the specimen, so that a better
Whole field view is ensured.

4. Since the device is clamped to the shaft of the fatigue testing machine, the
device as a whole is rigid and also the microscope is fastened to the rail of
the device, there is no chance of disturbance to the microscope during
measurement.
5. Does not consume any additional space for installation unlike the table tops
used for mounting the microscope.
The proposed invention as narrated herein above should not be read and construed
in a restrictive manner, as some modifications, adaptations and alterations are
possible within the scope and limit of the invention as defined in the encompassed
appended claims.

WE CLAIM :
1. A mounting device for mounting travelling microscope with broad
accessibility to the location and orientation of specimen for crack
length measurement, the device consisting of a pair of rails (1) welded
with at least one pair of C-clamps (2a) at either ends, the male portion
of the C-clamp (2a) welded to the pair of rails and the female portion
(item 2b) of the clamp allows integration of the device with the shaft
of fatigue testing machine, wherein the pair of parallel rails in arc
shape provided with stiffeners (3) to improve rigidity.
2. The device as claimed in claim 1, wherein the device is adjustable in
respect of height and orientation of the specimen by moving the
traveling microscope (6) over the pair of rails.
3. A process in a device as claimed in claim 1, for mounting a traveling
microscope on a fatigue testing machine to accurately measure crack
length of welded samples, the process comprising the steps of :-
placing the assembly of the rails and C-clamp (male portion) over the
hydraulic shaft of the fatigue testing machine; fastening the female
portion to the male portion of the C-clamp to hold the assembly to the
shaft; placing the travelling microscope over the mounting rail
according to the orientation of the specimen; viewing the specimen
through the microscope for a first hand check; adjusting in respect of
illumination, the microscope along the rail till the view is clear;
mounting the travelling microscope over the rail, including fine tuning

the levelling screw to ensure horizontal levelling of the base of the
microscope; and adjusting the cross wire on the specimen where
measurement is to be taken.