Title of Invention

A HOLOGRAPHIC INTERFEROMETRY RECORDING DEVICE FOR TESTING DISBONDING OF THE GAS TRUBINE COATINGS AND EXPLOSIVE CLADDED MATERIALS

Abstract The invention relates to a device for non-destructive testing of gas turbine coatings and explosive-cladded materials by a new thermal stressting technique to detect disbonding, using holographic interferometry. The existing method of holographic non-destructive testing (HNDT) is inadequate as limited to smaller dimensions of detection with respect to diameter and depths of disbonded area. The improved device employs a novel method of thermal stressing of a component, conditions close to hyperbolic heat conduction phenomena. Double exposure holograms are recorded. The first exposure is at ambient temperature and the second exposure soon after withdrawing the heat source.
Full Text This invention relates to a device for non-destructive testing of gas turbine coatings and explosive-cladded materials by a new thermal stressing technique to detect disbonding using holographic interferometry.
Non-destructive testing of components by holographic interferometry makes use of a number of stressing process that are in application for the past several years.
There are disadvantages associated with the existing process having serious limitations in using detection of deviation in the gross structural deformative fringe system as a reference set to observe the disbonded areas.
One of the main disadvantages is that the existing process fails to detect smaller dimensions of the defects at greater depths of the disbonded areas in laminates and in metal to metal contacts.
Another disadvantage of the existing process is that inspite of successful applications of holographic non-destructive testing (HNDT) techniques, they are inadequate to deal with in detecting
the metal to metal interface defective bonded zones of gas

and turbine coating, by thermal and plasma spray, explosive-cladded materials.
Therefore, the main object of the present invention is to provide a device comprising holographic interferometry using

an improved thermal stressing technique.
Another object of the present invention is to provide a
new technique with parameters to excite the disbonded are in coatings and disbonding between substrate and the coating
is detected by HNDT.
Yet another object of the present invention is to provide a technique using an improved thermal stressing of a component, conditions of which is close to hyperbolic heat conduction phenomena.
A further object of the present invention is to provide a device to observe the disbonded areas directly eliminating the necessity of using the fringe control techniques to highlight the disbonded location.
Still further object of the present invention is to provide
a device wherein there is no limitations in detecting the minimum mensions like diameter, and depths of disbonded area and their ratio.
According to the present invention there is provided a device for non-destructive testing of gas turbine coatings and explosive - cladded materials by a new thermal stressing technique to detect disbonding using holoraphic interferometry
comprising a laser source using He-Ne laser of 25-mW, providing
laser beam through a beam splitter placed at 45° and two beams
are projected at mirrors placed at 45°, the reflected
beams are passed through spatial filter with first
reflected from beam splitter is projected onto a photographic
plate and the second beam to the same photographic plate being
reflected by the specimen and a heat source projecting onto
the substrate of the specimen with the coating at the back facing
the photographic plate, characterized in that, the holographic-
recording device records the first exposure at ambient
temperature thereafter the heating device is on for short
duration for thermal stress and the second exposure recorded
after the said heating source is withdrawn to record double
exposure holograms.
The nature of the invention, its objective and-further advantages residing in the same will be apparent from the ensuing description made with reference to non-limiting exemplary embodiments of the invention represented in the accompanying drawings.
FIG. 1 shows the holographic recording device.
FIG. 2 shows the heating device for thermal stressing.
In accordance with the present invention, the device comprises of a holographic recording set up shown in Fig. 1 and the heating arrangement for thermal stressing shown in Fig.2.
A laser source (1) Me- Ne laser 25 MW which in BEAMED through a beam spliter (2) placed at AS" angle. First beam pu.HSOH straight passes through and is reflected at mirror (3) placed at 45° angle. The reflected first beam is made to pass through a spatial filter (5) and optical lens (5). The first beam is then reflected from a test specimen (7) to the photographic plate (8). The coated surface (10) of the specimen (7) is facing towards the photographic plate (8). The second beam reflected from the beam splitter (2) is reflected again at a mirror (A) placed at 45° angle and passes through optical lens (6) and a spatial filter (6) projected straight to the photographic plate (8). A heat source (9) is provided for heating the specimen (7) at a point in the buck surface of the
(11) of contact area of one square centimeter for a short duration. The coated surface (10) is facing the photographic plate.
Double-exposed holographic interferometric method is used for detecting the disbonded areas. Thermal stresing is done by heating the specimen for a short duration. Double exposure re is at ambient temperature and the second exposure soon after withdrawing the heat source. The photographic plate is processed and image is reconstructed which has highlighted the disbonded areas in a) thermaly-sprayed gas turbine coating materials and b) explosive-cladded materials.
This device uses a novel method for full-field visual inspection of coatings of gas turbine components, as against:
point-by-point inspection, and also for detection of sub-surf act; defects .
The bonding defects of size 3 x 2 mm at the interface of the substrate and different coating materials used in gas turbines are detected.
The bonding defects of size 2 x 2 mm in explosive - cladded materials of copper and steel of 4 mm thickness each are detected. The device also uses another novel method of detecting smaller disbonded areas and at greater depths than the existing thermal stressing techniques.
The invention described hereinabove in relation to a non-limiting embodiment and as defined by the accompanying claims.



WE CLAIM ;
1. A device for non-destructive testing of gas turbine
coatings and explosive-cladded materials by a new thermal
stressing technique to detect disbonding using holographic
interferometry comprising a laser source (1) using He-Ne laser
of 25-mV providing a laser beam through a beam splitter (2) placed at 45° and two beams are projected at mirrors (3,4) placed at 45°, the reflected beams are passed through filter (5,0) with a first beam reflected from beam spliter (2) is projected onto a photographic plate (8) and the second beam to the same photographic plate (8) being reflected by the specimen (7) and a heat source (9) projecting onto the substrate (11) of the specimen (7) with the coating (10) at the the back facing the phtographic plate (8) characterized in that, the holographic recording device records first exposure at at ambient temperature thereafter the heating device is on for short duration for thermal stress and the second exposure recorded after the said heating source is withdrawn to record a double-exposure holograms.
2. A device using holographic interferometry as claimed
in claim 1, wherein the laser beam split by the beam splitter
(2), the first beam passing straight through the said beam
splitter (2) is reflected at the mirror (3) and passes through
an optical lens (5') and spatial filter--(5) is reflected from
the test specimen (7) and projected onto the photographic plate
(8).
3. A device using holographic interferometry as claimed
in claims 1 and 2, wherein the second beam reflected by the
beam splitter (2) reflect at mirror (4) and is projected at the
the photographic plate (8) through optical lens (6') and spatial
filter (6).
4. A device using holographic interferometry as claimed
in claims 1 to 3, wherein the holographic recording device
records the first exposure at ambient temperature.
5. A device using holographic interferometry as claimed
in claims 1 to 4, wherein the specimen (7) comprising substrate
(11) and coating (10), the said coating (10) faces the
photographic plate (8) and said substrate subjected to a heat
source (9) for a short duration to induce thermal stress to
record a second exposure after the said heat source (9) is
put off.
6 A device using holographic interferometry as claimed in claim 1, wherein the bonding defects of size 3 x 2 mm at the interface of the substrate and coating material is detected.
7. A device using holographic interferometry as claimed
in claims 1 & 6, wherein defects of size 2x2 mm in explosive
cladded material of copper and steel of 4 mm thickness are
detected.
8. A device for holographic interferometry for non-destructive testing as hereinabove described and illustrated.

Documents:

536-del-1997-abstract.pdf

536-del-1997-claims.pdf

536-del-1997-correspondence-others.pdf

536-del-1997-correspondence-po.pdf

536-del-1997-description (complete).pdf

536-del-1997-drawings.pdf

536-del-1997-form-1.pdf

536-del-1997-form-19.pdf

536-del-1997-form-2.pdf

536-del-1997-form-3.pdf

536-del-1997-gpa.pdf


Patent Number 213033
Indian Patent Application Number 536/DEL/1997
PG Journal Number 01/2008
Publication Date 04-Jan-2008
Grant Date 19-Dec-2007
Date of Filing 28-Feb-1997
Name of Patentee BHARAT HEAVY ELECTRICALS LIMITED
Applicant Address BHEL HOUSE, SIRI FORT, NEW DELHI-110049, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 RADHAKRISHNAMURTY GUTTA BHARAT HEAVY ELECTRICALS LTD., CORP. R & D DIVISION VIKASNAGAR, HYDERABAD-500093, INDIA.
PCT International Classification Number G01R
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA