FIELD OF INVENTION
This present invention relates to a device for structural health monitoring using
laser beam and a method for the same. More particular the invention relates to
structural health monitoring to detect onset of structural failure and its severity.
BACKGROUND OF THE INVENTION AND PRIOR ART
Structural failure is usually unpredictable resulting in huge loss, financial and
otherwise. Traditional destructive testing techniques are effective at determining
a failure threshold. But they do not aid in determining the onset of structural
failure before it occurs. Structural heath monitoring (SHM) systems address
these concerns. Some such systems employ small remotely operated sensors to
provide information and facility for continuous monitoring of position,
temperature and other physical quantities. Some SHM systems also use

ultrasonic transducers to detect displacement, delamination, cracking or other
local failures. These features are disclosed in the following Patents:
US 7411, 338 B1, US 2008 / 0183403 A1, US 2008 / 0255777, WO 2005 /
048317, WO 2008 / 094358.
The above disclosed Patents use piezo-electric ultrasound / EIM impedance
measurement sensors for SHM which require elaborate mechanism with an array
of sensors for the assessment of structural health. This invention uses a laser
beam based, simple and cost effective method and device to detect the onset of
structural deformation.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a device for structural health
monitoring using laser beam and a method for the same which can predict onset
of structural failure.
Another object of the invention is to propose a device for structural health
monitoring using laser beam and a method for the same which is simple and cost
effective with high sensitivity and reliability to predict structural failure before it
occurs.

SUMMARY OF THE INVENTION
A laser beam based technique is introduced to detect the onset of structural
deformation while in the elastic limit. A sensor is employed to locate the shift in
the laser beam position induced by the deformation of the structure.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention can now be described in detail with the help of the figures of the
accompanying drawings in which:

Figure 1 shows laser line structural health monitor.
DETAILED DESCRIPTION OF A PREFERRED
EMBODIMENT OF THE INVENTION
The device will detect the onset of failure of structures like columns and beams
before the failure threshold occurs.

The device consists of a hollow tube (07) capped with solid blocks at both ends
[01] and [02]. The hollow tube [07] is made of thin metal. The length of the
hollow tube i.e. the distance between the two blocks decides the sensitivity of
the measurement.
The solid blocks [01] and [02] have a cavity at the centre for fixing the laser
source [03] and sensor [04] respectively. The solid blocks [01] and [02] are so
designed that they are immune to any deformation of the structure.
The solid block [01] contains a low power laser source [03] with beam [06]
pointing to the other end of the hollow tube with solid block [02].
The solid block [02] is fixed with a target disc [05] and associated electronics
[04] to sense the position of the laser beam. Multiple implementations of the
target disc [05] and associated electronics [04] are possible. One such
implementation is using a high density photo diode array. Another such
implementation is using a CCD camera to capture the laser beam position.

The total assembly is lapped over the structure at the weakest point where a
failure is most likely to occur. The solid blocks [01] and [02] are fixed firmly on
the structure.
The assembly is so mounted that during healthy condition the beam falls exactly
at the centre of the target film [05]. When there is a deformation in the
structure, there is a displacement of the spot of incidence of the laser beam [06]
on the target film [05]. The amount of the displacement can be calibrated into
stress values or safety zones or levels.
The target disc [05] and associated electronics [04] captures the beam position
on the target film and transmits the information to an electronic controller.
Depending on the deviation of the position of the laser beam incident on the
target film from its default position, the controller is able to assess the stress
level / safety zone and predict onset of failure in the structure.

This method of structural health monitoring is capable of measuring deformation
of the structure in any direction about the axis of the column / beam. It can also
give information on an amplitude and frequency of vibrations of the structure.

WE CLAIM
1. A device for structural health monitoring using laser beam
comprising:
- a hollow tube [07] capped with solid blocks at both ends [01] and
[02];
- a plurality of solid blocks [01] and [02] having cavity at the centre
for fixing the laser source [03] and sensor [04];
characterized in that, the solid block [01] contains a low power
laser source [03] with beam [06] pointing to the other end of the
hollow tube [07] when the solid block [02] is fixed with a target
disc [05] and associated electronics [04] for sensing the position of
the laser beam.
2. A device as claimed in claim 1, wherein the hollow tube [07] is
made of thin metal.
3. A device as claimed in claim 1, wherein the length of the hollow
tube [07] being the distance between the two blocks [01, 02]
decides the sensitivity of the measurement.

4. A device as claimed in claim 1, wherein the blocks [01] and [02]
are fixed firmly on the structure.
5. A method for structural health monitoring using laser beam
comprising:

- lapping the assembly over the structure at the weakest point of
probable failure;
- fixing the laser source [03] in a cavity at the centre of the solid
block [01];
- fixing the sensor [04] in a cavity at the centre of the solid block
[02];
- fixing the solid block [02] with the target disc [05] and associated
electronics [04] to sense the position of the laser beam;
characterized in that, the assembly is so mounted that during
healthy condition the beam falls exactly at the centre of the target
film [05] and on a deformed structure the spot of incidence of the
laser beam [06] on the target film [05] is displaced when the
amount of displacement is calibrated into stress values or safety
zones or levels.

6. A method as claimed in claim 5, wherein the target disc [05] and
associated electronics [04] captures the beam position on the
target film and transmits the information to an electronic controller.
7. A method as claimed in claims 5 and 6, wherein the controller
assesses the stress level / safety zone and predicts onset of failure
in the structure by the amount of deviation of the position of the
laser beam incident on the target film from its default position.
8. A method as claimed in claims 5 to 7, wherein deformation of the
structure is measured in any direction about the axis of the column
and beam.

A device for structural health monitoring using laser beam consists of a hollow
tube [07] made of thin metal and is capped with solid blocks [01] and [02] at
both ends. The solid blocks have cavity at the centre for fixing the laser source
[03] and sensor [04] while the solid block [01] contains a low pressure laser
source [03] with beam [06] pointing to the other end of the hollow tube when
the solid block [02] is fixed with a target disc [05] and associated electronics
[04] for sensing the position of the laser beam. The assembly is so mounted
that during healthy condition the beam falls exactly at the centre of the target
film [05] and on a deformed structure the spot of incidence of the laser beam
[06] on the target film [05] is displaced when the amount of displacement is
calibrated into stress values or safety zones or levels.