This document discusses using an infrared camera to detect voids in adhesive joints known as Scotch-welds. Two aluminum plates were bonded with epoxy, but a square area was left unbonded to create a known defect. An infrared camera detected a temperature difference of 5 degrees Celsius over the defect area when the plates were heated, accurately finding the void in the adhesive joint. Infrared thermography proved effective for non-destructively detecting defects in adhesive bonds.

1. Detection of Voids in a Scotch-
Weld using
An Infrared Camera
-Akshay Kumar Varakala

2. Synopsis
 Scotch-Weld is an adhesive joint used for bonding structures or different elements
of mechanical equipment
 Various applications of Scotch Weld include sealing of pipes, bonding of cabins in
an automotive, waterproof applications in tanks, bonding of wind turbine blades
etc.
 The uneven distribution of adhesive or the voids left during the application of
adhesive results in poor strength of the bond and hence the chances of joint failure
is high
 In this experiment Active Infrared thermography was used to detect the voids in
the Adhesive Joints.

3. Introduction
 Infrared thermography is an attractive non-destructive evaluation technique, with a
wide variety of applications because of its full-field imaging capability.
 Infrared thermography is equipment or method, which detects infrared energy
emitted from object, converts it to temperature, and displays image of temperature
distribution.
 Infrared thermography is broadly classified into two types
• Passive thermography
• Active thermography
 In this project Active Pulsed thermography technique was used and a table lamp
was used as a heat source to thermally excite a specimen
 The specimen here is a Scotch welded aluminium plates

4. Introduction(Contd…)
Pulsed Thermography (PT)
 PT is an active thermographic method where a pulse of heat is applied to the surface of a component
and the thermal evolution on the surface is monitored using an infrared (IR) detector.
 The current work focusses on the use of PT in the reflection mode shown in Fig. 1a with heat source
and detector focussed on the same surface of the component.
 Heat is pulsed onto the surface of the component. The surface temperature decays as the heat front
propagates through the thickness of the material.
 If there is a region of different thermal properties this will cause a change in the rate of heat transfer
through that region and result in an area of different temperature on the surface directly over this
region , as shown in Fig. 1b. This region of different thermal properties may be a defect within the
material.

5. Specimen Preparation
 Two aluminium plates were taken and were properly surface finished to avoid the
surface defects
 3M Vinyl Epoxy was thoroughly mixed and was applied to the plate and a square
spot on the plates was left out without the application of epoxy. The plates were
then held tightly with uniform pressure to create an adhesive joint.
 The area were epoxy was not applied serves as a known defect.
 The surface of the plates was coated with a black water soluble paint to improve
the emissivity of the surface.

6. Experimental Setup
 The main components of the experiment are the IR Camera, Incandescent lamp and
a laptop with Thermosuite software.
 The Camera used was a Jenoptik VarioCam Head Hires 640 with a frame rate of 60
Hz.
 The detector has a spectral range of 7.5 to 14µm, a resolution of 640 x 480 pixels
and a thermal sensitivity of 60mK.

7. Working
 The specimen was placed at the focus of the camera and the incandescent light
was directed onto the surface of the specimen
 After a while the IR camera is used to image the specimen and the images were
observed in a Thermosuite software in the laptop and a subsequent analysis of
temperature gradient was done.
 To Obtain optimum results the whole apparatus was covered with a black cloth to
create a dark room atmosphere

8. Results
 The following images were captured using the IR camera
(A) (B)
Figure (A) shows temperature distribution when the apparatus is covered with black
cloth whereas figure (B) shows temperature distribution when there is no covering
 The red spot shows a temperature of 33.12 degrees Celsius whereas the other area
shows a temperature of 28 degrees Celsius indicating there is a defect at the spot.

9. Conclusions
 The difference in temperature gradient was observed at a distance of 30mm form
the edge of the plate
 The change in temperature was exactly observed at the spot where the defect was
placed and hence Infrared thermography was effective in detecting the voids or
defects in Scotch weld or adhesive joints.

10. Advantages
 Zero contact technique which is non-invasive
 Results are easily understandable and free from numerical calculations
Disadvantages
 To detect deeper defects the heating equipment should be of high frequency
which is very costly.
 In this project if the incandescent bulb is not focussed properly there are chances
of uneven distribution of heat onto the surface of specimen and also it is difficult to
account for losses due to convection and radiation

11. Future Prospects
 This technique can be further extended to identify the thickness of the epoxy or
adhesive applied and in turn determine the strength of the adhesive bond at
different points and identify the defective or weak regions in a structure with
adhesive bonds