This document discusses thermography and eddy current testing techniques used in non-destructive testing. It covers the principles of thermography, contact and non-contact inspection methods using liquid crystals, and instrumentation and applications of infrared radiation and detectors. It also discusses the generation of eddy currents, properties of eddy currents, probes, instrumentation, testing arrangements, and applications, advantages and limitations of eddy current testing.

1. M.KARTHIKEYAN
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING
AAA COLLEGE OF ENGINEERING & TECHNOLOGY, SIVAKASI
karthikeyan@aaacet.ac.in
ME8097 NON DESTRUCTIVE TESTING
AND EVALUATION

2. UNIT III THERMOGRAPHY AND EDDY CURRENT TESTING
(ET)
1. Thermography- Principles,
2. Contact and non contact inspection methods,
3. Techniques for applying liquid crystals, Advantages and
limitation
4. Infrared radiation and infrared detectors, Instrumentations and
methods, applications.
5. Eddy Current Testing-Generation of eddy currents, Properties
of eddy currents,
6. Eddy current sensing elements, Probes,
7. Instrumentation,
8. Types of arrangement,
9. Applications, advantages, Limitations,
Interpretation/Evaluation.

4.  Infrared radiation (IR), sometimes known as infrared light, is
electromagnetic radiation (EMR) with wavelengths longer than
those of visible light.
 Infrared radiations are also referred to as heat or thermal waves
or electromagnetic waves. This is because they have a heat-
inducing property.
 Sometimes infrared rays themselves are classified as near-
infrared and far-infrared rays.
 Near-infrared rays are used in electronic applications like TV
remote sensors and photography.
 Far infrared rays are more thermal in nature. Anything
generating heat gives out far-infrared radiation.

5. CHARACTERISTICS OF INFRARED RADIATION
 Infrared radiation can be emitted from all kinds of objects.
 Invisible to human eyes: This is considered to be one of the
characteristics of infrared radiation and is also useful for
security purposes.
 Small energy: The energy of infrared radiation is equal to the
vibrational and rotational energy of the molecules. This
characteristic is used in the identification of the molecules.
 Long-wavelength: The transmission becomes better as there is
less scattering through the medium.

6. WAVELENGTH OF INFRARED RADIATION
 1µm to 3µm which is known as the Band I or Short Wave
Infrared
 3µm to 5µm which is known as the Band II or Middle Wave
Infrared
 8µm to 14µm which is known as the Band III or Long Wave
Infrared

7. CHARACTERISTICS OF REGIONS OF INFRARED
Near-infrared The wavelength ranges from 0.75 to 1.4
micrometres.
This is used in material science, fibre optic
communication, and in the medical field.
Short
wavelength
infrared
The wavelength ranges from 1.4 to 3
micrometres.
This is used in telecommunications and for
military purposes.
Medium
infrared
The wavelength ranges from 3 to 8 micrometres.
This is used in the chemical industry and in
astronomy.
Long-
wavelength
infrared
The wavelength ranges from 8 to 15 micrometres
Astronomical telescopes and optical fibre
communications are possible with the help of
long-wavelength infrared
Far infrared The wavelength ranges from 15 to 1000
micrometres.
It is used mainly in the treatment of cancer
therapy.

8. APPLICATIONS OF INFRARED WAVES
HEAT SOURCE
There are two different industries that use infrared radiation as a heat
source and they are:
Medical uses:
 Infrared radiation are used for treating high blood pressure
 Used to reduce the inflammation of throat, ear and nose
 It eases kidney function
 Infrared radiation is considered to be one of the safest methods of
physiotherapy.
Manufacturing industries:
Industries which concentrate on manufacturing processes such as
forming of plastics, curing of coatings, plastic welding, etc use
infrared heaters in place of contact heating and convection ovens.

9. MASSAGE THERAPY
 Infrared rays are used for warming the skin and for relaxing the
muscles.
 Infrared rays are preferred because of their penetration quality
through the skin.
INFRARED PHOTOGRAPHY
 Infrared filters are used for capturing pictures in infrared
photography.

10. COSMETOLOGY APPLICATION
 Infrared rays are widely used for cosmetic applications such as
for treating skin injuries, smoothing of wrinkles, reducing the
occurrence of dandruff etc.
 The reason why infrared rays are used is that they can penetrate
through the skin up to 3-4 mm.
 They also warm the skin resulting in improved blood
circulation, continuous supply of oxygen and other nutrients to
the skin.

11. ASTRONOMY
 Astronomers use optical devices such as mirrors, solid-state
digital detectors, lenses to study objects from space with the
help of infrared waves.
 The images from these optical devices are obtained with the
help of an infrared telescope.

12. INFRARED COMMUNICATION
 Data transmission with the help of infrared radiation is very
common in short-range communication.
 For encoding the data infrared light-emitting diodes are used
which emit infrared radiation and is focused into a narrow beam
with the help of a plastic lens.
 At the receiver end, a photodiode is placed for converting
infrared radiation into electric current.

13. Who discovered infrared light?
a) Justin Baehler
b) Albert Einstein
c) Thomas Edison
d) William Herschel
MCQ - 1

14. Which of these is not a category of infrared light?
a) Mid
b) Near
c) In between
d) Far
MCQ - 2

15. What is infrared radiation?
a) The circulation of a fluid caused by heating it.
b) Transfer of heat inside a metal.
c) Heat energy transfer by electromagnetic waves
d) Transfer of light energy
MCQ - 3

16. How can we sense infrared radiation, even though we
cannot see it?
a) Taste it
b) Smell it
c) Feel it
d) Hear it
MCQ - 4

17. The hotter an object the more infrared radiation is given off
(T/F).
a) True
b) False
MCQ - 5

18. PART - A
1. How liquid crystals are used in NDT?
2. List out the limitations of Liquid Crystal Thermography
3. Write down the advantages of Liquid Crystal Thermography.
PART - B
1. Describe the working principle and techniques involved in
Liquid crystals inspection
QUESTIONS