This document discusses different non-destructive testing (NDT) methods used to detect defects in materials and objects without damaging them. It describes ultrasonic testing which uses high-frequency sound waves to find flaws inside metals and other materials. It also discusses eddy current testing which induces eddy currents in conductive materials using a magnetic field to detect variations caused by defects. Finally, it briefly mentions the Mohs hardness test used to determine the hardness of minerals based on their ability to scratch other reference minerals.

2. Muhammad Umair Bukhari
Engr.umair.bukhari@gmail.com
www.bzuiam.webs.com
03136050151

3.  Method of finding defects in an object without
harming the object.
 In the aircraft industry, NDT is used to look for internal
changes or signs of wear on airplanes. Discovering defects will
increase the safety of the passengers.
 The railroad industry also uses nondestructive
testing.
 If an airplane or a rail had to be cut into pieces to be
examined, it would destroy their usefulness.
 With NDT, defects may be found before they become
dangerous.

4.  The use of sound waves to determine defects is a
very old method. if a piece of metal is struck by
hammer, it will radiate certain audible notes, of
which the pitch and damping may be influenced by
the presence of internal flaws. However, this
technique of hammering and listening is useful only
for the determination of large defects.
 Ultrasonic is a fast, reliable and nondestructive
testing method which employs electronically
produced high-frequency sound waves that will
penetrate metals, liquids, and many other materials
at speed of several thousand feet per second.

5.  A more refined method consists of utilizing sound
waves above audible range with a frequency of 1 to
5 million Hz, hence they term ultrasonic.
 Quartz is a widely used ultrasonic transducer.
 A transducer is a device for converting one form of
energy to another.

6.  Ultrasonic waves are introduced to a material
 The receiving transducer on the opposite side
receives the vibrations and converts them into an
electrical signal that can be observed on the cathode
ray oscilloscope.
 If the ultrasonic wave travels through the specimen
without encountering any flaw, the signal received is
relatively large.
 If there is a flaw in the path of the ultrasonic wave,
part of the energy will be reflected and the signal
received by the receiving transducer will be reduced.

7.  The pulse-echo method uses only one transducer
which serves as both transmitter and receiver.
 When the sound wave enters the material being
tested, part of it is reflected back to the transducer
where it is converted back to an electric impulse.
this impulse is amplified and shown on the screen
of oscilloscope.
 When the sound waves reaches the other side of the
material, it is reflected back and shown as another
signal on the screen besides the first signal.

8.  Eddy-current testing uses to detect flaws,
irregularities in structure, and variations in
composition in conductive materials.
 There are several limitations, among them:
◦ only conductive materials can be tested,
◦ The material may cause bad readings,
◦ The depth of penetration into the material is limited

9.  In Eddy current testing, a varying magnetic field is
produced if a source of alternating current is
connected to a coil.
 When this field is placed near a test specimen
capable of conducting an electric current, eddy
currents will be induced in the specimen.
 The Eddy currents, in turn, will produce a magnetic
field of their own.
 The detection will measure this new magnetic field
and convert the signal into a voltage that can be
read on a meter.
 The testing devices are portable, provide immediate
feedback

10.  The scale consists of 10 different standard minerals
arranged in order of increasing hardness. For
example, TALC is on no. 1 , GYPSUM is on No. 2, etc
up to CORUNDUM is on No. 9 and DIAMOND on the
last 10th place.
 If an unknown material is scratched noticeably by
no. 6 and not by no. 5, the hardness value is
between 5 and 6.
 This test has never been used to any great extent in
metallurgy but is still used mineralogy.

11.  The primary disadvantage is that the hardness scale
is non uniform.
 When the hardness of the minerals is checked by
another hardness-test method, it is found that the
values are compressed between 1 and 9 there is a
large gap in hardness values