Nondestructive Testing

تاريخ التسجيل : 22/11/2009

DIGITAL TECHNOLOGY
Digital technology is virtually sweeping the nondestructive testing industry as
well as affecting every aspect of American life. We have digital television,
digital cameras and video recording systems, digital telecommunications,
digital global positioning, digital satellite radios, digital appliances, and personal
digital computers with high-speed memory and capacity that were
unheard of 20 years ago. Some optical and digital electronic gadgets just
recently introduced include small hand-held 10¥ binoculars with 8¥ digital
cameras, shirt-pocket MP3 players, and real two-way wrist radios with a range
of 11–2 miles. Dick Tracy had to wait a long time for that one. Can personal identification
chips with global tracking be far behind? Standard “Walkie-Talkie”
range has reached up to 10 miles.
High-speed computers with high-capacity memory and high-speed data
transfer can provide real-time evaluation and control in many nondestructive
testing applications. Huge amounts of information can be stored for later
review and analysis when desired. AMD beat Intel in the race to be the first
on the market to introduce a new 64-bit microprocessor chip. Have we reached
the ultimate in computer memory, speed, and data transfer capacity? No, the
future still lies ahead.
At the same time, wireless technology is advancing by leaps and bounds.
Most people seem to have cells phones rather than those old Alexander
1
INTRODUCTION
1
Introduction to Nondestructive Testing: A Training Guide, Second Edition, by Paul E. Mix
Copyright © 2005 John Wiley & Sons, Inc.
Graham Bell telephones with wires. The advantages of wireless for industrial
automation and the process control industries include worker and work
station mobility and the elimination of thousands of miles of expensive conduit
and cable. However, there are still many concerns regarding system design and
potential signal transmission problems such as signal interference, signal
hacking, sudden signal loss and retries, RF interferences, and multipath fading
from unwanted reflections. However, it is probably safe to say that we can look
forward to continued miniaturization and improvements in all forms of wireless
technology.
City parks in Austin,Texas currently offer wireless Internet access; however,
there are still some concerns that Bluetooth technology can be compromised.
Bluetooth is a universal radio interface in the 2.45GHz ISM frequency band
designed to function on a worldwide basis. A Bluetooth system consists of a
radio unit, link controller, link manager, and software. Spectrum spreading
facilitates optional operation at power levels up to 100mW worldwide. This
is accomplished by frequency hopping in 79 hops displaced by 1MHz, from
2.402 GHz to 2.480Hz.The maximum frequency hopping rate is 1600 hops/sec.
Bluetooth devices must be able to recognize each other and load the appropriate
software to use the higher-level abilities each device supports and existing
protocols.
Notebook PC computers can be used for remote networking using
Bluetooth telephone systems, Bluetooth phones, cellular phones and notebooks
for conference calls, speakerphone applications, business card exchange
and calendar sychronization. Bluetooth technology is an operating system that
is independent of any specific operating system.Advantages of Bluetooth technology
are:
• Data exchange; signals penetrate solid objects.
• Remote networking and maximum mobility.
• Omnidirectional with synchronous voice channels.
The main disadvantage is that signals can be monitored by a snooping device
from any direction or hidden location. Encryption with authenticity check is
possible using a challenge-response protocol utilizing a secret key or password.
Both devices must share the same secret key. The technology is suitable for
many industrial data-sharing applications.
Will wireless RF ID tags help scientists track mad cows from country to
country and state to state? Only if cattle ranchers and farmers all over the world
are forced to comply with this requirement and that isn’t very likely, is it?
1.2 SMALLER IS BETTER
Virtually all sensors, whether they are laser, infrared, acoustic, ultrasonic, or
eddy current, have benefited from the high-tech explosion as well. Generally,
2 INTRODUCTION
high-resolution sensors have become smaller, more sensitive, and more robust.
For flaw detection, many sensors can be focused more sharply as parts are
scanned at faster rates, resulting in high-speed, high-resolution flaw detection.
Eddy current and ultrasonic transducer arrays have greatly increased the
single pass surface area scanned, while decreasing scanning times.
Piezo-composite ultrasonic transducers have greatly increased the sensitivity
and range of ultrasonic transducers while reducing noise. In some applications
noncontacting ultrasonic probes with perfect air/gas (compressed fiber)
impedance matching can compete with laser profiling applications and other
methods for the detection of minute surface defects. Noncontacting sensors
also have some advantages in medical applications.
Micro-electromechanical systems (MEMS) have been around for about 20
years and are increasingly important to many manufacturing industries including
semiconductor, automotive, electrical, mechanical, chemical, medical, aerospace,
and defense. A very rapid growth of MEMS is expected over the next
decade.
Small, sensitive airbag accelerometers help protect us in our automobiles
and miniature flow valves provide beautiful letter-quality ink jet printing.
Other MEMS developments include:
• Micropressure and acceleration sensors for restricted spaces
• Microelectronic components such as capacitors, inductors, and filters
• Micromechanical components such as valves and particle filters
National security applications for MEMS include nonproliferation, counterterrorism,
land mine, chemical and biological warfare, and WMD stockpiling
detection. Spin-off applications, which benefit mankind, include biomedical
diagnostics, food and water safety, and industrial process and environmental
monitoring.
The design, fabrication, testing, and inspection of microcomponents and
assemblies challenge engineers and designers because the software, tooling,
mechanics, size and shape, fluidity, damping, and electrostatic effects encountered
in the microcomponent world are considerably different from those
associated with the more conventional macrocomponent world.
While MEMS may still be considered in its youth, the birth of nanotechnology
has progressed to at least that of a preschooler. Nanotechnology is now
widely recognized by the government and various technical groups. New products
are being developed and evaluated by many sectors. Nanotechnology has
been defined as the manipulation or self-assembly of individual atoms, molecules,
or molecular clusters into structures having dimensions in the 10 to 100
nanometer range to create new materials and devices with new or vastly different
properties. Scientists believe the ability to move and combine individual
atoms and molecules will revolutionize the production of virtually every
human-made object and usher in a new high-tech revolution.
SMALLER IS BETTER 3
DOE nanotechnology accomplishments include:
• Addition of aluminum oxide nanoparticles that converts aluminum metal
into a material with wear resistance equal to that of the best bearing steel
• Novel optical properties of semiconducting nanocrystals that are used to
label and track molecular processes in living cells
• Nanoscaled layered materials that can yield a fourfold increase in the performance
of permanent magnets
• Layered quantum well structures to produce highly efficient, low-power
light sources and photovoltaic cells
• Novel chemical properties of nanocrystals that show promise to speed the
breakdown of toxic wastes
• Meso-porous inorganic hosts with self-assembled organic microlayers
that are used to trap and remove heavy metal from the environment
Unlike one old science-fiction thriller, nanobots may not be able to cure a
young man’s cancer, phenomenally increase his personal endurance and
strength, and protect him against all harmful outside elements by stimulating
the growth of gills in his neck, growing eyes in the back of his head, and developing
an alligator skin for him, but it can make structural elements smaller,
stronger, lighter, and safer. In turn, nanotechnology can make larger structures
and all forms of transportation safer for us mere mortals.
Benoy George Thomas, in an article for PCQuest (September 2003, p. 174),
mentions that scientists Robert A. Freitas and Christopher J. Phoenix claim
that someday nanobots may change the very essence of life by replacing the
blood currently coursing through our arteries and veins with over 500 trillion
oxygen- and nutrient-carrying nanobots. In this scenario, the nanobots would
duplicate just about every function of blood, but do it more efficiently.
The bloodstream would be made up of respirocytes each consisting of 18
billion precisely aligned structural atoms. Each respirocyte would have an
onboard computer, power plant, and molecular pumps and storage hulls to
transport molecules of oxygen and carbon dioxide. These nanobots would be
a thousand times more efficient than the red blood cells (RBCs) they replace.
If it sounds too good to be true, then it probably is.
While nanotechnology has been heralded as the driving force for America’s
next industrial revolution, extreme care must be exercised along the way. At
present, the hazards and risks associated with nanoparticles are poorly
defined. Toxicologists at Southern University in Dallas have discovered that
C60 buckyballs (nanoparticles) in modest concentrations can kill water fleas
(a source of food for newly hatched fish) and cause damaging biochemical
reactions in the brains of largemouth bass fingerlings. Preliminary studies also
indicated that similar problems were observed when nanoparticles were
inhaled by animals. Therefore, the toxicology effects of nanoparticles must be
considered for all phases of work in this field.
4 INTRODUCTION
1.3 MEDICAL MARVELS
While doctors and scientists can’t yet make a fantastic voyage in a MEMS or
nanosubmarine through human arteries and blood vessels, they can virtually
examine every artery and cavity in the human body. Doctors can go through
the groin to open partially plugged carotid arteries leading to the brain,
remove small blood clots from the brain using a small corkscrew-shaped
device at the end of a microcatheter, or even correct small aneurisms in the
brain. And, doctors can even fuse vertebrae disks by going through an incision
in the front of the throat. There ought to be easier ways to get to some
of these places.
With the new SilverHawk procedure, developed by Dr. John Simpson, leg
arteries with 85% plaque blockage can be restored to normal flow and the
arterial wall plaque can be saved for additional medical studies. Figure 1.1
shows the SilverHawk tool. The composition of the removed arterial plaque
is then studied by heart doctors to help determine if early warning signs of
heart attacks and strokes can be developed for otherwise normally healthy
MEDICAL MARVELS

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