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NDT TESTING TIPS FROM NDTECH - NEWSLETTER #22-August 2001





1. Meet the New InterTest


2. Materials testing on-line via the Internet


3. Visual Crack Measurement System Uses Temperature-Sensitive

Paint


4. A Picture of Bridge Health


5. Publications


6. Scientific Information Available Online


7. Electromagnetic Smart Washer for Detecting Bolthole Cracking



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The NDTech Newsletter is published periodically by NDTech, a consulting
firm offering nondestructive testing services and instruments. This
newsletter is distributed by e-mail and covers brief descriptions of
some useful but less publicized radiographic, ultrasonic, penetrant,
magnetic particle, and other NDT methods. You will automatically
receive the newsletter, at no cost. If you wish to be removed from the
NDTech Newsletter, simply reply remove with "Remove" as the subject.



To find out more about NDTech and its nondestructive testing consulting
services and instrumentation, visit the NDTech website at
http:// www.ndtech.net



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1. Meet the New InterTest



EMCO InterTest, which has provided NDT and RVI tools to industry
for the last 20 years, was restructured this past June to form a new
company, InterTest.



InterTest consists of two new areas of responsibility: InterTest RVI
and InterTest NDT. InterTest RVI supplies remote visual inspection
equipment nationally, including such brands as IShot Imaging, Zibra,
Scholly, ELMO, Toshiba, and Sony. InterTest NDT represents
nondestructive testing equipment regionally throughout the Northeast,
including ultrasonic, eddy current, and alloy identification tools from
Panametrics, ibg, Rohmann, and Thermo MeasureTech.


IShot Imaging is a new brand of remote visual inspection tools from
InterTest. Various products available include camera modules for
underwater and confined-space use, robotic camera positioners,
auxiliary light packs, video borescopes, and retrieval tools.



To receive a free subscription to Innovations, the quarterly newsletter
of InterTest, e-mail mail@intertestinc.com or call 800-535-3626. More
information about iShot Imaging products can be found online at
www.intertestinc.com



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2. Materials testing on-line via the Internet



The world of materials testing is set to change with a new L1
million on-line testing facility launched to help customers world-wide
develop products and test materials rapidly and cost effectively from
the comfort of their own premises.


Analysis Online, developed by Exeter Advanced Technologies uses
universal browser software to bring test data, from advanced testing
equipment supplied by AMETEK Lloyd Instruments and other leading
companies, direct to the client in real time.


After a client submits a sample, experienced staff at Exeter set up
the instruments, perform the tests and collate the results. "Data
interpretation is the key here. The client can interact at any stage
using the browser on a standard PC and a 56k internet connection," said
Dr. Lee Bridger following the first successful live demonstration.


"Analysis Online is a really exciting opportunity and clients will be
able to test many materials using the wide range of equipment we have
supplied," said Mark Bartlett, Managing Director of AMETEK Lloyd
Instruments. Such equipment includes a 20 kN EasyTest test machine, and
DAVENPORT tm polymer test equipment including the HDT/VICAT test
station, a melt flow indexer and melt viscometer for PET. The company's
industry proven NEXYGEN tm application software is also used for
instrument control, accurate test analysis and clear data formatting.


In his keynote address to local businesses and academics, Ken Poulter,
Director of Government's Small Business Service hailed Analysis Online
as an "important interface between research and industry" to help
companies develop products and remain profitable.


The laboratory and software has been financed with an RDA grant of
L250,000. This is part of the L3m facility and has been supported by
contributions from the university and industry. The launch of Analysis
One coincides with further initiatives at the university of Exeter
including a new microscopy suite, electronics service, materials
characterization center and product development.


Analysis Online is now available at
www.analysis-online.co.uk where registered clients can
book the service and download the viewer software.



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3. Visual Crack Measurement System Uses Temperature-Sensitive

Paint



Aging US Air Force aircraft are plagued with structural failure
in secondary structures. The Air Vehicles Directorate devised a plan
to reliably identify and track structural crack growth and slow or stop
the crack growth with bonded composite repairs. However, knowing when
and where to apply repairs remains a problem. Fatigue cracks appear in
secondary aircraft structures subjected to high-cycle, out-of-plane
loads due to turbulent aerodynamic flow, exhaust flow, and high
acoustic environments. Out-of-plane loads excite resonant frequencies
of secondary structures. Damping is added to the repair to reduce the
vibration response that, in turn, reduces the stresses causing the
cracks.


Directorate researchers successfully demonstrated a new technique to
measure crack growth of plates that are vibrated at resonant frequency
on an electrodynamic shaker. The new Visual Crack Measurement (VCMS)
using temperature-sensitive paint (TSP) views and measures crack growth
while fatiguing a plate at sinusoidal resonance. The VCMS includes a
digital camera to record images of the vibrating plate on a personal
computer (PC). TSP is applied to the plate to enhance crack visibility
and obtain a temperature profile of the plate while it is cracking. As
the plate cracks, stress concentrations at the crack tip are observed
as temperature increases due to frictional heating. A camera views the
top painted surface of the plate and captures images of the vibrating
plate which are stored as PC files. Raw image files and ratio image
files are displayed on a monitor. Ratio images show the changes in
temperature at the areas of highest stress. A spectrum analyzer,
oscilloscope, visual tip displacements, and sound are used to identify
the first bending mode of the plate. A shift in frequency resonance
marks crack initiation.


For more information contact TECH CONNECT at (800) 203-6451 or place a
request at http://www.afrl.af.mil/techconn/index.htm. Reference
document VA-00-01.



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4. A Picture of Bridge Health



Many bridges and highway interchanges in the United States are
still providing valuable service but are years past their life
expectancy. One such example is the interchange of I-40 (east-west)
and I-25 (north-south) in Albuquerque, New Mexico, known as the Big I.
Albuquerque is unique in that virtually no other large city is
dependent on a single highway interchange for traffic flow and routing.
Originally built in 1966 with a life expectancy of 20 years, the Big I
interchange was designed to handle 30,000 to 40,000 cars a day.
Thirty-five years later and obsolete, it has more than 300,000 cars
passing through it each day. Commuters constitute nearly 90% of the
traffic load during peak hours.


A primary concern of all highway agencies (state and federal) is the
safety and maintenance of new and existing bridges, overpass, and
flyovers. Both roads and bridges are aging and reaching the end of
their life span. Fatigue failure is a concern in all bridge types. If
the selected structural system does not provide load path redundancy, a
fatigue failure could cause the collapse of the structure.



Currently, most highway bridge inspection in the United States is done
using visual inspection. The method relies heavily on subjective
evaluations based on the experience and skill of the inspectors.
Visual inspection can be expensive and time consuming, in addition to
the difficulty in accessing various portions of a bridge structure. A
condition rating ranging from 0 to 9 (in order of improving condition)
is assigned to describe the observed physical state of the bridge
element.




A study conducted by the Federal Highway Administration (FHWA)
Non-Destructive Evaluation Center (NDEVC) showed that these ratings
could vary on average by as much as +/-2 points between inspectors. In
addition, it is often difficult to describe the location and extent of
deterioration of a bridge member solely with a written explanation.



Other nondestructive evaluation (NDE) techniques for measuring bridge
deformation that use traditional transducers, such as dial gages or
linear potentiometers, require a fixed base to react against. A
temporary support has to be erected under the structure, which is both
expensive and often not feasible. Deflective measurements are
difficult (if not impossible) when the bridge spans over a highway, a
body of water, or a deep valley.



The problems of subjectiveness is visual inspective and fixed base
requirements in transducer techniques can be eliminated by using
close-range photogrammetry, a non-contact deflection measurement
technique. Close-range photogrammetry offers the capability to measure
the spatial coordinates (and subsequent displacements) of specific
points on a bridge structure in three dimensions.



Photogrammetry



Photogrammetry is a three dimensional coordinate measuring
technique that uses photographs as the fundamental medium for
measurement. In its broadest sense, photogrammetry converts or maps
flat two-dimensional images into the real three-dimensional world. The
fundamental principle used photogrammetry is triangulation. By taking
photographs from at least two different locations, lines of sight can
be developed from each camera to points on the object. These lines of
sight are mathematically intersected to produce the three-dimensional
coordinates of the points of interest.


The photogrammetric process consists of four steps: 1) field work/data
collection, 2) image processing, 3) analysis, and 4) measurement/3-D
modeling.



Data collection entails establishing a network of control points (X, Y,
Z coordinates) to establish a reference system between the photograph
and the real structure, and taking the photographs of the project area.
Control points normally consist of stick-on targets that are clearly
labeled so their ID can be read in the photograph. A minimum of four
control point must be established in every group of photographs. The
photographs can be taken with a variety of cameras; however, the result
must be digital image files. Digital cameras work the best for
schedule and efficiency, with no loss of accuracy.


The exact steps required for image processing depend on the choice of
camera, and the accuracy required for the final measurements.
Regardless of the camera type, all images must be prepared for use in
the analytical software. This preparation includes processing the
images into a common format and then storing these images in an archive
along with ancillary information associated with the image.



Analyzing the digital images is the heart of the photogrammetric
process. The exact location and orientation of each image at the time
of exposure is calculated. The position and orientation of a
photograph are called the exterior orientation of the photograph. The
steps needed to prepare for this calculation allow the various
photographs in a group to be mathematically tied together and tied to
the control point coordinate system.



Absolute orientation is the photogrammetric operation used to tie an
arbitrarily oriented group of photographs into a real-world coordinate
system. In mathematical terms the coordinate system of the photo group
(which is common to all photos after the relative orientation and
formation have been calculated) is brought into the space of the
control point coordinate system using a conformal transformation.



Pilot Project



The FHWA has teamed with New Mexico State University (NMSU) to
provide long-term health monitoring of the Big I bridges once
reconstruction project is complete. This will be the pilot project for
NMSU's photogrammetry technique. The principal investigators are Dr.
Ken White, Dr. David Jauregi, and Dr. Clinton Woodward. Part of the
reason that photogrammetry was considered for monitoring the Big I
interchange were the advances in technology that have been made in
recent years. Photogrammetry methods in the 1980s were restricted by
the lower resolution of digitalized images and inadequate computing
power to process the images into a three-dimensional model.



Begun on June 30, 2000, the Big I reconstruction project is expected to
be competed on June 30, 2002. (Two years would set a national record
for reconstructing a major freeway-to-freeway interchange in an urban
area.) The project contains 55 new or renovated bridges- what might
look like a single bridge may actually be two or more bridges joined
together. Eight of the bridges are segmental bridges made of precast
concrete segments- "flyover" ramps (curved, elevated bridges)
connecting I-25 and I-40 in the heart of the interchange- the first of
their kind in New Mexico. Project engineers chose precast, segmental
concrete box girders for the flyovers over the more-common steel-plate
girder. Segmental bridges offer several advantages: more economical,
low maintenance, can be erected faster, and more control of the
production time.



The high-strength concrete segments are 42 feet wide, 13 feet long, and
9 feet deep for two-lane segments and 32 feet wide, 15 feet long, and 9
feet deep for one-lane segments. There are 14 to 16 segments between
each pier. More than 660 segments- weighing 80 tons each- and 44 piers
will be used to construct the bridges. Workers use cables (prestressed
by 890,000 lbs.), high-strength steel bars, and a special construction
epoxy to support and join each segment.



When the reconstruction is complete, access to the bridges will be
difficult. NMSU chose close-range photogrammetry as the means of
deformation measurement due to the difficulty in using traditional
measurement instruments, such as dial gages and displacement
transducers, and the expense of laser systems. Close-range
photogrammetry has been used as a monitoring technique for quite some
time. However, it has been used mainly for industrial applications,
architectural documentation, and for monitoring dam and culvert
deformation. Although little work had been done in applying
close-range photogrammetry to the measurement of highway bridge
deformation, the investigators believe this technique can accurately
monitor the Big I bridge and flyovers. However, this is a research
project and part of it is to establish how accurate the photogrammetry
technique is in monitoring large, inaccessible structures under live
load.



In a previous field study, White, Jauregui, and Woodward investigated
deformations of a prestressed concrete bridge and a steel girder
bridge. They made photogrammetric measurements of the initial girder
camber of the prestressed concrete bridge and compared them with level
rod readings. In addition, dead load deflections of the girders under
the weight of the concrete deck and traffic barriers were measured and
compared to those obtained with a total station. A comparison of the
measurements with the dead load deflection diagram was also made. On
the steel girder bridge, photogrammetric measurements were made of the
girder deformations under truck loading. The measurements were
compared to those obtained using traditional systems and the results
from a finite element analysis of the bridge.



Typically, deformation measurement photographs are taken of a structure
every 2 years. But because the Big I interchange is a fracture
critical structure, high-resolution photographs will be taken at least
once a year. The investigators anticipate that photos will be taken
every 3 months during the first couple of years of the interchange to
establish a baseline for the project. Then the monitoring interval
will be extended to between 6 months and 1 year.


The necessary high-resolution photographs will be taken with a digital
camera. Some traditional film photographs may also be taken of the Big
I interchange. They will be scanned on a high-resolution scanner and
uploaded to the computer. With this method, they may give better
results than the digital photographs. The digitalized photographs will
then be used to create a three-dimensional computer model of the
interchange. Deformation measurements must be accurate within 0.001 of
an inch, the minimum for a structure under a live load.



For more information contact NTIAC at (800) NTIAC-39/(800)684-2239, or
visit their website at http://www.ntiac.com.



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5. Publications



Handbook of Nondestructive Evaluation - Charles Hellier.
Nondestructive testing had become the leading product testing standard,
and this book is the unparalleled one-stop, A-to-Z guide to this
subject . Covering the background, benefits, limitations, and
applications of each, this decision-simplifying resource looks at both
major and emerging NDE methods, including visual, penetrant, magnetic
particle, radiographic, ultrasonic, eddy current, thermal infrared, and
acoustic emission testing. In clear, understandable terms, the book
shows you how to interpret results and formulate the right decisions
based on them, making it a welcome resource for engineers,
metallurgists, quality control specialists, and anyone else involved in
product design, manufacture, or maintenance. The Handbook is also the
ideal prep tool, if you're seeking certification in AWS/CSWIP, ASNT
Level III, ACCP, and IRRSP programs.


This paperback book was published by McCraw-Hill Professional
Publishing and is available from www. amazon.com. It was published in
March 2001 and has 603 pages. The book is priced at $99.95.



Nondestructive Testing Handbook: Volume 3, Infrared and Thermal
Ranging, 3rd Edition- Xavier P.V. Maldegue (technical editor) and
Patrick O. Moore (editor). This volume is probably the most
international NDT Handbook volume yet, containing 82 papers from
contributors in 13 countries. Topics include history, standards,
personnel qualification, heat transfer, radiometry, errors and noise,
contrast cameras and equipment, image processing, infrared tomography,
liquid crystals, thermocouples, and techniques. Applications include
metals, aerospace, electric power, chemical and petroleum,
infrastructure and conservation, and electronics. For thermographers
unfamiliar with nondestructive testing, the introduction includes a
survey of other methods.


This hardcover book is available from the American Society for
Nondestructive Testing at www.asnt. org. It was published in March
2001 and has 732 pages. The book is priced at $135.00 for ASNT
members, $181.25 for nonmembers.



Theory and Practice of Infrared Technology for Nondestructive Testing-
Xavier P.V. Maldegue. Infrared technology is becoming more popular
because of the availability of new infrared images and the need for
nondestructive testing in many fields. The book is divided into three
sections, Fundamental Concepts, Active Thermography, and Active and
Passive Thermography: Case Studies. Beginning with heat transfer, the
reader is introduced to all aspects of infrared thermography including
optic fundamentals, types of images, image analysis, experimental
concepts, and applications. The author is a well-known authority on
infrared thermography.


The hardcover book was published by John Wiley & Sons, Inc, and is
available from bn.com. It was published in March 2001 and has 704
pages. This book is priced at $125.00.



Stress Analysis of Cracks, Third Edition- Hiorshi Tada, Paul C. Paris,
and George R. Irwin. Now in a new hardbound format, this extensive
source of crack stress analysis information is nearly double the size
of the previous edition. Along with revisions, the authors provide 150
new pages of analysis and information. The book can serve as an
excellent reference, as well as a text for in-house training courses in
various industries and academic settings.


This hardcover book is available from ASME International at
www.asme.org. It was published in 2000 and has 696 pages. The book is
priced at $120.00 for ASME members and $150.00 for nonmembers.



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6. Scientific Information Available Online


Utilizing a powerful search engine from Lion bioscience,
Heidelberg, Germany, TheSceitnificWorld Inc., Boynton Beach, Fla.
(www.thescientificworld.com), enables the scientific
community to perform online queries across a comprehensive set of
research databases. More than 20,000 scientific journals are available
form thousands of publishers, and scientists have the flexibility to
purchase only the articles that are needed.




>From March 2001 publication of R&D Magazine
(www.rdmag.com)


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7. Electromagnetic Smart Washer for Detecting Bolthole Cracking



Engineers at the Marshall Space Flight Center, Alabama have
designed a new device, called the Smart Washer, that can
electromagnetically detect bolthole cracks in metal structures. The
device is a metal washer that contains a wire coil embedded onto the
bottom surface of the washer. An alternate current drives this coil
and induces eddy currents around the bolthole. These eddy currents
develop electromagnetic fields that interact with the driving field of
the coil.



A sensor is built into the Smart Washer, enabling direct contact with
the bolthole lip, which is a natural crack-formation site. The sensor
is therefore ideally positioned for crack monitoring, and since the
Smart Washer is a permanent part of the structure, technicians can
detect bolthole cracks without removing the bolt.



Another advantage is that unlike bolts, washers are not critical
structures. Since washers distribute bolt loads onto surfaces, Smart
Washers can accommodate a sensor without degrading structural
strength.



The Smart Washer technology has several novel features. First, unlike
many sensing systems, the design allows a long cable between the local
electronics of the Smart Washer and the measurement circuitry. If this
cable is routed to an access port, then technicians can inspect
boltholes by connecting a hand-held instrument.


Secondly, it is easy to fabricate Smart Washer sensing coils, and the
measurements involve well-understood techniques that require relatively
few components. The simplicity of the Smart Washer provides a robust,
rugged system that can withstand field conditions.


Finally, because washers are not critical structures, designers are
more willing to replace standard washers with Smart Washers, thereby
adding embedded bolthole monitors to new and existing designs.



The unique capabilities of the Smart Washer have been successfully
demonstrated during destructive tests. Smart Washers were mounted on
1/8-in. (3.2-mm) thick aluminum 2219-T87 coupons, where each coupon
contained a 0.5-in. (13-mm) diameter drilled hole. The coupon was
installed in a fatigue test machine, and the Smart Washer was fastened
to the coupon with a stainless steel nut and bolt. Cyclical tensile
loading induced a bolthole crack, and the Smart Washer sensor signal
was recorded as the crack grew.



The Smart Washer successfully detected crack initiation and growth in
conditions of dynamic loading, static loading, and unloaded conditions.
In all cases, the Smart Washer could reliably detect 0.050-in.
(1.27-mm) long cracks, and could track crack growth out to lengths
approaching 0.200 in. (5.08 mm).


This work was done by Bruce McKee, Yuri M. Shkarlet, Atten Khatkate,
Tom Banas, Richard Ingram, and David Perkins of Innovative Dynamics,
Inc., Cornell Research Park, for Marshall Space Flight Center. For
further information, access Technical Support Package (TSP) free
on-line at www.nasatech.com under the Mechanics category.




From May 1998 Issue of NASA Tech Briefs
(www.nasatech.com)



NDTech website: http://www.ndtech.net


Email: info@ndtech.net




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