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NDTECH - NEWSLETTER #20 - May 2001


1. Visual Inspection on the Internet

2. FAA Improves Inspections of Safety Critical Aircraft Turbine Parts

3. News From NTIAC

4. AE System Chosen for P-3C Fatigue Cycle Monitoring

5. Derailment Blamed on Track Fractures


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://


1. Visual Inspection on the Internet

Visual inspection is one of the most common methods for
materials examination. Information on visual examination can be
obtained by browsing the Internet, and in this connection, the
following websites may be of interest to the non-destructive testing

The New Zealand NDT Association offers information on a wide range of
NDT methods and presents a good introduction to visual inspection.

The NCSA Engineering with Visual Analysis homepage describes the
use of computer visualization to assist in the identification and
characterization of flaws not always detectable by the conventional NDT


One application of visual analysis is the stimulation and
visualization of acoustic microscope measurements used to detect
delamination in composite materials. Information on the NCSA's current
visual analysis applications and facilities can be obtained through
their website In addition, multimedia modules for material and
engineering scientists can be obtained free of charge using
anonymous ftp( see INSIGHT Vol.37, N 8, pp620-623)


Results from the use of direct volume visualization techniques for
automatic detection of explosives are presented at the Invasion
Technologies Inc. homepage. A description of this new method as well
as both attractive and useful 3-D illustrations are accessible at:


The Tops NASA server provides technical information sheets on
specific research projects, such as stroboscopic light sheet flow
visualization technique for condition monitoring of helicopter rotors,
and laser light sheet flow visualization technique. These technical
references can be accesses by typing stroboscopic at the search engine
at http


A request for further information, publication or technical
references is also available on-line for each technical information

Another NASA-related source of information on visual inspection can be
reached at:

http://robotics.jpl.nasa.gov/ tasks/ rsi/ homepage.html.

This site offers a full description of a machine vision system
for automated visual surface flaw detection on orbiting space
platforms. Detailed information on a an inspection robot remotely
operated by an operator for both visual and non-visual inspections also

An introduction to computer-integrated visual inspection for automatic
examination of circuit boards, as well as a list of relevant
publications, is presented at:


Similarly, information on automated geometric visual inspection
of 3D objects can be obtained at:


The homepage of Visual Inspection Technologies Inc.


describes products and services offered in the field of remote
visual inspection It is well designed and advertises videoimagescopes,
fiberscopes and boroscopes.

Another commercial site on visual inspection is that of UXR at:


The UXR homepage provides technical information on a wide range
of boroscopes and fiberscopes, The time taken to download images of the
equipment is the only drawback of the site.

Remote visual inspection is relied upon for the detection ,analysis and
documentation of defects normally inaccessible to the human eye.
Olympus Systems equipment for remote visual inspection in complex
machinery and inside pipes are presented at:


An application of visual inspection to the paper industry can be found

http:// www.kochsiek.de/english/umroller.html, where technical data of
a visual inspection winder to control quality of pre-limited
material is described.

The Web site of the Center for Applied Optical Sciences at:

http://www.caos.aamu.edu/. Describes various research areas from
holography to optical metrology, and is worth visiting by those
interested in such topics and wishing to establish contact with other

A well illustrated introduction on visual non-destructive testing on
works of art proposed by the Applied Optics Group of the University of
L'Aquila at:


One can learn of the use of holographic contouring techniques to
locate and size defects on a fresco 1667 or a carving of the XIIIth
century. A supercomputer analysis of a holographic inferograms for
displacement using the Fourier transform method is presented by the D.L
Gould at:

http: //www.ncsa.uiuc.edu/Edu/SuperQuest/new/proj4.html. You can see
his work using AVS visualization software.

The server of the Basic Industrial Research Laboratory of the
Northwestern University in Illinois offers technical reports which
cover a wide variety of subjects from the application of infrared and
visual imaging for the inspection of protective
coating(http://www.iti.nwu.edu/pubs/tr10.html) to optical global
bridge inspection

Technical information in a D-sight surface inspection system to
visually enhance signs of impact damage and interlayer corrosion on
aircraft parts is accessible at:

http:// www.netcore.ca/~diffract/dais.htm.

The Optical Metrology Laboratory at the Center for Applied Optics has
extensive facilities for analysis of complex surfaces, measurement of
ultra-smooth surfaces and precision coatings. Optical scattering and
other standard tools, such as stylus and non-contact profilometers, are
available to provide analysis in several formats( http://

Model and vibration analysis of bonded and composite structures can be
carried out using holographic infermetry as described at the homepage
of the Polaris Research Group at:


The optical Testing Digest newsletter is an electronic periodical,
supported and administered by the SPIE, which provides information on
topics such as computer -aided photo-elastic stress analysis,
forthcoming meetings and job opportunities. One can download this
newsletter at:

http://www.spie.org/otd, or subscribe for free e-mail delivery.

It is also worth consulting the Cordis site to be aware of current NDT
research projects carried out through the Brite-Euram scheme, including
topics such as pulsed digital holography and shearography
(http://www.cordis.lu:80/brite-euram /src/1147.htm).

Finally, information on a ' futuristic' project for holographic
fullbody security scanning can be enjoyably read at:



2. FAA Improves Inspections of Safety Critical Aircraft Turbine

Two years ago the FAA embarked on an aggressive program to
reduce the occurrence of fatal aviation events by 80%. This effort is
known as the Safer Skies initiative.

Although air travel currently enjoys a historically low rate for fatal
events per million takeoffs, strong industry growth could drive up the
number of annul fatal events in the next decade. In an effort to
maintain public confidence in air travel, the FAA is taking proactive
measures to significantly reduce occurrence of these fatal events.

One of the programs in the Safer Skies initiative mandating in-service
inspections of the safety critical turbine engine parts each time they
are fully disassembled . Turbofan engines contain heavy, rapidly
rotating parts. If one of these parts cracks and fails, it can lead to
an uncontained failure. Although uncontained engine failure events
involving fatalities are very rare( about 1 per 10 million takeoffs ),
uncontained high energy fragments pose a serious risk to passengers,
crew and airframe integrity.

A review of the last 15 years of aviation data revealed that a
significant number of the parts that failed were either not inspected
at prior overhaul shop opportunity or were inspected incorrectly. This
historical review also revealed that many of he parts that had been
inspected prior to failing had cracks large enough to be detected by
existing inspection methods; some cracks were even visible to the naked

To remedy this situation the FAA, in partnership with engine
manufacturers, airlines and overseas regulatory agencies, has developed
a prioritized approach for mandating in-service inspections of the most
important features on the most safety critical parts.

A detailed review of turbofan engine parts was conducted ,looking at
the part history and potential for hazardous failure. Specific part
details and features were identified as needing in-service inspection
if found to be highly stressed, prone to operational or handling
damage, or susceptible to material anomalies or other damage . Once
the parts were identified, the manufacturers developed detailed
in-service inspections that ensure a high probability of defecting

The FAA requires these new inspections when a part identified as most
safety critical is completely disassembled. These requirements affect
entire US fleet of turbofan powered large commercial aircraft. Most of
the newly developed inspections use eddy current or focused
fluorescent penetrant (FPI) techniques. FPI continues to be the wide
field method of choice for these parts; eddy current inspection (ECI)
is predominantly used for critical features and deep holes.


3. News From NTIAC

Summaries from the latest meeting of the MatTec NDE
Communication Group are available on the NTIAC website. This government
group, which is part of the Materials Technology(MatTec) subcommittee
of the National Science and Technology Council, is comprised of
representatives from various federal agencies that meet annually to
discuss NDE programs and plans. The information on NTIAC's website
consists of brief summaries of the presentations made at the group
meeting in May 2000.

Two new publications will be available soon from NTIAC:

- Nondestructive Evaluation for Conditionbased
( NDE for CBM), NTIAC-CR-00-01, $55 US/ $65

-Nondestructive Evaluation of Adhesive Bonds,
NTIAC-SR-00-01, $75 US/$85 International .


4. AE System Chosen for P-3C Fatigue Cycle Monitoring

Lockheed Martin Aeronautical Systems has purchased a 24-channel
version of Dunegan Engineering Consultants AESMART 2000 acoustic
emission instrumentation system . The systems first application will
be to monitor crack growth on a full-scale P-3 Orion
aircraft undergoing spectrum fatigue cycling. The primary objective is
to detect crack initiation and analyze crack growth rates in complex
components and in areas of the aircraft that are difficult or
impossible to inspect by traditional methods.

Primary features that suit the AESMART 2000 ideally to monitoring
complex structures ,such as aircraft, are it's ability to 1) eliminate
extraneous noise signals at the front end and to record only data that
relate to crack growth, 2) estimate the depth of growing cracks in
complex structures, and 3) multiplex all channels on a single cable.

The fatigue test is one component of the US Navy's P-3C Service Life
Assessment Program ( SLAP). Tests will be conducted at the
Lockheed-Martin facilities in Marietta, Georgia.

The AESMART 2000 system is the result of innovative research conducted
by DECI personnel over the past five years ,during which several
patents have been awarded for the innovations.


5. Derailment Blamed on Track Fractures

On October 17,2000, the London-Leeds (UK) express train
traveling at over 115 mph derailed, killing 4 people and injuring 70
more. The train had been approaching a fast bend when a defective
section of track shattered into 300 pieces. The nine-car train broke
into two sections when it derailed. Three cars ended up on their
sides, with the roof of the buffet car torn completely off.

The section of rail that fractured was laid in 1995 and was designed
for high-speed usage on relatively tight bends such as the crash site.
The type of track normally lasts at least 10 years, but signs of
deterioration were noted in January 2000 after a routine weekly visual
inspection. Timed replacement of part of the line was done in May 2000,
with the second section due for replacement in early November 2000.

In a second interim report published in late January 2001, the Health
and Safety Executive stated that they had found surface cracks up to 40
mm (approximately 1.5 inches) in length, together with several 30 mm
deep transverse cracks in the faulty track. (See attached sketch
and photo.)

After the track pieces were collected from the accident site,
the rail was reconstructed (the 300 pieces represented 90% of the
original rail) and visually examined. This examination showed that
extensive spalling (i.e., flaking of metal) of the running surface of
the head of the rail had occurred. One example included a spalled area
approximately 100 mm (4 inches) in length, 30 mm in width, a d
approximately 3 mm in depth. The fracture surfaces of some of the
spalled areas were bright but in other areas the surfaces were dark.

Widespread surface cracking on the rail head was also observed. Most of
these cracks appeared to have originated between the crown of the rail
and the gauge corner. One sample showed large numbers of surface cracks
up to 40 mm in length that has grown at an angle of 25 degrees to the
transverse direction and in the direction of travel. Where fractures
had occurred transversely through the entire rail section many of the
fracture surfaces showed that failure had occurred predominantly in a
brittle fracture mode. However, approximately 50 of the samples
exhibited evidence of fatigue crack growth. Several transverse
fractures contained fatigue cracks that were in excess of 30 mm in
depth, and these fatigue were at angles ranging from 20 to 35 degrees
from the vertical.

The rail had been ultrasonically inspected to detect rolling contact
fatigue cracks (gauge corner cracks), as prescribed in Railtrack Line
Specification RT/CE/S/055 Issue 1A, February 1998, less than three
months before the crash. Ultrasonic techniques are broadly suited to
the inspection of rails and are the only methods currently in use in
the UK for examining large quantities of rail in situ. However, these
techniques do not appear to be based on a comprehensive description of
the shape and precise location of rolling contact fatigue cracks (gauge
corner cracks) in rails, nor developed specifically to detect this type
of defect.

The result is that, when considering transverse fatigue cracks of the
type that caused the rail failure, only cracks within a certain angular
range (15 to 25 degrees from the vertical in either direction) will be
detected reliably by these techniques. Shallow cracks (probably those
less than 5 mm deep) and cracks very close to the gauge corner are
unlikely to be detected. However, this is not necessarily a problem as
industry information indicated that small cracks of this type are
unlikely to cause failure in the short term. In addition, the
techniques are not intended to measure the dimensions of cracks, rather
they provide an indication of whether cracks of significant depth
(greater than approximately 5 mm) are present.

Rolling contact fatigue cracks (gauge corner cracks) tend to occur in
clusters and, it is unlikely that all the significant cracks would be
at an undetectable angle. There is some evidence to suggest that deep
cracks, or at least those likely to lead to failure, are associated
with surface spalling which can be detected by visual examination. To
put it another way, in the absence of spalling, fatigue cracks tend to
be shallow even when they have significant surface length.

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