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TimesNDT TESTING TIPS FROM

NDTECH - NEWSLETTER #20 -  May 2001



                                                                                               Z/29



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



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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. 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

community.



 The New Zealand NDT  Association offers information on a wide range of

NDT methods and presents a good introduction to visual inspection.        

                                        http://www.irl.cri.nz/~spedding/ndta/ndtavi00.html.





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

methods. 



        http://www.ncsa.uiuc.edu:80/Pubs/access/93.2/VisualAnalysis.html





 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:



        http://www.crs4.it~zip/bag.html.



 



 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 



        http://www.larc.nasa.gov:80/tag-www.larc.nasa.gov/tops-index/.





 A request for further information, publication or technical

references is also available  on-line for each technical information

sheet. 





 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

presented.





An introduction to computer-integrated visual inspection for automatic

examination of circuit boards, as well as a list of relevant

publications, is presented at:



        http://www-isl.ece.arizona.edu/~chrisy/civi.html.  





Similarly, information on automated geometric visual inspection

of 3D objects can be obtained at:



http://arachnid.cs.cf.ac.uk/Dave/VIS_APP_LAB/subsection3_4_2.html





 The homepage of Visual Inspection Technologies Inc.



                http://www.v-i-t.com/vit 





 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:



                 http://fbsolutions.com/uxr/.





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:



http://www.olympus.plus.at/olympus/ruis.html





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

at:



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

researchers.





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:



http://ing.univaq.it/~laser/research/research.html.





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

techniques(http://www.iti.nusu.edu/pubs/shubit.html).





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://

eb-p5.eb.uah.edu/oso/node25.html)





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:



http://w3.gwis.com:80/~polaris/whatis.html.





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:



http://www.utopia.com:80/mailing/rre/Holographic.Full-Body.Security.Scanning.html.







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2. FAA Improves Inspections of Safety Critical Aircraft Turbine

Parts



     



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

 eye.





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

flaws.





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.





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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

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

International.



-Nondestructive Evaluation of Adhesive Bonds,

NTIAC-SR-00-01, $75 US/$85 International .





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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.





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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.