Re: Nondestructive testing of railroad wheels at the German Bahn AG

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Re: Nondestructive testing of railroad wheels at the German Bahn AG
Posted by: Ingolf Hertlin , E-mail: ihertlin@rte.de, on June 09, 1998 at 07:52:58:
In Reply to: Nondestructive testing of railroad wheels at the German Bahn AG posted by : Rolf Diederichs on June 06, 1998 at 20:46:23:
Ultrasonic inspection seems to be talk of the town following the terrible railway accident last week. This forum is an ideal place to continue the discussion of ultrasonic inspection technology (and limitations – see the contribution of Rolf Diederichs and the article from H. Hintze) under experts, but remains in the US area. The following questions and additional remarks may be provocative in this area and on this forum, but may be essential in the general NDT field:
1. Does anybody know whether resonant inspection testing technology (in sound and / or ultrasound range) was considered and tested as an alternative acoustic - and very effective - NDT technology for inspection purposes?
We have reached very good results in the last two years with sound resonant technology in industrial applications for acoustic material testing for:
- crack detection (internal and external cracks),
- structure / texture modifications (in casting),
- hardness,
- inclusions,
- composite material
The principle is simple: hit (or stimulate for resonant testing in the US range) the probe definitely, measure the resonant sound, calculate the characteristics in real time (in fractions of a second with digital signal processors) and compare them with characteristics from ok (reference) probes (this is a simple learning procedure).
The advantages are:
a) Small material changes cause changes in the resonant behaviour of the object: You get an answer from the whole body and not from local fractions. It is his language!
b) Easy to perform and fast! 100 % testing is no problem.
c) Objective and reliable if the reference pieces are defined (e. g. by other methods like US, x-ray and so on)
d) Inexpensive in comparison to other technologies.
The disadvantages are:
a) small surface defects can not be recognized,
b) the reference data must be confirmed by other methods,
c) it is true that it is older than US technology but has up to now limited dissemination because it is considered as a human subjective assessment than as an objective procedure,
d) characteristics can not be gained automatically but only in conjunction with a (human based) signal analysis. But we have developed robust procedures which allow a reliable air-borne signal analysis in an extremely noisy industrial environment (more than 90 dBA)
2. Are there made any investigations or are there latest findings how fast a beginning damage of railroad wheels under continuous stress may lead to dangerous conditions? Or to say it with other words: is it really sufficient to inspect the wheels all some thousand kilometers or is it (in addition) not necessary to install an online system for fast monitoring and decision?
I could imagine that a small defect at the surface can rapidly work out to a severe damage under continuous and impulsive stress conditions. This would mean that offline inspection methods are useful but must be combined with online systems.
RTE Akustik + Prueftechnik GmbH in Pfinztal near Karlsruhe has recently developed a small DSP based box that could be used in vehicles like coaches, cars, lorries and industrial machines to perform online evaluation of sound and vibration signal analysis. What is needed is only the software and characteristics for the special application for online wheel inspection (not limited to trains!).
3. Has anybody heard of investigations and research work on the correlation between the overheating of an iron wheel and the noise it generates under these conditions? Or again in other words: isn’t it worth to extend the discussion to fast online material testing? We should not forget some very terrible accidents with tankers and other lorries on the motorways and in cities!
All comments are welcome!
Ingolf Hertlin

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: Ultrasonic inspection seems to be talk of the town following the terrible railway accident last week. This forum is an ideal place to continue the discussion of ultrasonic inspection technology (and limitations – see the contribution of Rolf Diederichs and the article from H. Hintze) under experts, but remains in the US area. The following questions and additional remarks may be provocative in this area and on this forum, but may be essential in the general NDT field: : 1. Does anybody know whether resonant inspection testing technology (in sound and / or ultrasound range) was considered and tested as an alternative acoustic - and very effective - NDT technology for inspection purposes? : We have reached very good results in the last two years with sound resonant technology in industrial applications for acoustic material testing for: : - crack detection (internal and external cracks), : - structure / texture modifications (in casting), : - hardness, : - inclusions, : - composite material : The principle is simple: hit (or stimulate for resonant testing in the US range) the probe definitely, measure the resonant sound, calculate the characteristics in real time (in fractions of a second with digital signal processors) and compare them with characteristics from ok (reference) probes (this is a simple learning procedure). : The advantages are: : a) Small material changes cause changes in the resonant behaviour of the object: You get an answer from the whole body and not from local fractions. It is his language! : b) Easy to perform and fast! 100 % testing is no problem. : c) Objective and reliable if the reference pieces are defined (e. g. by other methods like US, x-ray and so on) : d) Inexpensive in comparison to other technologies. : The disadvantages are: : a) small surface defects can not be recognized, : b) the reference data must be confirmed by other methods, : c) it is true that it is older than US technology but has up to now limited dissemination because it is considered as a human subjective assessment than as an objective procedure, : d) characteristics can not be gained automatically but only in conjunction with a (human based) signal analysis. But we have developed robust procedures which allow a reliable air-borne signal analysis in an extremely noisy industrial environment (more than 90 dBA) : 2. Are there made any investigations or are there latest findings how fast a beginning damage of railroad wheels under continuous stress may lead to dangerous conditions? Or to say it with other words: is it really sufficient to inspect the wheels all some thousand kilometers or is it (in addition) not necessary to install an online system for fast monitoring and decision? : I could imagine that a small defect at the surface can rapidly work out to a severe damage under continuous and impulsive stress conditions. This would mean that offline inspection methods are useful but must be combined with online systems. : RTE Akustik + Prueftechnik GmbH in Pfinztal near Karlsruhe has recently developed a small DSP based box that could be used in vehicles like coaches, cars, lorries and industrial machines to perform online evaluation of sound and vibration signal analysis. What is needed is only the software and characteristics for the special application for online wheel inspection (not limited to trains!). : 3. Has anybody heard of investigations and research work on the correlation between the overheating of an iron wheel and the noise it generates under these conditions? Or again in other words: isn’t it worth to extend the discussion to fast online material testing? We should not forget some very terrible accidents with tankers and other lorries on the motorways and in cities! : All comments are welcome! : Ingolf Hertlin

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