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- since 1996 -

GB Inspection Systems Ltd.
A leading UK manufacturer of Ultrasonic Probes, Accessories, Supplier of NDT Equipment and more.

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Technical Discussions
David Hermanutz
Consultant,
Hbndt.com, China, Joined Jul 2012, 85

David Hermanutz

Consultant,
Hbndt.com,
China,
Joined Jul 2012
85
02:24 Aug-29-2000
Ultrasonic correlation to Bolt Torque values.

Ultrasonic correlation to Bolt Torque values.

recently I have been involved with the measurement of bolts to determine the torque value by an ultrasonic lenght measurement. The idea was based on a simple, accurate measurement of bolt stretch as compared to a ramp up of kN torque on the bolt. Due to the complex geometry of the bolt (inconel, cold rolled, internal hex head and counterbored thread) and limitiations on probe selection to fit in the hex head the backwall was impossible to detect. I was able to pick a signal at 53mm (48mm bolt) that behaved in a repeatable fashion corresponding to torque loading.

The reference indication went from a 0 kN torque at 53.14 to 40 kN torque at 55.2 +- 0.06mm.
The bolt was manually measured to have stretched only 0.2mm.
The reference indication was impossible to detect on another 12 identical bolts.

The inaccuracy of UT measure compared with a manual measurement would indicate a shear wave velocity.

Considering mode conversion and shear wave content in the pulse Is this a feasable explanation of the indication measurement?

Is there a better way to test for torque values from the head without mechanical adjustment?

The correlation needs to stand up to scrutiny in a scientific paper.


    
 
 
Dave Utrata
R & D,
Center for NDE, Iowa State University, USA, Joined Feb 2000, 37

Dave Utrata

R & D,
Center for NDE, Iowa State University,
USA,
Joined Feb 2000
37
06:25 Aug-31-2000
Re: Ultrasonic correlation to Bolt Torque values.
My experience with bolt elongation methods is that the best readings are always obtained if you can do some prep work on the incident and reflecting surfaces, which obviously is a luxury you wish you had in this case. You don't mention the diameter of the bolt, unless I misread your note, but would hazard a guess that this is not a beefy diameter fastener, say on the order of 25 mm. I suspect that you are seeing a complex mode conversion in your sound path due to unique reflection conditions.

I'd recommend using a ray-tracing UT model to see just how close a combination of compressional and shear wave transit times would explain your phenomenon. I think that Imagine 3D from UTEX might handle the fastener geometry well if you can get a CAD file of the bolt.

The key point for me is that you didn't get reporducible results on this reference; that tells me that a slight geometric variation in your one bolt somehow favored the odd creation of a signal that generally follows torque for elongation, but is not as well behaved as one might like.


    
 
 
Michael Trinidad
Consultant,
LMATS Pty Ltd , Australia, Joined Jan 2003, 138

Michael Trinidad

Consultant,
LMATS Pty Ltd ,
Australia,
Joined Jan 2003
138
06:57 Sep-21-2000
Re: Ultrasonic correlation to Bolt Torque values.



    
 
 
Udo Schlengermann
Consultant, -
Standards Consulting, Germany, Joined Nov 1998, 176

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
176
06:30 Sep-26-2000
Re: Ultrasonic correlation to Bolt Torque values.
bolts were removed they fracture immediately. The fractures were shear.

: My question is:

: Would the indication been a defect to small to be adequately detectable or could the probe have detected that the bolt internal grain structure was so distorted prior to a crack actually initiating?

: Kindest Regards

:
: Michael Trinidad




    
 
 
Geoffrey Rowe
Geoffrey Rowe
01:55 Feb-26-2001
Re: Ultrasonic correlation to Bolt Torque values.
Mr. Hermanutz,
The usual problems with ultrasonic bolt gages have been dramatically reduced with a new technology.

The "multi path" echo that you used to trigger your bolt gage sounds like it was distorted when the bolt was tensioned. This distortion probably caused the triggered "zero crossing" to shift in a non-linear fashion. Sometime the distortion is bad enough to cause "peak jumping" (30% error or greater).

A new technology has greatly reduced these problems. Even NASA used this technology on its Space Station bolts because the bolts were small and had weak echoes.

See any of the following web pages:
http://arvc.com/nasa_story.htm
http://arvc.com/SureBolt.htm
http://arvc.com/see_animation.htm


I hope this is of value to you.

Geoff Rowe
American Remote Vision Corp.


: Ultrasonic correlation to Bolt Torque values.

: recently I have been involved with the measurement of bolts to determine the torque value by an ultrasonic lenght measurement. The idea was based on a simple, accurate measurement of bolt stretch as compared to a ramp up of kN torque on the bolt. Due to the complex geometry of the bolt (inconel, cold rolled, internal hex head and counterbored thread) and limitiations on probe selection to fit in the hex head the backwall was impossible to detect. I was able to pick a signal at 53mm (48mm bolt) that behaved in a repeatable fashion corresponding to torque loading.

: The reference indication went from a 0 kN torque at 53.14 to 40 kN torque at 55.2 +- 0.06mm.
: The bolt was manually measured to have stretched only 0.2mm.
: The reference indication was impossible to detect on another 12 identical bolts.

: The inaccuracy of UT measure compared with a manual measurement would indicate a shear wave velocity.

: Considering mode conversion and shear wave content in the pulse Is this a feasable explanation of the indication measurement?

: Is there a better way to test for torque values from the head without mechanical adjustment?

: The correlation needs to stand up to scrutiny in a scientific paper.




    
 
 
Geoffrey Rowe
Geoffrey Rowe
02:00 Feb-26-2001
Re: Ultrasonic correlation to Bolt Torque values.
Mr. Utrata,
A new technology has greatly reduced the challenges associated with bolt gages (weak signals, peak jumping, non-linear distortion due to multipath mixing, hard to use, long training times,... etc.). Even NASA used this technology on its Space Station bolts because the bolts were small and had weak echoes.

See any of the following web pages:
http://arvc.com/nasa_story.htm
http://arvc.com/SureBolt.htm
http://arvc.com/see_animation.htm


I hope this is of value to you.

Geoff Rowe
American Remote Vision Corp.

: My experience with bolt elongation methods is that the best readings are always obtained if you can do some prep work on the incident and reflecting surfaces, which obviously is a luxury you wish you had in this case. You don't mention the diameter of the bolt, unless I misread your note, but would hazard a guess that this is not a beefy diameter fastener, say on the order of 25 mm. I suspect that you are seeing a complex mode conversion in your sound path due tounique reflection conditions.

: I'd recommend using a ray-tracing UT model to see just how close a combination of compressional and shear wave transit times would explain your phenomenon. I think that Imagine 3D from UTEX might handle the fastener geometry well if you can get a CAD file of the bolt.

: The key point for me is that you didn't get reporducible results on this reference; that tells me that a slight geometric variation in your one bolt somehow favored the odd creation of a signal that generally follows torque for elongation, but is not as well behaved as one might like.




    
 
 

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