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- since 1996 -

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Technical Discussions
Syed Ali
Syed Ali
04:52 Jun-16-2009
Acoustic Resonance

Acoustic Resonance is a NDT method for testing and characterization of wide range of materials. The resonance can be achieved using continuous or long burst of excitation with frequency sweeping to find out the resonance frequencies.

Is it possible to achieve and measure resonance frequencies modes of a material with a given thickness using a very broadband spike pulser type excitation.

Any comments, guidance or personnel experience experimenting with Acoustic Resonance would be appreciated.
Thanks
Syed Ali

    
 
 
Godfrey Hands
Consultant,
PRI Nadcap, United Kingdom, Joined Nov 1998, 293

Godfrey Hands

Consultant,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
293
08:31 Jun-16-2009
Re: Acoustic Resonance
In Reply to Syed Ali at 04:52 Jun-16-2009 (Opening).

Yes it is possible to excite resonance using a very broadband "spike" type excitation. It is also possible to excite these with a hammer. In this case the audible resonances can be heard, whilst instrumentation will detect higher frequencies.
Any resonance technique will however suffer from variations in resonances caused by small differences in dimensions, heat treatment, cooling rates, residual stresses etc.

There are one or two companies using this (impact excitation) method, and the company Quasar (now part of Magnaflux) using the swept excitation and some very powerful mathematical techniques to compensate for the variables mentioned above. Please see www.quasarintl.com.
Regards,
Godfrey Hands

    
 
 
Syed Ali
Syed Ali
16:10 Jun-16-2009
Re: Acoustic Resonance
In Reply to Godfrey Hands at 08:31 Jun-16-2009 .

Thanks for your quick response. I understand that spike pulser is a possibility which are so widely used in conventional NDT and yet not used so often for resonance. Can you comment on the limitations of this approach versus using a multiple cycle excitation, sweeping the frequencies.

Thanks
Syed Ali

    
 
 
Godfrey Hands
Consultant,
PRI Nadcap, United Kingdom, Joined Nov 1998, 293

Godfrey Hands

Consultant,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
293
08:11 Jun-17-2009
Re: Acoustic Resonance
In Reply to Syed Ali at 16:10 Jun-16-2009 .

Hi,
With a broadband excitation (Spike Pulser) as you suggest, all of the energy imparted to the component will be spread over a wide range of frequencies, and this will not be of equal amounts of energy at each frequency.
With (for example) swept Sine-Wave excitation, all of the energy is at the exciation frequency (albeit briefly) and then sweeps on to the next frequency with a very small frequency shift. This second approach takes longer than spike, but gives much better results, and it is not necessary to fourier transform the received signal, as all of the recieved energy can be attributed to the excitation frequency.

However having said that it takes longer, in component mass-production inspection, annual throughputs in the order of hundreds of thousands of parts are possible with suitable automation.

Hope that answers your question.
Regards
Godfrey Hands

    
 
 
S.V.Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
03:53 Jun-19-2009
Re: Acoustic Resonance
In Reply to Godfrey Hands at 08:11 Jun-17-2009 .

I thank Godfrey for the excellent explanation. I would like to add that we used the resonance technique with the sweep frequency tied to the AC mains frequency (50 cycles per second in India) for wall thickness testing of pressure tubes for PHWRs. The tubes were of zircaloy and the thickness was ranging from 4 to 4.3 mm. This was in 1968 to 1973 or so.

Later on we shifted to the pulse echo equipment and the testing speeds are much higher.

I feel there is no specific advantage of trying to use the resonance method now for thickness determination.

    
 
 
Ingolf Hertlin
Ingolf Hertlin
09:47 Jun-26-2009
Re: Acoustic Resonance
In Reply to Syed Ali at 04:52 Jun-16-2009 (Opening).

Both excitation methods (impact, piezo) have their advantages and disadvantages. In addition you must not only consider the excitation but also the signal acquisition methods (microphone or solid vibration at a specific position with piezo sensor or laser vibrometer)

Piezo / piezo:
+ high frequency range
+ low energy for fragile material
- time consuming (depends on frequency range ...), at least 3 or more seconds
- low resolution in lower frequency range (audible area)
- contact quality / position is very important / has great impact
- excitation only in vertical direction possible (only transversal waves can be evaluated)
- vibration measurement only at the position of the sensor
- no evaluation of characteristics in the time domain (damping ....)

Impact / microphone:
+ broadband resonance generation (up to about 80 kHz)
+ very fast (down to 0.5 seconds for complete evalutation)
+ multiple excitation, microphones and measurements in all directions (all vibration modes of the part!!)
+ frequency and time domain analysis
+ automatic temperature and dimensional compensation
+ high resolution (< 1 Hz)
- not for fragile material
- engineering necessary to determine the excitation positions (FEM helps a lot)

Sure that I have not mentioned all advantages and disadvantages. We use the impact excitation for a wide range of material (metal, ceramics, composite) since 15 years very successfully. Have a look on our web site www.rte-acoustics.com or www.rte.de

Ingolf

    
 
 
Syed Ali
Syed Ali
14:36 Jun-26-2009
Re: Acoustic Resonance
In Reply to Ingolf Hertlin at 09:47 Jun-26-2009 .

Many thanks for all who provided their expert comments about Acoustic Resonance and its unique applications.

Syed Ali

    
 
 
Anil Kumar Srivastava
Anil Kumar Srivastava
10:30 Apr-02-2014
Re: Acoustic Resonance
In Reply to Godfrey Hands at 08:31 Jun-16-2009 .

How we can Judge the defect of slag p orosity and Lack of fuseion in weld defect throgh ART

    
 
 

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