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- since 1996 -

Sonotron NDT
Original developer and manufacturer of advanced ultrasonic instruments
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Technical Discussions
Alan Yu
Alan Yu
11:39 Aug-20-2010
how to find shear wave velocity

Hi Everyone,

How can I find the shear wave velocity in a not know material? Is there any relation between the longitudinal wave and shear wave velocity? Please help. Thank you all.

Best Regards,
Alan

 
 Reply 
 
Godfrey Hands
Consultant,
PRI Nadcap, United Kingdom, Joined Nov 1998, 303

Godfrey Hands

Consultant,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
303
14:29 Aug-20-2010
Re: how to find shear wave velocity
In Reply to Alan Yu at 11:39 Aug-20-2010 (Opening).

Hi Alan,
It depends how accurately you need the answer, and what equipment you have available.
If you have a flaw detector and a 0 degree TRANSVERSE or SHEAR wave probe, you can take a sample of the material of known thickness, and using thickness and time of flight you can calculate it fairly accurately.
If you do not have a 0 degree shear wave probe, but do have a shear wave angle probe, take a flat sample of known thickness, and drill a cross drilled hole in it, then apply the probe from the side of the sample to detect the hole.
Your instrument and probe should be calibrated for steel.
Knowing the probe index point and location of the hole, you can measure the path. Compare this to the "measured" steel equivalent.
You can also measure the angle that your sound path has travelled along, and compare this to the true (steel) angle of the probe, then using Snells Law, calculate the velocity.

Hope these techniques help you

Godfrey

 
 Reply 
 
S.Senthilkumar
Engineering, QA/QC/NDT
NOV (National Oilwell Varco), Angola, Joined Mar 2006, 42

S.Senthilkumar

Engineering, QA/QC/NDT
NOV (National Oilwell Varco),
Angola,
Joined Mar 2006
42
14:52 Aug-20-2010
Re: how to find shear wave velocity
In Reply to Alan Yu at 11:39 Aug-20-2010 (Opening).

Hi Alan,

Theoritically V (T) ~ 1/2 V (L)
Where T is Transverse
L is Longitudinal.

or

You should know Testing Material
Shear Modulus
Young's Modulus of Elasticity
Poisson's Ratio
Density

Then you can calculate.

S.Senthilkumar

 
 Reply 
 
Dao Huu Xuan
Other,
Vietnam, Joined Feb 2007, 18

Dao Huu Xuan

Other,
Vietnam,
Joined Feb 2007
18
15:46 Aug-20-2010
Re: how to find shear wave velocity
In Reply to S.Senthilkumar at 14:52 Aug-20-2010 .

Hi Alan,
An approximate experimental technique and simply:
1- Take a flat sample of known thickness from the unknow velocity material.
2- Make a square notch as same as API reference block with the notch depth is about 1mm.
3- Using 45 degree angle probe with digital flaw detector. Calibrate the ZERO and index point by using V1 or V2 bolck. Adjuct the X-VALUE to the index point value.
4- Maximize the response echo from the notch. Record the actual Depth and Stand-off (horizontal distand from front of probe to the notch)
5- On the instrument menu, adjust both VELOCITY and ANGLE so that the DEPTH and the STAND-OFF on the instrument are reflect the actual value in step 4 above.
6. Now, velocity is know.

NOTES: As thicker material as more acuracy. May be confirm on full skip and multi-skip to compare.

Thanks,

Dao Huu Xuan

 
 Reply 
 
Udo Schlengermann
Consultant, -
Standards Consulting, Germany, Joined Nov 1998, 177

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
177
18:11 Aug-20-2010
Re: how to find shear wave velocity
In Reply to Alan Yu at 11:39 Aug-20-2010 (Opening).

Dear Alan,
The best way to determine ultrasonic velocities is to measure them. The most accurate way is to use a material sample with parallel faces, so you can use a series of multiple echos to calculate the velocities on a longer travel path within the known (mechanically measured) thickness of the sample.
For both wave modes normal-beam probes are available, i.e a probe for longitudinal waves, coupled by a fluid of low viscosity - and a shear wave probe, coupled by a high viscosity fluid. The frequencies must be chosen to allow good penetration of the material.

If your material is ideal elastic (Hooke's law) then (and only then) you can calculate the elasticity modulus E and the shear modulus G with the measured long and trans velocities together with the measured density of the material.
The opposite way, to calculate the velocitities by known elastic moduli E, G and density for real material does not deliver precise results.
As said, these equations are only valid for ideal elastic materials, i.e. some metals, not for solid materials in general.
As described in the other replies, if you do not want to buy a normal-beam shear wave probe you can use the mode converted transverse wave generated by a transverse wave angle beam probe.
If you manufacture a half-cylinder of your material and place your angle beam probe in the centre of the block you can generate multiple shear wave echos (without taking care of the angle), and you will get higher accuracy with your calculated shear velocity (same principle as with the well known standardised calibration blocks for angle beam testing: K1 and K2.)

Best regards from a GE pensioner.
Udo Schlengermann

 
 Reply 
 
M.S.RAO
M.S.RAO
19:06 Aug-20-2010
Re: how to find shear wave velocity
In Reply to Alan Yu at 11:39 Aug-20-2010 (Opening).

Simple way to find shear wave velocitly
take a piece of unknown material find accurate thickness, if have USM 35 or USM 25.
go main menu get AUTO CAL
take one edge as referance 1 at first skip, take second skip as refrance 2, record both echos and store calibration.
now go back to main menu you will find the material velocity on disply which used for calibration.

 
 Reply 
 
David Bunch
David Bunch
00:39 Aug-22-2010
Re: how to find shear wave velocity
In Reply to Alan Yu at 11:39 Aug-20-2010 (Opening).

Take a flat piece of the material you are going to test, and drill two side drilled holes in it. Drill one of them a quarter of the thickness, drill the other three quarters of the thickness.

Take your probe and maximize the reponse from the first hole. Adjust your probe delay until the sound path matches up with what it should be. Then take your probe and maximize the signal from the second hole. Adjust your velocity until it matches what the soundpath for this hole should be. Keep repeating this process until you can maximize the signal response from either hole and get the correct soundpath.

This is a technique that the Level III for a major power corporation uses to have his technicians calibrate on various steel-alloy metals (P11, P22, etc).

 
 Reply 
 
Bharat
R & D
India, Joined Aug 2010, 10

Bharat

R & D
India,
Joined Aug 2010
10
08:29 Aug-26-2010
Re: how to find shear wave velocity
In Reply to Alan Yu at 11:39 Aug-20-2010 (Opening).

Hi Alan,

There is no perfect relation between Longitudinal and Shear wave. Tomeasure Shear wave velocity follow below steps and it universal method. For this you need to have Angle probe and any reference reflector.

As we know V=d/t so travel time t=d/v (round trip we are avoding it will compensate)

so calibrate flaw detector for know shearwave velocity (Vel kn) and I mean on IIW block.
Then measure distance (Sound path in unknown velocity block) Dun, and actual distance is Dac.

Now Actual velo=( Dun * Vel kn)/ Dac

 
 Reply 
 
ALan Yu
ALan Yu
12:17 Aug-31-2010
Re: how to find shear wave velocity
In Reply to Alan Yu at 11:39 Aug-20-2010 (Opening).

Thank you all for your advises.

 
 Reply 
 
Vicky
NDT Inspector, Blue Star Limited
IE , India, Joined May 2009, 29

Vicky

NDT Inspector, Blue Star Limited
IE ,
India,
Joined May 2009
29
11:58 Sep-01-2010
Re: how to find shear wave velocity
In Reply to Alan Yu at 11:39 Aug-20-2010 (Opening).

Hi alan methods of calculating velocity of shear wave depends how actually you what to get it. One is if you are having the material and the equipment then rather then craking your heads with formulaes simple ways are given by various of peoples or rather you can use this formulae for get the velocity of by applying maths.

0.5
VL = E(1-µ)
P(1+ µ ) (1-2 µ)



Vs = 0.87 + 1.12µ X Vt
1+ µ


0.5
Vt = E
2P(1+ µ )


Where in here
E-Youngs Moduls
µ- Poissons ratio
P-Density of the material.



I hope this would be quite usefull for you best of luck

regards
Vicky

 
 Reply 
 
andrew cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
19:53 Sep-23-2010
Re: how to find shear wave velocity
In Reply to Alan Yu at 11:39 Aug-20-2010 (Opening).

How to calculate shear wave velocity in a material.
1 Accurately measure the thickness of the material.
2 Measure back from the top corner the same measurement distance as the thickness.

3 Mark with a fine line this measured point.

4 Place a 45˚ probe on the top surface facing the bottom corner.

5 Move the exit point of the probe to align with the marked line.

6 Multiply the thickness by 1.41.

7 Adjust the velocity until the corner reflector is equal to the above sum.

8 Read the velocity from the screen.

 
 Reply 
 
Nicholas Harper
Nicholas Harper
17:34 Apr-22-2015
Re: how to find shear wave velocity
In Reply to Udo Schlengermann at 18:11 Aug-20-2010 .

If I have a known measurement and two parallel surfaces at 5.35 inches apart and a Shearwave probe with no shoe can I calculate velocity from that? If so to what accuracy?

 
 Reply 
 
Nicholas Harper
USA, Joined Apr 2015, 1

Nicholas Harper

USA,
Joined Apr 2015
1
18:01 Apr-22-2015
Re: how to find shear wave velocity
In Reply to Udo Schlengermann at 18:11 Aug-20-2010 .

If I have a known measurement and two parallel surfaces at 5.35 inches apart and a Shearwave probe with no shoe can I calculate velocity from that? If so to what accuracy?

 
 Reply 
 
Godfrey Hands
Consultant,
PRI Nadcap, United Kingdom, Joined Nov 1998, 303

Godfrey Hands

Consultant,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
303
18:33 Apr-22-2015
Re: how to find shear wave velocity
In Reply to Nicholas Harper at 17:34 Apr-22-2015 .

Nicholas,
I think that the probe type which you are mentioning here is the type where you have a straight beam probe and you add on different wedges in the front to generate shear waves at different angles.
Mostly this probe is a Longitudinal Wave probe, and relies on mode conversion to Shear at the refraction interface.
Do the math (Snells Law and look up the velocities of the material of the wedge - often Lucite - and the material which the angle is correct for (possibly steel)
What you need is a probe with a crystal cut to generate shear waves.

Another possible way to do this is to use a straight Longitudinal Wave probe, and turn the gain up high. You will see that a Longitudinal Wave probe also generates a small amount of Shear Wave. You can often see this as a smaller amplitude signal between the first and second Back-Wall Echos.

Hope this helps.

Godfrey

1
 
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