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Technical Discussions
Arman
Engineering,
Turkey, Joined Oct 2014, 42

Arman

Engineering,
Turkey,
Joined Oct 2014
42
15:48 Mar-24-2020
Perspex vs Rexolite

Hi,

Does anyone have any idea what is (are) advantage(s) of Rexolite over Perspex? As far as I know, Rexolite is now widely used in ultrasonic (conventional / PA / ToFD) wedges. As Rexolite is more expensive there should be a significant advantage of using it.

Thanks
Arman

 
 Reply 
 
Ali
NDT Inspector,
Iran, Joined Mar 2013, 117

Ali

NDT Inspector,
Iran,
Joined Mar 2013
117
16:20 Mar-24-2020
Re: Perspex vs Rexolite
In Reply to Arman at 15:48 Mar-24-2020 (Opening).

Perpex wedges have lot of ultrasound attenuation compare to Rexolite.

1
 
 Reply 
 
Edward Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1303

Edward Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1303
17:29 Mar-24-2020
Re: Perspex vs Rexolite
In Reply to Arman at 15:48 Mar-24-2020 (Opening).

Ali is correct. Perspex (also called Lucite) is the trade name for polymethylmethacrylate (PMMA) and has acoustic velocity around 2720m/s and an attenuation at 5MHz of about 0.57dB/mm. Rexolite is the tradename for cross-linked polystyrene. It has an acoustic velocity of about 2340m/s and an attenuation at 5MHz of about 0.15dB/mm. Therefore, over a few mm in the wedge it is not too significant, but over a few cm it can make a noticeable difference and another effect will be that higher frequency content is more likely to be reduced in the PMMA.

1
 
 Reply 
 
Joe Buckley
Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT, United Kingdom, Joined Oct 1999, 528

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
528
17:35 Mar-24-2020
Re: Perspex vs Rexolite
In Reply to Edward Ginzel at 17:29 Mar-24-2020 .


I was always taught that Perspex Phased array wedges should not be used above 2 MHz, and Regular wedges (or delay lines) not above 5 MHz.

1
 
 Reply 
 
Nick Bublitz
Other,
VeriPhase, USA, Joined May 2010, 136

Nick Bublitz

Other,
VeriPhase,
USA,
Joined May 2010
136
18:32 Mar-24-2020
Re: Perspex vs Rexolite
In Reply to Arman at 15:48 Mar-24-2020 (Opening).

Some other advantages of rexolite:
1. isotropic material with constant velocity in each axis
2. Impedance close to water
3. tight machining tolerances

1
 
 Reply 
 
Arman
Engineering,
Turkey, Joined Oct 2014, 42

Arman

Engineering,
Turkey,
Joined Oct 2014
42
19:27 Mar-24-2020
Re: Perspex vs Rexolite
In Reply to Edward Ginzel at 17:29 Mar-24-2020 .

Dear Edward,
Thanks for your valuable information of attenuation rates. I believe stated attenuation rates are for longitudinal wave in Perspex and Rexolite. Do you know what are attenuation rates of shear wave in these 2 materials. I'm asking this because I understood from a discussion in this forum that shear wave attenuation is far more than of longitudinal which helps dampening of unwanted shear waves in wedge material. Is this a true statement?

Thanks a lot

 
 Reply 
 
Edward Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1303

Edward Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1303
21:15 Mar-24-2020
Re: Perspex vs Rexolite
In Reply to Arman at 19:27 Mar-24-2020 .




I did not specifically measure attenuation rates for these materials but I did make power spectrum comparisons. The uploaded image is for the PMMA analysis. You can also notice the downshift in frequency maximum for the shear component.
Both materials can support a shear mode but the amplitude of the shear component is much lower than the compression mode. For PMMA the shear component is about 12dB lower and for cross-linked polystyrene it is about 10dB lower. However, most probe manufacturers design their wedges with the appropriate wedge-angles and suitable damping to avoid seeing internally reflected signals that originate from inside the wedge for either mode.
3
 
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