Composite/metallic shim in Ultrasonic Inspection

[albertoruenes]

Hi all,

I would like to hear any opinion in the subject of Ultrasonic inspection in composite laminates having a metallic insert or shim.

I have heard about some Ultrasonic inspections where the shim is not detected, some of the theories is that the composite/metal compaction is good that the ultrasonic inspection is not able to capture it.

Thanks,

 

[SWComposites]

It all depends on the details - relative thicknesses, type of scan, frequency of sound waves, location of metal in the stack, etc.

 

[albertoruenes]

Thank you for your quick response SWComposites,

Could you recommend some books or manuals related to this topic?

Thank you

 

[gvanbeek]

Late to the discussion but here is some additional information:

UT works on the reflection of waves at interfaces. How much is reflected is based on the difference in acoustic impedance of the material. Acoustic impedance= {density of the material} x {velocity of the wave in the material}. So if you have a metallic plate that is close to the acoustic impedance of the surrounding composite, more of the wave will pass through the material than be reflected, thus making the plate difficult to detect.

This page has the equation for % reflection from interfaces of different acoustic impedance:

https://www.nde-ed.org/EducationRes...ltrasonics/Physics/reflectiontransmission.htm

Here are some online training references that should be helpful:

https://www.nde-ed.org/EducationResources/CommunityCollege/Ultrasonics/cc_ut_index.htm

http://www.olympus-ims.com/en/resources/tutorials/precision-thickness-gaging-theory/