How do I re-calibrate a composite reference standard?

[Curios33]

Can someone advise a source for a procedure or instructions to conduct periodic calibration of composite reference standards? The subject standards were produced from multiple plys of epoxy / carbon fabric, and are used to provide a reference standard check of ultrasoinc inspection devices, prior to inspecting an aircraft structure.

The standards are machined to various specifeid thicknesses, are painted with an aircrfat grade topcoat paint. The thicknesses are engraved on the surfaces.

While we can readily measeure the thickness, what other tests would be required to confirm laminate integrity? (i.e. no delaminations).

 

[IRstuff]

Wouldn't you have historical data for known good samples and known good instruments that you can compare against?

An alternative is to create a reference delaminated sample.

TTFN

FAQ731-376

 

[CompositeGeek]

There is nothing to calibrate or adjust. You can check for wear and tear or damage but that is it.

You should have a technical dwg of the standard that showing location of built in defects used in NDT acceptance and set up. Then you inspect the standard using a tighter NDT requirement than the one applied to the standard. Example std is used to set up detection of 0.5sqin defect extent, blah blah. You perform NDT check for damage using a method that finds defects at the 0.25sq in level or better.

All of this should have been documented when the NDT standard was created.

Composites and Airplanes - what was I thinking?

There are gremlins in the autoclave!

 

[Compositepro]

My experience is with c-scanning laminates for voids. The technique used is to look for the echo from a glass plate located behind the laminate (under water). A 0.25" dot of lead foil is placed on the back side of the laminate. The The trigger threshold for drop in echo amplitude is adjusted so that you get a 0.25" circle on the C-scan printout.

I have heard of people making calibration standards for A-scans by curing laminates with pieces of teflon film inside.

 

[CompositeGeek]

Yes Compositepro is describing the technique of making the kind of standard I was describing above.



Composites and Airplanes - what was I thinking?

There are gremlins in the autoclave!