Reference objects for realistic simulations of defects for shearography

Speaker:
van den Bos, Barend; DEKRA Industrial AB; Sweden

Authors:
van den Bos, B.; DEKRA Industrial AB; Sweden
Strand, J.; DEKRA Industrial AB; Sweden
Ydrefors, L.; DEKRA Industrial AB; Sweden
Crabus, G.-S.; Dantec Dymanics GmbH; Germany

ID: ECNDT-0368-2018
Download: PDF
Session: Composite General 1
Room: G1
Date: 2018-06-11
Time: 13:30 - 13:50

Shearography is an optical method primarily used to detect defects in “laminar” structures, such as polymer composites, sandwich structures and other bonded structures. Shearography is one of very few active NDT methods, and by that we mean that it is subjected to some kind of structural load during the inspection, and that the inspection result reflects the response to that load.
In NDT, reference objects play a vital role. They are used to adjust or verify the setting of the NDT equipment and to assure repetitive results. They can also be used to relate the signal from an indication to something with a known extension.
In traditional methods, eg ultrasonics and eddy current testing, there are well established guide lines on how to design, produce and relate to reference objects. As an example, it is widely accepted that a teflon insert between two layers in a composite represents a delamination for ultrasonics. For shearography, considered to be a young method, it is still fuzzy. Searching for recommendations on how to create reference defects, you will not find much and certainly not on how the response from different artificial defects relate to the response from real defects.
In this paper one specific structure, a composite sandwich, is being studied. Realistic defects have been made in the laminate and in the bond line between laminate. Different ways to create artificial reference defects have been introduced. The shearography response from both realistic and artificial defects will be compared. From this conclusions are drawn on the relation between the different artificial defects and real ones.
Implementing realistic reference objects will increase the acceptance and maturity of shearography inspections.