Fracture Toughness of Honeycomb Sandwich Panels

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The discussion focuses on determining the fracture toughness of honeycomb sandwich panels with aluminum and GFRP facings, particularly through microscopic analysis using SEM and TEM. The challenge lies in creating specimens from the ductile honeycomb core, which may not retain its hexagonal shape under compression. Participants emphasize the importance of understanding the orientation of tensile fields relative to the honeycomb and aluminum skins, as this affects fracture behavior. They suggest following ASTM standards for ductile materials to assess fracture toughness and highlight potential complications arising from mixed-mode fracture mechanics. Overall, the conversation underscores the need for precise orientation and characterization to accurately evaluate the panels' fracture toughness.
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I need to get the Fracture Toughness of Honeycomb Sandwich Panles of Aluminum & GFRP facings such that i want to get in the microscopic analysis with the help of SEM & TEM (Scanning Electron Microscope) (Transmission Electron Microscope)...what is the procedure of making specimen of honeycomb core ...coz it is quite ductile & it doesn't remain in shape of hexagons whne compress in a mould...
 
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Does the composite structure look like the material in this paper?

http://people.ccmr.cornell.edu/~atz/hc_fracture.pdf


Also, I presume you are interested in mode I. In what orientation with respect to the honeycomb, i.e. what is the orientation of the tensile field with respect to the aluminum skin or honeycomb?
 
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I'm probably streching since don't have any sort of information about the core, but it being likely ductile (?) behavior wise and if you want to focus solely on the core you could follow 'typical' ductile material J - integral testing routines for determining fracture toughness or fracture resistance depending on what sort of information you're in need for (probably the former). ASTM has a standards for this, E1820 under committee E8 and the older E1737 is a good one as well.

Before taking such as approach would consider the questions posed by Astronuc, since if it becomes a mixed-mode multimaterial fracture mechanical problem quite a bit of issues arise what affect the characterization (especially if you want quantitative information about fracture toughness rather than just evidence about its fracture behavior).
 
yes the Panels are exactly of same kind shown in that particular research paper...we need to calclate fracture toughness of Honeycomb Sandwich Panels of Aluminm Facing (Top & Bottom Layer) Honeycomb Sandwich Panels ,GFRP Facing Honeycomb Sandwich Panels,
 
Can you indicate the orientation of the crack with respect to plane formed by the aluminum panels and honeycomb? In other words, is the plane of the crack propagating perpendicular to the Al/GFRP plane?

Normally one can find the fracture toughness of the Al and the GFRP, then one has to apply those to the structure.

If the crack plane is perpendicular to the plane of the Al/GFRP panel, then the crack in Al is certainly Mode I, but I believe more complicated in honeycomb, and then there is the bond between Al and GFRP, which I think might be Mode III.
 

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