Honeycomb Core Crush - Core Height Correction Factor

[HughG]

Hi,

I have been using the "Honeycomb Core - Crushing, Joint Support Load" failure option with v5.6.38 to calculate crushing margins. I am using a 3D model with Hex elements to represent the honeycomb core. I have local crushing loads introduced into the structure from attached fittings. I have verified by hand calculation that Hypersizer is using the Hex element compressive stress directly against the allowable crush stress for the honeycomb core material (the stress report did not show this, but that's another issue). This is as expected and a useful way to size such regions.
However, my analysis methodology requires the allowable crush stress to be factored by the same height correction factor used to knock-down the shear stress allowable. Currently if I go to the honeycomb material form, the Shear strength correction factor is listed on the 'Stiffness tab' (which is confusing because it applies to the Strength, and not the Stiffness). I need to use this same correction factor for the Crushing allowable, or maybe have another factor definition that applies to Crush.

[Rocketman007]

In summary you are stating that a transverse shear honeycomb core height correction factor should be applied to the core crush allowable derived at a nominal thickness.

If you have access the original Hexcel document showing the core shear height correction factor, most likely you will find that this document makes no reference to any correction factor for the core crush allowable.

When working with Goodrich I noted that the methods group implied the honeycomb core height correction factor is applied to both shear and core crush. This interpretation may not have been correct. Please verify a reference for a core crush correction.

If Goodrich subsequently tested honeycomb core with various core heights and showed a core crush height correction is valid, one would assume this core crush corrections not likely to be the same factor when compared to the core shear height correction. At this time Hypersizer (V5.7.6)  will not accommodate a core crush correction.

If a core crush height correction is deemed valid, the best interim solution is to determine the maximum core thickness in your design configuration and enter the appropriate core crush allowable. If this answer is not satisfactory let me know and I will call you for a more detailed discussion.

Dave

[HughG]

I've been looking into this some more, and I do see your point. I've questioned our methodology and have possibly opened a can of worms here ;-)

Anyway, I've seen data to suggest little or no effect on metallic core for differing heights. But I've also seen stuff from 2 different sources to suggest there is a height effect for non-metallic cores. It's not as much of a knockdown as the shear knockdown, but it does appear to be there. I'm not really fussed though because I'm only using metallic core, but you might want to think about adding support for a separate knockdown factor for core crush.