Sandwich skin - shear properties

[irq]

Do you know any standard, where I can find the determination of the material shear properties of the prepreg skin build in thin sandwich construction? The standard bone shaped shear tensile specimen seems to be not appropriate in this case.

 

[SWComposites]

are you refering to in-plane shear of the facesheets, or thru-thickess shear of the panel.

 

[irq]

The aim is to obtain the in-plane shear allowable of the thin sandwich skin. Please write me a short message (odzew [at] poczta [dot] fm) - I will provide you more details, as there is only way I can share more. Thanks.

 

[SWComposites]

A "picture-frame" type panel test is sometimes used; this is where loading bars are fastened to the edges of a square panel, the bars are connected by pins at the corners, then a tensile load is applied to two opposite pins. There is a draft ASTM standard, but I don't know of a publicly released one.

 

[irq]

How can I get this draft standard? Not much detail information is available regarding this test. Can I replace this test by another one e.g: 4-point bending test of the sandwich with facesheets positioned under 45 ̊, than estimate the failure stress on compression side and later on shear stress?

 

[tienne]

Hi you can find plenty of information about the picture frame test online. The ASTM is working on a work item WK35142.

To me the 4 bending (on long beam) test will allow you to get the allowable of the matrix in bending when you put the fiber a +- 45.

 

[mmhaynes]

The ASTM C273 Standard for Shear Properties of Sandwich Core Materials is what you want, I think. Its an easy test once you have the fixturing, I've done it at both elevated and cryogenic temps.

Mark Haynes
Senior Engineer
Composite Technology Development

 

[irq]

mmhaynes: ASTM C273 is the standard for determination of sandwich core shear properties. The "picture-frame" test is correct one for my application and determination of in-plane shear of skin properties, unfortunately not standardized until now.

I am particularly interested how much the values of in-plane shear for facesheets can differ in both methods: biaxial picture-frame test (skin-core-skin) and standard tensile test of the prepreg plies positioned under 45 ̊. The latter one is much easier to perform. Another question is how much the number of plies impact the shear properties of the skin material.

 

[tienne]

Hi IRQ !

Did you perform any picture frame test on honeycomb panel ? Do you agree with the fact that 4 points bending will not give you biaxial loading but uniaxial (compression on one side and tension on the other). In such test depending on the fiber direction you can determine the modulus of the fiber or resin with long beam and the core shear with short beam.

Let me know what you have found, I was involved in such project.

Thks