instruments used in flexural testing of honeycomb sandwich panels

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#1

what exact relevance do strain gauges have in flexural testing of honeycomb sandwich panels ?
what particular property/variable can be calculated from the longitudinal strain data from the top and bottom face skins and how?location of strain gauges ?

we are primarily concerned about the stiffness values of the overal panel when testing as per ASTM D7250…

can strain gauges be done away with in favor of DIC{digital image correlation},given the constraint of having to install several gauges for a large number of test samples?

how much information can a DIC video camera provide for a given flexural test of a sample?be it 3-point or 4point?

#2

When we test panels in flexural mode (3 or 4 pt) we normally just use crosshead displacement to get the bending stiffness of the beam. If you have a stiff test frame and test rig nearly all thee crosshead movement will come from the panel deflection. The deflections are normally high and the loads low. The engineers should then be able to calculate the strain in the skins from that. Strain gages are a pain- we rarely use them. We have a video system that is much easier and such a system could be used to get an accurate movement of the beam at any point if the engineers were worried about ultimate accuracy ( we have never been asked to do this but it would be simple).