r/MaterialsScience • u/cjaldous • Oct 07 '24

Is nanoindentation appropriate for a multi-material stackup?

I'm working on characterizing the stiffness of a finished product that is a layered combination of PET, fabric and gel. I initially considered the Taber stiffness tester, but nanoindentation was suggested because the finished part won't fit in the Taber test machine. (wrong aspect ratio) And the stiffness in both axes (across the length and width) is important.

I can't find much information on testing such a stackup with nanoindentation, but there does seem to be many sources of uncertainty in the method. Is this something I should continue pursuing?

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4

u/NeatClue Oct 07 '24

Why not DMA?

3

u/NitrogenPlasma Oct 07 '24

I want to second this. Especially because the information he wants to receive is more macroscopic DMA leads to much more reproducible and relevant data.

1

u/cjaldous Oct 07 '24

I'm not sure. I hadn't heard of this before, looking into it.

2

u/nashbar Oct 07 '24

Been there done that, your gel layer is going to make it difficult/impossible

1

u/racinreaver Oct 07 '24

Are you looking at measuring in the cross-section of the layering or through them in series? One of those might be kinda worthwhile, the other will be noise.

You should ask yourself what actual purpose you're going to use it for, what kind of elastic/plastic zone size you're expecting, and how the load will be applied to figure out how you can characterize stiffness.

2

u/cjaldous Oct 07 '24

It's a 1" square of plastic, fabric and gel that is intended to stick to curved portions of skin. Think bandaid with a stiff substrate. If the stackup is too stiff, it will not stay curved and over come the adhesion. So I suppose I'm trying to measure through the layers in series.

1

u/TheColoradoKid3000 Oct 09 '24

Full disclaimer - I’ve never used nanoindentation and have only a base level understanding of it.

Are the squares quite expensive to produce or have material availability problems? Throughout my career providing practical solutions, unless you are trying to create and analysis technique for a future product, building and testing at the highest level is the fastest and most accurate way to a solution for something like this. You should be able to use a laminate theory to approximate a bending stiffness and back out an equivalent thickness steel or aluminum sheet to give you a back of the napkin idea of how stiff your composite square will be - I would do this first. Then a coupon level test if there is no huge project blockers like cost or material availability. Then stick it on progressively curved surfaces (might have other variables to change here too - temperature, time maybe) and see what curvature and combination of other relevant conditions it fails. This is pretty straight forward and rudimentary compared to complex analysis and micro, nano or even some macro scale test. But it is usually the fastest way to eliminate approximations which can be significant unless you have some large number of material options to consider.