Im planning of testing new method (ie new to me!) of curing carbon/epoxy pre-pregs. I need to evaluate the degree of cure as cheaply as possibly initially so am looking for ideas. The plan is to manufacture some UD samples – 3 x 0 degree layers each and cure in the oven. These would be the base samples to reference off. The other curing method will also use 3 UD layers in the samples.
I was thinking a good initial way to evaluate the degree of cure is to bend test (ie clamp to desk and hang a weight off-cantilever style) the new samples against the base samples by loading a 90 degree to the fibre direction, thereby using the stiffness of the resin to resist bending.
The end goal will be to go through a thorough testing procedure but Im looking for an interim method where I can make big changes to curing schedules and have a simple easy method of evaluating? Any other ideas that you think could work?
Thanks
you should get a barcol hardness tester and use this to evaluate the hardness of the resin, this should give you some idea of your cure.
Thanks Sammy - but they’re about £500 here I think. Will definitely use better methods down the line, but this is early stages stuff. I might check ebay though!! thanks
Barcol guages are pricey. Got one , only used it twice…
Barcol testers are great if your not 100% about a laminate due to uneven curing or if you receive a composite part from an external supplier and are concerned in the slightest about quality.
As my Dad says - “What can’t speak, can’t lie!”
They are damned expensive, but incredibly accurate. I don’t really see a better way to test the cure stage of a laminate. These work on structures large or small and are non destructive and very portable.
As an alternative, I have been looking at digital Shore D hardness testers for some time…
Fleabay have units that start at £20.
My plan is: I would calibrate it on known samples that have been previously graded and tested in a lab and what ever number the tester repeatedly and reliably attained is the benchmark for all other samples to stand up to.
I am about to oversee the building of a project by a contractor and I would like to double check both prepreg and wet laminated areas to ensure that no problems exist with the cure.
Now, for my situation I am on the fence on this and my concern is that I will not get a repeatable, reliable number from my samples or I would doubt the results from it in the future.
Has anyone else used a Shore hardness tester on composites?
Thats pretty interesting: Can you actually have a fibre-filled sample in a barcol gauge or does it have to be just resin? I would imagine fibres, distribution, surface finish, etc could skew results would they? Excuse my ignorance, havent used one before!
That is correct - You apply it directly to the laminate.
The probe is quite small, and you simply select a flat area and press down firmly.
It does it’s thing and measures how far in the pin has been able to travel into the sample material.
This correlates to the hardness of the test subject.
The harder the material, the less indentation, the higher the number and vice versa.
I would like to test the Shore hardness testers, in essence they do the same thing, but have different pin head shapes that do the indenting.
I am just not sure if the Shore D scale is high enough for thermoset resins…
Ah ok, thats what I assumed based on the shore testing types but best to avoid assumptions I suppose! Thanks v much, I must do some digging into second hand units