Prepreg tack standard test? 1

[RPstress]

Traditionally where I am, tack is assessed subjectively, e.g. bend the material through 180 degrees and see how "well" it sticks to itself (basically if stays stuck on or quickly peels off).

Does anyone use (or know of) a more numerate test?

 

[avior]

We have a receiving procedure (maybe not the best) for tack test preinpregnated cloth:
- clean a steel plate using a solvent (M.E.K.) and dry it.
-cut the specimens of prepreg 2" by 2", apply the specimen to the plate using light hand pressure, remove the backing film, apply a second specimen on top of first one, remove the backing film and apply a third specimen using hand prssure (firm for last one).
- the steel plate with the three attached prepreg specimens shall maintain in a vertical position for 30 min at 72F+-5F (23C+-3C). the prepreg material shall adhere for this period of time
- a minimum of 3 determination shall be made, the failure of one specimen will indicate a rejection.

 

[Demon3]

I am not an expert in that exact field so I know of no specilized test. If you would like to quantify the tack you could do a peel test. You cut a strip of prepreg and stick it to a sheet of prepreg using set time and force. Then peel off the strip by pulling on it using a spring balance (e.g. for weighing fish etc). The angle of peel off needs to be constant from test to test. That will give you a quantified tackiness in terms of force needed to peel off the strip.

Another possible test would be to place e.g. a PTFE block on the prepreg sheet and tilt the sheet until the block slides off. This is a measurement of friction. It can be quantified using a digital spirit level available from hardware stores (around $50 from Sears, I have two of them). You record the angle at which the block begins to slide.

Good luck.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[GBor]

You may be able to modify the drum peel test similar to Demon3's procedure.

 

[Compositepro]

There are many tack test methods and the most common is the "Thumb" test. There is no universal test. Tack means different thing to different people and in different applications. For a tack test to be useful it should simulate the the actual process where tack is needed. Many tack test are implimented because they are "quantitative" yet there may be very little correlation to real world tack.

Tack actually involves all of these issues:
Resin visco-elasticity
Speed of surface wetting.
Contact area
Resin cohesive strength
Resin adhesive strength
Contact surface texture
Contact time and pressure

Almost all of these are strongly influenced by temperature and humidity.

 

[RPstress]

Many thanks all.

At the moment we're most interested in the separation of automatic tape layer prepreg material from its paper backer and its adhesion to the tool and material already deposited.

We can see several ways to invent a test that might work; we were interested in any methods out there that might have track record.

The issue of material remaining outlife vs. ambient temperature and himdity is a tricky one, and we we're hoping to do a series of tests which might give us some idea of the trade off between them.

 

[GBor]

If anyone knows of a test, it will be these guys:

http://www.materials-sciences.com