Low Barcol Hardness Readings after switching materials (Phenolic Prepregs 270°F cure) 1

[Cisnerjo]

Hello everyone, I would like to request support from the experts on this matter. We are switching from certain phenolic prepreg to a different one available from same manufacturer which mentions both are the same. We perform Hardness test per our own specification which request an average of 68-75 we are testing this new material, and we are getting Hardness results as low as 50 and maximum of 70. We changed the recipe and increase the soak time up the maximum requested by the manufacturer, also performed different bagging methods in order to attempt to increase Barcol Hardness results without much good results. We also are checking ASTM D2583, which it calls for a Polyester Laminate and its average request is 55. Is there any other way to attempt to increase Barcol Hardness results on them or should we attempt to perform testings to come up with a base line and modify our own specification to reduce it to whatever the results we get?

Please advice ! Thanks a lot !

 

[SWComposites]

from same manufacturer which mentions both are the same.

LOL. I would never believe that statement from the manufacturer without actual data to back it up.
Is Hardness a test that the material supplier performs for batch certification? is it listed on their product datasheet.
Frankly, in 40+ years in the composites world, I've never heard of a hardness test being used to evaluate a composite material. Are there any other properties that you are testing?

 

[Compositepro]

Phenolics are condensation cure polymers, meaning that water is generated during cure. This water is usually trapped in the polymer after cure and acts as a plasticizer. An oven bake after cure should be done to allow this water to diffuse out of your part. This needs to be done with some care, as trying to dry too fast will blister or delaminate the part due to internal steam pressure.

Also consider that the hardness reading will be different if taken over a fiber bundle or in a weave opening between fiber bundles.

 

[Cisnerjo]

LOL. I would never believe that statement from the manufacturer without actual data to back it up.
Is Hardness a test that the material supplier performs for batch certification? is it listed on their product datasheet.
Frankly, in 40+ years in the composites world, I've never heard of a hardness test being used to evaluate a composite material. Are there any other properties that you are testing?

Hi SWComposites thanks a lot for you reply and feedback. Actually, Manufacturer does not mention any specific readings for Barcol Hardness we are using our own specification as based line, but unfortunately readings we were getting with old material are not the same for the new one. Barcol hardness is internally used for in process oven load cure validation. We are testing Drum Peel and Flammability as a in process load verification as well.

 

[Cisnerjo]

Phenolics are condensation cure polymers, meaning that water is generated during cure. This water is usually trapped in the polymer after cure and acts as a plasticizer. An oven bake after cure should be done to allow this water to diffuse out of your part. This needs to be done with some care, as trying to dry too fast will blister or delaminate the part due to internal steam pressure.

Also consider that the hardness reading will be different if taken over a fiber bundle or in a weave opening between fiber bundles.

Thanks for you feedback I appreciate your reply Compositepro. After samples were cured, we performed some post cure on them in order to validate if Barcol Hardness got improved somehow. unfortunately, they decreased a bit compared with the ones obtained after regular cure. For now, we are considering keeping performing testings with new material in order to come up with a base line so we can modify our own specification with actual material results. We also increased the number of plies for this Hardness testing from 4 plies to 6 plies since this is a 7781 fiber style material trying to concur with ASTM D2583 that mentions .0625" (1/16") for the specimen thickness. Cure is performed at 270°F for 80mins, Postcure was performed at that same temperature free stand for 120 mins.

 

[SWComposites]

We are testing Drum Peel and Flammability as a in process load verification

"drum peel" test of a sandwich panel? that is going to verify the core to facesheet bond, not the facesheet strength
"flammability" will verify nothing about strength ("load").

and I'll say it again, I have no idea what hardness correlates to, if anything.