Hi All,

This week I've made some carbon infused door cards. The first 2 out of 4 had defects in a number of random locations but always only on an internal radius and never on a flat, between the duratec sunshield and 1st layer. I'm very certain these arn't due to bridging as I am very cautious and use an assortment of dibbers. Knowing I had an acceptable level of vacuum (3mbar absolute and 5mbar on the other card) with a leak drop test of less than 5mbar/hour I'm certain it isn't an air leak. Also, if it were bridging, it should have just filled the void with resin. I put these defects down to using a different brand of track spray that must have been incompatible.

The second set I made I went back to using tried and tested aerofix3 spray tack, being extra cautious to use the slightest mist and no bridging. However the same results. I've referenced close up pictures against other defects I've had in previous years and they look totally different. I don't believe they are air, but more to do with moisture. A few things to note are is that leaving the part overnight the cloudiness of the 'bubble' disappears and it's less noticeable, like it has evaporated somehow. I've been using Sunshield for awhile now and these parts were sprayed in 25*c, late afternoon and left overnight before I layed up the following morning then infused the morning after (38hours). Part was clean, with no chance of contamination on the surface.
Attached are two images of the new 'moisture bubbles' and the picture with the 12k tow is from a previous job that trapped some air. They look quite different.

Any ideas? Thanks.

Well if you think its moisture you can dry your fabric in an oven, and leave your part under vacuum longer to remove the moisture. The void in the corner looks like a slight bridge, but hard to tell from the photo. Are you degassing your resin before and after mixing the resin? Epoxy resin sucks up moisture. If the container has been open for awhile (and especially not sealed well) it will absorb moisture over time. You can put the resin (unmixed) in a bucket and degass it at higher temps (50-60C), for a couple hours.

Yes, they do appear slightly different to the kind of bridge 'bubbles' normally seen. However, if they can be penetrated to leave a noticeable gap between them and the cured fabric, it would seem to indicate air entrapment. Not certain on the part size or speed of infusion, but if there had been a small leak during the cure time, I'd expect to see some evidence in the flow media. Hopefully you can make a small hole in the middle and drip some infusion resin into them to fill the gaps. A tiny hole at either end helps evacuate the air and let the resin fill the space better. 

The only other thing I can think of is, perhaps, the spray tack. I only use Aerofix 3, as it'd generally very reliable and leaves no trace but it does contain acetone. I've noticed, very occasionally, that there's been some slight de-lamination between the in-mould coating and the epoxy underneath, but it's only been apparent on trimmed edges. I've put this down to using a little too much of the spray in certain areas, as it's clear that something has affected the bond between the coating and the epoxy. 

I'm quite careful only to use just a mist of it if that is all that's needed, but I've never seen anything similar on corners etc. where I might use a little more to hold the fabric. If your bubbles appear very shallow and not air-related, however, then perhaps it might just have something to do with the spray tack affecting the bond?