While doing the laminate repair, the notches filled with plain resin exhibits more voids and discontinuity in the notch edges. At the same time the resin reinforced with fiber shows good finishing and very less voids. Any specific reason? I can able to understand the high viscous fluids will have air bubbles. But I want to know the reason behind when the same fluid with fiber will have fewer voids.
Dear Ramesh, the observation you described may result from different effects. In the pure resin the bubbles are visible and they stay within the resin because of their surface stress and the viscocity of the resin. When adding the fibers, the fibers at least effect the shape of the bubbles (distorting them). It could be that they are still there but in this cases they form around or along the fibers, so they are harder to detect. It might be possible as well that the fibers influence the surface stress of the bubbles or act as sink and you actually end up with less bubbles. You could try to measrue the density respectively volume contents in your samples very precisely using Differential Scanning Calorimetry DSC and / or Thermogravimetric Analysis TGA in order to derive from this the bubble volume.
Best regards, Ruediger Rentsch
Part of the answer may pertain to permeability and resin diffusion modes. First, within the fibers, the permeability of the media is lower and the bubbles may be 'trapped' and agglomerate outside of the fabric. Furthermore, within the fibers an important part of the resin flow may come from capillarity. Once a capillary flow is induced, it is possible that air bubbles won't get in as easily.
Best regards,
Laurent
Maybe because when you do manufacturing with fibers (either processing pre-pregs or impregnating dry fabrics with resin), you apply pressure (at least vacuum)? The pressure helps to get rid of the entrapped air bubbles.
From practices point of view is simple. I understand that the reisn was low temperature type. The air going to resin during mixing process. I mean moment when resin and hardner were mixed. In every kind of wet lay-up technology you will have air in the resin. If you have to minimize air content you should use vacuum bag or/and additional pressure and low viscosity resin. Of course i write about repair in structure made using wet lay-up or, infusion or RTM. In case of repair autoclave maded laminate you can use only prepreg. I have bit experience with composite bonded repairs on airplanes and the general ruls is that prepregs should be repaired using prepregs and "wet lay-up should be repaired using wet lay-up.
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