So, I have a 95 winnebago T4 camper.  They have a notorious and well documented issue with cracking on the pop top ASA plastic roof.  I was prepping for a trip away and realised the crack mine has on one side opened up again

I took a 2 pronged attack.  I resealed the crack with ASA plastic rod (soldering iron to weld).
Secondly I had some 4-layer carbon fibre sheet left over that I decided to attach to give some support (mix of the profinish 210g and the twill 2/2 200g) with epoxy resin.  Wet lay on a mirror finish sheet of aluminium.  Over the length of the sheet, obviously some flex but its pretty rigid.  About 1.5mm thick measured.
I know from previous peoples attempts that bonding to ASA can be tricky but I had ET538 honeycomb bonding adhesive around so I figured I try this with the backup plan being putting a few holes/rivets through the top.
I roughed up the ASA, cleaned, put the adhesive on the CF and stuck on with gaffer tape holding in place (not easy to get a clamp on)
Left for 48 hrs and was shocked to find this:



I can't work out how this is physically possible!  the forces to do this must be huge.  Neither the CF or the ASA seem to expand much with temperature.  It clearly bonded well!  I welcome thoughts as to how this is possible.  May yet put matching on the other side but with a different adhesive.  Has it reacted to the ASA?

I suspect it is mostly heat expansion.  On a hot day, although the plastic doesn't expand much, it might be a few mm over the roofs whole length.  I suspect that area of the roof is where the tension ends up being as the thing cycles over time.  The resin has probably fully cured when the sun was hot and the roof hot and everything was at maximum expansion and now it shrunk down when cooling causing the effect you see. Remember that although the actual shrinkage of the plastic roof may only be a few mm over its full length, the effect over a crack or weakened area is likely to be a fair bit more as the panel tries to twist etc.  Hence the exaggerated effect you see there.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thanks for the response, I think you could be onto something with the twisting.  The heat bit doesn't easily add up in a direct way (ie I took the picture in daytime and fixed the bar in daytime).  I guess its possible that the gap widened when it got colder overnight and that it hardened in that form and then shrank back in the day.  Its getting cooler now and it seems that its straightening out!  I guess I need to try and get a second bar fixed higher up when it is at its most contracted but might need a faster setting adhesive for that.  

In the short term I will have to run with it as is and see!

Another extrapolation of your twisting idea.  I suggest that it is probably not the plastic expanding but the metal of the van and that the van is pushing and pulling the plastic roof causing the twisting and opening/closing of the gap.

Any suggestions on what I should try adhesive wise for a second piece?  
Thinking VM100 or ET500
ET500 is a bit faster and I want to catch it in the closed up state so I lean towards that. We also now know that ET538 bonds so possibly a good sign that 500 will?

How do you come to believe, that asa has a small thermal expansion value? Plastics usually have some of the highest thermal expansion factors. Asa has 80-100 × 10^-6/C°, aluminium 23, steel 10-12 and cfrp is close to zero.
To make things worse, cfrp is multiple times stiffer, so it accumulates the forces that build up over the joint. Gfrp would be a better choice, as it is less stiff and has a greater thermal expansion.

+x

 

oekmont - 5/21/2019 2:41:46 PM

How do you come to believe, that asa has a small thermal expansion value? Plastics usually have some of the highest thermal expansion factors. Asa has 80-100 × 10^-6/C°, aluminium 23, steel 10-12 and cfrp is close to zero.
To make things worse, cfrp is multiple times stiffer, so it accumulates the forces that build up over the joint. Gfrp would be a better choice, as it is less stiff and has a greater thermal expansion.

Thanks for the response, bad and overly quick research I think is the answer to your question!