|
oekmont
|
|
|
Group: Forum Members
Posts: 550,
Visits: 27K
|
Because of (simplified) leverage a sandwich structure has basically the same strength as a solid one. If you use a core like airex, rohacell or soric lrc, you can get 1,5mm core material, wich ends up to almost exactly 2mm with 240g+100g skins. 100g could be a biax cloth, wich isn't nearly that expensive as a 100g weave.
Are this very heavy stressed joints? You can bolt through the structural cores quite good, especially if you are using (cf) washers. M3 and m4 are quite "elegant" screw sizes, and since weight is critical you are likely using titan or even aluminium and therefore are not brute forcing the screws and use loctite. For heavy bolting you might consider cutting a hole in the core locally and filling it with around 1000g/m^2/mm-core carbon cloth before infusing.
|
|
|
|
|
polaraligned
|
|
|
Group: Forum Members
Posts: 13,
Visits: 284
|
+xIf the best strength to weight ratio is needed, sandwich would be the very best solution. Like 60-70% less weight compared to a solid 2mm material. +1
|
|
|
|
|
quinn
|
|
|
Group: Forum Members
Posts: 155,
Visits: 992
|
+xIf the best strength to weight ratio is needed, sandwich would be the very best solution. Like 60-70% less weight compared to a solid 2mm material. I'm assuming I would have to go thicker than 2mm though to get equal or more strength than solid 2mm. The current design requires 2mm thickness and I'm assuming a 2mm thick sandwich would be weaker than solid 2mm right? definitely something to consider though for future designs. At one point I had thought about using thicker material with lighter core for better efficiency but these plate peices are fastened to aluminum parts with m3 and m4 screws. A lighter core will make it more likely to crush when fasteners are tightened right?
|
|
|
|
|
oekmont
|
|
|
Group: Forum Members
Posts: 550,
Visits: 27K
|
If the best strength to weight ratio is needed, sandwich would be the very best solution. Like 60-70% less weight compared to a solid 2mm material.
|
|
|
|
|
scottracing
|
|
|
Group: Forum Members
Posts: 460,
Visits: 5.2K
|
+x+xThe easy cheaty way is to infuse two plates of half the thickness and bond them together. Achieving equal pressure over 0.5mx0.5m isn't that easy. But you can vacuum bag two thick glass plates. This will give you 2.5t of distributed pressure. Does it need to be solid carbon? if sandwich fits your needs, you could use a flow media core, like soric, and infuse between two glass plates. Or less recommentable, just regular flow media between the carbon layers (not for structural use). Best possible strength to weight ratio is needed so a sandwich probably wouldn't be best. I'm thinking maybe I don't really need perfect finish on the backside so maybe I'll just do regular infusion and live with peel ply texture on the inside. It's visible in a few places, but there's electrical components and things mounted to it. This is side frame material for my rc helicopters. Out of curiosity, how are larger manufacturers doing this? Any time I buy 2mm plate, it's glossy both sides. larger manufacturers use prepregs in a heated platen press.
|
|
|
|
|
quinn
|
|
|
Group: Forum Members
Posts: 155,
Visits: 992
|
+xThe easy cheaty way is to infuse two plates of half the thickness and bond them together. Achieving equal pressure over 0.5mx0.5m isn't that easy. But you can vacuum bag two thick glass plates. This will give you 2.5t of distributed pressure. Does it need to be solid carbon? if sandwich fits your needs, you could use a flow media core, like soric, and infuse between two glass plates. Or less recommentable, just regular flow media between the carbon layers (not for structural use). Best possible strength to weight ratio is needed so a sandwich probably wouldn't be best. I'm thinking maybe I don't really need perfect finish on the backside so maybe I'll just do regular infusion and live with peel ply texture on the inside. It's visible in a few places, but there's electrical components and things mounted to it. This is side frame material for my rc helicopters. Out of curiosity, how are larger manufacturers doing this? Any time I buy 2mm plate, it's glossy both sides.
|
|
|
|
|
oekmont
|
|
|
Group: Forum Members
Posts: 550,
Visits: 27K
|
The easy cheaty way is to infuse two plates of half the thickness and bond them together.
Achieving equal pressure over 0.5mx0.5m isn't that easy. But you can vacuum bag two thick glass plates. This will give you 2.5t of distributed pressure.
Does it need to be solid carbon? if sandwich fits your needs, you could use a flow media core, like soric, and infuse between two glass plates. Or less recommentable, just regular flow media between the carbon layers (not for structural use).
|
|
|
|
|
Steve Broad
|
|
|
Group: Forum Members
Posts: 408,
Visits: 4.1K
|
+xInfusion seems to be the way to go, but you only get one finished face with peel ply texture on the other. What's the best way to get 2 finished faces? I tried a small 150mm square by just clamping 2 peices of aluminum tooling plate together and it worked perfect with really good fiber to resin ratio, but I need some larger 500x500 plates (2mm thick). I could use 2 plates of glass backed up by something else like mdf maybe, but I imagine just clamping around the outsides is not going to squeeze the middle well enough unless I get tricky with the clamping. Maybe some thick peices that span across with clamps on outside to hopefully put enough pressure in the middle. Any other good way to do this other than clamping? If clamping is the best option, what's the best choice of clamping plate material and method for doing it? If I was going to use this clamping method, I would use 5mm (minimum) steel plates backed with 50mm thick timber (planed flat) each side to spread clamping load. I imagine that trying to do this using infusion would be tricky so I would wet lay the carbon and clamp using a hydraulic press. You may have to experiment with the pressure to find the optimum. However, I would prefer to use vacuum and you wouldn't need the timber. Never used infusion (went from wet lay to prepreg) so can't comment on whether this would be suitable. If using a press you can exert more pressure than possible using vacuum only, so results could rival autoclave but only trying it will tell :-)
|
|
|
|
|
quinn
|
|
|
Group: Forum Members
Posts: 155,
Visits: 992
|
Infusion seems to be the way to go, but you only get one finished face with peel ply texture on the other. What's the best way to get 2 finished faces? I tried a small 150mm square by just clamping 2 peices of aluminum tooling plate together and it worked perfect with really good fiber to resin ratio, but I need some larger 500x500 plates (2mm thick). I could use 2 plates of glass backed up by something else like mdf maybe, but I imagine just clamping around the outsides is not going to squeeze the middle well enough unless I get tricky with the clamping. Maybe some thick peices that span across with clamps on outside to hopefully put enough pressure in the middle.
Any other good way to do this other than clamping? If clamping is the best option, what's the best choice of clamping plate material and method for doing it?
|
|
|
|