JohnSw wrote:The glued and screwed construction uses aluminum tubing with aluminum angle pieces at the joints. These angle pieces are held in place with glue (probably epoxy) and a screw through each leg. Sunnybrook and Cedar Creek are two manufacturers that uses this method of construction. I looked for a picture to illustrate but didn't see a good one in their literature.
If I was going to use an aluminum frame, I'd use fittings, glue, and rivets to hold it together. The rivets are temporary backups for the glue if it fails. BTW, Lotus is using that construction method on some of their cars. The advantage is you can use the higher strength aluminums, and not loose strength due to welding. 40k to 60k PSI strength aluminums often become 20k PSI at the weld joint. They then need to be heat treated and solution aged to regain most of their original strength. Due to uncontrollable changes during welding, not all of the original strength can be recovered. With a properly designed glue joint it will retain the original strength through the joint. Weight savings over steel can be from 30% to 50% depending on the aluminum alloy used. It does require going to larger diameter tubes and taller I-bean sections to get the maximum weight savings. This is mainly due to aluminum being less able to handle constant flexing.
My understanding from a race car trailer manufacturer is VHB taped joints are strong enough to allow the skin to be a stressed skin. The secret is in making them wide enough. That way there is enough bond area that the shear strength of the VHB tape is high enough. Auto body glues will also work. For the side walls they were using 40mm square tubes with one piece, pre painted, 3mm thick aluminum, plastic, aluminum sandwich panel skins. They just used fittings with rivets at the tube to tube joints. They relied on the skins to limit flex at the joints. One of the secrets to a good glue or VHB tape joint is cleanliness. Properly clean and treat the joint just before applying the glue or tape. Don't touch the joint area with your fingers after cleaning it.
VHB tape will isolate steel from aluminum if it isn't riveted.