Thread: Question about cracks when bending metal

Good morning,

I was hoping someone could enlighten me about the likelihood of relatively thin sheet metal cracking when bent. I'm trying to work out which sort of metal and thickness would suit my purposes best, as I was on the verge of buying 1mm thick aluminum sheets when I read that it cracks easily when bent, which would be very problematic for me.

This may sound a little odd, but what I'm wanting to do is incorporate an engineering-style action into a live action role play game. I want to simulate engineers having to repair a breach in a spaceship's hull by (lightly) hammering out a number of twisted/folded pieces of metal and reassembling them into their original shape, much like a jigsaw.

I had planned just to buy some sheets of metal, snip them into a rough jigsaw, and bend the pieces to make them look like wreckage. But research has since led me to believe that this amount of bending, and then unbending from the players, could likely cause the metal to crack and break if I'm not careful.

So can anyone please offer advice as to how this may work? I'm assuming aluminum is right out, but would another type of metal be more forgiving?

Many thanks,

Saau

Al should work if you get the right grade - possibly something like 5083 but your supplier should be able to help you. Some grades crack easily but provided you leave a reasonable bend radius, you should be right. Perhaps anneal the Al after bending - coat the inside with soap and play a torch over the back. When the soap browns you are at annealing temperature. Let it air cool.

Michael

Thanks, that's useful to know. I'm not looking at getting sharp angles, just enough to make the metal look twisted and wrecked. I just don't want the pieces falling apart in the middle of the game.
Cheers,

Saau

Al would be the go. The cracking you are probably thinking of is a product of 'work hardening', repeated bending/unbending of the same line of fold will harden the sheet locally and eventually it will break/tear. Sometimes with some materials, when access to appropriate cutters, one can deliberately fold an unwanted flange back and forth until it harden and eventually it gets to the point where it can be torn off or broken off .

Al in your situation, with a bit of bending and flattening (use a soft mallet), is probably unlikely to get to a 'work hardening' stage, were it to then Michael's advice will address the issues. Get a bit and experiment.

The correct grade and temper are the most important parameters for you to get right I would think. Something like 6061 T6, although strong, would likely break after just a few bends back and forth, I'm not certain, but road signs are made from this alloy or something similar I think, and it is quite stiff and rigid compared to an old aluminium sauspan of similar thickness. Aluminium cookware was generally made from nearly pure aluminium, which makes it quite soft, but resistant to cracking when being bent back and forth. As has been suggested, your supplier should be able to help you make the best choice for your application.

If aluminium is bent along the grain it will split also, depending on the grade.
Kryn