icentropy wrote:actionpaintball wrote:Standard rule of thumb [very generic] is that steel is 3X heavier, and 3X stronger (tensile) over aluminum.
The rule of thumb i've always used is aluminum is you have to use 50% more aluminum to come up with the same amount of strength. And by using aluminum instead of steel you'll end up saving around 1/3 of the weight because of the added thickness. This is in comparison will low carbon mild steel.
If you bump up the aluminum to a reasonable quality such as 6061 and temper (or buy tempered) to T6 the ratio gets better. 7050 or 7075 to the T7 temper is basically just as strong as mild steel so you are saving the full weight amount, but you can't really bend or weld T7 material without loosing a large amount of the strength. The correct way to make things out of aluminum is the way AMG made our bodies and rail guards. It's all made out of 6061-0 temper, bent, welded, etc. THEN heat treated to T6 so the whole structure is quite strong.
The aluminum on the light bar and the brackets was plenty "strong" to hold up the bar. Its the side-to-side motion that fatiqued the aluminum to the point of failure. Stop the side to side motion one way or another and the problem will go away. IMO, the easiest way to do that if you still had the whole setup and hadn't mounted it, would probably be just to make some 45° angle brackets (stiffeners) on the corners, that or just make brackets so thick that they keep the assembly ridgid enough to not move. That's not really the correct way to do is as you're basically just overcoming a bad design with excessive use of material but heck that's what i'm gonna do mostly due to lazyness .
I see way too much shock and cyclic stress analysis everyday...wanted to keep it simple You would have thought they would at least have done some field testing.