Climbers and riggers should all be familiar with fatigue limits.
It can be as high as 50% max tensile strength for steel, but I use 30% as my working figure when rigging, and I regularly re-inspect and age-retire gear (at least use annualized color coded markings).
When I’ve rigged circus in the past I’ve taken to replacing aluminum gear I find with steel, especially if it’s going to be installed for a while.
That said, I climb on aluminum. I just age out my equipment. I’d hate for my last thought to be “huh... I guess aluminum really does degrade with repeated stress.”
I had an aluminum bicycle where the front fork failed suddenly. Not instantly but in maybe one or two seconds (just slowly enough to let me not have a terrible fall). My next bike was chrome/steel.
Years ago I totaled a mountain bike in a strange pinched-wheel-in-crack accident that bent the frame in two places but left me uninjured.
When I commented to a bike designer/engineer that it was a strange failure, he said that it was intentional, at least on hardtail mountain bikes like mine. A bent frame is ruined but doesn't lead to a catastrophic loss of control. A detached wheel or twisted fork would be next to impossible to control to a stop.
He looked at my frame and explained that that the two bends were in exactly the place they'd been designed to be, just behind the last butting. It's an impressive bit of forethought.
My guess on road bikes with steel forks, though, is that it's a matter of aerodynamic performance calling for compactness to reduce frontal area, something that would be harder to do in aluminum, and for far less weight savings than the longer tubes on the frame.
There's always titanium... The only big drawback is the cost...
I was told once that the reason for that was stiffness: apparently aluminum forks are stiffer, so unsuspended ones are way less comfortable (in terms of vibrations being transmitted to the frame and handlebars) than steel unsuspended forks.
It can be as high as 50% max tensile strength for steel, but I use 30% as my working figure when rigging, and I regularly re-inspect and age-retire gear (at least use annualized color coded markings).
When I’ve rigged circus in the past I’ve taken to replacing aluminum gear I find with steel, especially if it’s going to be installed for a while.
That said, I climb on aluminum. I just age out my equipment. I’d hate for my last thought to be “huh... I guess aluminum really does degrade with repeated stress.”