Exactly....
The reason that most aluminum frames are so stiff is that the manufacturers have made the frames such that they perform really well, and have a margin of safety. So most riders will not face the heartbreak of aluminosoriosis. Nevertheless, the aluminum fatigue phenomena is real, just one that most riders won't have to worry about.
I have seen trashed
mountain bikes--some were acute incidents (big hits) but some were chronic (that is, fatigue-related) failures. Some at the downtube/headtube junction, a few were at the chainstays.
Also, I saw two old aluminum road frames that had come apart under unknown circumstances--they were in a frame scrap pile--but it seemed that they were failures and not crashes. Both were old school small-tubed aluminum. I think both were French. And, finally, I was recently reading about some frame abuse testing and the aluminum Klein frame failed at a cable entrance.
Also, haven't we all seem handlebar and stem failures over the years? I personally broke my share of back-in-the-day stems and bars, many French. AVA were my favorite breakers. Almost drove a stem through my sternum once on a downhill run. Now, I don't use stems or bars that are heavily used after about five years. I saw a guy go endo on his commuter because his ttt quill stem let go.
Aluminum does the job, just don't ask it to do the job for ever and ever.
steel515 said:
aluminum framebuilders use oversize tubes to make frame stiffer
as well as use thick tubing to produce durable, stifff, and light (aluminum less dense than steel) frame.