This is a classic fatigue failure -- looks like a fracture had existed for a while before it sheared off. There's a small write up in RR42 about the exact same failure (and location, probably safe to say this one of the highest stress areas in a crank arm).
http://www.cyclofiend.com/Images/pdf/RR42_web.pdf see page 7 As far as prevention, a better alloy (steel) will allow more load cycles. Aluminum alloys can take a magnitude less cycles before failure, but mostly dependent on composition, load environments etc. As far as shear failure prevention after crack initiation, could have run an NDT inspection and seen the crack... however this is not economic on bike parts. On Thursday, February 12, 2015 at 2:31:07 AM UTC-6, Benedikt wrote: > > I seem to remember seeing a similar post to this a few weeks/months ago > but here it is ... > My VO crank that had 13,000 miles on it busted this morning on my way into > work. I was at a stop. Pushed down with my right foot, locked my left clip > in, pushed down with the right and "clunk" crank arm came right off. > Fortunately I wasn't going that fast, hammering down the road. What causes > this? Do ALL cranks have a life span? These are an aluminum alloy. > Here's a pretty good picture of the break - > https://www.flickr.com/photos/neutralbuoyancy/16320815710/ > > - Brian in Seattle > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
