Saturday, March 7, 2009

Steel Fork Blade Failure

The following graphic shows an old steel fork of a bicycle which, during some repair work at a bike shop, lost its right blade due to a failure at the crown of the fork. The pictures are from Rivendell Bicycle's 2009 web reader, in an article titled "Time & Misplaced Crown Point Broke An Old Fork, Too".

The failure, at the crown on the rear side of the fork, is attributed to the "catching" of the rearward flex of the fork from braking. The flex was directed to a point of the crown which became a stress-riser. Over 30 years, a crack formed, crept around the blade under increasing stress of continued riding. The last picture labels the zones of failure and explains how this fatigue worked its way and some tell tale signs of the failure that can be observed by anyone.

In the rest of the article not shown here, Rivendell writes :
"And just for the record, we consider this fork to be worn out, not defective. It was a well-ridden 30 year old bike, and just wore out. Things wear out, even good things. Its hard to call this a defect. Still, there was a reason, as you'll see-and keep in mind that this fork lasted five to ten times as long as many carbon forks made today can expect to last."


Anonymous said...

Interesting. Why did the right blade fail before the left?

Jack said...


Anonymous said...

Hmmm... a bicycle made of spaghetti? The Flying Spaghetti Monster is pleased by your creative explanation. May you be touched by his noodley appendage and prosper.