Thread: 3TTT Death Stem
View Single Post
Old 11-25-17, 08:50 PM
  #5  
dddd
Ride, Wrench, Swap, Race
 
dddd's Avatar
 
Join Date: Jan 2010
Location: Northern California
Posts: 8,114

Bikes: Cheltenham-Pederson racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.

Mentioned: 113 Post(s)
Tagged: 0 Thread(s)
Quoted: 1106 Post(s)
Liked 562 Times in 396 Posts
What I think is the main cause of such failures is any extreme torque that is transmitted from stem to steerer, as when a bike is crashed or when someone tries to forcibly twist out a stuck stem.


The sort of shear forces generated in the quill by such causes will greatly stress the quill at the top of the slot, and the crack can be seen to follow just such a path of maximum shear stress.


Having seen how the walls of a house fail from shear stress during an earthquake, and having studied statics and mechanics of materials, leads me to such a conclusion. The concentration of stress at the top of the slot could have been reduced by even a small radius if the stem's maker had figured on whatever caused this stem to fail, but the history of this item is unknown and it very well may have been seriously abused.
dddd is offline