Footpeg bolt failed while riding

Wade Bartlett wade.bartlett at gmail.com
Mon Aug 27 04:39:14 PDT 2007


> Wade Bartlett wrote:
>> The fracture face shows absolutely no metallurgical problems <snip>

Jim Stewart wrote:
> Wade - can you expand on your comments? I guess I see the fracture 
> progressions at the thread root. How about the almost horizontal 
> striations through the core of the bolt?
> Any further clues that appear to the experienced eye?

As noted earlier, a better microscope would tell more, and might 
possibly find some metallurgical defect, though I doubt it.
OEM bolts are a commodity which only very rarely has such troubles.

A marked-up photo with commentary is here: 
http://www.flickr.com/photos/8103911@N04/1248686108/

"Lots of little fractures at periphery (inside red ovals) were all 
created while the bolt was still whole...the only way to do this would 
be overtorque: that's what started the failure.  Subsequently, a bending 
fatigue fracture progressed from the big red arrow upwards. The bolt was 
in compression on the TOP and in tension at the BOTTOM, and the crack 
propagated in steps of varying intensity, with each &quot;stopping 
point&quot; indicated by a &quot;beach mark&quot;, some of which are 
pointed out by black arrows. Near the end, the steps are very small and 
they are so bunched that I've just put a black oval there. Final 
fracture (near the top of the picture) was accompanied by significant 
bending. The &quot;rough&quot; triangle at the upper right (near 2-3 
o'clock) suggests good toughness, but I'd consider that preliminary 
until it was under a better microscope."

Peace. -W

************************************
Wade Bartlett, PE
Mechanical Forensics Eng'g Svcs, LLC
179 Cross Road
Rochester NH 03867
603-332-3267
http://mfes.com
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