Re: Broke another spoke. Fix or get new wheel?

Joe Riel wrote:
jim beam <nospam@xxxxxxxxxxx> writes:


the part that's hard to understand is why [...]
witchcraft like spoke
squeezing is so readily accepted by non-engineers as a fatigue
eliminator in a material that fundamentally can't have such a property
because it doesn't exhibit any known endurance limit.


What does endurance limit have to do with it? Are you saying that no
form of stress relief (say annealing) can affect the fatigue
resistance of stainless-steel? Or just that mechanical
"stress-relief" (via overload and relaxation) cannot?


no endurance limit means it's impossible to eliminate fatigue. only use of a material /with/ an endurance limit like mild steel, /not/ stainless steel, can do that.

endurance limit is significant also because materials that have that property also exhibit strain aging. and the theory presented in "the book" and as "explained" here many times, relies on deforming the material under this strain aging regime. but stainless spokes don't strain age. continued deformation if the material is not strain aging simply increases dislocation density, a known factor in fatigue nucleation.

regarding the efficacy of mechanical stress relief, we have several problems, not least of which is the fact that we're dealing with highly worked cold drawn steel wire that /relies/ on its deformation history for its strength. yes, it can be mechanically stress relieved to some extent, but the strain necessary to cause that is typically cited at being in the 1% - 2% range /immediately after/ initial deformation - waiting a few hours or days, before performing further work adds to internal stress, it doesn't mitigate it. besides, we're not able to cause strain of that magnitude with a manual squeeze [and we wouldn't want it anyway given the permanent spoke elongation it would cause] and we're performing the act weeks or months after initial formation.

bottom line practical reality; electron microscopy of real world fatigue fracture surfaces show cracks always initiate at surface defects or inclusions. mitigation of these initiators, inclusions by vacuum degassing and by attention to surface finish quality, have a significant effect on fatigue life. some vague unquantifiable hand waving from a guy whose book contains multiple fundamental errors and that alleges as his sole "evidence" to have 300,000 miles on a pair of wheels where hubs, rims and [after much probing reluctantly admits] spokes have all been replaced, does not.
.

Relevant Pages

  • Ebooks - Database
    ... 775 Damage in Composite Materials* ... 787 Composite Materials: Testing and Design (6th ... 798 Probabilistic Fracture Mechanics and Fatigue ... 813 Long–Term Behavior of Composites* ...
    (sci.med.cardiology)
  • Ebooks - Database
    ... 775 Damage in Composite Materials* ... 787 Composite Materials: Testing and Design (6th ... 798 Probabilistic Fracture Mechanics and Fatigue ... 813 Long–Term Behavior of Composites* ...
    (sci.med.nutrition)
  • Re: New hub from Shimano
    ... concentration at the fatigue crack could cause failure. ... Since you content your wheel with missing spokes is a functional ... I want proof that the wheel with missing spoke will/will not ... Does Jobst ...
    (rec.bicycles.tech)
  • Re: Spokes 102, straight and butted spokes
    ... Fatigue is normally demonstrated by the spoke breaking in the ... Embedded stress in the spoke ... elbow and at the nipple from fabrication and installation added to the ...
    (rec.bicycles.tech)
  • Re: Aluminum - The Middle Child of Frame Materials?
    ... As does every bicycle frame, ... fatigue limit is certainly of academic interest, ... In addition, even for materials with a fatigue limit, it only applies ... > Anecdotal evidence cannot change metallurgy. ...
    (rec.bicycles.tech)
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