yet another residual stress redux

[jim beam]

points that appear clear:

1. yielding can reduce residual stress. [see point i. below.]

points that are not:

i. that further yielding can increase residual stress. as one local
region yields and decreases, the next in line can increase. and this is
time dependent.

ii. that residual stress is the cause of spoke fatigue. residual
stress profiles for bent spokes do not match with those observed for
fatigue initiation, i.e. it should be that fatigue initiates at regions
of high tensile residual stress. instead, initiation is seen to
initiate at a points of low tensile or even compressive residual stress.

iii. that points with higher local residual stress are not bearing more
of any applied stress than the rest of the material. [that's
particularly interesting!]

iv. that stainless spoke steel does not have strain aging region of its
stress/strain graph so it does not strain below its yield point - as
would mild steel.

v. that allusions to local "micron" yielding betray ignorance of
dislocations, their local strain fields, and the effects of high
dislocation densities in highly cold worked materials - like spoke wire.

bottom line:

wheel builds benefit from the process of "stress relief" because it
seats everything properly, keeps spokes from going slack and
correspondingly keeps wheels true in service. but there ain't nothing
magical about it, certainly not regarding fatigue. the best way to
avoid spoke fatigue is to use straight pull spokes. next best thing is
to use quality material in spoke manufacture. bringing up third place
is ensuring spokes don't go slack in service thereby increasing their
bending cycle.