capo-hardening/string breakage

[Fred Sturm]

There seems to be some concern that a too-hard capo causes string
breakage. Is there real, solid evidence for this? Not just anecdotal
stuff. My take on string breakage at the capo is that the causes are, in
order of importance:
1) Hard playing - this definitely includes playing during tuning,
especially hard blows, _especially_ blows so hard that they require the
use of a "pounder" (my own stabilization technique relies mostly on
hammer manipulation, together with what I view as "reasonably" sharp
blows. I get good stability, and have very minor string breakage
problems. My own anecdotal evidence <g>)
2) Design issues, principally sharpness of deflection angle and radius
of capo.
3) Friction, which includes lubricity or lack thereof as well as
development of corrosion on either string or capo or both. As well as
that form of bonding whose name escapes me - more or less a
mechanical/molecular phenomenon.
and only lastly,
4) Hardness of material or material surface.
	Seems to me that the difference in "give" between a relatively soft
material, like brass agraffes, and a relatively hard surface, like
hardened cast iron capo, can't really be that great. I am no
metallurgist, but my understanding is that the basic difference between
a harder metal surface and a softer one is that the softer one will
deform more easily. It's not like it is "springier," and so absorbing
more of the impact than a hard surface would, hence resulting in less
damage to the string. And the deformity only goes so far, within the
parameters of materials used as string terminations. Why would the
miniscule amount of deformity caused during individual hammer blows
protect the wire to any significant degree?
	Is my reasoning faulty? Is there really some metallurgical reason a
harder surface would result in more string breakage? (Within the range
of hardnesses we are dealing with).

Fred Sturm
University of New Mexico