DT Swiss straight gauge 2mm spoke. Velocity deep-V rim. Rear wheel, single-speed disk hub, so spoke tension is essentially the same on both sides. The spoke came just far enough through the nipple that I could cut a slot with a hacksaw and back the spoke out. The spoke was about three full turns from bottoming out the nipple. These pictures are of the piece of the spoke that was in the nipple.
Spokes break at the elbow. Everybody knows that. Why did this spoke break in the nipple? Manufacturing defect? Damage during wheel building (by me)? Some random damage from falling into one of Seattle's piano-swallowing chuckholes?
From the pictures, it looks like a fatigue failure from some damage near the end of threading on the spoke.
I took these pictures with the Lytro camera Aki gave me for Christmas. Not really a useful camera for portraits, but actually pretty good as a macro camera. Being able to take pictures with multiple, very thin focal planes is pretty much ideal for this kind of picture.
Thanks to Chris Heg for insights into what fatigue looks like.