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Handlebar failed due to corrusion under handlebar tape.
Bontrager handlebar, circa 2002. Probably made of aluminum. Unknown service history. Failed due to corrosion, corrosion was hidden under handlebar tape.
In upper picture, note the dent on the inside of the right-hand section, close to the bottom of the picture. That is probably a groove to hold the cable under the bar tape, to keep the cable from moving around during use.
Broke without warning while rider was braking. Rider was not injured.
See also FAIL-210.html.