Seven titainum frame failure near bottom bracket

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Seven titanium frame, seat tube and down tubes broken where they meet the bottom bracket shell.

From http://sub20olh.blogspot.com/2008/06/very-sad-day.html as of 2008/07/02.

  

Ridden by 90+ kgf rider 10-15,000 km/yr for about 7 years in hilly terrain.

Rider reproted a "click" from the bottom bracket area.

The root cause of the failure is unclear. Some similar failures have been attributed to tubes not welded inside the junction, 'fixed' by manufacturing so one tube is welded completely to the bottom bracket shell, then install and weld the other tube.

It seems likely it was the seat tube that broke first, then the crack spread to the down tube. The down tube takes more total load, but is larger and is largely under torsion loads which are spread around its periphery. The seat tube takes mostly side-to-side bending loads, which are thus concentrated on the two sides, and for bicycles with large down tubes has extra load from the down tube entering the seat tube weld HAZ.

It is common to use a gusset from the seat tube to the bottom bracket.

See also FAIL-085.html.