Crank Failure At Square Taper

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Crank failed along face of square taper. Sugino Impel.

     

This failure is interesting in part because the failure is in the middle of a face rather than a corner. The center of the face has lower loads and thicker material, so is not a common failure site. This failure is also interesting because of the "step" shape in the failure. Failures often follow a curved path do not usually have such a step. FInally, this failure is interesting because the darkened area (which indicates the start of the failure) is quite small, suggesting the material was close to its load limit in normal service, even though the load tends to be lowest in the center of the face, where it broke.

Service history unknown. The crank shows a matte finish that suggests corrosion; it was in service in an area that gets snow, and may get salted streets.

The Sugino Impel is a relatively cheap cast-aluminum crank, made across a range of years — probably from the mid-1990's and maybe earlier.