Rotational Bending Fatigue:
This shaft broke clean at a
90° angle to its axis of rotation. The likely cause is a
misalignment between the shaft and its power source that makes the
shaft flex slightly with each revolution.
Fractures like this
occur in areas of concentrated stress that is at least perpendicular
to the shaft axis.
The marks shown on this shaft indicate that it
was unevenly loaded or unbalanced. The smoother area near the
edge is were the fracture started. The curved ripples get
gradually courser, with a rough, shell-like spot where the shaft