crack orientation in a shaft, rotating bending+static torque 1

[tamagraine]

I'm looking for a way to predict the crack propagation direction in a shaft with static torque and a rotating bending moment.

Thanks

 

[swall]

This is a gross oversimplification, but the fatigue crack front (emanating from a single origin) will tend to shift towards the direction of shaft rotation. This is most true for a situation where you have a low nominal stress and a low stress concentration.With high nominal stress, you will get multiple origins, and you won't see a noticeable shift.

 

[desertfox]

Hi tamagraine

Fatigue cracks always grow under tensile stresses.If I were you I would start by working out my maximum principle stresses using a Mohr circle and there orientation on your shaft, once you have the orientation and size of the maxium principle stress then you can start to consider fatigue.
Fatigue cracks grow at 90 degrees to the tensile stress.

hope this helps

regards Desertfox

 

[metman]

What is the geometry at the connections (end constraints). Collars, splines, woodruff key seats, std rectangular keyseats using std square key stock, flex joints, other?

For example: if you have splines, you have logitudinal bending plus spline tooth bending plus spline root concentration plus torsional stress to enter into your Mohr's circle analysis.