Machinery and Localized Stresses

[Shannow]

Originally Posted by MolaKule
In the casting of the axle, it would have been better to allow a greater thickness of metal at the rod-hub interface and then use a rounded-tip end mill to machine a fillet. After that, proper heat treating could increase the overall strength of the axle.



Typically casting that would not have been the best idea in the first place if expected to avoid fatigue cracking, although forging was mentioned in the OP.

Interestingly you can take a poorly manufactured part (the sharp edge), and do a number of things to improve the fatigue resistance...as mentioned, cutting a radius helps immensely...but you can even cut a round ended notch, reducing the effective diameter of the shaft, which significantly reduces the moment of inertia in bending by the ratio of diameters to the power of 4, but the notch effect more than makes up for it.

Could also pressure roll the fillet, making the finished article have compressive stresses in the radiused areas, and if effectively done, make fatigue cracking virtually impossible to initiate.

 

[MolaKule]

There are any number of casting and processing methods that could improve strength but processing was not the original question. It was simply a sidebar with which to frame the question.

The original question (open to all) centered on the type of geometry needed to reduce localized stresses and that was the fillet, a radiused, transitional geometry.

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