Machinery and Localized Stresses

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MolaKule

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A basic rod and disk are forged and machined to make a wheel axle, with the rod at a right angle to the disk. The other end of the rod is splined inside the differential housing.

The disk is further machined and tapped to make a wheel hub.

It was later found that cracks were occurring where the rod meets the disk.


Supply the missing word:

A ___________ geometry at the rod-disk interface would have prevented cracks from forming.



Open to all.
 
Not sure of the exact nomenclature you're looking for but you need a radiused transition at that location in order to prevent a localized stress riser.

Also, depending on the raw material being forged and the post forge quenching process, a tempering or solution annealing heat treatment will also aid in preventing cracking of the finished product.
 
I would like to amend my answer to concave radius. Reading the question again, I think that fits the answer for geometry better than the term fillet.
 
Lots of good responses and thanks for contributing your answers.

See the PDF file below, Page 8, bottom illustration.
Stress Concentrations See Page 8

Stress concentration is a problem of load-bearing mechanical parts, which is reduced by employing fillets in areas of expected high stress. The fillets distribute the stress over a broader area and effectively make the parts more durable and capable of bearing larger loads.

So any answer that gave a "radius" or a "fillet" gets a definite thumbs up because those types of geometries reduces stress concentrations!
thumbsup2.gif


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.
 
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