Rear axle broke right inside cover

[Shawn T. W]

I calculated it. A mechanical engineer would see that the axle is 30.7% weaker compared to full material (bending forces, torsion calculation I leave to yourself), not considering notch effects etc. .

While I'm not doubting you ... May I suggest that Kubota may have taken that into consideration, and just used a stronger alloy?

Let's say they used "alloy A123" at that diameter it had a strength off "100 Lbs" and then bored the hole for whatever reason in it and now it's only good for "70 Lbs" ... So they chose a alloy "B456" that at that diameter was good for "200 Lbs"! Then bored the hole in it, so while weaker than before the boring, it still was good for "140 Lbs"

?

A few broken axles, even on a"new" tractor, which this wasn't ... Compared to the hundreds of thousands of tractors that haven't broken an axle yet, is nothing to have a "class action lawsuit" about, especially since they are different models!

 

[McMXi]

In this day and age these types of components are reliably designed using FEA and different combinations of geometry, materials, and loading conditions. Its not infallkble but it does not make basic mistakes.

Dan

Shear, bending and buckling stresses in shafts are well understood and have been for many, many, many decades. Material selection and heat treatment are also well understood. Many parts aren't designed using FEA, even today, but rather are based on empirical data collected over decades in combination with known best practices.

As for FEA, it's only as good as the inputs so mistakes can and are made, and given the cost of software and paying engineers to use it, it's typically used for more elaborate modelling of parts with complex geometry and loads. Even then, parts are tested empirically to validate the model.

 

[TheOldHokie]

Shear, bending and buckling stresses in shafts are well understood and have been for many, many, many decades. Material selection and heat treatment are also well understood. Many parts aren't designed using FEA, even today, but rather are based on empirical data collected over decades in combination with known best practices.

As for FEA, it's only as good as the inputs so mistakes can and are made, and given the cost of software and paying engineers to use it, it's typically used for more elaborate modelling of parts with complex geometry and loads. Even then, parts are tested empirically to validate the model.

My experience was seversl decades ago and involved bigger and more complicated systems where FEA was used on everything and took hours of super computer time to run the models.

I dont know what tractor designers do today but my ancient (2008) copy of Autocad Mechanical has 2D FEA modeling built in and and wiĺl model any shaft I can draw in a matter of minutes.. Why would Kubota engineers pass that up?

Dan

 

[McMXi]

My experience was seversl decade ago and involved bigger and more complicated systems wher FEA was used on everything and took hours of super cimputer time to run the models.

I dont know what tractor designers do today but my ancient (2008) copy of Autocad Mechanical has 2D FEA modeling built in and and wiĺl model any shaft I can draw in a matter of minutes.. Why would Kubota engineers pass that up?

Dan

There's no doubt that Kubota engineers use FEA, but I would guess that they use it on far more complex parts rather than relatively simple parts that haven't changed much over the last 50 years or more. Talking of Kubota engineers, I had three of them (from Japan) come to my house last winter along with three product managers out of Texas. It was a cold day but they were excited to see an MX and M in action.

 

[whitetiger]

The thread is title a Broken Axle which happens of several models, I was simply sharing what I have been seeing going on the Topic of Broken Axle...

It's not my suit, But i'm watching it.

Several machine shops verified it as a design flaw, But you do not have to be a mechanical engineer to see it.

Still waiting for "Who verified the break as a design flaw??????