Still, a human has to put in the load cases. This is where things can go wrong.
That was my real-world example which is a complex problem to solve due to myriad variables. You have to understand the types of forces, where they act, when they act, how they're affected by other forces and so on. Lots of assumptions have to be made and that's why at the end of the day it's empirical data from actual testing that is required. FEA is just anther tool in the tool box.Still, a human has to put in the load cases. This is where things can go wrong.
I found interesting what worst case load is; a friend of mine had to calculate a rear axle differential at university. Highest strain, as he explained to me, was when one wheel was spinning freely at full revs and then the vehicle falling down after a jump on very good grip asphalt. Not sure if this is applicable to tractors though
Any process including pen and paper is subject to human error and the same sort of misanalysis in your example. Modeling with FEA isnt infallible but it lets a designer do a far more comprehensive analysis. In the long run that produces more reliable outcomesStill, a human has to put in the load cases. This is where things can go wrong.
I found interesting what worst case load is; a friend of mine had to calculate a rear axle differential at university. Highest strain, as he explained to me, was when one wheel was spinning freely at full revs and then the vehicle falling down after a jump on very good grip asphalt. Not sure if this is applicable to tractors though
Many of the bigger engineering companies such as Northrup Grumman use CATiA but not sure what is common in the automotive industries. I'll have to ask my boss what John Deere uses. He was in charge of hundreds of engineers before he left last year.
Back in the mid-70's the family business was designing and installing fire protection systems. Grids of pipe, sometimes involving hundreds of nodes, required complex iterative and recursive calculations with a slide rule, but an experienced engineer could save a lot of time and effort by starting off somewhere in the middle -- an educated guess -- and refining from there with a slide rule (special Hazen-Williams scales -- not off-the-shelf), laboriously jotting results on a paper forerunner which lent it's name to the electronic "spreadsheet" of today. A good engineer's guess would often be within 5% of the final results.And to the moon, appr. 300000km away, 24 bit mantissa floating point should be good enough to get you back to within a mile or so. Ever seen the Apollo computers?
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There are a lot of unanswered questions and so far 8 failures out of how nany units in the field?Back in the mid-70's the family business was designing and installing fire protection systems. Grids of pipe, sometimes involving hundreds of nodes, required complex iterative and recursive calculations with a slide rule, but an experienced engineer could save a lot of time and effort by starting off somewhere in the middle -- an educated guess -- and refining from there with a slide rule (special Hazen-Williams scales -- not off-the-shelf), laboriously jotting results on a paper forerunner which lent it's name to the electronic "spreadsheet" of today. A good engineer's guess would often be within 5% of the final results.
We were approached by a salesman selling shared time on their engineering mainframe (NCR if memory serves, but that might have just been the hardware not the service). He boasted that their platform could handle any engineering problem because it put Man on the moon. After a few attempts to demonstrate, they had to give up and admit their system couldn't handle the complexity.
Flash forward 15 years: PCs were becoming commonplace and DOS based software could handle the complexity and produce acceptable results in less time. Nowadays it's even built right in to the CAD software with near-instant results on the fly as a designer alters a layout.
I still have my hydraulics slide-rule. And a copy of the early software. But I no longer have a computer that can actually run that software -- and to be honest, only a vague recollection of how to work the slide rule.
Back to the topic at hand: A solid bar is stronger than a pipe of the same diameter, but a pipe is stronger than a solid bar of the same weight. in other words, much of the strength is in the perimeter, not the core. Boring that hole and the size of the bore is a design choice. It only becomes a design flaw if it fails to meet the specifications.
Kubota engineers have no control over customer choices. Farmer John bouncing down the field with a 600 lb load on a tractor rated to carry, say, a 400lb attachment does not make axle failure a design flaw.
I'm not saying that's what happened, just pointing out the possibility. I think proving to a jury that none of the tractors in question were ever abused is a tough row to hoe (sorry, couldn't resist
Is that your official ID? We can't seem ti get something that basic from the gentleman that started this discussion
So +/- 5%?
I would start by assuming 100% available engine stall torque was being applied to the transmission then multiply by the total gear ratio. That's going to be the limiting factor.
I think for calculation a higher torque than engine maximum torque would be used. When driving into a block the inertia of the engine with flywheel would create a much higher torque. Same applies when wheel spinning at full revs and suddenly getting good grip again.
This applies to off-roading in a Jeep for example more than a tractor. A V8 swap, big, heavy tires and lots of rpm in combination with being airborne with a sudden application of torque when the tire makes contact with the ground is the number one reason for u-joint and axle failures. Add in bead locks and the chance of failure increases. I have the 4.0L inline 6 with sensible 33" tires so very little chance of a problem. 25 years of off-roading in my Jeep TJ and have never broken anything.
