John, it's obvious you know what you're talking about. I have adjusted the 1.22 diameter so that it "goes red" on FEA the same time that the snap ring grooves and the minor dia of splines do. The shaft will still torsion twist at the 1.22 dia a few degrees at max torque. I may actually adjust it to 1.20 dia to make sure it is the weak link.
Even then, 1.20" is substantially stronger than 1.062".
Vaughn Winters is convinced that the material change alone has solved the problem. He said that nobody has broken one yet. My math says the problem is not solved. We can put down way more torque than anybody else in low gear. Even with these changes, I will have to limit low gear boost to 11 psi to keep crankshaft torque under 1300ft/lbs of torque as it will be multiplied by 2.48.
Winters will not be paying the $5000 plus bill to get our car and team back in forth to the salt never mind the heartbreak and labor of fixing it or worse yet a spoiled back up run.
I offered to pay for a run of these shafts to be made with an increased torsion section and an increased relieved section behind the QC splines (increased to minor diameter). They couldn't be bothered. We are in the meat of race preparation season now so they are crazy busy. I was a little upset that they would not share the spline information so I could have someone else make them. It's not a big deal as I can reverse engineer them but why make it hard for me. It's not like I'm not buying their stuff.
Rob,
Per your previous post, Winters said: "Vaughn Winters is convinced that the material change alone has solved the problem. He said that nobody has broken one yet. My math says the problem is not solved. " From this I would assume that Winters changed from some previous material ( my guess would be 4340 aircraft quality steel) to 300M. 300M is nothing more than a very high quality 4340 (it does have some additional vanadium and silicon) that has been double and sometimes triple vacuum remelted in an inert atmosphere. The strength properties are effectively the same as 4340, the advantage that 300 M brings is its purity provides extended fatigue life. which allows it to be used in smaller sections, i.e. lighter, at higher hardness levels and still provide sufficient strength and fatigue life. I my way of thinking Winters has not done a sufficient job of properly applying this material. Normal use of 300M is at tensile strength levels of around 280,000 psi which is provided by hardness of around Rc 50-52. At Rc 30 the tensile strength is approx. 140,000 psi so it is possible to literally double the strength of the shaft at the same dimensions by merely doing a correct heat treat and draw. Obviously the advantage of going to a higher heat treat it that you do not have to increase the shaft diameter to get sufficient strength and you will still have the same amount of shock attenuation (shaft wind up) as the standard shaft.
Heat treat should be done in a vacuum or inert atmosphere oven and the shaft must be hung vertically. You must use a very reparable heat treat facility with experience with 300M.
I would highly suggest you contact some one like Latrobe Steel, Latrobe,PA and discuss your application and also what they would suggest for the proper heat treat and which one of their several 300M steels they would recommend for your application.
The other option if you are not going to heat treat and just go to the increased diameter would be to use aircraft quality (vacuum melted) 4340, normalized, which will have the same tensile and yield strengths as 300M but be considerably less expensive.
Rex
Rob,
After meeting you @ the PRI show and inspecting the broken shaft, my opinion about the failure remains the same. I still think that the shaft was overloaded and failed due to "machining" of the OD in the small center section. Without any inspection instruments, it appeared to my naked eye that the failure precipitated on the coarsely machined outer surface, a surface so coarsely machined, that it appeared to be "finely threaded". I suggested at the time that you consider a surface treatment such as surface "micro-polishing", in an effort to remove surface defects on any replacement part. My opinion remains the same. In the photo you posted, there is an obvious defect at the surface. I suspect that is where the failure originated.
After reading through this thread, I have some further thoughts. Some of this is, to me at least, stating the obvious.
1/ Trust your own judgment and engineering. I think you are in the best position to evaluate a solution using the recommendations of specialists.
2/ You might want to have the remains of the old shaft analyzed by a good metallurgist, even if Winters has given you a specification.
That would:
A/ Define the failure.
B/ Determine the material.
C/ Determine the material condition/heat treat. In my opinion these are important issues that need resolution, and the cost would be small.
3/ A material or size change alone will not solve the issue. It needs to be a comprehensive solution that includes heat treatment and surface finishing, as Rex has
suggested.
4/ Increased shaft strength will probably reveal the next weak link, as many have pointed out. It may be impossible to predict where that next failure will occur, unless
some part is "designed" to fail. I'm uncertain of whether designing a "failure link" is a good idea for your vehicle. It would be paramount to retain control of the vehicle
in the event of a drive train failure, again stating the obvious.
5/ Since the failure of this part requires so much "down time" for repairs, you are no doubt analyzing a solution that would prevent a repeat.
6/ It is always disappointing when a supplier becomes "uncooperative". But it is the nature of this business.
I hope you can at least get some "moral support" from the rest of us following along.
Mark