hardening of 4340 for ultimate strength
hardening of 4340 for ultimate strength
(OP)
Hello, I'm designing a flywheel for storage of 7 MJ. Currently I'm achieving that spinning at 14500 rpm a 500mm diameter (20 inch) x 120mm (4.7 inch) 4340 cylinder.
I'm assuming I can harden it to 2020 MPa (293000 ksi) ultimate strength according to this matweb datasheet:
http ://www.mat web.com/se arch/DataS heet.aspx? MatGUID=b5 fe87c8cdde 4431b62ad9 90d4f2042c
FEA shows I'm working with a factor of safety of 2.6.
My questions:
- Is that ultimate strenght value realistically achievable?
- Is my factor of safety adequate?
Thank you.
I'm assuming I can harden it to 2020 MPa (293000 ksi) ultimate strength according to this matweb datasheet:
http
FEA shows I'm working with a factor of safety of 2.6.
My questions:
- Is that ultimate strenght value realistically achievable?
- Is my factor of safety adequate?
Thank you.





RE: hardening of 4340 for ultimate strength
You should be designing to the yield strength and/or shear strength properties in tension with a suitable factor of safety against plastic deformation, versus using ultimate tensile strength.
I would say 2.5 for a design safety factor for flywheel application (rotating application) is suitable.
Will these flywheels be in concrete vaults underground?
RE: hardening of 4340 for ultimate strength
Yes, actually I'm desiging against yeld strength, I only copied ultimate strength as an example.
My idea for containment would be encasing it in a 25mm (1 inch) thick steel cylinder, above ground, a single hole in one side for the axis connecting to an eddy current clutch for energy discharge. Would you consider that containment inadequate?
Thanks.
RE: hardening of 4340 for ultimate strength
Yes. I wish I could provide more technical information but I was involved with a recent evaluation of a flywheel energy storage system.
RE: hardening of 4340 for ultimate strength
Using 4340 alloy steel hardened to 293ksi Ftu (Rc 54) is probably overly optimistic. Take a look at the published data for aircraft quality vacuum melt 4340 (AMS 6414) here:
http://latrobesteel.com/technical_datasheets.cfm
This manufacturer gives a recommendation for oil quench and temper at 400degF to achieve max tensile properties of 276ksi Ftu/222ksi Fty/11% elong.
As for a FS of 2.6 on your analysis, the appropriate FS should be that defined by whatever design or regulatory standard is covering your flywheel's installation. And does your analysis show a positive margin based on that FS? A FS of 2.6 is fairly conservative if your analysis is done carefully. A thorough stress analysis of a high speed flywheel structure must take into account all of the combined dynamic loads, along with the appropriate Kt factors.
Hope that helps.
Terry
RE: hardening of 4340 for ultimate strength
RE: hardening of 4340 for ultimate strength
"My idea for containment would be encasing it in a 25mm (1 inch) thick steel cylinder, above ground,..........."
probably not
http:
http:
Dan T
RE: hardening of 4340 for ultimate strength
Aero engine manufacturers have a heavy load to bear when it comes to "containment" of rotating disc & blades to prevent catastrophic airframe damage. Debris is not permitted to penetrate fuselages nor wing/empennage structure. Debris can spew-out forward or aft (if it has a high probability of not striking the airframe)... so only partial containment is necessary. The worst offenders are the large fan blades and discs. Imbalance loading after a failure must also be dealt with... along with the potential for fire/explosion, searing-hot-air leaks and electrical arcing/sparking. These problems are NOT trivial and require more than intuition and R-O-Ts to solve.
I recently ran across the following graphic demonstrations of tire inflation safety cages for aircraft tire/wheel Assys. The problem of containment is just as severe and non-intuitive... with the complicating factor of the instantaneous expansion of the contained pressurized air [nitrogen preferred]. The videos on the following website over-inflate aircraft tires deliberately, to test various protective cage designs. You think this is a simple problem, yet existing cage designs failed miserably [IE: spectacularly/catastrophically]. Click on the corresponding image for a detailed short video.
http://www.alberthaviation.com/TireCageVideos.htm
Regards, Wil Taylor
RE: hardening of 4340 for ultimate strength
I also agree with Tmoose's statement that your protections system will "probably not" be adequate.
The truck tire videos illustrate the amount of energy contained within a volume of compressed air. I suspect that the energy contained within your flywheel to be similarly significant. If your flywheel breaks off a piece from the edge of your wheel, how much energy is that piece containing that is now traveling at 14500 rpm x 3.1416*20 inches (>800 miles per hour if I do my math correctly)? If your wheel breaks into pieces completely ... 1" of steel plate will not contain it.
RE: hardening of 4340 for ultimate strength
RE: hardening of 4340 for ultimate strength
I'm not planning on using vacuum because I don't want to store the energy for any amount of time. Charge it and use it when full, then charge it again.
I figure I can build the flywheel with integrated motor and eletromagnetic clutch for less than half what a 400 hp motor with PLC control will cost me.
It's a hobby project. It's for a glider launch winch. Power is needed for 20 seconds only.
As for containment I might just overbuild it -- if I could be sure it would be safe. 10 inch concrete shell with 1 inch steel wall perhaps? It does have to be above ground so that we can move it.
If I have to destroy a flywheel to test the containment then it won't be cheaper anymore, though.
RE: hardening of 4340 for ultimate strength
RE: hardening of 4340 for ultimate strength
RE: hardening of 4340 for ultimate strength
RE: hardening of 4340 for ultimate strength
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein