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Ed, do you have any specs for 4335V Mod? I'm looking online but not finding much. The C350 Maraging gave us 35% more torque before failure over 4140, but it was brittle torsion break with barely any twist at all. And that was heat treating below peak UTS properties so we got more fracture...

We already manufactured the design (geometry is fixed) with C350 with a large improvement in Torque capability (compared to 4140). The question is, would C300 possibly be an improvement over C350 even though it has lower strength (YS and UTS)? Because there are stress concentrations and flaws...

Is there a general guideline for the application of ultra-high strength alloys with low fracture toughness and ductility? We are comparing the use of Maraging C300 vs C350 in a splined shaft. Maraging's low distortion in HT is a huge plus for us. C300 looks like the best blend of high yield...

Finally got a chance to test the new C350 parts. Gave us about 35% more torque capability in failure testing over 4140. Haven't done fatigue tests yet. Would love to get a hold of some Aermet or Ferrium alloys.

@EdStainless What material did you end up using for those shafts if you don't mind me asking? Was it the 4335 Vmod you mentioned? May end up being that a lower strength but tougher alloy will perform better than the C350. We'll have to test and find out. The splines have been shot peened in...

The load is fully reversing (bi-directional). Those are some really interesting suggestions about pre-stressing the part or shot peening under load - never heard of that before. On FEA, the stress was reduced without the center bored out. Maybe a certain diameter will show an improvement...

The existing design works at our current loads. We are looking to drop-in a higher performing material so we can raise the input torque. It is a "legacy" design that we can't modify any further. Torque is applied gradually with minimal shock loading. Splines have not contributed to failure...

@EdStainless The transition is as long as possible (mating parts dictate the maximum size). One thing is, now that it is an elliptical transition, the machining toolpaths will be more prominent than using a standard radiused corner bullnose endmill... It will be blended by hand to eliminate...

Based on SN curves, Ferrium C61 and S54 look like they're almost as good as it gets. I found this previously, thought it was a nice toughness comparison of high strength materials: https://www.carpentertechnology.com/blog/toughness-index-for-alloy-comparisons

@mfgenggear So, focus on material fatigue strength at 1E4 cycles? C350 has a relatively low fatigue life - 110 ksi @ 1E7 cycles I believe. The part has been analyzed with FEA, but it fails at higher loads than calculated by hand and FEA. Maybe it is strengthening past it's yield point?

The failure mode is always ductile torsion failure right at the radius where the input to the shaft steps up to meet the splines. I should add that this is not a typical "shaft" - it's used in a static loading application. 0 RPM. 4140 has acceptable service life, but at lower torque than is...

We're looking to maximize the amount of torque we can apply to a short splined shaft (~10,000 reversing cycles). We have been using 4140 previously. What would be the most important material property to achieve this? We are looking at Aermet 100, Ferrium C61, MP35N... Seems 300M is recommended...

For anybody interested, I finally got around to machining the piston on a harbor freight lathe. I posted the pictures here: https://www.practicalmachinist.com/forum/threads/line-boring-metal-3d-print.408998/page-4 Went to get advice from that forum and ended up getting the usual, BAHHHH it's...

It's like the new "torque vs HP" argument - although I think that one's been resolved 😆

Yes, a steady state dyno won't show increases in BRAKE power because the reduced reciprocating inertia isn't being accelerated. But I don't see why this matters. That extra initial 1.5 kW (2hp) does have an effect during acceleration. The engine will be used dynamically on a dirt bike, not...

I think we all get that in theory, reciprocating the piston, wrist pin, and connecting rod is net-zero work done - this is due to equal amounts of kinetic energy being given to and received back from the crank assembly over 360 degrees of rotation. This does not seem to mean that there is no...

You don't need a trendline or integration to see that the lighter reciprocating components have higher average power on that chart. The thread is not about how much power is freed up with lower piston mass, but is there more power with a lighter piston - the answer is YES, lighter pistons do...

You realize we're referencing this graph, right? There's no time spent below zero, and if you did find the area under the blue curve, it would be higher than the red curve. Meaning, the lighter weight reciprocating components make more power, faster, than the heavier OEM Honda parts on average...

If you tortured that data any more, it would confess to anything! That 200 rpm higher likely did have some effect on the power gains - it also confirms my suspicions that lower reciprocating mass would allow the engine to make power faster: So, the blue line (light weight con rod and wrist...

Look closely 3DDave, you might've missed another observation... The engine with less reciprocating mass has higher peak power AND lower dips in power (during acceleration obviously).