furcifer said:
Punx0r said:
Given the context of the discussion which was about the breaking strength of components (and because you didn't specify) I took "designed to hold 1000lbs" as being failure point = ~1001lbs.
I actually said the nominal failure point of a lifting component rated for 10 tonnes with a factor of safety of 5 is 50 tonnes.
No, design is design. Ultimate or nominal is the point at which something breaks. Given we are talking mostly about metal this would be the yield stress or strength.
I"m not sure why you're jumping from statics to dynamics, I suppose you must be more familiar with statics?
"design is design", well thanks for clarifying that... I'm not sure what you're on about any more. I tell you a sample piece of lifting equipment is destructively tested with failure point at 50 tonnes and you reply telling me metal parts fail at the yield point. I'm telling you, the failure point of a part (metal or otherwise) is usually determined by the application/user. It can be yield or it can be UTS. It is when it fails to function as required anymore.
And the distinction between statics and dynamics is what? Just because it's a different chapter in your book doesn't they are non-overlapping domains in the real world. You've jumped from EV drivetrains to frames, to furniture, to bridges. Feel free to tell us which of those applications doesn't see dyanmic loads.
furcifer said:
Punx0r said:
Partly correct. The factor of safety is fudge factor used because the exact loadings, resulting forces, material properties, manfacturing tolerances and environmental and useage characteristics are not precisely known. It attempts to fill the gap between how you think a part will behave and how it actually behaves in the real world. Remember, you must account for (guess[timate] at) known-unkowns as well as unknown-unknowns.
Partly correct. It's not a single factor though, it's a sum. By adding load or torque you don't change material properties, tolerances, environment etc. which are all factors in the overall factor of safety.
Once again I'm struggling to understand what point you are trying to make - I suspect it is, as someone else has said, that you are just arguing for the same of arguing. Want to try being a pedant because I used the word "factor" in "fudge-factor" not in its strictly mathematical sense? Fine, but try not to fall into the trap of being wrong while doing it. A factor of safety is not "a sum", it is, depending on how it's expressed, a number (5) or a ratio (5:1). It is the product of a sum, it is not a sum itself. 2 x 2 = 4 is a sum.
Once again, you are assuming only linear relationships between power/torque and any possible effect on the components. You are wrong.
Please, please, get this into your head: If you have a mass-produced component designed to handle x-load and you place a y-safety factor on it, that does not mean you can allow the user to load the part to x * y. Failures will occur. End of.
furcifer said:
Punx0r said:
There's no rule saying safety factors must be integers and they commonly aren't. Air travel would be more interesting if they were as it'd either be very dangerous or much slower, shorter and more expensive if SF had to be 1 or 2 instead of 1.25 or 1.5.
Correct, my bad. I was trying to decided on what to use to explain it is a multiplicative constant and used integer not thinking about the fact they don't include decimals.
Typically we add up the decimals and round to .5 or a whole number. I've never seen anything 1.25 on it's own, but sure it's possible.
"number" works pretty well to describe it. Use of jargon with the intent of appearing knowledgeable isn't recommended as it often backfires.
Indeed, it is possible. It's apparently used in aerospace. It comes with rigourous design, exhaustive testing and a diligent inspection and maintenance regime in service. All things required to ensure reliable operation when safety factors are low.
furcifer said:
Punx0r said:
That's a negative, ghost-rider. Unless the drivetain was over-specified (badly engineered from a value perspective) in the first place, you cannot increase power through it by any appreciable amount without a noticable increase in failure rate. Automotive OEMs spend a lot of money testing a lot of components to determine what is required to fulfill the design requirements of a vehicle.
It's still within the FoS so you never seen changes to drive train unless it's like a crazy huge difference. Something that's really only possible with ICE's. So you have to take a car with 250hp, boost it to 1000hp and add huge tires before you start bending axles.
Lol, this is just funny now. For one, electric motors have a much better short-term overload capability compared to ICEs. Most motors will take a 5-10x overload for ~10 seconds (long enough to complete a 1/4 mile run). What ICE can do that?
Secondly, no you can't typically take an ICE vehicle with 250HP and safely boost it to 1000HP. Put down the crackpipe.
furcifer said:
Punx0r said:
You seem to think if a gearbox is rated for 200Nm, has a SF of, say 3, and designed to last 200,000 miles that you can run it at 600Nm and expect it to last at least 67,000 miles...
lol, no that's what you've been saying.
OK, you've clearly been hitting the pipe waaaay too hard.
YOU said an OEM manufacturer can take an EV designed for nominal motor output and software enable a ludicrous mode with no changes required to anything. Myself and others in this thread keep trying to tell you all the different ways you are wrong, buit you won't listen. Once again, applying a factor of safety to a component design does not give you an indefinite overload capacity.
furcifer said:
The FoS has nothing to due with longevity. I think you're confusing it with "grade". Usually the grade signifies how a part will wear, whereas the FoS is how strong a part is.
Once again with the pipe... You might as well go and argue the sky isn't blue. Over-spec'ed, over-built equipment lasts longer. Have you ever built an Ebike, or just a regular bicycle?
Tell me this: why does lifting equipment for objects required a 5:1 safety factor but equipment for lifting people requires 10:1?
furcifer said:
Punx0r said:
If anything I'd expect components from yesteryear to typically have had more design margin. Such things tend to get steadily trimmed to reduce cost and weight.
Yes and no. It's counter balanced by changes in materials and production tolerances etc. Your average car today will see many more miles than cars of the past. I doubt if Ford ever dreamed of offering a 100 000 mile warranty. The life span of a K car is probably less than the first oil change interval on some cars today.
Right, so the design life on ye olde cars was a lot less, so any doesn't have to last that long before it's considered to have a large design margin... It's been a long time since you could overheat an ICE without causing serious damage and I don't recall Henry Ford using plastic suspension components. An example of that won't last 100 years even kept in an air-conditioned museum with zero miles on the clock.