I thought-think-was taught that steel has a load limit below which it can withstand a theoretically infinite number of cycles (flexes), but that aluminum has no such thing. Permanent bending load limit is the Yield strength. Yield strength is the force required to bend a material to the point where it doesn't snap back all straight again. Spring steel (used in springs) has a high yield strength; paperclip steel (used in ________) is the opposite.
On this topic, vaguely: I was at a materials testing facility two days ago, and remember the hooplah I set off when I suggested that maybe modulus varies with UTS (sorry for the jargon, but I'm too tired to explain). I got so much "correction" mail that I was forced into a slightly insincere recantation. Well...the head guy at this place was saying that a crank arm made of X would be stiffer than one of idental design made of Y, and so I said politely, "Oh really?" and he said of course, and I said what about modulus's independence of UTS? and he said no way, we've done this test a zillion times, and then showed me a tech insider's website that listed diff moduli for two alum alloys of diff strengths. I'm just here to cause trouble. I won't respond to an discussions on this, on account of I've beenthere done that...and I will always play my "two year diploma, what kind of fool listens to me?" card, if pressed. On Wednesday, March 20, 2013 8:08:03 PM UTC+8, Ron Mc wrote: > > great photo Philip. > I put 30 years on a GB Maes bend. > Jim, as far as the "cycle and S-N curve" goes, only cycles that are 70% or > greater of the permanent bending load count. Everything below that is > within the endurance limit. > > On Monday, March 18, 2013 6:15:07 PM UTC-5, Philip Williamson wrote: >> >> So aluminum bars sag before breaking? I only ask, because I'm a 250 lb >> guy using 25 year old WTB offroad drops on a fixed gear bike... offroad >> sometimes. >> http://www.flickr.com/photos/philipwilliamson/8547042814/ >> >> Philip >> www.biketinker.com >> >> On Monday, March 18, 2013 2:49:21 PM UTC-7, William wrote: >>> >>> Jim >>> >>> I think that's what I said. The cycle life is determined by how it's >>> loaded, and is captured on an S-N curve. You are correct that a tiny load >>> is at the ultra-long life end of the S-N curve. If the S-N curve tells us >>> that the cycle life is 50million cycles, and if you do 100,000 cycles per >>> year, then Bob's your uncle, it's 500 years of life. >>> >>> For all us (relatively) normal people, we have no clue what cycle we are >>> on. So we are left with judgement. Like "I weigh 170, and I don't reef on >>> my bars too hard, so I think I'll worry after 20 years or when I notice my >>> bars sagging, whichever comes first". Someone else may decide "I weigh >>> 110, and it's a path bike. I'll never replace bars out of fear". Finally, >>> another person might say "I weigh 240 and sprint to every single city limit >>> sign, and climb out of the saddle on my fixie on every hill. 5 years >>> sounds like a good plan" >>> >>> The thing that shocks me is how often I see people using bars that are >>> visibly sagging. The tops of the handlebars drooping downward, and the >>> hooks no longer parallel. That's scary. >>> >>> On Monday, March 18, 2013 2:21:42 PM UTC-7, Jim Thill - Hiawatha Cyclery >>> wrote: >>>> >>>> The number of years is irrelevant. Some skinny person who rides upright >>>> and gingerly on smooth roads 5 miles per week is going to get 500 years >>>> out >>>> of the bar. >>>> >>>> On Monday, March 18, 2013 4:10:09 PM UTC-5, William wrote: >>>>> >>>>> You pose two questions: >>>>> >>>>> 1. Anyone know anything about aluminum bar life? >>>>> >>>>> I know a little bit about fatigue life of materials. Any metal that >>>>> is cyclicly loaded will fatigue and fail eventually. Just about every >>>>> metal has a similar look to it on an S-N curve (Wikipedia that for an >>>>> explanation). The take home is that almost everything eventually wears >>>>> out >>>>> and fails. It's just a matter of when. Steel is a notable exception. >>>>> If >>>>> steel is cyclicly loaded at a low enough Stress, then it essentially >>>>> never >>>>> fatigues. Incredible stuff. Anyway, Aluminum does fatigue and >>>>> fail...eventually. When? It depends on how much you are stressing it >>>>> and >>>>> how many cycles you put on it daily. >>>>> >>>>> 2. Do I need to throw away the old used set of bars I have? >>>>> >>>>> Nitto is going to say what they say because they generate these S-N >>>>> curves and test the heck out of their products. They do see parts fail >>>>> after lots of cycles, and what they recommend is going to be >>>>> conservative. >>>>> When Nitto says 5 years, I think 20. I do not think 50 years. You >>>>> don't >>>>> know when your bars are going to fail unless you know REALLY accurately >>>>> what the loading history of your bars is. In other words, you have no >>>>> idea. Anybody who decides to buy and ride used equipment assumes some >>>>> additional risk because you just don't know for sure what the history is. >>>>> If you think you would feel a lot more comfortable replacing your >>>>> handlebars, then I'd say do it. >>>>> >>>>> On Monday, March 18, 2013 12:50:43 PM UTC-7, Michael wrote: >>>>>> >>>>>> In a cool interview with Nitto exec Mr. Yoshikawa, Grant asks this >>>>>> question. Nitto exec leaves it up to consumer. So I was wondering if >>>>>> anything to be concerned about. Anyone know anything about aluminum bar >>>>>> life? >>>>>> Do I need to throw away the old used set of bars I have? Don't want >>>>>> any accidents. >>>>> >>>>> -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. 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