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#51
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The Basics of Wheel Alignment and Wheelbuilding
Weisse Luft wrote in message ... These stainless steels are all austenitic, meaning they have no ferromagnetic properties in their annealed state. Plastic deformation changes this structure to partially ferritic structure making highly cold worked stainless steels (with some exceptions like 316, a molybdenum modification of 18-8) slightly magnetic. In addition, this crystaline change greatly increases the yield strength and is HIGHLY ansitropic in its effects. Not that it is relevant but what is "ansitropic" TJ |
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#52
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The Basics of Wheel Alignment and Wheelbuilding
"jim beam" wrote
ah, this explains everything! stainless steel has been developed that has an endurance limit! and it's used in bicycle spokes!!! no. this is one of the fundamental flaws of "the book". it cites material behavior for mild steel, which /does/ have an endurance limit, and then presumes to describe behavior in stanless steel, which does not. just exactly how this lends credibility to a revolutionary means of eliminating metal fatigue is something i have yet to come to terms with. http://www.hghouston.com/ss_cwp.html |
#53
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The Basics of Wheel Alignment and Wheelbuilding
"Weisse Luft" wrote
The overstressing procedure forces changes in the elbow, causing it to conform to the flange hole AND causing deformation of the flange hole itself. Because of this, the stresses of the bend is now spread over a longer range of the bend. Cyclic loading consistent with riding is now operating this joint in a purely elastic range rather than exposing tiny areas of the bend to very high stresses over very small areas. Practically speaking, whether momentary overloading increase spoke fatigue life by reducing residual manufacturing stresses or by "bedding in" the spoke/flange interface is immaterial, as long as it works, it's a procedure that should be followed. For the "bedding" theory to be correct, it would require that the bulk material in both the spoke and flange to be taken beyond yield. I don't think that's the recommended practice. Your version of "bedding", since it involves higher forces, would necessarily also perform the reduction of residual stresses, so the claim that it works by that particular mechanism would seem impossible to prove. In fact, those of us who don't stress relieve to yield, yet observe improved spoke lifetimes, would seem to have experiences which refute that theory. |
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The Basics of Wheel Alignment and Wheelbuilding
dianne_1234 wrote:
On Sun, 01 Aug 2004 19:03:14 -0700, jim beam wrote: his "stress relief" theory on the other hand is entirely subjective, Can you suggest some ways such a theory might be tested? fogel pretty much says it all. what /i/ would do is just set up a fatigue testing machine and start stretching. other ways to detect residual stress include x-ray diffraction, but obviously, that's much more of an industrial research/academic exercise rather than something we can replicate "at home". |
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The Basics of Wheel Alignment and Wheelbuilding
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#56
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The Basics of Wheel Alignment and Wheelbuilding
Peter Cole Wrote: " Practically speaking, whether momentary overloading increase spoke fatigue life by reducing residual manufacturing stresses or by "bedding in" the spoke/flange interface is immaterial, as long as it works, it's a procedure that should be followed. For the "bedding" theory to be correct, it would require that the bulk material in both the spoke and flange to be taken beyond yield. I don't think that's the recommended practice. Your version of "bedding", since it involves higher forces, would necessarily also perform the reduction of residual stresses, so the claim that it works by that particular mechanism would seem impossible to prove. In fact, those of us who don't stress relieve to yield, yet observe improved spoke lifetimes, would seem to have experiences which refute that theory. Yielding occurs only in a partial cross section of the spoke during the stress relieving process. Because the entire cross section does not go to yield, the tension can and does remain the same. Anisotropic means properties that differ with respect to axis. A very common anisotropic material would be wood. With regard to cyclic fatigue, one has to only look at the spring industry to see what works. For long life, most springs are entirely cold worked, that is no post forming heat treatment is used. That cold working is the same as the final stress relieving process some of us follow when wheel building. Now on compression, tension, aluminum and stainless. Its true aluminum is best in compression while spokes can only take a tensile load but in a wheel, we have a pretensioned structure. That spoke takes a compressive load, manifested as a decrease in tension. And the wheel is under a compressive load from the sum of the sopke tensions but it also can take a tensile load, manifested by a reduction in the compressive stress. -- Weisse Luft |
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The Basics of Wheel Alignment and Wheelbuilding
Trevor Jeffrey wrote:
Weisse Luft wrote in message ... These stainless steels are all austenitic, meaning they have no ferromagnetic properties in their annealed state. Plastic deformation changes this structure to partially ferritic structure making highly cold worked stainless steels (with some exceptions like 316, a molybdenum modification of 18-8) slightly magnetic. In addition, this crystaline change greatly increases the yield strength and is HIGHLY ansitropic in its effects. Not that it is relevant but what is "ansitropic" TJ "directional" is a simple translation. wood is anisotropic. metals get like this when their grains are all elongated in the same direction, wire being the classic example. |
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The Basics of Wheel Alignment and Wheelbuilding
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#59
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The Basics of Wheel Alignment and Wheelbuilding
Peter Cole wrote in message 5PqPc.195614$a24.110765@attbi_s03... Practically speaking, whether momentary overloading increase spoke fatigue life by reducing residual manufacturing stresses or by "bedding in" the spoke/flange interface is immaterial, as long as it works, it's a procedure that should be followed. I do not believe that all constructors using the method of overtensioning spokes have had an equal benefit. As I have said previously, overtensioning, accidentally, partially forms the bend in the spoke at the crossing point so as to reduce the angular displacement at the hub during the cyclic variation of loading. With a reduced angular displacement at the hub interface the MTBF is increased due to the lowered rate of fatigue. The fatigue rate is primarily dependant upon the angular displacement and not the tensile force or variation in thereof. Relatively the momentary overloading is a waste of time compared to specifically shaping the spoke correctly. TJ |
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The Basics of Wheel Alignment and Wheelbuilding
Mark McMaster wrote:
jim beam wrote: Mark McMaster wrote: jim beam wrote: wrote: snip Spoke-squeezing is an intriguingly mysterious subject to research. I remain agnostic, wavering one way and the other, but haven't seen any experimental data or analyses involving bicycle spokes. If you have the 3rd edition, perhaps you could peek at the Wiedemer stuff and give me your thoughts on it? you may also want to consider this question: q: elevator safety certification requires loading the cab to double it's "safe working load". this is to test the wire ropes that suspend it. the reason is that fracture mechanics predict that this process will typically reveal by failure any latent flaws. but, if we extend spoke squeezing theory, wouldn't this overload procedure also prevent fatigue of elevator cables? a: no. elevator cables still fatigue and need regular testing, inspection & replacement. This proves nothing one way or the other about the affects of squeezing spokes to reduce residual stress. There is no question that reducing residual (tensile) stresses can increase fatigue life. There is also no question that spokes (or elevator cables) will still fatigue if the cyclic load is high enough (i.e. above the endurance limit). The question is whether squeezing the spokes provides any significant beneficial reduction in residual stress, or increases the endurance limit. Mark McMaster ah, this explains everything! stainless steel has been developed that has an endurance limit! and it's used in bicycle spokes!!! no. this is one of the fundamental flaws of "the book". it cites material behavior for mild steel, which /does/ have an endurance limit, and then presumes to describe behavior in stanless steel, which does not. just exactly how this lends credibility to a revolutionary means of eliminating metal fatigue is something i have yet to come to terms with. Ah, as usual, you dodge the question rather than addressing it. Whether or not a material has a true endurance limit or not doesn't change the question of whether momentarily overloading the spokes can reduce residual stress and/or increase fatigue life, which is central to the argument. But then, you appear to be far more interested in being a contrarian than to actually knowing what is going on. That momentarily overloading the spokes results in increased spoke life has been reported by many sources. Not just here in the RBT newsgroup but by others as well, both inside and outside the industry. For example, here is the Bontrager wheel manual which shows how their "wheel stressor" is used to momentarily overload the spokes: http://www.bontrager.com/workshop/do...eel_manual.pdf So, just what is the mechanism that causes the spokes to have improved fatigue life after momentarily overloading them? If you do not believe that Brandt is correct about relieving residual stresses in the spokes, than what other explanation do you propose? And about stainless steel having an endurance limit: Whether any material has a true and absolute endurance limit is often debated. However, under a common usage of the term (fatigue strength at 10^7 cycles is a common definition), the types of stainless steel used in spokes does have an endurance limit (but then, you probably knew that). We can dispose of that red herring. Here are some data on some stainless steels of the type used in spokes (for example, Wheelsmith uses 304, DT uses 18-8), including their endurance limits: http://www.hghouston.com/ss_cwp.html http://www.band-it-idex.com/pdfs/sta...el/302_305.pdf http://www.askzn.co.za/tech/tech_grade_304.htm Mark McMaster gotta scram for work so let's chat later, but be careful when talking about endurance limits - they're easily confused with fatigue limits, which may sound the same but are techically very different. |
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