Just a thought: A PVC Frameset
09-18-07, 08:52 AM
#26
Making a kilometer blurry
PVC is not an efficient spring like AL, Ti, or steel. Much of the energy from flex will turn to heat.
Think about making wind chimes. If the material would make a good wind chime, then the it will return your energy. Note that carbon fiber wind chimes would not work... so you kind of need it to be stiff for efficiency's sake (this is because of the properties of the epoxy).
Hmm. Can you imagine making a nice set of Reynolds 953 wind chimes? Maybe a 39t chainring to hold the strings at the top and a cog for the knocker.
09-18-07, 09:10 AM
#27
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Now there is epoxy. It is not really stiff, nor light. However, pre set, it flows alright at normal temperatures (I work with it a lot with the only protection being rubber gloves because the stuff is kinda messy) so it can impregnate the carbon weave relatively easily by using vacuums. Once set, it holds the carbon weave in place. In reality, this is the major role the matrix plays. Using more only decrease the specific strength of the carbon fiber composite (makes heavier without increasing the strength) Lately companies (easton is a big leader in this) have been using carbon nano tubes in the matrix to displace some of the epoxy (use less epoxy) because the CNT's are less dense then the matrix they displace.
09-18-07, 09:37 AM
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In the MTB world, I think thermoplastics have been used a few times... I think the Cannondale Super Raven had a carbon frame with a thermoplastic matrix, and I think GT and K2/Proflex had thermoplastic bikes too. I believe my old Proflex 857 had a thermoplastic matrix in its carbon fiber swingarm, but I'm not sure.
09-18-07, 09:46 AM
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I think everyone missed my point.
NO.
That is all.
NO.
That is all.
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09-18-07, 10:03 AM
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I had a dream last night where a Specialized Ruby was made out of a mylar balloon. I tore up the rear end, but the rest held it's shape pretty well. Anyone else thinking what I'm thinking?
09-18-07, 10:08 AM
#31
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Originally Posted by asmallsol
......
.....
The science behind them is pretty interesting...
.....
The science behind them is pretty interesting...
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09-18-07, 10:11 AM
#32
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First, the claim is not that flex is good, but that a certain amount of flex is not bad.
PVC is not an efficient spring like AL, Ti, or steel. Much of the energy from flex will turn to heat.
Think about making wind chimes. If the material would make a good wind chime, then the it will return your energy. Note that carbon fiber wind chimes would not work... so you kind of need it to be stiff for efficiency's sake (this is because of the properties of the epoxy).
Hmm. Can you imagine making a nice set of Reynolds 953 wind chimes? Maybe a 39t chainring to hold the strings at the top and a cog for the knocker.
PVC is not an efficient spring like AL, Ti, or steel. Much of the energy from flex will turn to heat.
Think about making wind chimes. If the material would make a good wind chime, then the it will return your energy. Note that carbon fiber wind chimes would not work... so you kind of need it to be stiff for efficiency's sake (this is because of the properties of the epoxy).
Hmm. Can you imagine making a nice set of Reynolds 953 wind chimes? Maybe a 39t chainring to hold the strings at the top and a cog for the knocker.
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09-18-07, 10:19 AM
#33
Making a kilometer blurry
09-18-07, 12:17 PM
#36
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or is it just a big marketing thing. i had a discussion w/ a post-doc yesterday as to why CNT's will die out as a research field unless there are some serious applications -- didn't realize anyone was tossing them in bike parts. i'm really curious now if they'd be just as well of using fullerines which are easier to make for the displacement.
09-18-07, 12:38 PM
#38
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the reference didn't indicate that the cnt's made it stronger by themselves, but lighter by displacing epoxy. i still think it's buzzword hype, though
09-18-07, 12:46 PM
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09-18-07, 02:45 PM
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Hmmmm..... Where abouts are you studying?
Just reminding you that all structural steels have a modulus of elasticity of 205GPa regardless of whether it's normalised steel, annealed steel, quenched steel, Mild Steel, Carbon Steel, CrMo, Reynolds 531, Columbus Spirit etc etc
Just reminding you that all structural steels have a modulus of elasticity of 205GPa regardless of whether it's normalised steel, annealed steel, quenched steel, Mild Steel, Carbon Steel, CrMo, Reynolds 531, Columbus Spirit etc etc
Wrong, when you can the processing of steel, the MoE is going to change depending on the micro structure. Please, go to Matweb.com and see for yourself.
MoE for different alloys
SS alloy 304 193GPa
1020: 207 GPa
17-7PH 204Gpa
440A 200GPa
Now take a carbon steel. The mechanical properties will be much different if you quench the steel instead of allowing time for diffusion of carbon to create micro structures such as pearlite, bainite ect. Take a piece of piano wire, As is, its one of the strongest steels out there. Typically it is a form of tempered martensite. It is flexible, yet EXTREMELY strong. Now heat that wire up to the point were its glowing. This will be the austenite region. Quench the steel, and the material will turn to meta-stable Martensite. It is an extremely stiff material (however, I can't find any numbers online because its a useless material, so no one tests it) but the downside is, it's so brittle, you can snap it in your hand like dry spaghetti. Now heat that up again to just below the austentic region, and hold it there, allowing time for diffusion. Now when you quench, the material will be slightly less stiff as a result of larger grains (lower MoE) but much less brittle.
Last edited by asmallsol; 09-18-07 at 03:02 PM.
09-18-07, 02:59 PM
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Actually they are starting to use them in flat panel displays to replace the current electron field emitters which resemble icebergs, and go with the CNT so they can fit more of electron field emitters/area and result in a clearer picture. More of an application of EE then ME.
09-18-07, 03:13 PM
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09-18-07, 04:31 PM
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09-18-07, 05:21 PM
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09-18-07, 05:24 PM
#47
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As usual, you've all managed to miss the point. If a PVC frame needs repair, all you need is duct tape.
I'd say that makes it the ideal frame material.
I'd say that makes it the ideal frame material.
09-18-07, 05:35 PM
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or is it just a big marketing thing. i had a discussion w/ a post-doc yesterday as to why CNT's will die out as a research field unless there are some serious applications -- didn't realize anyone was tossing them in bike parts. i'm really curious now if they'd be just as well of using fullerines which are easier to make for the displacement.
That being said... that sheeit is expensive, and I can only dream about such toys...
09-18-07, 07:48 PM
#49
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no, not really but its closer to 4% for some of those grades listed. It could make a difference for building a spring or something like that. The only reason why I mentioned the original detail was because from the source I got the spec from had that in the details, so I mentioned it. I like info to be more through rather then less.
09-18-07, 08:18 PM
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Copied from wikipedia
Specific tensile strength of various materials
Material Strength Density Specific Strength
Unit MPa g/cm³ kN·m/kg
Concrete 10 2.30 4.34
Rubber 15 0.92 16.3
Brass 580 8.55 67.8
Oak 60 0.69 86.95
Polypropylene 80 0.90 88.88
Nylon 75 1.15 97.3
Magnesium 275 1.74 158
PVC 59 1.16 50.8
Aluminium 600 2.70 222
Steel 2000 7.86 254
Titanium 1300 4.51 288
Silicon carbide 3440 3.16 1088
Glass fiber 3400 2.60 1307
Vectran 2900 1.40 2071
Graphite 4300 1.75 2457
Kevlar 3620 1.44 2514
Spectra fibers 3510 0.97 3619
CNT 62000 1.34 46268
So yea, you'd need as is, 4 times the weight. However, one thing to note with this steel has a higher specific strength (very similar) even though the density is about 3 time heavier and a little less then twice Titanium. With similar figures, all three metals should end up weighing about the same. Equal stengths would mean that the Ti bike would be the lightest, then steel, then aluminum.