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> More expensive bikes are built from lighter and stronger materials (such as carbon fiber) I would recommend anyone thinking carbon fiber makes stronger bikes

by zurn 14y ago

> More expensive bikes are built from lighter and stronger materials (such as carbon fiber) I would recommend anyone thinking carbon fiber makes stronger bikes to visit a topical image blog at http://www.bustedcarbon.com/ http://www.bustedcarbon.com/ :) The weight issue is addressed elsewhere in comments...

001sky 14y ago
That is a cool link. Carbon has tensile but not shear strength. As the evidence shows.
- 001sky 14y ago
  In absolute terms, Tenstile (psi x1,000) for Ti Vs CFRP Tensile = 145 vs 215 Shear= 135 vs 1.5 <<that is why things go crack. Carbon Fiber Reinforced Polymer (CFRP) Composition: 70% carbon fibers in epoxy matrix Property Value in metric unit Value in US unit Density 1.6 10³ kg/m³ 101 lb/ft³ Tensile modulus (LW) 181 GPa 26300 ksi Tensile modulus (CW) 10.3 GPa 1500 ksi Tensile strength (LW) 1500 MPa 215000 psi Tensile strength (CW) 40 MPa 5800 psi Thermal expansion (20 ºC, LW) 0.0210-6 ºCˉ¹ 0.0110-6 in/(in ºF) Thermal expansion (20 ºC, CW) 22.510-6 ºCˉ¹ 12.510-6 in/(in* ºF) LW- Lengthwise direction, CW- Crosswise direction [1] http://www.substech.com/dokuwiki/doku.php?id=epoxy_matrix_composite_reinforced_by_70_carbon_fibers&DokuWiki=62d982a57ddac09b194d27c46bf89e90 http://www.substech.com/dokuwiki/doku.php?id=epoxy_matrix_co... [2] http://www.substech.com/dokuwiki/doku.php?id=titanium_near-alpha_alloy_ti-8al-1mo-1v http://www.substech.com/dokuwiki/doku.php?id=titanium_near-a.... These are directinally correct for raw materials; the actual alloys and engineered structures will take into account obvious characteristics of the material.
nl 14y ago
I hate, hate, hate the anti-scientific view that busted carbon promotes. Carbon fiber's failure mode is different to metal - it breaks rather than bends. In most cases crashes that destroyed carbon frames would have also destroyed metal frames - but a frame bent out of alignment doesn't look as spectacular. It is possible to build a bike from carbon fiber that fails in surprising ways (eg, clamping it in a bike carrier). That's because CF allows more flexibility in building with it, not because it is inherently weak. If you want a strong carbon frame buy a cheap one. They typically use the same number of layer of fiber all over the frame (instead of trying to minimize weight in low strain parts) and they use plain woven fiber aligned randomly. That makes the bike heavier than a high-end frame, and not as strong for expected stresses (pedalling) as it could be for the same weight but it makes it more robust in the even on unexpected strains.
- zurn 14y ago
  How about these quotes from the first page: "She spent a few days in the hospital over this. On a normal ride with friends and frame let go" "This shot is of a friend’s seat post sometime after he adjusted the saddle height" "Just 'popped' when I stood up to do a fast sprint" "I managed to mostly avoid it but got pushed into a barricade and when I looked down my bike was in two pieces" "I was sprinting through busy downtown San Jose traffic with a guy a fixed gear when my seatpost went "ka-RACK." Fixie kid laughed." (well that's just the first half of the page, will stop pasting now)
  - nl 14y ago
    I'm not sure what your point is? Yes, people get injured when they have bike crashes. Yes (as I noted), carbon can fail. Metal can too! [1] is a much better survey of random broken bikes than bustedcarbon. [2] is a good summary of the hysteria around breaking carbon frames and some of the facts. Here's a pic of a broken titanium (!) bottom bracket: http://www.pardo.net/bike/pic/fail-001/FAIL-143.html http://www.pardo.net/bike/pic/fail-001/FAIL-143.html Assorted mostly steel and aluminium broken frame pics: http://www.pardo.net/bike/pic/fail-001/FAIL-167.html http://www.pardo.net/bike/pic/fail-001/FAIL-167.html [1] http://www.pardo.net/bike/pic/fail-001/000.html http://www.pardo.net/bike/pic/fail-001/000.html [2] http://isolatecyclist.bostonbiker.org/2011/02/21/carbon-bicycle-forks-cautions-facts-and-misconceptions/ http://isolatecyclist.bostonbiker.org/2011/02/21/carbon-bicy...
    - zurn 14y ago
      I guess one point is that carbon fails catastrophically more often, your metal links point to breaks where the bike still stayed in one piece. Yeah, they're not unheard of with metal bikes, but much more rare. The injury quote was about her getting injured because the carbon frame just fell apart with no warning (no crash, except after the frame failure of course).
      - 001sky 14y ago
        I guess one point is that carbon fails catastrophically more often - There are "scientific" reasons why these things break for no apparent reason. b/c carbon is prone to developing "flaws", not all of which are visible (to naked eye). These happen either through previous impact damage or fatigue cycles. - Carbon failure can cascade (snap...snap...snap...). Once the structure is compromised, the lack of sheer strength combined with different-from-design force vectors...are not good (a two-sided trianle = wishbone...) Look at how many carbon parts had multiple, complete failures. - A metal frame will dent or bend if damaged; it doesn't hide flaws nearly to the same extent. You might get a hairline crack, but unlikely 3-4 snapped cross-sections. -Obviously, getting hit by a truck or whatever doen't matter what you are riding.

by zurn 14y ago

001sky 14y ago

That is a cool link. Carbon has tensile but not shear strength. As the evidence shows.

001sky 14y ago
In absolute terms, Tenstile (psi x1,000) for Ti Vs CFRP Tensile = 145 vs 215 Shear= 135 vs 1.5 <<that is why things go crack. Carbon Fiber Reinforced Polymer (CFRP) Composition: 70% carbon fibers in epoxy matrix Property Value in metric unit Value in US unit Density 1.6 10³ kg/m³ 101 lb/ft³ Tensile modulus (LW) 181 GPa 26300 ksi Tensile modulus (CW) 10.3 GPa 1500 ksi Tensile strength (LW) 1500 MPa 215000 psi Tensile strength (CW) 40 MPa 5800 psi Thermal expansion (20 ºC, LW) 0.0210-6 ºCˉ¹ 0.0110-6 in/(in ºF) Thermal expansion (20 ºC, CW) 22.510-6 ºCˉ¹ 12.510-6 in/(in* ºF) LW- Lengthwise direction, CW- Crosswise direction [1] http://www.substech.com/dokuwiki/doku.php?id=epoxy_matrix_composite_reinforced_by_70_carbon_fibers&DokuWiki=62d982a57ddac09b194d27c46bf89e90 http://www.substech.com/dokuwiki/doku.php?id=epoxy_matrix_co... [2] http://www.substech.com/dokuwiki/doku.php?id=titanium_near-alpha_alloy_ti-8al-1mo-1v http://www.substech.com/dokuwiki/doku.php?id=titanium_near-a.... These are directinally correct for raw materials; the actual alloys and engineered structures will take into account obvious characteristics of the material.

nl 14y ago

I hate, hate, hate the anti-scientific view that busted carbon promotes. Carbon fiber's failure mode is different to metal - it breaks rather than bends. In most cases crashes that destroyed carbon frames would have also destroyed metal frames - but a frame bent out of alignment doesn't look as spectacular. It is possible to build a bike from carbon fiber that fails in surprising ways (eg, clamping it in a bike carrier). That's because CF allows more flexibility in building with it, not because it is inherently weak. If you want a strong carbon frame buy a cheap one. They typically use the same number of layer of fiber all over the frame (instead of trying to minimize weight in low strain parts) and they use plain woven fiber aligned randomly. That makes the bike heavier than a high-end frame, and not as strong for expected stresses (pedalling) as it could be for the same weight but it makes it more robust in the even on unexpected strains.

zurn 14y ago
How about these quotes from the first page: "She spent a few days in the hospital over this. On a normal ride with friends and frame let go" "This shot is of a friend’s seat post sometime after he adjusted the saddle height" "Just 'popped' when I stood up to do a fast sprint" "I managed to mostly avoid it but got pushed into a barricade and when I looked down my bike was in two pieces" "I was sprinting through busy downtown San Jose traffic with a guy a fixed gear when my seatpost went "ka-RACK." Fixie kid laughed." (well that's just the first half of the page, will stop pasting now)
- nl 14y ago
  I'm not sure what your point is? Yes, people get injured when they have bike crashes. Yes (as I noted), carbon can fail. Metal can too! [1] is a much better survey of random broken bikes than bustedcarbon. [2] is a good summary of the hysteria around breaking carbon frames and some of the facts. Here's a pic of a broken titanium (!) bottom bracket: http://www.pardo.net/bike/pic/fail-001/FAIL-143.html http://www.pardo.net/bike/pic/fail-001/FAIL-143.html Assorted mostly steel and aluminium broken frame pics: http://www.pardo.net/bike/pic/fail-001/FAIL-167.html http://www.pardo.net/bike/pic/fail-001/FAIL-167.html [1] http://www.pardo.net/bike/pic/fail-001/000.html http://www.pardo.net/bike/pic/fail-001/000.html [2] http://isolatecyclist.bostonbiker.org/2011/02/21/carbon-bicycle-forks-cautions-facts-and-misconceptions/ http://isolatecyclist.bostonbiker.org/2011/02/21/carbon-bicy...
  - zurn 14y ago
    I guess one point is that carbon fails catastrophically more often, your metal links point to breaks where the bike still stayed in one piece. Yeah, they're not unheard of with metal bikes, but much more rare. The injury quote was about her getting injured because the carbon frame just fell apart with no warning (no crash, except after the frame failure of course).
    - 001sky 14y ago
      I guess one point is that carbon fails catastrophically more often - There are "scientific" reasons why these things break for no apparent reason. b/c carbon is prone to developing "flaws", not all of which are visible (to naked eye). These happen either through previous impact damage or fatigue cycles. - Carbon failure can cascade (snap...snap...snap...). Once the structure is compromised, the lack of sheer strength combined with different-from-design force vectors...are not good (a two-sided trianle = wishbone...) Look at how many carbon parts had multiple, complete failures. - A metal frame will dent or bend if damaged; it doesn't hide flaws nearly to the same extent. You might get a hairline crack, but unlikely 3-4 snapped cross-sections. -Obviously, getting hit by a truck or whatever doen't matter what you are riding.