Steel (Metal) Vs Carbon

Ravi Kempaiah

Ravi Kempaiah

Well-Known Member
Region
Canada
City
Halifax
Well, some people think Carbon frames on bikes is slightly over-hyped but there is no denying to the fact that Carbon composites have changed our lives in so many ways.

I have seen many Carbon forks giving up and also the air/coil suspension ones.
I would like to keep this thread open for any discussion related to Metal Vs Carbon.

Here is an excellent video showing the difference in strength between steel and carbon shafts. Carbon can withstand almost 4 times the limiting Torque on steel shafts.

 
Wow.
Carbon fiber is super strong and Richard Hammond has the coolest job in the world!
 
It is indeed ultra strong. :)
I guess ST1 has Carbon forks and if you go over rough bumps, you only need to worry about the spokes on the rear wheel because these Carbon forks can take some good abuse.
 
Yeah, and I find the carbon soaks up a lot of road noise/vibration too. I rode (and still will this summer) a lot of road bike so this Stromer is like a total cruiser considering. An interesting thing, the rear spokes on the ST1 are 3mm instead of the regular 2.5. They are actually moped rated spokes! which can make it interesting when you need to adjust them.... I guess you go to the local motorcycle shop??
 
Wow, James..!!
I had never known that ST 1 uses 3mm spoke..!!
The highest I have seen is 12G = 2.6mm.
Even my Jumper comes with 14G on the front and 13G on the rear.
Seems like ST 1 has 11G which is almost motorcycle quality spoke. I guess you need that kind of spoke for carrying that gearless motor. Also, for truing them, you will have to go to your dealer or motorcycle shop.

http://www.bikeforums.net/archive/index.php/t-767354.html
 
The video is indeed very impressive! Some thoughts crossed my mind when watching. Even though the carbon failed at a much higher torque level, 4,728 newton meters vs. 1,376 it completely fractured whereas the steel maintained a connection and just bent. Also, these were both in pristine condition before testing. What kind of impact does temperature, sunlight and vibration have on these materials? I love the idea of carbon fiber but have always felt uneasy about how it would respond to scratching at a bicycle rack or sunlight shining down on it all day there.

I assume these things have been considered and that the coatings and layers are all designed to endure. I'm just curious about all of the other dimensions being challenged real world environments... especially over time. Depending on how you use a bicycle it may not be maintained as a race car would. Can anyone share their thoughts here? I've owned carbon bikes, I'm all for it just looking for feedback. Here's some stuff I found:

Background:
  • Carbon fiber is also known as graphite fiber, carbon graphite or just CF.
  • It starts as very thin strands of fiber made from carbon atoms that are bonded together in crystals aligned parallel to the long axis of the fiber (the crystal alignment gives the fiber high strength-to-volume ratio). These strands are finer than human hair (about 5–10 μm "nanometers" in diameter).
  • The strands are twisted together like yarn (called a tow) and woven into fabric which usually comes in 3k, 6k and 12k weights - a 3k fabric has 3,000 strands in each tow and a 6k has 6,000 respectively.
  • Carbon fiber fabric comes in a variety of weaves that have different strength properties. The most common are plain weave, harness satin weave, twill weave and unidirectional. Weave impacts product strength. A unidirectional weave creates a carbon fiber sheet that’s very strong in the direction of the fibers, but weak in the opposite direction. Plain and twill weaves, on the other hand, have more uniform strength since they’re strongest at the points where the fibers cross in either direction.
  • To make a carbon fiber sheet (also known as a composite), carbon fiber fabric is saturated or infused with epoxy resins and heated at high temperatures. Shaped pieces are made by layering several pieces of fabric over a mold, saturating them with resin and heating it until the resin has infused through all layers.
Strengths:
  • Carbon fiber is five times stronger than steel and one third of its weight. It is a low density material with very high strength to weight ratio.
  • When made with the appropriate resins, carbon fiber is one of the most corrosion-resistant materials available.
  • Carbon fiber can be UV resistant with use of the proper resins. Also, carbon fiber is transparent to radiation and invisible in x-rays, making it valuable for usage in medical equipment and facilities or checking your ebike at the airport.
  • Carbon fiber expands and contracts much less in hot and cold conditions than steel or aluminum.
  • It's durable, having superior fatigue properties compared to metal, meaning components made of carbon fiber won’t wear out as quickly under the stress of constant use
Weaknesses:
  • Carbon fiber will break or shatter when it’s compressed, pushed beyond its strength capabilities or exposed to high impact. It will crack if hit by a hammer and is considered somewhat brittle. Machining and holes can also create weak areas that may increase its likelihood of breaking.
  • It's expensive, and while prices have dropped significantly since ~2010, demand has not increased enough to increase the supply substantially. As a result, prices will likely remain the same for the near future. Less expensive similar materials include glass fibers and plastic fibers.
So it sounds like carbon fiber is great but machining and putting holes in it (braze ons, bottom bracket, dropouts) can create vulnerability. I think this is why many carbon frames use aluminum or steel for these areas and meld with carbon for the larger parts of the frame. It also sounds like you can prevent UV damage by using different resins. I don't like the idea of someone being able to wreck my bike with one hit from a hammer... or a less malicious scenario where a bike just tips into mine.

Around 2007 I was riding with some friends on carbon road bikes from San Francisco to Sausalito on what's know as the Tiberon Loop and my friend's frame just cracked. He knew something was wrong because it was rattling and didn't feel right but it still worked so we just rode all the way home and then he found the crack. His frame had failed and indeed, it was rather old and had been shipped. I was glad it wasn't a catastrophic failure, CF is pretty amazing stuff but again, knowing its vulnerable points can empower us to protect it better and I'm still trying to figure out what those opportunities are.

Sources: Protech Composites, Wikipedia
 
Great source of info, Court. Thanks for sharing.
No wonder we are witnessing huge number of bikes with Carbon frames ( weight savings ~ 3kgs).

As a nanotechnologist who has worked on graphene and carbon nanotubes, I have seen remarkable progress in the processing of carbon composites in the last 4 years alone.
  • When made with the appropriate resins, carbon fiber is one of the most corrosion-resistant materials available.
This is the key point. Carbon fibers are brittle but so is hydroformed aluminum on many bikes but the key is making layer-by-layer composites either by spinning or coating and you get phenomenal strengths. Most TIG welded structures have something called heat affected zone (HAZ) that are prone to failure. Steel is tougher and that is why you see that necking. Carbon can be made tough as well.

Regarding your points on resistance to scratching, it highly depends on what type of QC was implemented at the manufacturing facility. Most of them use some kind of surface coating (a quick YT search yielded this). If they used large pieces then crack propagation could be fast but these days molding process is changing rapidly. Just like how we have different variety of Lithium-ion batteries, carbon frame quality varies. Some batteries die in a year or so while others last for 3-4 years. Tesla even promises 8 year battery life at ~ 70%.

So, carbon is a great material but its manufacturing process, QC, material source etc., all matters. Even light-weight hydroformed aluminum cracks because we have all this fancy hollow tubes for running the wires, welded spots for braze-ons etc. A bike owner can not go and check all these intricate details, so better to have a solid warranty from reputed manufacturers before shelling out lot of cash.

A sample video of what is involved in carbon bike frame manufacturing.

 
quality control is vital. Stromer had a voluntary recall on carbon forks last year to address a bad batch
 
Okay, I found a good example of why carbon bicycles give me pause. Dave recently ordered a 2013 Easy Motion Neo Carbon and Chris (a shop owner that carries these bikes) and Undercover Brother (a rep from BH) both expressed concern for over tightening components:

When you're assembling it be careful not to tighten anything to tight as you could damage the carbon fiber. Ideally use a torque wrench, but if you don't have one just take it easy when tightening the seat post and the stem. There are some other precautions when handling and caring for carbon fiber, but maybe the resident expert Ravi can chime in on that.
Click to expand...

to Chris's point, make sure you use an appropriate torque wrench as it is very easy to over-torque bolts and ruin a great bike, especially critical when working with carbon.
Click to expand...

So maybe in the lab and testing facilities carbon fiber designs are as strong (or stronger than steel) while being lighter but it seems that in practice they require special attention. I'm not a hater here at all, I've owned carbon road bikes but I feel like a list of "how to care for carbon bikes" would be helpful in providing more transparency to its true limitations or weaknesses.
 
The old answer to this type of issue is to be sure that the the form ( idea, shape and material used) is going to fit the function (intended use). This is almost infinitely applicable in an abstract way. But to bring it down to the particular instance which concerns us here, I don't want a fancy titanium, or a carbon fiber frame, when aluminum will do just fine, and I don't want an aluminum frame when plain steel will work. Minimalism is the way to go: saving you and I money, time, effort, and resources.

Don't need no high end, uppity ebike to commute.... But to climb Pike's Peak or drive across the county?...Wanna race or maybe impress the office cutie? ....Now where's my Optibike? So decide first what you want to do, then pick the appropriate tool.

To carry this minimalism even further: You don't want to take a jet, when you can drive the car, you don't want to drive the car when you can ride your ebike, and finally you don't want to ride the ebike when you can just walk to your destination. And better than that: just live where you work or work where you live = I ain't gonna commute no more!
 
Ravi Kempaiah said:
Well, some people think Carbon frames on bikes is slightly over-hyped but there is no denying to the fact that Carbon composites have changed our lives in so many ways.

I have seen many Carbon forks giving up and also the air/coil suspension ones.
I would like to keep this thread open for any discussion related to Metal Vs Carbon.

Here is an excellent video showing the difference in strength between steel and carbon shafts. Carbon can withstand almost 4 times the limiting Torque on steel shafts.

Click to expand...
What happens to the comparison when stretching or compressing forces are applied? Can the direction of the threads be altered to accommodate these forces and if so does a weakness occur elsewhere therefore? Steel cabling comes to mind when considering stretching forces, steel springs when considering compression and torsion bars for twisting. It seems to me the variable, controllable tensile strength and plasticity of steel on demand is what gives it value as opposed to say carbon fibers strong but undefinable fatigue limit or brittleness (thanks wikipedia). Therefore, I can't imagine carbon fiber cabling, springs, torsion bars or swords! However...

That being said, another carbon based material: graphene may be able to replace steel, plastics, and etc. as a universal construction material (bike frames included). This is a extremely interesting subject, perhaps you can tell us about your work in that field or at least speculate as to what may be, as long as you don't violate any confidentiality agreements.
 
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That is a great observation Calvin...!
I work on carbon materials like graphene but I am not into making tough composites. I have couple of friends at RICE and Univ of Texas, Austin and they did a lot of work on this.
He commented that, since these carbon frames/shafts are made of carbon fibers, by cleverly aligning the nanometer sized fibers, one can get varied range of strengths and toughness. Look at this video:

 
Thanks for the video. I am familiar with machines that braid copper, aluminum, and steel wire utilizing spools like the one depicted. Some of these specialized machines can even braid wire of small diameter. Has anyone tried to braid these filaments or threads and thereby enhancing carbon nanotube's stretchability?
 
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calvin said:
Thanks for the video. I am familiar with machines that braid copper, aluminum, and steel wire utilizing spools like the one depicted. Some of these specialized machines can even braid wire of small diameter. Has anyone tried to braid these filaments or threads and thereby enhancing carbon nanotube's stretchability?
Click to expand...
If I may answer my own question: yes they have: Google (braiding carbon fiber). Also see: http://www.bikerumor.com/2012/12/05/3d-woven-braided-carbon-fiber-concept-road-bike-by-jacob-haim/
 
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Dave said:
I am an avid tennis player and keep up with the latest racquet technolgies, Graphene is now being used is Head's latest series of racquets. Looks like they can do almost anything with braiding carbon fiber.
https://www.head.com/tennis/products/racquets/tour-radical/?region=us
Click to expand...
Well now that is cool. But I think that the racquet is made out of carbon fiber and not graphene at all. Actual graphene is still too difficult and expensive to make. A layer, one inch square, costs about $60.00. http://www.ibtimes.com/what-graphene-5-incredible-facts-about-miracle-material-you-need-know-1399503
Graphene is becoming a buzz word and companies are trying to blur its definition in order to apply the word to promote their products. (Naughty marketing technique number 3.1)
 
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Phenomenal engineering in those bikes from Munich. The cost per tooling would be very high as they have not gotten into mass production.
As more and more people move to lighter and stronger frames, the technology would develop rapidly. No one imagined we would have Wi-Fi, GPS, 13 MP camera in a small phone back in 2004 and in 10 years... a lot has been done.
Carbon is not new, it was used in Lockheed Sr-71 Blackbird etc but for day to day use like racquets, bike frames, it is becoming increasingly popular. At this stage, not all Carbon frames are prone to compression/stretch failure, if protected well, they can outperform metal framed bikes.
 
I'm starting to like carbon and its derivatives (especially diamonds) and carbon is so .... like everywhere!
 
Here's a guy that builds steel frames locally that completely disproves the notion that steel has to be heavy: www.silentcycles.com. So awesome.

Carbon is sweet, but be aware that it flexes and batteries don't. So integrated batteries with carbon frames can be a little squeaky.
 
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