Predicting the properties of lightweight carbon fiber composites

Carbon fiber-reinforced plastics represent a promising lightweight replacement for heavy steel. However, for carbon fiber to be widely adopted, new, more economical composites need to be developed. Unfortunately, carbon fiber properties are difficult to model, as they depend on complex features such as fiber loading, length distribution and orientation.

Now researchers at the DOE’s Pacific Northwest National Laboratory (PNNL), in partnership with Toyota, Magna, carbon fiber supplier PlastiComp, and software provider Autodesk, have developed a set of predictive engineering tools that could speed the development of more economical carbon fiber materials.

Currently, in order to test new composite components, carmakers must build molds, mold parts, and test them – a long and costly process. Using the PNNL-led team’s engineering software, manufacturers will be able to evaluate the structural characteristics of proposed new carbon fiber composites without building molds, allowing designers to experiment and explore new ideas much more quickly.

The team used Autodesk Moldflow software to predict fiber orientation and fiber length distribution in molded components. Using materials from PlastiComp, long carbon fiber components were molded and the fibers extracted for measurement. PNNL then compared the predicted properties from the simulation software to the test results of the molded fibers, and found that the software tool successfully predicted fiber length distribution in all cases and fiber orientation in 88 percent of cases.

PNNL worked with Magna and Toyota to analyze the performance gains and costs of long carbon fiber components versus standard steel and fiberglass composites. PNNL found the polymer composite studied could reduce the weight of auto components by over 20 percent. However, production costs can be 10 times higher than those of steel.

Download the reports:

 

Source: Pacific Northwest National Laboratory

  • Dennis Worley

    So how does BMW do mass production with the i3 and keep costs down?

    • freedomev

      It doesn’t. Have you seen it’s price? A lot for a tiny EV.

  • freedomev

    As a 45 yr composite designer, builder. the author was right when they said CF was too expensive and hard to model.
    Fact is CF isn’t a good auto composite at all. I can and do build far better, stronger in many ways car unibodies in Kevlar like fabrics, medium tech composites that cost 20% as much and perform much better while being lighter, stronger.
    In cars, crash loads are so far above others, it is the controlling spec. And Kevlar type fabrics far outclass CF one needs is less weight, not more at a fraction of the cost.
    As for the i3, since it weighs as much as a metal version, what is the point? It should weigh, cost 40% less if they really wanted too done right in composites.
    Another thing is how hard CF is to wet out in resin as you can’t tell if there is a big air bubble or resin starvation. This nearly bankrupted Boeing trying to get CF planes in commercial use as all the parts kept failing the tests.

    • sickofgovwaste

      Great comment–why isn’t the industry keyed in on this? Seems like a no-brainer…

      • freedomev

        Likely they fear the very low production start up costs of composite cars. One can build 6/yr and make good money start up costs are so low.
        Now with recent law changes allowing 25yr or older looking cars only need hot rod regulations, many start ups could be in our future..

    • Aaron Miller

      A great many things stated here are simply incorrect.
      Aramid composites are not in any commercial sense 20% the cost of carbon fiber composites. They are not stronger when properly designed, and are not lighter.
      Raw material costs are perhaps only 20% less expensive, but when stiffness per volume is considered, they are actually *more* expensive: more complex cutting and machining operations are required, much lower stiffness, less efficient fiber loading, moisture absorption issues, resin bonding issues.
      Perhaps of biggest concern to automotive, surface cosmetic problems.
      It is as noted, a lower density, but this does not make up for the other concessions it makes to carbon composites.
      Carbon fiber wets out very easily if the process is well designed, and no production or quality control would allow for resin starvation or laminate voids, so this is no concern for automotive scale production.
      For these reason no serious automotive, aerospace or defense engineer will design a structural system with aramid. Kevlar has its place, and the place is not here.
      For the moment, composites are not ready to significantly replace metals in the automotive industry, regardless of the fiber chosen, but the costs are declining rapidly.

      • freedomev

        Except one doesn’t need CF stiffness as it has too much already in medium tech FG but it does need the toughness of Kevlar types. Or don’t you know that?
        So mine is a blend of Kevlar types and medium tech composites.
        Ask Boeing how easy wetting out CF is? ;^)
        Dam near bankrupted them.
        CF has a lot of stiffness, making it very brittle vs Kevlar types that stay together spreading the load and containing sharp cracked composites in a crash when designed right.
        This allows a much lighter layup.
        So to get the same protection, you’ll need much more CF in car service. CF has it’s place like aircraft, fishing polls but for car bodies that have to pass a crash and economic tests, not so much.
        And unlike you I have one in my shop for a 2 seat sportwagon the much stronger than steel unibody composite parts, doors, hood, only weighs 235lbs.
        And I’m building a 63 Vette looking all composite EV for production in only 1800lbs.
        And if CF is so great why does the i3 BEV weigh 2600lbs? Even 2 of my 2 seat EVs weighs less than that and not a thread of CF in it.
        And I’ve been replacing metal with composites for 45 yrs so no problem for me. What’s your problem with it?
        Fact is for me, a car is a tiny lightly loaded structure compared to the size, loads I design for normally.

        • Dennis Worley

          I started building my 12m cat [yacht] in 1972..Balsa core..2 layers of 2oz chopped strand mat ether side …strong and light. by the time it was launched in 1980 they where using foam core in nz and my boat was considered heavy! she can still do 17 knots if you are brave enough though!
          I would like to see photos of your stuff …I am at dennispworley@yahoo.co.nz

          • freedomev

            Interesting you mention cats as I built quite a few along with trimarans and proas.
            The only one online, most were done before there was an online, is here
            https://www.facebook.com/javacatcharters/
            My FreedomEV can be found by googling it under image in yahoo, google, etc. It is the white or black 3wh subcar that pops up. Though as big as some 4wh cars.
            It’s really just the unibody with wheels propped up but gives you a good idea. If building 63 Vette looking EV versions wasn’t much more profitable, I’d be producing it. I have most of the tooling.
            I couldn’t find your cat but you do some cool stuff others should check out ! Keep up the good work.

        • Aaronj

          This still has a significant amount of misinformation.
          In-plane stiffness is controlled by laminate schedule, resin selection, and part geometry. Final part toughness also results from these same conditions. While it’s true at carbon fiber as a dry fiber is brittle relative to aramid, it cannot be evaluated alone, and load distribution, especially in high energy events like a crash, depends on good design. Nevertheless Kevlar suffers here through poor compressive performance. Nothing about a Kevlar fiber composite is automatically tougher than one made of other fibers: good design makes all the difference.

          The Boeing comment is very strange. They have not now, or in the past, had any more problems wetting out carbon fiber than any other fiber. When used in prepreg form, which accounts for most of their consumption, they are not doing the wetout at all, it’s done by their prepreg supplier. When involving resin infusion, their processes are simple, well defined, reliable, and experience no wetout problems. Some of their 40+ year old wet layup procedures, mostly employed to produce autoclave tooling ultimately used for prepreg, are still a standard for how well and simply carbon fabrics can be wet out.
          Nothing about carbon fiber nearly bankrupted Boeing or any other aerospace manufacturer. Carbon composite aircraft are lighter, stronger and significantly more durable than their aluminum counterparts. There is a reason they redesign major components of existing successful aircraft like the 777 and transition them to carbon fiber composite wings.

          Carbon composites very easily pass automotive industry crash testing. By definition they would never get into production if they did not.
          The lightest race bodies are carbon fiber (also occasionally fiberglass), but not aramid, for more reasons than I have listed above. Happy to go through them all but I’m afraid it would bore most people to tears. Sub-200lb full sized car bodies have been around for more than 20 years, even in fiberglass. It is simply not the case that Kevlar composites can make a lighter body of equal performance.
          What I may have or not have in my shop would have nothing to do with any of this.
          The i3 BEV is not 2600lb because it employs carbon fiber, it is 2600lb because of the thousands of design compromises made between performance, manufactuability and price that happen along the path from idea to production vehicle. A custom produced one-off could certainly be made far lighter if cost or time to produce were not a factor. And for it to be as light as possible while retaining performance, it would certainly not be aramid based, either.
          I have no problem with Kevlar or any other fiber. They all have their place. Nothing about it is a secret, though, and auto manufacturers are very well aware of what it can do and what it cannot.
          Bottom line: composites (of any fiber type) are slow to arrive to mass produced vehicles for cost reasons. That will change, and is changing. Kevlar will have a (very) small place in this, but carbon composites will take the lead.

        • Aaronj

          This still has a significant amount of misinformation.
          In-plane stiffness is controlled by laminate schedule, resin selection, and part geometry. Final part toughness also results from these same conditions. While it’s true at carbon fiber as a dry fiber is brittle relative to aramid, it cannot be evaluated alone, and load distribution, especially in high energy events like a crash, depends on good design. Nevertheless Kevlar suffers here through poor compressive performance. Nothing about a Kevlar fiber composite is automatically tougher than one made of other fibers: good design makes all the difference.
          The Boeing comment is very strange. They have not now, or in the past, had any more problems wetting out carbon fiber than any other fiber. When used in prepreg form, which accounts for most of their consumption, they are not doing the wetout at all, it’s done by their prepreg supplier. When involving resin infusion, their processes are simple, well defined, reliable, and experience no wetout problems. Some of their 40+ year old wet layup procedures, mostly employed to produce autoclave tooling ultimately used for prepreg, are still a standard for how well and simply carbon fabrics can be wet out.
          Nothing about carbon fiber nearly bankrupted Boeing or any other aerospace manufacturer. Carbon composite aircraft are lighter, stronger and significantly more durable than their aluminum counterparts. There is a reason they redesign major components of existing successful aircraft like the 777 and transition them to carbon fiber composite wings.
          Carbon composites very easily pass automotive industry crash testing. By definition they would never get into production if they did not.
          The lightest race bodies are carbon fiber (also occasionally fiberglass), but not aramid, for more reasons than I have listed above. Happy to go through them all but I’m afraid it would bore most people to tears. Sub-200lb full sized car bodies have been around for more than 20 years, even in fiberglass. It is simply not the case that Kevlar composites can make a lighter body of equal performance.
          What I may have or not have in my shop would have nothing to do with any of this.
          The i3 BEV is not 2600lb because it employs carbon fiber, it is 2600lb because of the thousands of design compromises made between performance, manufactuability and price that happen along the path from idea to production vehicle. A custom produced one-off could certainly be made far lighter if cost or time to produce were not a factor. And for it to be as light as possible while retaining performance, it would certainly not be aramid based, either.
          I have no problem with Kevlar or any other fiber. They all have their place. Nothing about it is a secret, though, and auto manufacturers are very well aware of what it can do and what it cannot.
          Bottom line: composites (of any fiber type) are slow to arrive to mass produced vehicles for cost reasons. That will change, and is changing. Kevlar will have a (very) small place in this, but carbon composites will take the lead.