When people say that composites (especially carbon fiber) fail suddenly, I don't think they are talking about fatigue life. Like you say, carbon fiber composites are (as far as I know) the best performing materials we have for cyclic loading. I think they mean that as the stress increases to the point of fracture, they yield completely and abjectly (one might say catastrophically). Whereas 4140 cromoly steel, when it yields, it continues to put up a hell of a fight for every mm of additional deflection past yield. It may be defeated but it makes you work for every mm even in defeat. This has major implications for energy dissipation in things like crashes and whatnot. A 4140 roll cage will continue to protect you even as it yields. But carbon, once it yields, it is all over. Total surrender. Sometimes this matters. I know you guys know all this because you are very smart. But maybe you didn't get why people say carbon fiber fails suddenly.
Im glad i saw this comment as i was coming to say the same. In a lot of cases where you see failure of CF parts you see things like rims or frames on bicycles. Objects that may have had sharp impacts in an area in addition to loads near yield. If a rim is perfect but in a single day hits 500 rocks thats a lot of impacts.
they should have mentioned in the video that carbon fiber composites are brittle (and as you said fail catastrophically), compared to the ductile behavior of steel. The brittle behavior of cfc isnt a bad thing per se but you need to engineer around its shortcomings
@@ak1s4 I think they were trying to avoid using the word "catastrophically." This video was partly intended as a defense of carbon because a lot of people have a lot of misconceptions after the titan sub implosion event. That is my take anyway. It is all fine you just need to make sure you design within the limits of the material. Carbon is still lighter even when you allow a more generous safety margin than you would with steel.
By definition, materials that exhibit behaviours similar to carbon are called brittle. These include concrete and glass, among others. Ceramics are also part of this family. In the case of carbon, the ultimate stress (fu) is very high, but it can't deform too much, so the overall energy absorption (ie the area under the stress-strain diagram) isn't that big. Like I said that doesn't mean anything bad.
Really important comment. There are three different failure processes here. One is single momentary overstress, another is fatigue damage (tens or hundreds of cycles of high stress), the third is cyclic stress (thousands or millions of cycles of less high stress). Carbon fiber: abrupt complete failure from momentary stress beyond yield limit, gradual loss of strength from accumulated fatigue damage, no change of properties from cyclic stress Steel, especially mild steels: gradual energy-absorbing yield from stress beyond yield limit, gradual loss of strength from accumulated fatigue damage (primarily corrosion-induced) with large critical crack size, no change of properties from cyclic stress Aluminum, especially high tensile aircraft aluminum: some energy-absorbing yield from stress beyond yield limit, gradual loss of strength from accumulated fatigue damage with much smaller critical crack size, work hardening from of cyclic stress. The move from aluminum to carbon fiber for long-life commercial aircraft is primarily because those aircraft have to stripped down to bare metal every 10-15 years and minutely inspected for cracks, especially around stress concentrators like windows and rivets. Not all composite fibers are the same. Kevlar is a bit lower tensile yield strength than carbon fiber, and more costly and heavier, degrades quickly when exposed to UV, and has substantially less compressive strength. But Kevlar absorbs a huge amount of energy when pulled beyond it's tensile elastic limit. In the high-cycle low stress regime it also absorbs energy, making it "dead". This makes it good for armor and rotor blades, or bits exposed to ramp rash like leading and trailing edges, or radomes (noses and antenna covers) where carbon's conductivity is a problem. Kevlar's lack of compressive strength makes it a poor choice for most aircraft structure. I'm frankly astonished that people build boat hulls out of carbon fiber, but it's so obviously superior for airplanes and wind turbine blades that the cost has come way down as the production volume has gone way up. $/stiffness for Chinese carbon fiber is now just 30% greater than fiberglass! Kevlar and fiberglass are a far better materials for a boat hull that should limp home safely after accidentally smacking a pier, rock, or reef (or another boat).
As an aerospace engineer, composites in compression do have strength but because of the sudden failure modes, buckling can be a serious problem and is hard to predict in comparison to an isotropic material. This is especially true in asymmetric composite layups that have complex material responses where compression can cause torsional loads
Sorry, really curious, so I'm asking every expert commenter here: If I'm designing a car's frontal impact structure out of a CFRP, with a titanium reinforcement within, such that it can appropriately dissipate a high speed collision's energy and then still have some composite material volume left for any potential secondary collisions or impacts.....what kind of fiber would I need? How would they need to be aligned? What resin? How much resin? Should the titanium pipe be wrapped by layers of carbon fiber threads around it or wound like a spring? Or should the fibers be facing the direction of the impact/compressive load of the collision head on?
@@corpsecoder_nw6746 I can’t really give any meaningful advice there- the composites ive worked with are pretty much done for once they incur any major damage- but that may not be the case as much with isotropically distributed fibers in a ductile matrix? Not too sure hopefully you get some good answers
@@corpsecoder_nw6746it's a massive topic, search how carbon fiber is used in racecars. Most of them have a steel alloy roll cage, Carbon Fiber panels, and a lot of times they have special carbon fiber deformation zones, that dissipate (absorb)crazy amounts of energy in the collision (a lot more than steel would) . Also carbon fiber supercars handle high speed collisions very well, because of the energy absorbing qualities of CF.
Exactly! Concrete and Glue joints have some measurable tensile strength to them but you don't design anything to rely on those as the failure modes are sudden and unpredictable.
@@corpsecoder_nw6746ok first off, titanium is way to rigid to use in crumble zones/crash structure. second, it is very rare and very hard to make a crash structure out of carbon fiber. There are only a handful of manufacturers that do that (i.e rimac) and even then it's still only partial. It's usually aluminum subframes combined with a carbon monocoque center. (for reference I would recommend looking at the Aventador chassis, it's a little bit older of a platform but it is still what most supercars cars look like underneath) Other than that I can go into specifics, I assume a larger weave would be be best for rigidity, but if you want it to "deform" (aka probably still shatter) on impact, probably a smaller thinner one
The grain of truth is that CFRP loaded in compression or shear is very sensitive to the quality of the interlaminar bond, and this can be affected by layup quality, contamination, consolidation, and damage. Any of these factors can initiate a delamination which results in catastrophic failure.
@@bishopdredd5349the titan submersible imploded mainly due to ignorance, miscalculations, expired prepreg, improper layup method, design faults in particular of the titanium ring interface and all kind of different shortcomings. It has been determined the load capacity margin was next to non existent for the depth it was going to.
Anyway, the resin bond between the layers and "contamination" is not really the problem with compression. Instead it much more affected by the orientation of the Weave/fibres and the amount of resin during layup that limits the bucking load capacity of the fibres.
Yeah, his explanation about compressive strength is guided by their use of the material, I think. If they would make titanium planes, he'd talk differently.
I rewatched this and drank a shot every time he said carbon fibre. My face feels like a void but on the up side I no longer feel fatigued, stressed, in tension or compression.
@@davidf2281 Sounds like you’re in a state of non linear deformation (aka slumped on the sofa) due to under estimating load cycle capacity resulting in insufficient ultimate strength.
The compressive strength of carbon fiber is dominated by Euler column buckle. The resin's job is to prevent lateral displacement of the fibers leading to rupture. The failure mode is rupture/buckling rather than tearing. The straighter the fibers align with the axis of compression, the easier it is to restrain the effects due to Poisson's ratio. Things get more complicated when the axis of compression moves. Optimization is the balance of what is gained vs what is lost. A general purpose material is sub optimal if it can resist phantom loads that cannot be generated during the useful life of the material.
if I'm making a car's impact structure with CFRP and say I have a titanium pipe for reinforcing said structures. Say, I want the internal occupants to not experience more than 10gs in a 60mph crash, the structure should have some "meat"/volume left for a 2nd crash like that (40mph) without being much harsher (under 20gs) on the occupants....how much CF do I need? What kind of fiber? What kind of resin? How much resin-to-fiber? What way should the fibers be aligned? How do I use the titanium pipe to maximize strength and resilience of the material for secondary impacts/compressions? How dense will the CF fibers and resin be? How much volume? How much weight will it be? How much would it cost? Can it be made to be inert to natural weathering or would I have to paint it to shield it from UV and rain and other gases?
+/-45 degree woven glass epoxy or carbon fiber tubes. Placed behind a bumper reinforcement bar. And mounted to the chassis hard points near suspension and engine mounts.
This series is fantastic. Something I would love to see in a future episode is the practical maintenance of various types of carbon fiber components; so when they are damaged for whatever reason, what are the methods and processes to isolate and replace the damaged area, and discussion of resulting strength or changes in characteristics of the repaired sections.
Sorry, really curious so I'm asking every expert commenter here: If I'm designing a car's frontal impact structure out of a CFRP, with a titanium reinforcement within, such that it can appropriately dissipate a high speed collision's energy and then still have some composite material volume left for any potential secondary collisions or impacts.....what kind of fiber would I need? How would they need to be aligned? What resin? How much resin? Should the titanium pipe be wrapped by layers of carbon fiber threads around it or wound like a spring? Or should the fibers be facing the direction of the impact/compressive load of the collision head on?
What i know about composite repair, on experimental glider airplanes: Grind away the damaged section. Create a 70/1 incline on the good composite sections to glue on the new layers. This way, you can replace part of it without loosing strength. Also, to figure out what was in there, do a burn test. Cut out a sample of the whole structure. Pyrolyze the resin. Take a good look at the now visible layers. Yeah, i don't think the last bit is adequate for planes that need to pass certification :D but on those, you can look up the layers in your paperwork, of course.
Very good. Thank you. One important factor in compressive strength is the layup of the fibre. The woven material has transverse strength through the thickness of the build. This increases the strength in a number of ways. From my observations of the Carter Copter wing development, some of the early problems were related to the fiber being stronger than the resin allowing strands to pull through the resin under extreme tensile load causing failures especially near embedded parts. Talking about the submarine hull failure, from what I saw the hull was wound rather than “knitted” so there was very little strength radial through the build. How I imagine that the failure would have progressed would have been tinkling of the inner build on the inner side as the resin gave way and failed in layers. The loading of the sub’s hull was an extreme case. Very few structures are loaded in that way. Something to keep in mind when designing and making spars, though. Another useful piece of knowledge is that carbon fibre is conductive and its resistance increases (or decreases, I can’t remember) under tension. This means that you can build in continuous material stress evaluation, with the native material, by embedding electrodes in various locations in loaded panels. I have made a living over 20 years using carbon fibre in ways it was never intended for. It is a truly awesome material.
Can I count watching this as part of my Continuing Education/ Professional Development time? Excellent summary, and just makes me want to learn more about the analysis, design, and manufacturing of composites.
I once tensile tested sandwich core foam with plain weave carbon fiber and noticed there is necking forming until a sudden rupture. I wonder if it's mostly attributed to the foam core for the plastic yielding behavior. The relationships between fibers and cores would be an interesting topic to cover. Awesome video.
if I'm making a car's impact structure with CFRP and say I have a titanium pipe for reinforcing said structures. Say, I want the internal occupants to not experience more than 10gs in a 60mph crash, the structure should have some "meat"/volume left for a 2nd crash like that (40mph) without being much harsher (under 20gs) on the occupants....how much CF do I need? What kind of fiber? What kind of resin? How much resin-to-fiber? What way should the fibers be aligned? How do I use the titanium pipe to maximize strength and resilience of the material for secondary impacts/compressions? How dense will the CF fibers and resin be? How much volume? How much weight will it be? How much would it cost? Can it be made to be inert to natural weathering or would I have to paint it to shield it from UV and rain and other gases?
Any half decent in depth video has talked about the way the haul was wound, not just the fact that it was carbon. Also, not that carbon can’t do it or doesn’t have any compression strength, but rather that it wasn’t the optimal material…which is all true.
@@gpaull2 yeah, WET strands woven around a titanium core?! That's just asking for a disaster. Now if it was properly engineered dry carbon, the results would have been WAY different.
The carbon fiber pressure hull was a stupid use of carbon fiber. I remember i was at a conference like 10 years ago. And some one did a presentation on a carbon fiber pressure hull and we where talking about how it was a dumb idea back then. I would maybe have used it for un-manned rov or auv maybe. If it actually made it lighter or better in some way.
@@mshepard2264 Not necessarily. The buoyancy added by the carbon fiber is a good attribute for a submersible. Every material has its limitations, but generally these can be overcome by good design. I think the main issue in this case was arrogance that led to poor design and fabrication. It is no different that the issues with aluminum that were discovered early on with pressurized airlines such as the De Havilland Comet. Saying that carbon fiber shouldn’t be used for a submersible due to one failure is like saying aluminum shouldn’t be used for airliners given that the Comet had multiple failures before the cause was found and mitigated through design.
I've been cutting honeycomb core for over a decade. Probably the hardest thing for people to get their head around is that there is a nearly infinite number of combinations available. Honeycomb core has a few key properties. Materials, cell shape, and no it isn't all hexagons, cell size and density. Change any of these and you have a completely different material. Just looking at density which is measured in pounds per cubic foot. I would break it into 3 broad categories. Lite would be under 5# medium between 5# & 7# and heavy 7# and up. Heavy you can cut almost like a solid, run an end mill into it to remove material. Try that with medium or lite core and you'll make a proper mess. To say nothing about how density affects work holding. Even the size of the part significantly impacts it's behavior. A 0.500" thick sheet is very different from a 1.000" thick sheet. By the way, I can count on one hand the number of times we have cut carbon fiber based core. And ribbon direction. Ribbon direction, ribbon direction, ribbon direction. Get that wrong and nothing you do after that matters, the part is scrap.
This is exactly what I was looking for. If I'm making a car's impact structure with CFRP and say I have a titanium pipe for reinforcing said structures. Say, I want the internal occupants to not experience more than 10gs in a 60mph crash, the structure should have some "meat"/volume left for a 2nd crash like that (40mph) without being much harsher (under 20gs) on the occupants....how much CF do I need? What kind of fiber? What kind of resin? How much resin-to-fiber? What way should the fibers be aligned? How do I use the titanium pipe to maximize strength and resilience of the material for secondary impacts/compressions? How dense will the CF fibers and resin be? How much volume? How much weight will it be? How much would it cost? Can it be made to be inert to natural weathering or would I have to paint it to shield it from UV and rain and other gases?
@corpsecoder_nw6746 You're asking me? Sorry I couldn't answer even if I was an engineer with a masters in material science focused on composites. Too little information on your design. That isn't a suggestion for you to provide more detail. I like to help but this well beyond my knowledge.
"DarkAero, Inc" Does it correct. I know this fine start-up aircraft company follows FAA requirements, and I am pretty sure DarkArero, Inc has a set of ASME & ASTM reference manuals or digital library with both the latest additions and adenda . Thank you DarkAero, for another college level presentation.
Excellent summary about material limitations between metal and composites! I've heard similar discussions about material selection for building road bicycles. I've ridden both and there certain attributes I like about both. The same goes with some of the aircraft I've flown too!
Excellent high level overview. Keep in mind carbon fiber parts have half the bearing capability for fasteners that metal ones do, that is why you often see pad-ups around bolt and hi-lock holes. Also the edge margin for fasteners has some non-linear response so your edge margin and edge distance between fasteners needs to be quite a bit larger between fasteners.
Very good video. Perhaps a word or two about how to choose different fiber grades, orientations and matrix material for various applications would have come handy, but would probably not fit into such a short video. Thanks! ~ 4:30 - I had to look up your medieval units and their arcane, arbitrary abbreviations*. OK, so ~1GPa and ~1.4GPa, respectively. *) So you don't have to: "KSI" is kilo pound-force per square inch; it's about 6,9MPa (mega pascals)
KSI is such a cursed unit. Going up to mega is MPSI, why are the pounds dropped from KSI? Why are you using metric prefixes with non-SI units? Why not TPSI for Thousand Pound-force per Square Inch?
I think the sudden breakage of carbon fiber components has to do with two things. 1) the ability to see and inspect possible stress locations and 2) the amount of loading on the part. If you can't see where the carbon fiber is starting to fracture the completion of the stress fracture is going to appear as sudden. Also, if the stresses are high loads, when stress fractures begin to appear the fractures are going to progress much more quickly than light loads. As compared to metals, the fractures appear to be sudden because we tend to see signs of potential failure easier in metals goving us more warning.
One of the things I love about carbon fiber isn’t so much carbon fiber itself, which is great for space and aerospace, but other composites you can weave with it. What really interests me is the possibility of using it as a base and combining it with Carbon Nanotubes, Graphene, metals, and other components to increase either conductivity or insulation properties. Just think of Carbon Fiber as The Base canvas in a chemical factory. - Combining carbon nanotubes and graphene is hard enough as it is (and isn’t exactly as performant as todays best materials at all) but when you use other components based on properties, Now you are getting somewhere. The day where we have the right combination of cvd, and plasma sintering of carbon nanotubes, graphene, foams, with other components is coming- until then, carbon fiber acting as a base is the best we’ve got in terms of being able to make a carbon neutral to carbon negative material that’s useful across a Wide Spectrum. From CO2 and carbon farming- to a graphene carbon composites in Aerospace and everything in between that Everyone can use. All that, combined with renewables and hydrogen generation Can be the carbon sink we need to mitigate climate change.
Excellent video 👏 👌 most of people talking about CF don't know sheet about it. Cf is excellent stuff if used properly. Titan sub ( and pseudo engineers who criticize CF) got blamed for carbon fiber use, if it's a bad material, overlooking a pile of pf mistakes made designing, and using, that sub 😢
If your annual inspection actually includes a thorough ultrasonic test then composite is probably a better material. The big advantage for aluminum is that critical crack length even for parts that see 2/3 of their ultimate stress is ~1/4", long enough that it can be spotted with a mirror and flashlight. You also can't lump all metals together below about half the ultimate stress steel can endure unlimited cycles. Carbon fiber and aluminum do not have this property.
Yes, I do think there's an important subtlety here around the definition of failing "without warning". Most people's intuitive notion of that phrase is that a "warning" is human-perceptible and will give you a chance to act when your structure is failing. I get that ultrasound scans can reveal fatigue/damage in carbon composites, but I think at a fundamental level the plastic deformation of metals makes people feel better about them from a human perspective.
This statement does not consider most scenarios. Especially aluminum parts made from rolled sheets have a microstructure leading to a crack-nucleation life of 0. This means, that any loading, no matter how small, will damage the material - you mentioned this point. However these type of defects usually propagate insde the material and cannot be picked up through visual inspections. Without preventive maintenance, such a part will become brittle and eventually fail abruptly. On the other hand theoretical models show, that a well designed and manufactured CF-part may even have an unlimited crack-nucleation life. And once the part fails, it usually does not just snap but it will rather absorb a lot of energy during destruction. This does not make a difference from an engineering point of view, but I guess on my bicycle I rather have a frame, that gives me a couple of seconds reaction time before completly falling apart.:D
I appreciate all the engineering work your team is doing and the effort it takes to produce a video like this. The “umm, actually” moment for me was the DAMAGE SIZE / FATIGUE CYCLES OR TIME graph. Even if you’re making a salient point there’s not much data for others to work with
Also - 3D fibre layup (through layer stitching/tufting allows a whole other degree of stiffness to the layup controlling the inter layer lamination / layer separation strength.
I found out the hard way that 'carbon fiber' does not like abrasion. When I got my first carbon fiber fishing rod I put it on my rod holders in my pickup and bunji corded it down with a few other rods. Then I drove about 3 hours to the river to fish. I discovered that one of the metal guides was vibrating against the carbon fiber rod body and it had cut a line about 1/16" deep in the rod. I cleaned up the abraided groove and epoxied it and was able to salvage the rod but I learned to never allow any thing to rub or vibrate against the rod while carrying it. I has lived in a rod bag ever since.
Thats one of the reasons they use Basalt fiber in Boats and sporting equipment as well as artificial limbs. Its also natural ..has a huge temp tolerance ballistic and abrasion resistance .. its cheap green and requires or produces very little like water or carbon dioxide in its manufacture.. it makes up a huge part of the earths crust and its been squeezed out by the tens of millions of Tonnes daily... and even more in the past. If you need it lighter combine it with flax hemp or jute fibers.. Its actually more resistant to delaminating than carbon epoxy and highly chemical and salt resistant. Its cheaper to make.
People forget a composite wing bears loading when flexing up or down, remember that when you are on a plane taking off, it stretches more then compresses ether direction
I'm looking for heat resistance. I am a glass artist and essentially, I want to be able to flatten molten glass (approx 1900 degrees F) with a piece of carbon fiber. I have used graphite blocks for this in the past. Would some kind of carbon fiber 'screening' or stiffer material work for this?
Nice video! Would‘nt it be worth mentioning that the generalization on metal fatigue behaviour is only correct for cubic face centered metal lattices, not for cubic room centered.
Worth mentioning is burning and burnt composites are hazardous. Air Force crash recovery kits contain pails of commercial liquid floor wax to spray on composite wreckage as fixative to contain (most) friables. If using composites in hobby work don't chuck the leftovers into your burn pile, bag and dispose of safely.
From a repair perspective, how is DarkAero going to ensure that any repairs done to the wing (in the eventual event of impact damage by bird strike, dodgy ground handling, etc.) retain the desired surface roughness? How about burns from lightning strikes if, you know, someone is silly enough to fly close enough to a CB cloud to get struck? How long would those repairs take?
Yes, in certain applications. Standard modulus CF tubing is stronger and lighter than 4130 Chromoly. It flexes similarly. The challenges come down to how to bond it to metal and resulting galvanic interactions, how to bond it other carbon fiber structures and other materials,and cost vs benefit. Please don’t take my word for it and do your own research. There are lots of resources on the web including manufacturers data, testing videos, as well as the excellent videos by DarkAero. I have looked into this extensively and this is all just off the top of my head.
Depends on how you plan to attach tubes together. A full blown monocoque should be lighter than a similar sized steel tube frame anyway, and for chassis rigidity I'd go with the former
If I'm designing a car's frontal impact structure out of a CFRP, with a titanium reinforcement within, such that it can appropriately dissipate a high speed collision's energy and then still have some composite material volume left for any potential secondary collisions or impacts.....what kind of fiber would I need? How would they need to be aligned? What resin? How much resin? Should the titanium pipe be wrapped by layers of carbon fiber threads around it or wound like a spring? Or should the fibers be facing the direction of the impact/compressive load of the collision head on?
Have you looked at laminations and composites using Basalt fibers.. its not as light but its ballistic and ability to resist tearing shattering and temperatures and chemical attack make it an excellent partner in such roles ... Im coming at it from the hammering and flexing of boat hulls in the ocean and Kit cars ..military uses.. and civil engineering as a light super stable replacement for steel in structures exposed to fire hurricanes ..earthquakes. Its also a Zero added carbon material beyond its melting to form a fiber. Temp stability -250dec C to 800C plus. You can wrap exhaust manifolds in it its none hazardous/itchy easy to work.
Orientation of Individual Fibers, Fibre Dimension, interlayer stitching, assembly orientation, and inter-assembly factors, also matter. As well as if any Core Material is used, to create a Sandwich, rather than a single Skin of material!
*Video Summary: Carbon Fiber Myths That Aren't True by DarkAero, Inc* - *Myth 1: All Carbon Fiber is the Same* - Carbon fiber composites are customizable, blending fiber and resin properties. - Variables like fiber type, resin type, fiber orientation, and manufacturing process affect the composite's properties. - *Myth 2: Carbon Fiber Has No Strength Under Compression* - Carbon fiber composites have significant compressive strength, contrary to the belief that they only support tensile loads. - Compressive strength is influenced by fiber orientation and the resin matrix. - *Myth 3: Carbon Fiber Can't Handle Damage and Repeated Loading* - Carbon fiber has better fatigue resistance than metals. - Damage can be assessed over a wider window using techniques like ultrasonic inspection. - *Key Takeaways* - Carbon fiber composites are not uniform; they can be tailored for specific applications. - They have both tensile and compressive strength. - They offer better fatigue resistance than metals and can be monitored for damage.
I have been watching your videos and must commend you on your professional and focused mission. However I am reminded of the scene in Jurassic Park where Jeff Goldblums character asks, " Dinosaurs. Are there any dinosaurs on this tour? "
with so many different combinations of weave and resin, how would one then test for cyles? such as if you were designing an aircraft in the utility category that requires to be loaded to 4.4g? also how would you then input said data from test samples into a design software? as much of it does not exist and must be manually entered to get accurate data. such as a stress analysis when initially coming up with air frame structure but also with regard to determining composite structures such as that of sandwich plates in wing sections, or the aerofoil itself? would you build a wing section then test that to destruction?
Love the content ( fellow engineer ) Recommended you slow down the delivery and pause on key issues and facts. Put the effort into the promotion you are clearly investing in this amazing project.
When used as a pressurized vessel the strands of carbon fiber has a very high tensile strength and the matrix is just keeping everything in place. When a carbon fiber vessel is compressed from the outside, the primary strength comes from the matrix, the carbon fiber isn’t really doing much and is susceptible to collapse once the matrix gives out.
Hi great video! However, it’s apparent that you have likely gotten a lot of questions about carbon fiber after the demise of the Titan. I hear what you say, and I admit that carbon fiber is much better in your application than Stockton Rush’s application. I think an excellent follow on video would be for you to critique the titan design in light of what you know about carbon fiber. I think that would provide an even better contrast to the points that you make in this video. Thanks!
I second your comment! As I watched the video, I couldn't help but think about the Titan -- and how three things likely led to its demise: first, using insufficient and untested material for the task it was put to (if I recall correctly, the shell was only 6 inches thick), second, not using any techniques to check for stresses in the hull between dives, and third, having no idea how many times something like the Titan could dive before failing. Titan was a failure of sloppy engineering, not a failure of carbon fiber materials!
yea same. People's faith in carbon fiber has gone. Meanwhile motorsport fans have seen so many drivers walk out of multiple impact pileups/crashes/collisions thanks to a carbon-fiber reinforced polymer w/aluminium-honeycomb-matrix safety cell and crash structures. Although I do feel like crashes like Hubert Spa 2019 and van't Hoff Spa 2023 were cases where CFRP wasn't strong for 2nd crash after the material dissipated the 1st one.
sad thing is thermal sensitivity of the room temperature epoxies their E performance gradually degrade from 60C to 100C high temp epoxies are hard to come by and are not easy to cure correctly
Bond a piece of CF to a piece of titanium. The difference in deflection under pressure stands a good change of failing at the joint. Not that CF itself failed, but the metallic interface could act like a knife-edge if the titanium deflects less that the CF.
Thank you for not jumping on the media bandwagon of saying cf has no compressive strength. It's too bad this video wasn't around a few months ago when everyone was running their mouth as if they were experts.
what kind of wiring do you use for your wiring harness? is it stiff on purpose? is there shielding in it? i'd love to learn about the electrical system!
Well, the idea of destruction free testing and the bigger window between detection of the damage to the point where this damage reaches a critical size failed pretty spectacularly in the case of the Titan, don't you think?
Nice overview. I've been wondering, if you're designing a carbon fiber part specifically for compressive strength, does it help to add a bit of something like glass (e.g. fiber or micro-beads) along w/ the carbon fiber & resin? Or does it not work that way?
The direct compression strength of glass FRP is much lower than carbon. Pure carbon fiber aligned with the compression forces is the way to go. This has been tested.
So would you spiral wind carbon filaments in a carbon/resin composite cylinder using fiber donated by Boeing because it was no longer certified for aerospace use, and then not autoclave it, and use it in a deep diving submersible without checking it for voids, then dive it repeatedly against the formal written advice of a significant number of expert submersible engineers? Seriously, I realize there isn't enough to comment on, and you're an awesome engineer, and a great teacher.
Also what would the compressive/impact strength be for 2 blocks of CFRP stacked on top of one another? Can the increased volume (height) offer just more volume of crushable material without losing compressive strength per unit volume?
can carbon fiber composite use metal or ceramic as the bonding medium instead of resin ? since wouldn't a metal/ceramic medium be much more resistant to de-lamentation than resin ?
An interesting question and I don't know the answer. But most ceramics are fairly brittle. You would want something with fracture strength for longevity. And it must elongate at least as much as the carbon fiber before yielding. Even though carbon fiber is brittle, I think it may stretch more than most ceramics.
@@mckenziekeith7434 i was thinking that the carbon fiber layer would essentially act like reinforce bar like rebar does in reinforce concrete. Where the fiber stop the prorogation of crack. Effectively eliminate the fracture weakness. Carbon fiber has almost no thermal expansion, so i thought that would pair with ceramic pretty well, since ceramic have very low thermal expansion as well.
@@keenheat3335 for sure about the tempco. About the rest I don't know for sure. The idea of a ceramic "glue" with graphite fibers is for sure interesting. It would be an interesting material. I have often wondered if sodium silicate could be used instead of epoxy to wet out composite fibers. Sodium silicate can be fired in a kiln. It is used as a ceramic glaze.
One thing I thought is it's not great with impact aramid and glass are better, the other is that I can't use it with polyester. It's also stiff and difficult to work with.
One knit picky point I want to make. When you're talking about metals that eventually fail you're only talking about metals that do not have a safe minimum cyclic loading, ie aluminum. Steel does have a minimum cyclic loading that it can withstand indefinitely. Unfortunately due to the industry which you are in, that is not an option because steel is a hell of a lot heavier than aluminum per unit performance as you already know. I'm just trying to make it clear that not all metals behave like aluminum, only because I do not want misinformation to spread. Other than that, this was a great video
Myth #4: carbon fiber is scary and only engineers with magical knowledge can use it. (People only hear engineers talk about maximizing strength to weight of carbon, so they asume carbon is too complicated for them. But in reality anybody can use it, and they should use it! It's OK to make parts that are not perfectly optimized. An over-built carbon part is still massively lighter and stiffer than the equivalent fiberglass part. For non-critical parts, I say send it. Experiment and learn. You won't regret it!)
as long as we agree that carbon fibre isnt a perfect solution for every aplication aswell, you wouldnt build aa piston out of carbon fibre due to heat strain and limited impact resistance metals can take a blunt hit with more forgivness compared to a carbon fibre part which can and will shatter under if force is applied perpendicular to the weave direction
This may seem like a stupid question, but who is actually qualified to certify a composite aircraft? The construction of these aircraft limit your ability to inspect the various surfaces and components and failures would be easily overlooked. One can follow all the accepted methods of construction and defects or flaws could cause catastrophic failure as a result. While all of this looks promising, the resins themselves appear to be the Achilles heel of the technology. Unless you can bind the parent material with something of equal or greater strength you run the risk of failure.
Maybe part of the 'mythology' stems from the public's lack of understanding of column failure (Euler's formula). Just my speculation. All thin cross sections are vulnerable to column failure.
Didn't you guys post a similar video about a month ago? I watched it but couldn't find it to rewatch later. Was there something incorrect in the other video?
It has a bunch of nearly unresolvable design flaws. It's not going to fly safe without some major changes, a hard pill to swallow when they've been painting themselves as "experts".
@@ccengineer5902Would be instructive to have a short list of these defects. I am sure there are many aircraft and composites engineers out there would be interested to read through it.
As with anything: "it depends". You can make a CRFP that is VERY conductive, but you can also make it extremely nonconductive as well. It has a VERY wide range of properties.
You make it sound like it's the perfect material for submarines as well. Ignoring the Titan which used expired carbon fiber and didn't use a prepreg autoclave process, why hasn't someone else try to build a properly manufactured carbon fiber sub?
Thank you! During the aftermath of the OceanGate tragedy, a lot of misconceptions about carbon fiber were promulgated, especially carbon fiber in compression. Thank you for clarifying much of this and correcting misunderstandings.
Wood is the original composite structure for airplanes… Steel tube, fabric, and wires, make an interesting form of macro composite structures as well… Vne and Vna keep the plane from exceeding the inherent structural strengths of the materials… When carbon fiber structures start exceeding their ultimate strength…. The fiber starts to pull away from the matrix leaving visible scars… We don’t need to go to submarine depths to prove composites don’t work… there are limits for everything. But, in the marine world boats have used fiberglass composites for many decades… proving the values of selecting the right fiber and fabrics for the job… Go Dark Aero! 😀
@@mckenziekeith7434 is it technically the same, molecular speaking, is it a bunch of layers of graphene? And if it is , the orientation and size of those layers would be highly important and dependent on the manufacturing process.., how do you know what you're getting? When you try and look it up or ask they just say it's proprietary information... I mean it's easier to find more out about the "top secret" "carbon carbon" graphite fiber used for ballistic missile re-entry shields then it is for the consumer stuff!!! (If I remember correctly it's pyrolysized nylon in a hydraulic press)
Unless you design *tensile rings* into your compression sample... it is clearly not strong compressively. Practical realities trump theoretical numbers.
When people say that composites (especially carbon fiber) fail suddenly, I don't think they are talking about fatigue life. Like you say, carbon fiber composites are (as far as I know) the best performing materials we have for cyclic loading. I think they mean that as the stress increases to the point of fracture, they yield completely and abjectly (one might say catastrophically). Whereas 4140 cromoly steel, when it yields, it continues to put up a hell of a fight for every mm of additional deflection past yield. It may be defeated but it makes you work for every mm even in defeat. This has major implications for energy dissipation in things like crashes and whatnot. A 4140 roll cage will continue to protect you even as it yields. But carbon, once it yields, it is all over. Total surrender. Sometimes this matters. I know you guys know all this because you are very smart. But maybe you didn't get why people say carbon fiber fails suddenly.
Im glad i saw this comment as i was coming to say the same. In a lot of cases where you see failure of CF parts you see things like rims or frames on bicycles. Objects that may have had sharp impacts in an area in addition to loads near yield. If a rim is perfect but in a single day hits 500 rocks thats a lot of impacts.
they should have mentioned in the video that carbon fiber composites are brittle (and as you said fail catastrophically), compared to the ductile behavior of steel. The brittle behavior of cfc isnt a bad thing per se but you need to engineer around its shortcomings
@@ak1s4 I think they were trying to avoid using the word "catastrophically." This video was partly intended as a defense of carbon because a lot of people have a lot of misconceptions after the titan sub implosion event. That is my take anyway. It is all fine you just need to make sure you design within the limits of the material. Carbon is still lighter even when you allow a more generous safety margin than you would with steel.
By definition, materials that exhibit behaviours similar to carbon are called brittle. These include concrete and glass, among others. Ceramics are also part of this family. In the case of carbon, the ultimate stress (fu) is very high, but it can't deform too much, so the overall energy absorption (ie the area under the stress-strain diagram) isn't that big. Like I said that doesn't mean anything bad.
Really important comment.
There are three different failure processes here. One is single momentary overstress, another is fatigue damage (tens or hundreds of cycles of high stress), the third is cyclic stress (thousands or millions of cycles of less high stress).
Carbon fiber: abrupt complete failure from momentary stress beyond yield limit, gradual loss of strength from accumulated fatigue damage, no change of properties from cyclic stress
Steel, especially mild steels: gradual energy-absorbing yield from stress beyond yield limit, gradual loss of strength from accumulated fatigue damage (primarily corrosion-induced) with large critical crack size, no change of properties from cyclic stress
Aluminum, especially high tensile aircraft aluminum: some energy-absorbing yield from stress beyond yield limit, gradual loss of strength from accumulated fatigue damage with much smaller critical crack size, work hardening from of cyclic stress.
The move from aluminum to carbon fiber for long-life commercial aircraft is primarily because those aircraft have to stripped down to bare metal every 10-15 years and minutely inspected for cracks, especially around stress concentrators like windows and rivets.
Not all composite fibers are the same. Kevlar is a bit lower tensile yield strength than carbon fiber, and more costly and heavier, degrades quickly when exposed to UV, and has substantially less compressive strength. But Kevlar absorbs a huge amount of energy when pulled beyond it's tensile elastic limit. In the high-cycle low stress regime it also absorbs energy, making it "dead". This makes it good for armor and rotor blades, or bits exposed to ramp rash like leading and trailing edges, or radomes (noses and antenna covers) where carbon's conductivity is a problem. Kevlar's lack of compressive strength makes it a poor choice for most aircraft structure.
I'm frankly astonished that people build boat hulls out of carbon fiber, but it's so obviously superior for airplanes and wind turbine blades that the cost has come way down as the production volume has gone way up. $/stiffness for Chinese carbon fiber is now just 30% greater than fiberglass! Kevlar and fiberglass are a far better materials for a boat hull that should limp home safely after accidentally smacking a pier, rock, or reef (or another boat).
As an aerospace engineer, composites in compression do have strength but because of the sudden failure modes, buckling can be a serious problem and is hard to predict in comparison to an isotropic material. This is especially true in asymmetric composite layups that have complex material responses where compression can cause torsional loads
Sorry, really curious, so I'm asking every expert commenter here: If I'm designing a car's frontal impact structure out of a CFRP, with a titanium reinforcement within, such that it can appropriately dissipate a high speed collision's energy and then still have some composite material volume left for any potential secondary collisions or impacts.....what kind of fiber would I need? How would they need to be aligned? What resin? How much resin? Should the titanium pipe be wrapped by layers of carbon fiber threads around it or wound like a spring? Or should the fibers be facing the direction of the impact/compressive load of the collision head on?
@@corpsecoder_nw6746 I can’t really give any meaningful advice there- the composites ive worked with are pretty much done for once they incur any major damage- but that may not be the case as much with isotropically distributed fibers in a ductile matrix? Not too sure hopefully you get some good answers
@@corpsecoder_nw6746it's a massive topic, search how carbon fiber is used in racecars. Most of them have a steel alloy roll cage, Carbon Fiber panels, and a lot of times they have special carbon fiber deformation zones, that dissipate (absorb)crazy amounts of energy in the collision (a lot more than steel would) .
Also carbon fiber supercars handle high speed collisions very well, because of the energy absorbing qualities of CF.
Exactly! Concrete and Glue joints have some measurable tensile strength to them but you don't design anything to rely on those as the failure modes are sudden and unpredictable.
@@corpsecoder_nw6746ok first off, titanium is way to rigid to use in crumble zones/crash structure. second, it is very rare and very hard to make a crash structure out of carbon fiber. There are only a handful of manufacturers that do that (i.e rimac) and even then it's still only partial. It's usually aluminum subframes combined with a carbon monocoque center. (for reference I would recommend looking at the Aventador chassis, it's a little bit older of a platform but it is still what most supercars cars look like underneath)
Other than that I can go into specifics, I assume a larger weave would be be best for rigidity, but if you want it to "deform" (aka probably still shatter) on impact, probably a smaller thinner one
The grain of truth is that CFRP loaded in compression or shear is very sensitive to the quality of the interlaminar bond, and this can be affected by layup quality, contamination, consolidation, and damage. Any of these factors can initiate a delamination which results in catastrophic failure.
There are a lot of ways to introduce latent faults during manufacture.
The Titan submersible implosion is probably a good example of this.
@@bishopdredd5349the titan submersible imploded mainly due to ignorance, miscalculations, expired prepreg, improper layup method, design faults in particular of the titanium ring interface and all kind of different shortcomings. It has been determined the load capacity margin was next to non existent for the depth it was going to.
Anyway, the resin bond between the layers and "contamination" is not really the problem with compression. Instead it much more affected by the orientation of the Weave/fibres and the amount of resin during layup that limits the bucking load capacity of the fibres.
Yeah, his explanation about compressive strength is guided by their use of the material, I think. If they would make titanium planes, he'd talk differently.
I rewatched this and drank a shot every time he said carbon fibre. My face feels like a void but on the up side I no longer feel fatigued, stressed, in tension or compression.
I did the same; am now in my plastic deformation region and can never recover.
@@davidf2281 Sounds like you’re in a state of non linear deformation (aka slumped on the sofa) due to under estimating load cycle capacity resulting in insufficient ultimate strength.
@@MrFloneil dude i wish this thread was longer lol
The compressive strength of carbon fiber is dominated by Euler column buckle. The resin's job is to prevent lateral displacement of the fibers leading to rupture. The failure mode is rupture/buckling rather than tearing. The straighter the fibers align with the axis of compression, the easier it is to restrain the effects due to Poisson's ratio. Things get more complicated when the axis of compression moves. Optimization is the balance of what is gained vs what is lost. A general purpose material is sub optimal if it can resist phantom loads that cannot be generated during the useful life of the material.
if I'm making a car's impact structure with CFRP and say I have a titanium pipe for reinforcing said structures. Say, I want the internal occupants to not experience more than 10gs in a 60mph crash, the structure should have some "meat"/volume left for a 2nd crash like that (40mph) without being much harsher (under 20gs) on the occupants....how much CF do I need? What kind of fiber? What kind of resin? How much resin-to-fiber? What way should the fibers be aligned? How do I use the titanium pipe to maximize strength and resilience of the material for secondary impacts/compressions? How dense will the CF fibers and resin be? How much volume? How much weight will it be? How much would it cost? Can it be made to be inert to natural weathering or would I have to paint it to shield it from UV and rain and other gases?
so you're saying the titanium pipe and the fibers facing the direction of impact/crash?
+/-45 degree woven glass epoxy or carbon fiber tubes. Placed behind a bumper reinforcement bar. And mounted to the chassis hard points near suspension and engine mounts.
This series is fantastic. Something I would love to see in a future episode is the practical maintenance of various types of carbon fiber components; so when they are damaged for whatever reason, what are the methods and processes to isolate and replace the damaged area, and discussion of resulting strength or changes in characteristics of the repaired sections.
So many variables that a definitive video on this topic would be lengthy and even at that, incomplete.
Yea, that would be awesome and maybe those would work with glassfiber parts too?
Sorry, really curious so I'm asking every expert commenter here: If I'm designing a car's frontal impact structure out of a CFRP, with a titanium reinforcement within, such that it can appropriately dissipate a high speed collision's energy and then still have some composite material volume left for any potential secondary collisions or impacts.....what kind of fiber would I need? How would they need to be aligned? What resin? How much resin? Should the titanium pipe be wrapped by layers of carbon fiber threads around it or wound like a spring? Or should the fibers be facing the direction of the impact/compressive load of the collision head on?
What i know about composite repair, on experimental glider airplanes:
Grind away the damaged section. Create a 70/1 incline on the good composite sections to glue on the new layers.
This way, you can replace part of it without loosing strength.
Also, to figure out what was in there, do a burn test.
Cut out a sample of the whole structure. Pyrolyze the resin.
Take a good look at the now visible layers.
Yeah, i don't think the last bit is adequate for planes that need to pass certification :D
but on those, you can look up the layers in your paperwork, of course.
Very good. Thank you. One important factor in compressive strength is the layup of the fibre. The woven material has transverse strength through the thickness of the build. This increases the strength in a number of ways. From my observations of the Carter Copter wing development, some of the early problems were related to the fiber being stronger than the resin allowing strands to pull through the resin under extreme tensile load causing failures especially near embedded parts. Talking about the submarine hull failure, from what I saw the hull was wound rather than “knitted” so there was very little strength radial through the build. How I imagine that the failure would have progressed would have been tinkling of the inner build on the inner side as the resin gave way and failed in layers. The loading of the sub’s hull was an extreme case. Very few structures are loaded in that way. Something to keep in mind when designing and making spars, though. Another useful piece of knowledge is that carbon fibre is conductive and its resistance increases (or decreases, I can’t remember) under tension. This means that you can build in continuous material stress evaluation, with the native material, by embedding electrodes in various locations in loaded panels. I have made a living over 20 years using carbon fibre in ways it was never intended for. It is a truly awesome material.
Can I count watching this as part of my Continuing Education/ Professional Development time?
Excellent summary, and just makes me want to learn more about the analysis, design, and manufacturing of composites.
Hahaha those damn PEO rules back at it again.
I love flying and these vids. I always get a kick out of how smart these guys are when so young / baby faced.
That was a really clear lecture. Thanks for taking the time to write it.
I once tensile tested sandwich core foam with plain weave carbon fiber and noticed there is necking forming until a sudden rupture. I wonder if it's mostly attributed to the foam core for the plastic yielding behavior. The relationships between fibers and cores would be an interesting topic to cover. Awesome video.
if I'm making a car's impact structure with CFRP and say I have a titanium pipe for reinforcing said structures. Say, I want the internal occupants to not experience more than 10gs in a 60mph crash, the structure should have some "meat"/volume left for a 2nd crash like that (40mph) without being much harsher (under 20gs) on the occupants....how much CF do I need? What kind of fiber? What kind of resin? How much resin-to-fiber? What way should the fibers be aligned? How do I use the titanium pipe to maximize strength and resilience of the material for secondary impacts/compressions? How dense will the CF fibers and resin be? How much volume? How much weight will it be? How much would it cost? Can it be made to be inert to natural weathering or would I have to paint it to shield it from UV and rain and other gases?
Glad you’re addressing the “compression” nonsense that’s been spouted lately
It is amazing the nonsense spouted since the submersible implosion.
Any half decent in depth video has talked about the way the haul was wound, not just the fact that it was carbon. Also, not that carbon can’t do it or doesn’t have any compression strength, but rather that it wasn’t the optimal material…which is all true.
@@gpaull2 yeah, WET strands woven around a titanium core?! That's just asking for a disaster. Now if it was properly engineered dry carbon, the results would have been WAY different.
The carbon fiber pressure hull was a stupid use of carbon fiber. I remember i was at a conference like 10 years ago. And some one did a presentation on a carbon fiber pressure hull and we where talking about how it was a dumb idea back then. I would maybe have used it for un-manned rov or auv maybe. If it actually made it lighter or better in some way.
@@mshepard2264 Not necessarily. The buoyancy added by the carbon fiber is a good attribute for a submersible. Every material has its limitations, but generally these can be overcome by good design. I think the main issue in this case was arrogance that led to poor design and fabrication. It is no different that the issues with aluminum that were discovered early on with pressurized airlines such as the De Havilland Comet. Saying that carbon fiber shouldn’t be used for a submersible due to one failure is like saying aluminum shouldn’t be used for airliners given that the Comet had multiple failures before the cause was found and mitigated through design.
Easily one of the best educational videos I've come across on this topic.
Not a good choice for submarine pressure hull, good choice for F1 and aeroplanes.
I've been cutting honeycomb core for over a decade. Probably the hardest thing for people to get their head around is that there is a nearly infinite number of combinations available. Honeycomb core has a few key properties. Materials, cell shape, and no it isn't all hexagons, cell size and density. Change any of these and you have a completely different material. Just looking at density which is measured in pounds per cubic foot. I would break it into 3 broad categories. Lite would be under 5# medium between 5# & 7# and heavy 7# and up. Heavy you can cut almost like a solid, run an end mill into it to remove material. Try that with medium or lite core and you'll make a proper mess. To say nothing about how density affects work holding. Even the size of the part significantly impacts it's behavior. A 0.500" thick sheet is very different from a 1.000" thick sheet. By the way, I can count on one hand the number of times we have cut carbon fiber based core. And ribbon direction. Ribbon direction, ribbon direction, ribbon direction. Get that wrong and nothing you do after that matters, the part is scrap.
This is exactly what I was looking for. If I'm making a car's impact structure with CFRP and say I have a titanium pipe for reinforcing said structures. Say, I want the internal occupants to not experience more than 10gs in a 60mph crash, the structure should have some "meat"/volume left for a 2nd crash like that (40mph) without being much harsher (under 20gs) on the occupants....how much CF do I need? What kind of fiber? What kind of resin? How much resin-to-fiber? What way should the fibers be aligned? How do I use the titanium pipe to maximize strength and resilience of the material for secondary impacts/compressions? How dense will the CF fibers and resin be? How much volume? How much weight will it be? How much would it cost? Can it be made to be inert to natural weathering or would I have to paint it to shield it from UV and rain and other gases?
@corpsecoder_nw6746 You're asking me? Sorry I couldn't answer even if I was an engineer with a masters in material science focused on composites. Too little information on your design. That isn't a suggestion for you to provide more detail. I like to help but this well beyond my knowledge.
"DarkAero, Inc" Does it correct. I know this fine start-up aircraft company follows FAA requirements, and I am pretty sure DarkArero, Inc has a set of ASME & ASTM reference manuals or digital library with both the latest additions and adenda . Thank you DarkAero, for another college level presentation.
Excellent summary about material limitations between metal and composites! I've heard similar discussions about material selection for building road bicycles. I've ridden both and there certain attributes I like about both. The same goes with some of the aircraft I've flown too!
Excellent high level overview. Keep in mind carbon fiber parts have half the bearing capability for fasteners that metal ones do, that is why you often see pad-ups around bolt and hi-lock holes. Also the edge margin for fasteners has some non-linear response so your edge margin and edge distance between fasteners needs to be quite a bit larger between fasteners.
Another great presentation. Thank you. The rebar/concrete comparison to fabric/resin really CEMENTED the point.
I see what you did there
Great presentation and information. Thx.
Wow thanks for this, you've confirmed and clarified some things for me regarding carbon fiber.
Another excellent & informative video!
Very good video. Perhaps a word or two about how to choose different fiber grades, orientations and matrix material for various applications would have come handy, but would probably not fit into such a short video. Thanks!
~ 4:30 - I had to look up your medieval units and their arcane, arbitrary abbreviations*. OK, so ~1GPa and ~1.4GPa, respectively.
*) So you don't have to: "KSI" is kilo pound-force per square inch; it's about 6,9MPa (mega pascals)
KSI is such a cursed unit. Going up to mega is MPSI, why are the pounds dropped from KSI? Why are you using metric prefixes with non-SI units? Why not TPSI for Thousand Pound-force per Square Inch?
I came here to learn and i leave smarter and come back for other videos! Nice work
Absolutely excellent video on CF strength and fatigue (compared to metals). Thank you!
Excellent video, one of the very few I had to slow down to 0.75x so that I didn’t miss information.
I think the sudden breakage of carbon fiber components has to do with two things. 1) the ability to see and inspect possible stress locations and 2) the amount of loading on the part. If you can't see where the carbon fiber is starting to fracture the completion of the stress fracture is going to appear as sudden. Also, if the stresses are high loads, when stress fractures begin to appear the fractures are going to progress much more quickly than light loads. As compared to metals, the fractures appear to be sudden because we tend to see signs of potential failure easier in metals goving us more warning.
Very informative! Thanks.
One of the things I love about carbon fiber isn’t so much carbon fiber itself, which is great for space and aerospace, but other composites you can weave with it.
What really interests me is the possibility of using it as a base and combining it with Carbon Nanotubes, Graphene, metals, and other components to increase either conductivity or insulation properties.
Just think of Carbon Fiber as The Base canvas in a chemical factory.
- Combining carbon nanotubes and graphene is hard enough as it is (and isn’t exactly as performant as todays best materials at all) but when you use other components based on properties, Now you are getting somewhere.
The day where we have the right combination of cvd, and plasma sintering of carbon nanotubes, graphene, foams, with other components is coming- until then, carbon fiber acting as a base is the best we’ve got in terms of being able to make a carbon neutral to carbon negative material that’s useful across a Wide Spectrum.
From CO2 and carbon farming- to a graphene carbon composites in Aerospace and everything in between that Everyone can use.
All that, combined with renewables and hydrogen generation Can be the carbon sink we need to mitigate climate change.
Excellent video 👏 👌 most of people talking about CF don't know sheet about it. Cf is excellent stuff if used properly.
Titan sub ( and pseudo engineers who criticize CF) got blamed for carbon fiber use, if it's a bad material, overlooking a pile of pf mistakes made designing, and using, that sub 😢
Thank you for the great lessons. Please show more.
If your annual inspection actually includes a thorough ultrasonic test then composite is probably a better material. The big advantage for aluminum is that critical crack length even for parts that see 2/3 of their ultimate stress is ~1/4", long enough that it can be spotted with a mirror and flashlight. You also can't lump all metals together below about half the ultimate stress steel can endure unlimited cycles. Carbon fiber and aluminum do not have this property.
Yes, I do think there's an important subtlety here around the definition of failing "without warning". Most people's intuitive notion of that phrase is that a "warning" is human-perceptible and will give you a chance to act when your structure is failing.
I get that ultrasound scans can reveal fatigue/damage in carbon composites, but I think at a fundamental level the plastic deformation of metals makes people feel better about them from a human perspective.
This statement does not consider most scenarios. Especially aluminum parts made from rolled sheets have a microstructure leading to a crack-nucleation life of 0. This means, that any loading, no matter how small, will damage the material - you mentioned this point. However these type of defects usually propagate insde the material and cannot be picked up through visual inspections. Without preventive maintenance, such a part will become brittle and eventually fail abruptly. On the other hand theoretical models show, that a well designed and manufactured CF-part may even have an unlimited crack-nucleation life. And once the part fails, it usually does not just snap but it will rather absorb a lot of energy during destruction. This does not make a difference from an engineering point of view, but I guess on my bicycle I rather have a frame, that gives me a couple of seconds reaction time before completly falling apart.:D
I appreciate all the engineering work your team is doing and the effort it takes to produce a video like this.
The “umm, actually” moment for me was the DAMAGE SIZE / FATIGUE CYCLES OR TIME graph. Even if you’re making a salient point there’s not much data for others to work with
Also - 3D fibre layup (through layer stitching/tufting allows a whole other degree of stiffness to the layup controlling the inter layer lamination / layer separation strength.
I heard that weaving sometimes reduces compressive strength
Thank you for another excellent video tutorial. Great work.
9:20 I’m not sure if I’m happy to hear that it has reduced or eliminated the need to do corrosion or fatigue inspections
This is the textbook example of a quality presentation.
I found out the hard way that 'carbon fiber' does not like abrasion. When I got my first carbon fiber fishing rod I put it on my rod holders in my pickup and bunji corded it down with a few other rods. Then I drove about 3 hours to the river to fish. I discovered that one of the metal guides was vibrating against the carbon fiber rod body and it had cut a line about 1/16" deep in the rod. I cleaned up the abraided groove and epoxied it and was able to salvage the rod but I learned to never allow any thing to rub or vibrate against the rod while carrying it. I has lived in a rod bag ever since.
Thats one of the reasons they use Basalt fiber in Boats and sporting equipment as well as artificial limbs.
Its also natural ..has a huge temp tolerance ballistic and abrasion resistance .. its cheap green and requires or produces very little like water or carbon dioxide in its manufacture.. it makes up a huge part of the earths crust and its been squeezed out by the tens of millions of Tonnes daily... and even more in the past.
If you need it lighter combine it with flax hemp or jute fibers..
Its actually more resistant to delaminating than carbon epoxy and highly chemical and salt resistant. Its cheaper to make.
Someday in the next TWO years ... i will be attending your clases in the US ( .... from India ❤)
People forget a composite wing bears loading when flexing up or down, remember that when you are on a plane taking off, it stretches more then compresses ether direction
I'm looking for heat resistance. I am a glass artist and essentially, I want to be able to flatten molten glass (approx 1900 degrees F) with a piece of carbon fiber.
I have used graphite blocks for this in the past. Would some kind of carbon fiber 'screening' or stiffer material work for this?
Nice video! Would‘nt it be worth mentioning that the generalization on metal fatigue behaviour is only correct for cubic face centered metal lattices, not for cubic room centered.
Worth mentioning is burning and burnt composites are hazardous. Air Force crash recovery kits contain pails of commercial liquid floor wax to spray on composite wreckage as fixative to contain (most) friables. If using composites in hobby work don't chuck the leftovers into your burn pile, bag and dispose of safely.
From a repair perspective, how is DarkAero going to ensure that any repairs done to the wing (in the eventual event of impact damage by bird strike, dodgy ground handling, etc.) retain the desired surface roughness? How about burns from lightning strikes if, you know, someone is silly enough to fly close enough to a CB cloud to get struck? How long would those repairs take?
Could CF tubing be an ideal selection to replace and to reduce weight etc. of a 4130N tubing structure?
Yes, in certain applications. Standard modulus CF tubing is stronger and lighter than 4130 Chromoly. It flexes similarly. The challenges come down to how to bond it to metal and resulting galvanic interactions, how to bond it other carbon fiber structures and other materials,and cost vs benefit. Please don’t take my word for it and do your own research. There are lots of resources on the web including manufacturers data, testing videos, as well as the excellent videos by DarkAero. I have looked into this extensively and this is all just off the top of my head.
Depends on how you plan to attach tubes together. A full blown monocoque should be lighter than a similar sized steel tube frame anyway, and for chassis rigidity I'd go with the former
If I'm designing a car's frontal impact structure out of a CFRP, with a titanium reinforcement within, such that it can appropriately dissipate a high speed collision's energy and then still have some composite material volume left for any potential secondary collisions or impacts.....what kind of fiber would I need? How would they need to be aligned? What resin? How much resin? Should the titanium pipe be wrapped by layers of carbon fiber threads around it or wound like a spring? Or should the fibers be facing the direction of the impact/compressive load of the collision head on?
Have you looked at laminations and composites using Basalt fibers.. its not as light but its ballistic and ability to resist tearing shattering and temperatures and chemical attack make it an excellent partner in such roles ...
Im coming at it from the hammering and flexing of boat hulls in the ocean and
Kit cars ..military uses.. and civil engineering as a light super stable replacement for steel in structures exposed to fire hurricanes ..earthquakes.
Its also a Zero added carbon material beyond its melting to form a fiber.
Temp stability -250dec C to 800C plus. You can wrap exhaust manifolds in it its none hazardous/itchy
easy to work.
A very informative video. It's too bad the builders of the Oceangate sub didn't watch this first.
Orientation of Individual Fibers, Fibre Dimension, interlayer stitching, assembly orientation, and inter-assembly factors, also matter. As well as if any Core Material is used, to create a Sandwich, rather than a single Skin of material!
*Video Summary: Carbon Fiber Myths That Aren't True by DarkAero, Inc*
- *Myth 1: All Carbon Fiber is the Same*
- Carbon fiber composites are customizable, blending fiber and resin properties.
- Variables like fiber type, resin type, fiber orientation, and manufacturing process affect the composite's properties.
- *Myth 2: Carbon Fiber Has No Strength Under Compression*
- Carbon fiber composites have significant compressive strength, contrary to the belief that they only support tensile loads.
- Compressive strength is influenced by fiber orientation and the resin matrix.
- *Myth 3: Carbon Fiber Can't Handle Damage and Repeated Loading*
- Carbon fiber has better fatigue resistance than metals.
- Damage can be assessed over a wider window using techniques like ultrasonic inspection.
- *Key Takeaways*
- Carbon fiber composites are not uniform; they can be tailored for specific applications.
- They have both tensile and compressive strength.
- They offer better fatigue resistance than metals and can be monitored for damage.
I have been watching your videos and must commend you on your professional and focused mission. However I am reminded of the scene in Jurassic Park where Jeff Goldblums character asks, " Dinosaurs. Are there any dinosaurs on this tour? "
What's your take on the titan implosion? Would it be possible to make a composite material submersible hull?
Well presented 👍😎
Excellent presentation.
with so many different combinations of weave and resin, how would one then test for cyles? such as if you were designing an aircraft in the utility category that requires to be loaded to 4.4g? also how would you then input said data from test samples into a design software? as much of it does not exist and must be manually entered to get accurate data. such as a stress analysis when initially coming up with air frame structure but also with regard to determining composite structures such as that of sandwich plates in wing sections, or the aerofoil itself? would you build a wing section then test that to destruction?
Another great vastly informative video .bravo ! - happy reservation holder
Love the content ( fellow engineer ) Recommended you slow down the delivery and pause on key issues and facts. Put the effort into the promotion you are clearly investing in this amazing project.
When used as a pressurized vessel the strands of carbon fiber has a very high tensile strength and the matrix is just keeping everything in place. When a carbon fiber vessel is compressed from the outside, the primary strength comes from the matrix, the carbon fiber isn’t really doing much and is susceptible to collapse once the matrix gives out.
Hi great video! However, it’s apparent that you have likely gotten a lot of questions about carbon fiber after the demise of the Titan. I hear what you say, and I admit that carbon fiber is much better in your application than Stockton Rush’s application. I think an excellent follow on video would be for you to critique the titan design in light of what you know about carbon fiber. I think that would provide an even better contrast to the points that you make in this video. Thanks!
I second your comment! As I watched the video, I couldn't help but think about the Titan -- and how three things likely led to its demise: first, using insufficient and untested material for the task it was put to (if I recall correctly, the shell was only 6 inches thick), second, not using any techniques to check for stresses in the hull between dives, and third, having no idea how many times something like the Titan could dive before failing.
Titan was a failure of sloppy engineering, not a failure of carbon fiber materials!
yea same. People's faith in carbon fiber has gone. Meanwhile motorsport fans have seen so many drivers walk out of multiple impact pileups/crashes/collisions thanks to a carbon-fiber reinforced polymer w/aluminium-honeycomb-matrix safety cell and crash structures. Although I do feel like crashes like Hubert Spa 2019 and van't Hoff Spa 2023 were cases where CFRP wasn't strong for 2nd crash after the material dissipated the 1st one.
@@alpheusmadsen8485the carbon fiber used on titan was apparently unairworthy carbon fiber bought from Boeing, so it was doomed from day 1
sad thing is thermal sensitivity of the room temperature epoxies
their E performance gradually degrade from 60C to 100C
high temp epoxies are hard to come by and are not easy to cure correctly
Bond a piece of CF to a piece of titanium.
The difference in deflection under pressure stands a good change of failing at the joint.
Not that CF itself failed, but the metallic interface could act like a knife-edge if the titanium deflects less that the CF.
Excellent introduction for us non-engineers. Thank you.
Thanks for the info.
Thank you for not jumping on the media bandwagon of saying cf has no compressive strength.
It's too bad this video wasn't around a few months ago when everyone was running their mouth as if they were experts.
What`s the ultrasound device you are using? Could it be used to study wood + fiberglass structures?
what kind of wiring do you use for your wiring harness? is it stiff on purpose? is there shielding in it? i'd love to learn about the electrical system!
Well, the idea of destruction free testing and the bigger window between detection of the damage to the point where this damage reaches a critical size failed pretty spectacularly in the case of the Titan, don't you think?
Good refresher. I realized years ago CF design was a specialty in itself, A specialty I do not possess.
one problem i have with epoxy glue is its fake stability in water, how to have good resin stability with water?
Nice overview. I've been wondering, if you're designing a carbon fiber part specifically for compressive strength, does it help to add a bit of something like glass (e.g. fiber or micro-beads) along w/ the carbon fiber & resin? Or does it not work that way?
The direct compression strength of glass FRP is much lower than carbon. Pure carbon fiber aligned with the compression forces is the way to go. This has been tested.
I would have liked a deeper look at why carbon fiber composites are stronger in compression than the resin they are made with.
I'd love to hear your take on carbon compression forging. How does it stack up to, say- forged aluminum ?
So would you spiral wind carbon filaments in a carbon/resin composite cylinder using fiber donated by Boeing because it was no longer certified for aerospace use, and then not autoclave it, and use it in a deep diving submersible without checking it for voids, then dive it repeatedly against the formal written advice of a significant number of expert submersible engineers?
Seriously, I realize there isn't enough to comment on, and you're an awesome engineer, and a great teacher.
Hey guys! Can you make a video about the antenna? I remember you guys were considering an alternative type of antenna for this bird…
Would be way stronger if you rotated every layer by 45 degrees.
Also what would the compressive/impact strength be for 2 blocks of CFRP stacked on top of one another? Can the increased volume (height) offer just more volume of crushable material without losing compressive strength per unit volume?
can carbon fiber composite use metal or ceramic as the bonding medium instead of resin ? since wouldn't a metal/ceramic medium be much more resistant to de-lamentation than resin ?
An interesting question and I don't know the answer. But most ceramics are fairly brittle. You would want something with fracture strength for longevity. And it must elongate at least as much as the carbon fiber before yielding. Even though carbon fiber is brittle, I think it may stretch more than most ceramics.
@@mckenziekeith7434 i was thinking that the carbon fiber layer would essentially act like reinforce bar like rebar does in reinforce concrete. Where the fiber stop the prorogation of crack. Effectively eliminate the fracture weakness. Carbon fiber has almost no thermal expansion, so i thought that would pair with ceramic pretty well, since ceramic have very low thermal expansion as well.
@@keenheat3335 for sure about the tempco. About the rest I don't know for sure. The idea of a ceramic "glue" with graphite fibers is for sure interesting. It would be an interesting material. I have often wondered if sodium silicate could be used instead of epoxy to wet out composite fibers. Sodium silicate can be fired in a kiln. It is used as a ceramic glaze.
Your thinking of cmc’s.
One thing I thought is it's not great with impact aramid and glass are better, the other is that I can't use it with polyester. It's also stiff and difficult to work with.
One knit picky point I want to make. When you're talking about metals that eventually fail you're only talking about metals that do not have a safe minimum cyclic loading, ie aluminum. Steel does have a minimum cyclic loading that it can withstand indefinitely. Unfortunately due to the industry which you are in, that is not an option because steel is a hell of a lot heavier than aluminum per unit performance as you already know. I'm just trying to make it clear that not all metals behave like aluminum, only because I do not want misinformation to spread. Other than that, this was a great video
Myth #4: carbon fiber is scary and only engineers with magical knowledge can use it. (People only hear engineers talk about maximizing strength to weight of carbon, so they asume carbon is too complicated for them. But in reality anybody can use it, and they should use it! It's OK to make parts that are not perfectly optimized. An over-built carbon part is still massively lighter and stiffer than the equivalent fiberglass part. For non-critical parts, I say send it. Experiment and learn. You won't regret it!)
Can I use it to build a submersible?
So composites can last longer than metals before fatique fracture. How does that "eliminated the need" fatigue inspections?
The need is never eliminated, it's pathetic to assume so
as long as we agree that carbon fibre isnt a perfect solution for every aplication aswell, you wouldnt build aa piston out of carbon fibre due to heat strain and limited impact resistance metals can take a blunt hit with more forgivness compared to a carbon fibre part which can and will shatter under if force is applied perpendicular to the weave direction
Say something about CFC-CFC welding
This may seem like a stupid question, but who is actually qualified to certify a composite aircraft? The construction of these aircraft limit your ability to inspect the various surfaces and components and failures would be easily overlooked. One can follow all the accepted methods of construction and defects or flaws could cause catastrophic failure as a result. While all of this looks promising, the resins themselves appear to be the Achilles heel of the technology. Unless you can bind the parent material with something of equal or greater strength you run the risk of failure.
Maybe part of the 'mythology' stems from the public's lack of understanding of column failure (Euler's formula). Just my speculation. All thin cross sections are vulnerable to column failure.
Didn't you guys post a similar video about a month ago? I watched it but couldn't find it to rewatch later. Was there something incorrect in the other video?
8:33 you can do that in metals too for the most part.
I think I speak for everyone when I ask “what’s the update on the dark aero? When is she going to spread her wings?”
You do not speak for everyone. Many of us are patient, and would prefer that they take as much time as they need to make sure their aircraft is safe.
@@user2C47 providing a progress update doesn’t preclude safe progress numbnuts
It has a bunch of nearly unresolvable design flaws. It's not going to fly safe without some major changes, a hard pill to swallow when they've been painting themselves as "experts".
@@ccengineer5902Would be instructive to have a short list of these defects. I am sure there are many aircraft and composites engineers out there would be interested to read through it.
@@ccengineer5902 this is new to me. What design flaws does it have?
Nice video! One question though, I know what carbon-fiber is, but what is 'carbnfrber"?
Lmao
I love composites not only do they look cool but they can do cool things!
Great video, I was waiting for some submarine commentary, but you held back
What about lightning? It cause catastrophic damage or not
As with anything: "it depends". You can make a CRFP that is VERY conductive, but you can also make it extremely nonconductive as well. It has a VERY wide range of properties.
There's common misconceptions regarding fiberglass versus carbon fiber as well which could be another good video topic.
You make it sound like it's the perfect material for submarines as well. Ignoring the Titan which used expired carbon fiber and didn't use a prepreg autoclave process, why hasn't someone else try to build a properly manufactured carbon fiber sub?
When are we going to see the Dark Arrow take flight?
Thank you! During the aftermath of the OceanGate tragedy, a lot of misconceptions about carbon fiber were promulgated, especially carbon fiber in compression. Thank you for clarifying much of this and correcting misunderstandings.
Correction; in reinforced concrete the concrete takes the compressive load and the rebar/cable takes the tensile load.
Wood is the original composite structure for airplanes…
Steel tube, fabric, and wires, make an interesting form of macro composite structures as well…
Vne and Vna keep the plane from exceeding the inherent structural strengths of the materials…
When carbon fiber structures start exceeding their ultimate strength…. The fiber starts to pull away from the matrix leaving visible scars…
We don’t need to go to submarine depths to prove composites don’t work… there are limits for everything.
But, in the marine world boats have used fiberglass composites for many decades… proving the values of selecting the right fiber and fabrics for the job…
Go Dark Aero! 😀
Is there such a thing as graphite fiber and can it be made synthetically?
Carbon fiber and graphite fiber are synonyms. Every time you hear about "carbon fiber" the person could have said graphite fiber instead.
@@mckenziekeith7434 is it technically the same, molecular speaking, is it a bunch of layers of graphene? And if it is , the orientation and size of those layers would be highly important and dependent on the manufacturing process.., how do you know what you're getting? When you try and look it up or ask they just say it's proprietary information...
I mean it's easier to find more out about the "top secret" "carbon carbon" graphite fiber used for ballistic missile re-entry shields then it is for the consumer stuff!!! (If I remember correctly it's pyrolysized nylon in a hydraulic press)
@@petevenuti7355 There are a few different grades of material. Engineering strength data is available (modulus and yield strength and other things).
Unless you design *tensile rings* into your compression sample... it is clearly not strong compressively. Practical realities trump theoretical numbers.
Aren't the Airbuses having delamination issues after lightening strikes?