- 15 hours ago
with exceptional mechanical behaviour and unique functionalities
by César Augusto, Brightlands Materials Center
Additive manufacturing (AM) techniques have been extensively explored in the last decades due to their potential to transform existent production technologies. Fused filament fabrication (FFF) is a very versatile AM technique, although it is widely used for prototyping due to their limited mechanical properties, especially in between layers. To approach this matter, a novel technique was developed in which the strength in between layers was increased in 184%. Also included in the topic are embedded continuous carbon fibers with unique functionalities, used to monitor the structural health of 3D printed parts in real time, decreasing the need for periodical inspections.
by César Augusto, Brightlands Materials Center
Additive manufacturing (AM) techniques have been extensively explored in the last decades due to their potential to transform existent production technologies. Fused filament fabrication (FFF) is a very versatile AM technique, although it is widely used for prototyping due to their limited mechanical properties, especially in between layers. To approach this matter, a novel technique was developed in which the strength in between layers was increased in 184%. Also included in the topic are embedded continuous carbon fibers with unique functionalities, used to monitor the structural health of 3D printed parts in real time, decreasing the need for periodical inspections.
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TechTranscript
00:00My name is Cesar, Cesar Augusto. I am a materials engineer and I work as a scientist at the
00:14Bredlands Materials Center in the south of the Netherlands. And today I'm going to be discussing
00:20two different projects that we work on. One is to improve interlay adhesion in 3D printed parts
00:28with normal filaments. And the second one is our developments in continuous fiber printing for
00:36structured health monitoring. So with no further ado, I will just give a small introduction of who
00:44we are. So Bredlands Materials Center is an independent research and development center
00:50in the field of polymeric materials. It is located in the south of Limburg, in Helene,
00:56and it was established by TNO and the province of Limburg. At the moment we have three different
01:05three different programs. Sustainable buildings that focuses on decreasing the energy consumption
01:09of buildings by developing and optical materials and coatings. Lightweight automotive that work on
01:18development of composite materials for lightweight mobility applications. And additive manufacturing,
01:24which is the program I make part of, in which we get normal 3D printing process and try to use them to
01:34high-end use applications. So today I'll be talking about two separate individual projects. The first one
01:43is a project in which we developed an add-on device that increases considerably the
01:50the strength of 3D printed parts, especially interlayer edition. So depending on the alignment of the fibers
01:58and, of course, on the printing parameters, you can reach different types of strengths. And the second one
02:07is continuous fiber printing for structure health monitoring in which the fibers, they work as fully
02:15integrated sensing elements.
02:16So I will start with the first part of the project, which is the high strength in fused
02:24filament fabrication with plain polymers or composite polymers. So to start with, I will give a small
02:30introduction of fused filament fabrication because we all know pretty well, but I think it's worth mentioning
02:38because it's because of the way it works that we we see a need in to improve improving its characteristics. So it
02:47starts with a polymeric filament that is fed into a print head that is hot and move moves in the x and y direction. And
02:56there is a nozzle of around 0.4 millimeter in most cases, in which the polymeric material is squeezed and forms a drawing in the
03:05in the in the print, in the print bed. This print bed moves in the z axis and layer by layer, a 3D printed object is built. So the
03:19nature of the process gets us products that are layered. So if you can see on the on the right hand side, there is a hook
03:29that was printed and all the layers were detached from each other. So it's, it's very visible.
03:35how the process works. So layer by layer, you glue all these layers together and then you get a 3D printed
03:42object. But in the case of that, that hook, the layers, they delaminated and then you can see that
03:48this can be an issue in 3D printed objects for their strength. So if you look into the process, you see that
03:56the layers are stacked together over each other or side by side. And this yields a strength that is
04:05much different in the printing direction, comparing to the vertical direction. So for unfilled polymers, for polymers that don't have
04:17fillers or fibers, the strength runs around 70% of the in-plane strength because you're trying to break the
04:25the filaments on their printing direction. But if you try to pull these layers apart because of the poor
04:32diffusion or the poor connection between these layers, they go up to 70% in strength. And for composites, due to
04:42their rheologic features, like for instance, the fibers or the fillers, they, they, they make it hard for
04:52diffusion to occur in between each layer, there is a, a decrease in strength that goes around 20 to 40%.
05:00So this, the, the, the, the features of fused filament fabrication brings us to a couple of issues that
05:10might encounter. They are, for instance, insufficient interlay adhesion, as you can see in the picture,
05:16the, the, the part just cracks, just cracks because, because of warping. And also parts are highly
05:24anisotropic. They have different strengths in different directions. And because of these reasons,
05:30fused filament fabrication is mainly used for visual inspections or prototypes. So in this project,
05:35what we tried to do was to transform these 3D print, 3D printing technology into reliable and
05:44functional end use application parts. There are several different technologies in the market. I just
05:51brought a couple to, to, to, to illustrate because most of them use a preheating technology, but they are
05:59rather complex. For instance, the first one on the left shows a technology that needs a conductive
06:05coated filament and it forms a plasma between a disc in the, in the green head and, and the filament.
06:12The second and the third one, they use infrared and laser light respectively. And they also only heat up
06:20the substrate ahead of the nozzle. And one of the biggest advantages of the device that we, that we
06:30developed is that it works for all printing directions. So this technology that we call the
06:36be right technology is an add on device that also uses a preheating technology and therefore induces
06:43bonding between layers and it covers all the printing directions. So what we do is, uh, we, we design it,
06:50this, uh, this technology for a commercial printer, in this case, the German wrap wrap. And, uh, we attach it
06:56to, to the printer and, uh, by attaching it to the printer, we, um, we yield a much higher strength.
07:03So some advantages would be, it is very simple to use. It is virtually suitable for most printers.
07:10That means that with few modifications, of course, every printer has a different design,
07:14a different, uh, print head or a different, uh, nozzle. Uh, so with small modifications,
07:20it can be suitable for most of the printers. Uh, it yields more isotropic parts because if you
07:25increase interlayer addition, you decrease the difference between the in-plane strength and the,
07:32and the, the, the interlayer strength and, uh, part parts, they can be suitable for end use
07:37applications depending on, of course, the strength that you need for, uh, the application in view.
07:44And, um, the, the, the, we, we, we have worked with one composite, which I will show in the next slide,
07:50but we are working now on different materials, uh, and, uh, it's also important
07:55to mention that an additional energy source is required because of course, as the other
08:00technologies in the market, you need, um, um, you need to, to preheat your substrate.
08:10So we used this technology first with a polyamide six, uh, reinforced with 30% of, uh, glass fibers
08:18in weight. And what we observed is that, uh, first we, we, we thought that we would have an increase
08:25only in, in interlay addition because that's, that's what we were focusing in. And of course,
08:31um, that's, uh, if you, if you preheat the substrate and you forget a better diffusion,
08:36uh, you will definitely have a better, uh, interlay addition, but we didn't expect to get up to 34%
08:43of increase in the XX direction, in the in-plane direction, but it was, uh, very pleasant to see
08:50that, uh, we increase in more than 180% the, the strength in the Z axis. Uh, you, you may think that
08:59these strengths are, are very, very low, but if you think about, we are talking here of a composite,
09:04uh, with short glass fibers. So the, the fibers itself, they, they, um, they yield a much lower
09:12interlay addition because of the rheologic fixtures of, uh, of a composite. So on the right hand side,
09:19it's possible to see that there is a part printed with this material and applying with beer, applying
09:24the beer right and, uh, with 35% infill. So it's a, a complex part with, uh, with, uh, hangs, for instance,
09:32for the thread. And, um, with only 30% infill, we can, we can yield with this device a complex shape
09:41with high strength. And, um, to, to wrap up this, this first time, this, this first part of the
09:50presentation, I would like to, to, uh, to, to say that this, this device would be suitable for, for those
09:57who are seeking, um, who have, uh, a sufficient X, Y in plane strength, but lacking Z, or they want to,
10:06to yield more isotropic parts, or they have a, a printer without a heat, heated bed or a heated chamber.
10:14And, uh, it's also worth mentioning again, that this, um, this device is more suitable for robust
10:21machines like the German wrap wrap in which we, we used it. And, uh, it is not yet commercially
10:27available. So it's, uh, under development, uh, by Breitland, Breitland's material center.
10:32Breitland's material center is a research and development, uh, center. So, uh, we make a
10:37bridge between industry and, uh, technology. So, uh, what we look are, uh, our partners that would
10:44like to improve their process or material dealers that would like to deliver stronger and more
10:49isotropic parts. And of course we are always willing to, to try the, be right on your material,
10:54your part or your printer, because what we really want to do here is to go one step further and, um,
11:01and, um, and discover and, and, and try to, to know what, what the, the, the device is capable of.
11:07So with, with this, I will wrap up this first part of the presentation and now we'll go to the
11:14second part, which is the structural integrity, integrity monitoring with continuous carbon fibers.
11:21So first we were talking about high strength or, um, or better interlay adhesion, better Z strength
11:28in normal 3d printing. That's, that will be with normal, uh, polymeric filaments with normal, uh,
11:35short fiber composites. And now we're going to talk about continuous carbon fibers
11:40that are not only used for, uh, increased, uh, mechanical properties and, uh, low, um,
11:50low weight, uh, high strength materials, but also in this case for sensing functionalities. So if you
11:56imagine, um, all the, all the, um, all the applications out there that use, uh, carbon fibers or that use
12:04composites and we can see that in many cases we have catastrophic failure, we have, um, um, parts
12:12that they, they break and, uh, and, and, and they, they can cause a very serious accident. So imagine how,
12:20how, how interesting would be to know on site, on time, uh, what are the solicitations that you're having
12:27on your part and, uh, uh, what are the strengths, what are the, the, the, uh, the, the stresses that
12:33your part is being submitted to. So what we're trying here to do is to know exactly, uh, on time,
12:39on site, what is going on on your part. So that could be for, uh, for bike friends, for instance,
12:45that, uh, in the past they, they, they broke catastrophically. There were people that were
12:50severely injured because of that. So what we are trying to do is to avoid that.
12:57So the carbon fibers, um, they are extremely, um, um, promising as Fedor just, uh, mentioned in the
13:06presentation before, what we are using here is also the, their printer, the anisoprint. And now we
13:12will be talking about it in, in the next slides and why we are using their printer. Um, and, um, in,
13:17in this case, in this, in this project we are working on, carbon fiber can work as a reinforcement
13:23and as a strain sensor. So what we get from it is that there is a constant load monitoring.
13:30You know exactly what stresses or strains are being applied in your part or in your bicycle
13:35or in your car at the same moment that you're using it. It will increase product lifetime because
13:41if you need to do, uh, some inspection because you are over the stresses that, uh, you should be,
13:47you can just go there and check it out or, or, or, or, or switch, change that part. It will increase
13:54safety. And the most important one, it will predict catastrophic events. So it will, uh, it will avoid
14:01catastrophic catastrophic events of happening. And most especially, uh, in, as in 3d printing,
14:09as, uh, federal, uh, mentioned it before, the, the, the fibers are integrated in the printing step.
14:15So you have the 3d, um, you have the 3d printer and you print your, your part and the sensors are
14:21going to be integrated inside the part. So there is a video here that shows a beam in which the,
14:29the continuous carbon fiber was printed before. And as you press it, as you apply a stress or a strain,
14:35you get a signal out of it. And then it shows exactly the solicitations that is part, that the
14:46part is being submitted to. So, um, uh, how, how the process is made. So, uh, we used a, an isoprint,
14:56a composer, an isoprint that has a continuous, uh, fiber filament. And the beauty of this machine is
15:02that is open hardware. So, uh, you can basically do whatever you, you want with that machine.
15:09There is a plastic extruder and that there is a composite extruder and with the plastic, you can,
15:13you can, um, you can print your matrix and with the composite extruder, you can print your, uh,
15:20continuous carbon fiber for reinforcement and in our case for sensing functionalities. And the most
15:26important feature of this machine is, is that it's open hardware. So we developed a, an application
15:33ourselves that we can actually, um, place the fiber in the exact positions that we, we want in with
15:39that. And with that, we can, um, uh, we can get the sensing functionalities that we, we, we desire.
15:48So, um, what it did was, uh, printing the continuous carbon fiber in customized positions.
15:55And then we took this part, like the beam I showed in the video before you connect to an
16:00electronic source, and then you get a response after the application of stimuli. This is, this
16:06stimuli could be a stress or strain. And then with that, you can also, uh, read in the plot that if
16:12you apply a stress or strain, you get a signal, uh, that could be a voltage, could be a resistance,
16:19or could be a current. And, uh, the step further that we are trying to achieve now is to fine tune
16:28these, uh, continuous carbon fiber sensing functionalities. So as you can see in the plot,
16:34we, uh, for strains of, uh, down to 0.01%, that is 0.0001, uh, we can, we can already have a, uh, a signal
16:47out of it. So, um, for very, very low strains, it's possible to already observe what is going on in
16:55the part that you're, that you're, uh, using and also for high strain. So what we're doing now is, uh,
17:02exploring what are the, the, the, the strains up to, down to, or up to that we can, um, that we can, um,
17:11we can get a signal out of it that we can use in the final application. And also what, uh, one step
17:17further that we're, we're going, we're going, uh, first we try to, to prove the concept with beams and
17:24with simple shapes. And now we are implementing in, uh, 3d products. There are some projects we
17:29are working on in which we are already, uh, placing the sensor inside and we already, uh, seen a, a, a
17:36big, um, a big, uh, difference in the, in the fact that you have only the part that no matter how
17:43complex it is and the part with the sensor in which you deform it and you'll get the signal out of it.
17:48And, um, the, the, the next step will be the calibration of the strain stress so that we
17:56can monitor accurately, uh, what are the stresses and the, the strains that we're submitting to
18:02and the precise location of the strain event. I think I have a click here. Yes, there. So we designed
18:08these, uh, these triangular bar, beam bar. I would, I would put that way. Um, and, uh, it, it is now
18:16functioning, but I don't have a video here. So if you, if you, if you take a glance into the red,
18:22the green and the white arrows, um, uh, we, we, we designed the sensors in a way that if you press
18:29the, the, the, the, the white bar or the red bar or the green bar, uh, you will have a different signal
18:37out of it. So you will know exactly which position you are applying the stress. So you can have a part
18:45or you can have, uh, uh, uh, you can have a, um, a complete, um, a complete final part in which you
18:54can, um, you can know exactly where the, where the, the, the, the strain or the stress is coming from.
18:59So, uh, it's not like you have the sensor only one part of your final product, but you can have
19:06in different parts and then you know where the stresses are being applied and how much, if they
19:10are too, too high, if they are inside the range that they should be and so on.
19:15And, uh, it's also important, uh, that these sensors, they work for a long, uh, number of
19:23cycles per se as a fatigue test. So in the, in the left plot, uh, you can see that the signal is
19:30changing over, over the cycles. Uh, so it's not stable and, uh, we are developing a sensor that is
19:38stable and can withstand a huge number of cycles without changing in the signal. So after the
19:44calibration, uh, we would have a sensor that would withstand a, a, a, a long, uh, long number
19:51of cycles and therefore you can rely on their response throughout time.
20:00So to wrap up everything, um, um, I, I would like to, to, to leave it very clear that, um,
20:06I discussed two different projects. One is, is the high strength of normal, uh, printed
20:12polymeric filaments, uh, that are short, short, um, reinforced with short fibers or plain materials.
20:20And the second one was the continuous carbon fiber printing in which we can, um, we can
20:26junction the, the high strength functionality of continuous carbon fibers and also the structure
20:33health monitoring of, of fibers in which they can be used as a self, uh, as integrated self-sensing
20:41functionality. And with that, um, I would like to thank you everyone for your attention. And if you have
20:48any, any question or any idea or any, anything you would like to, to say, just, uh, please pick up.
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