FREE-FORM FABRICATION OF CONTINUOUS CARBON FIBER COMPOSITES USING ELECTRIC FIELDS

An out-of-oven system for free-form fabrication of continuous carbon fiber composites includes a dielectric barrier discharge (DBD) applicator configured to create an electric field proximal to the continuous carbon fiber composite. The DBD applicator includes a first electrode disposed within a dielectric barrier, and a second electrode spaced apart from the first electrode. The first and second electrodes are configured to allow the continuous carbon fiber composite to pass therebetween to cure the continuous carbon fiber composite. The system uses Joule heating to cure the continuous carbon fiber composite.

TECHNICAL FIELD

The present disclosure relates generally to 3D printing and more particularly, but not by way of limitation, to 3D printing of continuous carbon fiber composites using electric fields.

BACKGROUND

Carbon fiber composites have many applications and are quite desirable when both light weight and strength are desired. 3D printing is a relatively recent improvement in the manufacture of carbon fiber composites. Among the benefits of 3D printing is the ability to create complex shapes. Current carbon fiber/thermoset 3D printing processes includes a print head through which a carbon fiber/resin tow is extruded. In existing processes, as the carbon/fiber resin tow is extruded, UV energy is applied to cure the resin and form a solid shape. However, most commercially relevant resins are heat-cured, not UV cured. Current methods for carrying out heat-cured production are limited to large thermal ovens.

SUMMARY OF THE INVENTION

This summary is provided to introduce a selection of concepts that are further described below in the Detailed Description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it to be used as an aid in limiting the scope of the claimed subject matter.

Out-of-oven additive manufacturing (AM) techniques are disclosed that allow for thermosetting carbon fiber reinforced composites (CFRCs) to be printed and rapidly cured using dielectric barrier discharge (DBD)-assisted Joule heating. Conventionally, CFRCs are produced by automated fiber placement machines (AFPs) that use large, cumbersome molds and time-consuming oven/autoclave treatments to cure CFRCs in the desired shapes. Recently, out-of-oven AM has garnered attention as a method to manufacture CFRCs without the use of molds. AM allows for on-the-fly printing and curing of thermosetting CFRCs; however, current out-of-oven AM techniques are limited to UV-curable, low viscosity, or rapid-curing resins. In contrast to conventional methods, the DBD and RF applicators discussed herein provide in-situ heating and curing during AM of continuous CFRCs using electric fields to locally heat resin as it is extruded from a print head of a 3D printer. The electric field is created by a field applicator that generates electric fields proximal to the carbon fiber/resin. Field applicators that may be used include a Radio Frequency (RF) applicator or a Dielectric Barrier Discharge (DBD) applicator. The systems and methods described herein are resin-agnostic, applying to most commercially available thermosetting resins. As the partially cured composite (prepreg) is deposited, Joule heating induced via an RF or DBD applicator allows the part to cure in the desired shape. This is possible because of the conductive carbon fiber susceptors inside the part. Composites manufactured by this method show properties similar to those manufactured in conventional ovens. Using the DBD applicators discussed herein, composites can be printed in free space or on stationary and/or mobile substrates. 2D structures, and 3D multilayered structures can be printed, and the process can be automated. This technology leverages the advantages of AM techniques to enable the printing of high-performance and lightweight materials in any desired shape.

The methods disclosed herein do not require direct contact of the applicator with the carbon fibers. In some aspects, the field applicator and/or print head are stationary and the system includes a means to move the workpiece around (e.g., a conveyor, robotic arm, moving table, etc.). In some aspects, the field applicator and/or print head move around a stationary workpiece (e.g., using a robotic arm or similar to a multi-axis mill).

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. The section headings used herein are for organizational purposes and are not to be construed as limiting the subject matter described.

The systems and methods disclosed herein allow for the creation of complex, 3D printed structures using continuous carbon fiber composites. In particular, the systems and methods use electric fields to provide heat-cured carbon fiber composites that do not require thermal ovens or molds. Unlike other conventional processes that rely upon UV for curing, the systems and methods cure resin using electric fields generated by an RF applicator or a DBD applicator. The RF system uses a fringing field RF applicator and an RF signal generator to generate an electric field proximal to the workpiece. The print head extrudes the carbon fiber/resin and either the print head or the workpiece moves to create the desired shape. During the printing process, the RF applicator generates an electric field that interacts with the carbon fibers to cure the resin via Joule heating.

Carbon fiber reinforced composites (CFRCs) are lightweight, strong, and corrosion resistant, making them desirable materials that have a wide range of applications in various areas such as defense, marine, aviation, and automotive industries. They can also be used in wind turbines to fabricate blades and structural trusses. In conventional processing of thermosetting CFRCs, automated fiber placement (AFP) machines deposit partially cured CFs in molds of the desired shapes; large, time-consuming ovens, and heat guns are used to heat and completely cure the deposited composite. Creating a mold each time a new shape is designed is a labor intensive and capital-intensive process. Since AFP machines occupy large volumes of space, they are often immobile; they cannot be used locally to create composites. Therefore, there is an increasing necessity to design a compact and convenient method to manufacture CFRCs.

A relatively new development in the production of these composites is out-of-oven AM of continuous carbon fiber composites. Out-of-oven techniques us a nozzle to deposit a carbon fiber prepreg (partially cured carbon fiber/resin tow) in a desired shape, followed by the immediate curing of the resin. However, these approaches typically require non-conventional resin chemistries or UV sensitive resins to achieve rapid curing. However, the majority of the commercially applicable resins are not UV curable.

One promising approach for out-of-oven heating is the use of electric fields. The electrical conductivity of carbon fibers makes them a prime candidate to undergo Joule heating when placed in the influence of external electric fields. The systems and methods described herein demonstrate how carbon fiber prepregs can be manufactured using an electric field generated by a radio frequency applicator. Since the electric field induce heat in the fibers themselves, this method can be used with a range of thermosetting resins surrounding the fibers. Thus, using electric fields to induce heating in the fibers from the inside out is especially useful for processing and manufacturing thermosetting composites. CFRCs can be cured rapidly using electric fields without degrading the fiber-matrix interface.

Another means of applying an electric field is using a DBD applicator. The DBD applicator ionizes the air creating a plasma. The plasma interacts with a polymer having carbon nanotubes as fillers causing them to undergo Joule heating. The DBD applicator includes a top electrode, which contains a dielectric disc. In various aspects, the DBD applicator generates an electric field in the range of about 1-50 kHz (center frequency of 26 kHz typically). The electric field is generated between this top electrode and a bottom ground electrode. The grounded conductive workpiece is placed between the two electrodes. An air gap is maintained between the top electrode and the workpiece. The electric field ionizes the air, and plasma streamers are created in this gap between the workpiece and the surface of the dielectric disk which creates a path for current to flow. When the workpiece connects with the plasma, a discharge current travels through the workpiece, to the bottom electrode. In some aspects, the DBD applicator can be converted into a handheld portable electric field generator.

Reference will now be made to more specific embodiments of the present disclosure and data that provides support for such embodiments. However, it should be noted that the disclosure below is for illustrative purposes only and is not intended to limit the scope of the claimed subject matter in any way.

FIG.1illustrates a DBD system100in accordance with aspects of the disclosure. System100includes a DBD applicator102that is electrically coupled to a voltage generator104. DBD applicator102includes first and second electrodes106,108. First electrode106is a high voltage electrode and second electrode108is a ground electrode. Voltage generator104may be, for example, a 24 V direct current (DC) generator.

A workpiece110is positioned between electrodes106,108, with an air gap and a dielectric barrier112positioned between workpiece110and electrode106. In some aspects, dielectric barrier112includes a gold foil with ceramic on top and bottom. Workpiece110may be, for example, a carbon fiber/resin extrusion from a print head. In some aspects, the print head and DBD applicator102are stationary and workpiece110is moved relative thereto to create a structure with the desired shape using additive techniques. In some aspects, workpiece110is stationary and the print head and DBD applicator102move about workpiece110to create a structure with the desired shape. When current is supplied by voltage generator104, a plasma discharge114is formed between high voltage electrode106and workpiece110, and current is allowed to pass between electrodes106,108. The resulting electric field heats up the carbon fibers of workpiece110. This heat is transferred to the surrounding resin, curing the resin. The curing process is carried out without DBD applicator102contacting workpiece110.

FIG.2illustrates a DBD system200in accordance with aspects of the disclosure. DBD system200operates in a fundamentally similar manner as DBD system100and includes a DBD applicator202with a pair of electrodes, but the pair of electrodes of DBD applicator202are configured differently. A high voltage electrode and dielectric barrier are configured as a dielectric disc204that includes a conductor206within. A nozzle tube208with a nozzle210at a distal end thereof extends through the center of dielectric disc206. Nozzle210both provides the carbon fiber/resin material and serves as a grounded electrode. A heater block212may be positioned around nozzle tube208to heat up the carbon fiber/resin prior to extrusion through nozzle210. DBD system200utilizes alternating current (in contrast to the direct current used in DBD system100). The dashed lines ofFIG.2illustrate the electric current that flows between dielectric disc204and nozzle210. When current is flowing, plasma214forms between a workpiece216and dielectric disc204. The electric field resulting from the current heats up the carbon fibers of workpiece216. This heat is transferred to the surrounding resin, curing it. Similar to DBD applicator102, DBD applicator202may be fixed with workpiece216moving relative thereto, or may move relative to workpiece216. The curing process is carried out without DBD applicator202contacting workpiece216.

FIG.3illustrates a DBD system300in accordance with aspects of the disclosure. DBD system300includes a BDB applicator302with a high voltage electrode inside a dielectric barrier304and a ground electrode306in the form of an aluminum plate. A workpiece308(i.e., the partially cured composite) rests on a conductive substrate310. Conductive substrate310may be, for example, a glass slide wrapped in aluminum foil. In practice, workpiece308is extruded by a print head onto substrate310. As workpiece308is extruded, electrode306passes beneath DBD applicator302to cure the partially cured composite. Similar to the above systems, the electric field created by DBD applicator302cures the resin without DBD applicator302contacting workpiece308. The movement of electrode306may be used in an additive manufacturing process to build layers. For example, multiple passes may be made, with each pass curing a new layer to build up workpiece308.

FIG.4illustrates an RF system400according to aspects of the disclosure. RF system400includes a fringing-field applicator402that, with a workpiece, behaves like an RLC resonance circuit. RF system400includes two copper traces404,406that electrically behave as inductors (L). Copper traces404,406sit on a substrate414, and an insulating layer (e.g., a layer of Kapton® polyimide tape) is placed on top of copper traces404,406. The small air gap between traces404,406acts as a capacitor (C). A workpiece adds a shunt resistance (R) and changes the gap capacitance. An RF source408provides a signal to fringing-field applicator402. A workpiece412is shown positioned above the two copper traces404,406. The frequency associated with maximum RF absorption is dictated by the dimensions of the applicator. In some aspects, dimensions are selected to obtain RF absorption in the range of 1-250 MHz. The RF electric fields are concentrated in the capacitor air-gap and couple with the conductive workpiece412(i.e., the carbon fiber composites). Capacitive coupling induces surface currents which lead to electromagnetic losses and thus heating in workpiece412. RF system400is ideal for thin structures as the electric field strength decays exponentially in the vertical direction. The concentration of the electric fields in the capacitor can be controlled by changing the applied RF power or the size of the gap between the traces. In some aspects, a thermal camera410can be used to monitor temperature of workpiece412to determine a degree of cure.

FIGS.5A and5Billustrate top and perspective views, respectively, of a DBD system500according to aspects of the disclosure. DBD system500includes a DBD applicator502that is positioned over a stage506that is configured to rotate about its central axis. Stage506sits on an aluminum plate504that acts as a ground electrode. A prepreg spool508is positioned proximal to stage506and feeds prepreg510to stage506. In some aspects, a stabilizer arm514guides and holds prepreg510to stage506for curing by DBD applicator502. Stage506rotates and pulls out prepreg510onto stage506. As stage506rotates, prepreg510passes beneath DBD applicator502and cures to form cured carbon fiber composite512. A high voltage supply516provides power to DBD applicator502and a ground518is coupled to aluminum plate504.

Working Examples

Preparing prepregs: Continuous unidirectional T700S carbon fiber tows were laid down flat and impregnated with a two-part thermosetting epoxy (EPON 828+Jeffamine T403 Hardener). The impregnated carbon was heated in an oven at 100° C. for 6 min to produce prepregs. These prepregs were then rolled onto a spool. The prepregs were made using the common commercial composition of EPON 828+Jeffamine T403. The curing kinetics of this resin system are known from our prior work, and one can predict the temperature and time needed to cure the resin completely. The curing kinetics of the resin were predicted based on the Kamal-Sourour model. The following parameters were selected for curing to occur at a temperature between 100-110° C.: m=0.402, n=1, and k=0.00542 s−1. A simulation of the kinetic model showed that the prepreg was 65% cured after 6 min at 100° C. For printing multi-layered structures, the prepreg was exposed to plasma from the DBD applicator at 100° C. for an additional 5 min to get to ˜90% cured. When fully curing a given layer (such as a free-standing bridge), the prepreg was exposed to the DBD plasma at 100° C. or above for 8 min to completely cure the sample.

DBD Experiments: A metallic electrode was embedded in a dielectric ceramic disc in the DBD applicator. The ceramic disk was approximately 3 mm thick and 70 mm in diameter. To generate plasma between the dielectric disk and a ground electrode, a 24 V Direct Current (DC) power was supplied to a frequency and power modulation device using a NICE-POWER DC Power Supply (Model: R-SPS3010). A high ratio winding transformer (286:1) received the frequency generator's 24 V peak-to-peak 25-32 kHz modulated square wave signal, and output a corresponding high voltage (8-10 kV) modulated signal to the ceramic disc applicator. A thermal camera (FLIR Systems Inc., A655sc) was used to observe the temperature of the sample from the side.

Preparing a continuous CFRC using DBD: The prepreg was dispensed through the DBD-generated plasma using a motor. For fabricating a suspended workpiece, a grounded copper wire was attached to the prepreg. For fabricating a workpiece on a substrate, the prepreg was laid on a grounded aluminum plate. To completely cure a prepreg, the prepreg was exposed to the plasma for 8 minutes at 100° C. The heating zone has a length of 50 mm. The translation speed of the prepregs was 6.25 mm/min.

The distance between the grounded prepreg and the DBD applicator was varied between 0-7 mm. The heating rate of the prepreg at each 1 mm incremental distance was recorded.

Fabricating Multilayered Structures

Additive manufacturing using in-situ curing: A first layer of prepreg was dispensed and laid across a ground plate. Based on the kinetics, at 107° C. the prepreg cured completely in 7 min. The resin needs to be only partially cured so that it can bond with the next layer. Thus, the first layer was cured for 5 minutes at 107° C. using the DBD applicator. The duty cycle was varied to maintain a temperature of 107° C. A second layer of prepreg was then laid on top of the previous layer. The second layer was cured for 5 minutes as well at 107° C., so that the third layer can bond with it. This process was repeated to create multiple layers.

Additive manufacturing using post cure: A first layer of prepreg was dispensed and laid across the ground plate. The second layer was then directly laid across the first layer. Similarly, the third, fourth and fifth layers were laid on top of the preceding layer. The entire structure was then exposed to the plasma for 25 minutes. The power of the DBD applicator was modulated to maintain the temperature of the top layer at 107° C.

Complex shapes: Multiple prepreg layers were moved relative to the DBD applicator by using an automated stage. The prepregs were deposited in the desired complex shapes and the layers were consolidated using rollers. The prepregs were then cured using the DBD generated plasma. For fabricating a multilayered rectangular composite, the prepreg layers were additively printed with DBD-assisted in-situ curing for 8 minutes each (at 100° C.) before printing the subsequent layer. For fabricating the helix, each prepreg layer was printed and in-situ cured using the DBD for 5 minutes each at 107° C. before printing the next layer. The next layer was offset by a slight angle)(<15°. For fabricating the circle, a pressing roller was used to consolidate the prepreg that was being deposited on the automatic rotating stage.

Characterization

Differential Scanning calorimetry: The glass transition temperatures and degrees of cure of samples were calculated using differential scanning calorimetry (DSC). These experiments were conducted using a TA Instruments DSC Q20 (New Castle, DE). The samples contained 3-5 mg of substance total. Nitrogen was used to purge the test chamber at a rate of 50 mL/min. The temperature was ramped up from room temperature to 200° C. at a rate of 3° C./min. For multilayered structures, a cross section cutting across all layers (5 layers) was used for testing. The samples were transported in a 0° C. container to prevent any curing at room temperature.

Mechanical Testing: Each sample for a lap shear test consisted of two unidirectional T700S CF prepreg tow pieces having a length of 5 cm and width of 0.8 cm, placed one on top of the other such that the overlap area had dimensions of 0.8 cm×0.8 cm. The two samples were completely cured at 100° C. for 14 minutes in the oven and using the DBD applicator. An Instron load frame with a 30 kN load cell was used for these tests; the displacement rate was set at 2 mm/min for all tests. ILSS assessment was carried out as per ASTM 2344 standards. The sample thickness was maintained at 4 mm, width at 8 mm, and length at 16 mm. A strain rate of 1 mm/min was used. The short beam strength was calculated using Equation 1 below:

Where Pmis maximum load observed during the test in N, F=short-beam strength in MPa b=measured specimen width in mm, and h=measured specimen thickness in mm.

Thermogravimetric Analysis (TGA): TGA measurements were done in a TA Instruments TGA 5500 in air to determine the mass fraction of the composites. The sample was loaded on a Platinum pan and temperature was ramped from room temperature to 400° C. at a rate of 20° C./min, then the temperature was held constant to observe degradation of the epoxy matrix.

Scanning Electron Microscopy (SEM): The cross-sections of 2 composites manufactured using the DBD-assisted method were polished and observed with a FEI Quanta 600 field-emission scanning electron microscope. For imaging, the cross-section image was divided into 9 sections and ImageJ software was used to calculate volume fraction and void fraction.

Results: electric fields were evaluated to determine if prepregs can cure during deposition to create freestanding CFRCs. To produce prepregs, continuous unidirectional carbon fiber tows were impregnated with epoxy and partially cured at 100° C. for 6 minutes in an oven. These prepregs were then rolled onto spools. These prepregs were then dispensed through the DBD-generated plasma. For as long as the tow is in the heating zone (residence time), the plasma couples with the CFs such that the CFs are heated and the surrounding epoxy cures. The DBD power was modulated in order to achieve a target temperature (100-110° C.). The curing kinetics of this resin system were used to predict the temperature and time needed to cure the resin completely. As described below, several different methodologies were used to dispense the prepreg and build up multilayered structures. In a commercial setting, this technology would be controlled by a robotic arm that dispenses prepregs with DBD-assisted in-situ curing to create self-supporting structures.

The DBD-assisted Joule heating method was first used to cure a stationary prepreg at a given temperature. A prepreg was laid on a grounded aluminum plate and was exposed to the DBD generated plasma. The sample underwent Joule heating and reached a steady state temperature of 100° C. when an input power of 35 W was applied to the DBD applicator. The prepreg sample was kept at this temperature for 8 minutes. To verify that the DBD-assisted Joule heating would completely cure the sample as expected, DSC measurements were carried out on the prepreg sample before and after exposure to DBD generated plasma.

DSC data confirmed that the kinetic model can be used successfully to predict the degree of cure of a sample, if the time and temperature are known. To completely cure a composite, the prepreg was heated at or above 100° C. for 8 min or longer. To create a multilayered structure, the first layer was heated at 100° C. (wall) & 107° C. (helix) for only 5 min so that it could bond to the next layer (discussed below). TGA in air was carried out on the completely cured composite. The CFs make up 55 wt % of the composite. The epoxy matrix burned off completely beyond 400° C. Based on the SEM images of the cross-section of the composites, it was observed that the fiber distribution was fairly uniform, with only a few voids present. The areal density calculations showed that CFs have a volume fraction of 63%. The void fraction was found to be 2.4%.

Next, the DBD applicator was used to create composites that held their shape in air without sagging or bending. A suspended continuous prepreg sample was unspooled and dispensed at a constant speed (6.25 mm/min) through the DBD generated plasma to rapidly heat and cure. The heating zone has a length of 50 mm. Thus, the prepreg is exposed to the plasma for 8 minutes. The prepreg remained suspended under tension with the help of a motor. This pulling motion of the motor also unspools the prepreg in the desired direction. In this case, a grounded copper wire brush was kept in contact with one end of the prepreg. The power was modulated to maintain the sample at a temperature of 100° C. (average power 35 W). The sample cured completely to form a stiff, suspended composite. This demonstrated that this technique can be used to create freeform self-supporting structures.

Next, the effect of the distance between the grounded sample and the DBD applicator (top electrode) was examined. This distance was varied from 0 mm to 7 mm, and the heating rates of the prepreg were recorded at each distance. The heating rate was highest when the sample was closest to the top electrode, as expected. Beyond a certain spacing (5 mm), plasma is not formed between the sample and the DBD applicator, i.e., no ionization of air occurs. This implies that the applicator needs to be within 5 mm of the sample for plasma to form and the sample to heat and cure.

DBD-assisted Joule heating can also be used to produce multilayer structures. In order to do so, the degree of cure must be controlled for each layer. If a given layer is insufficiently cured, the part will not hold its shape; however, if a given layer is completely cured, it will not bond to the next deposited layer. To investigate this phenomenon, the residence time of the first layer was varied, and lap shear tests were conducted to measure interfacial shear strength. Note that the temperature was maintained at ˜100° C. during this experiment. As expected, the data showed that the longer a layer is cured before laying another prepreg layer on top, the weaker the interfacial adhesion between the two layers is. To balance these two design considerations (maintaining shape and interfacial bond strength), a residence time of 5 minutes was selected for all experiments where multilayered structures were made. The simulation of the kinetic model showed that when the prepreg was made, it is 65% cured after 6 min at 100° C. When the prepreg was exposed to the DBD plasma at 100° C. for an additional 5 min, it was ˜90% cured. Similarly, when the prepreg is exposed to 107° C. for an additional 5 min it was ˜92% cured.

DSC data of heat flow versus temperature for a 5-layer wall structure that was additively manufactured with a DBD-assisted in-situ cure cycle where the average temperature was maintained at 107° C. was collected. The area under the exotherm in the DSC plot for the samples before and after exposure to the plasma was measured and compared to the area under the exotherm of a completely uncured sample. The mathematical relation to find degree of cure using DSC is shown in Equation 2 below:

α=1-Δ⁢HtΔ⁢H0Equation⁢2where α is degree of cure, ΔHtis the heat released during curing (obtained by area under the exotherm in DSC plot) of a sample with plasma exposure time t, and ΔH0 is the heat released during curing of a completely uncured sample.

In-situ curing allowed for each CF prepreg tow layer to cure for 5 minutes at 107° C. and retain its shape before a new layer was placed on top of it. Data confirmed the kinetic model prediction that the first layer cured to an α=˜0.92 when the prepreg is exposed to 100° C. for an additional 5 min. Then, the second layer was deposited on top of the first layer, followed by an additional 5 minutes of plasma exposure. While the second layer cured partially, the first layer cured completely due to heat conduction from the top layer. Similarly, a third, fourth, and fifth layer were deposited and cured. With this technique, a post-cure step in an oven is not needed to completely cure the entire structure. The DSC of a cross-sectional slice of the DBD-manufactured multilayered composite (consisting of all 5 layers) shows that the degree of cure was 1.

Next, the DBD-assisted Joule heating approach was used to produce a multilayered structure (a wall) of 20 CF tow layers. The structure retained its shape, and had flat and smooth edges, and sharp corners. For this method of additive manufacturing to be incorporated in industry, the mechanical properties of the fabricated structures using the DBD have to be similar to those fabricated conventionally. Lap shear tests were conducted on 2 samples: a sample manufactured through the DBD-assisted process and a sample cured in the oven. Both samples were cured at 100° C. for 14 minutes to ensure that they are completely cured. The two samples showed comparable shear strength of around 30 MPa. ILSS tests were also carried out to compare the short beam strength of the composite manufactured using oven and DBD. Thus, the multilayered structures fabricated using DBD-assisted Joule heating show similar mechanical strength to those fabricated in an oven.

Using this method, one can also create 3-dimensional self-supporting structures in air. A helical structure with overhang was fabricated using the DBD-assisted in-situ curing. The helix was created by depositing layers of prepreg successively along a central axis. Each new layer was rotated at an angle of 5° before deposition. Every layer was cured for 5 minutes at 107° C. before depositing a new layer on top.

Several structures of different shapes were created to demonstrate the practical use of the DBD applicator. In some aspects, the shapes can be laid by hand and cured using the DBD-assisted Joule heating method. This method can be used to create shapes with curved edges and/or straight edges. The symmetry and precision of creating a shape using this method depends on the accuracy with which the prepregs can be deposited.

To automate this AM process, a circular CFRC ring was fabricated using a stage that moved relative to the stationary DBD applicator (seeFIGS.5A and5B). The prepreg is deposited on the rotary stage and the stage simultaneously moves in a predetermined path to create the desired geometry. The stage had a stationary roller which pressed down on the as-deposited prepreg to guide the unspooled prepreg and consolidate the new layer onto prior layers. As the prepreg passes through the DBD applicator, the sample is heated and cured in the desired shape. Another approach that was explored was using a robotic arm to make a hands-free setup. The robot can pull or deposit the prepreg in the desired shape.

Although various embodiments of the present disclosure have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the present disclosure is not limited to the embodiments disclosed herein, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit of the disclosure as set forth herein.