Carbon Fiber Prepreg Research Articles

Detection of fiber waviness in carbon fiber prepreg using Eddy current method

In order to control the quality of carbon fiber reinforced polymer in the production process, a method of detecting fiber waviness in carbon fiber prepreg using eddy current (EC) probe is proposed. The EC probe includes orthogonal rectangular coils. The excitation coil is parallel to the designed fiber direction, so that the output voltage of the reception coil is only related to the bending of EC caused by fiber waviness. The phase of the output voltage is used for characterizing fiber direction. The results show that the probe is able to distinguish fiber direction as small as 0.5° and fiber waviness in prepreg can be detected. Moreover, algorithm of reconstructing fiber distribution is proposed and fiber waviness is visualized.

Fast curing unidirectional carbon epoxy prepregs based on a semi-latent hardener: The influence of ambient aging on the prepregs Tg0, processing behavior and thus derived interlaminar performance of the composite

The aging behavior of a fast-curing epoxy resin (EP) was examined over three months in unidirectional carbon fiber prepregs for the first time. The semi-latent, 120 °C curing one-pot formulation was developed based on industry-grade diglycidyl ether of bisphenol A (DGEBA) resins without the necessity of B-staging, to fully monitor the property change by aging without any post-processing influence. To extend the shelf-life compared to standard wet EP systems, the latent dicyandiamide (DICY) and a semi-latent urea-based catalyst were used, leading to full conversion within 15 min. The conversion was monitored by increasing Tg0 and rheology. High quality unidirectional carbon prepregs were manufactured and then investigated over three months regarding tackiness and resin flow. In parallel, laminates were autoclave-manufactured to evaluate the aging influence on the interlaminar properties. Thus, a correlation between decreasing gel-time, interlaminar adhesion and resulting multiple crack growth was observed via GIC and interlaminar shear strength (ILSS) testing. The investigations show a clear influence of the consolidation quality of the prepregs based on ILSS values and GIC values. A decrease of 19% in ILSS and combined with an erroneous increase of 63% of the GIC due to multiple delamination was observed in the worst case.

Online Cure Monitoring and Modelling of Cyanate Ester-Based Composites for High Temperature Applications.

A cure kinetics investigation of a high temperature-resistant phenol novolac cyanate ester toughened with polyether sulfone (CE-PES blend) was undertaken using non-isothermal differential scanning calorimetry. Thin ply carbon fiber prepreg, based on the CE-PES formulation, was fabricated, and plates for further in-situ cure monitoring were manufactured using automated fiber placement. Online monitoring of the curing behavior utilizing Optimold sensors and Online Resin State software from Synthesites was carried out. The estimation of the glass transition temperature and degree of cure allowed us to compare real time data with the calculated parameters of the CE-PES formulation. Alongside a good agreement between the observed online data and predicted model, the excellent performance of the developed sensors at temperatures above 260 °C was also demonstrated.

Morphological Characteristics and Wear Mechanism of Recycled Carbon Fibre Prepreg reinforced Polypropylene Composites

The polypropylene (PP) reinforced with recycled carbon fibres (rCF) was successfully produced using a Haake internal mixer via melt compounding. The compounding was performed at 180°C, rotor speed of 50 rpm and compounding period of 10 minutes. The standard samples for the pin on disc testing were prepared using injection moulding. The effect of rCF filler loadings of 0.5, 1, 3, 5, 7, 10, 13, 15 and 20 wt% was studied for the tribological properties. The results were compared with 100% PP. The morphological behaviours for the effect of low and high fibre loadings were observed using scanning electron microscopy analyses. The composites with low carbon fibre loading of up to 3 wt% imposed higher resistance to dry sliding friction. In contrast, the increment of fibre loading at 5 wt% to 20 wt% decreased the wear rate of the composites due to patch film and transfer film formation. The wear mechanism of the composites for different fibre loading was graphically sketched from morphological observation. As the conclusions, the composites showed promising self-lubricating properties, capable of wear reduction with significant physical and mechanical properties.

Quantifying effects of manufacturing methods on fiber orientation in unidirectional composites using structure tensor analysis

Important properties of fiber-reinforced composites, such as stiffness, compression strength, and fatigue resistance, are sensitive to fiber alignment. In this paper, we use structure tensor analysis on CT images to characterize the fiber orientations in three samples of unidirectional fiber-reinforced composites: pultruded carbon, pre-preg carbon, and non-crimp glass fiber fabric. Our results show that the fibers in the pultruded sample are more aligned than fibers in the two other samples. Through local quantitative analysis, we show that misalignment of the individual pre-preg layers contributes to the overall fiber misalignment in the material. For the non-crimp composite, we show that both the stitching of the unidirectional bundles and the backing bundles affect the fiber alignment in unidirectional bundles. Quantification of the misalignment caused by these effects allows manufacturers to tune production parameters, such as stitching thread tension, to minimize the misalignment of the fibers. All our notebooks, code, and data are available online.

Environmental impact assessment of zero waste approach for carbon fiber prepreg scraps

In the present paper, the environmental impact of an innovative technology, based on a zero-waste approach, for reclaiming carbon fiber prepreg scraps is assessed. The innovative process, proposed within the European project CIRCE, aims at reclaiming scraps produced during the cutting operation of virgin prepreg, avoiding the waste materials landfilling or incineration. The prepreg scraps were transformed into a ready-to-use raw secondary material by using two specifically developed automated systems for cutting and peeling of the scraps. By exploiting the prepared scraps in a compression molding process, recycled composite parts were produced. The evaluation of the environmental impact was carried out by means of the Life Cycle Assessment (LCA) approach, using the different impact assessment methodologies based on the Cumulative Energy Demand, Global Warming Potential and ReCiPe methods. Furthermore, tensile tests were performed at room temperature to investigate the mechanical properties of the recovered scraps products. In order to evaluate the environmental benefits of the innovative compression molding production with recovered prepreg scraps, the LCA analysis was also performed on two different traditional virgin production scenarios, i.e. the compression molding production with virgin prepreg and the autoclave processing with virgin prepregs, both used for the production of CFRP parts. The results show that the reclaim process leads to a strong reduction of the environmental impacts with respect to traditional composite production processes, demonstrating that such process can represent a valid alternative for a more sustainable manufacturing of composite products.

A comparative study of mechanical and machining performance of polymer hybrid and carbon fiber epoxy composite materials

Fiber-reinforced plastics are known as advanced composite materials thanks to their high strength and lightweight features. Carbon fiber reinforced polymers (CFRPs) are one of the high-performance and high-cost fiber-reinforced polymer (FRPs) materials. They are used in several high-performance engineering applications such as motorsports, marine, aviation, energy and defense industry. The cost of carbon fiber is higher compared to many other materials, more competitive and cost-effective productions will spur the demand for composite parts exponentially. Thus, hybrid laminate composite containing carbon and glass fiber materials were manufactured as an alternative for CFRP materials. Because using glass fiber prepreg instead of carbon fiber prepreg will lead the material to become cheaper. However, machining of the FRP materials is still an important issue. For this reason, the present study is focused on the mechanical and machining performance of the polymer hybrid and carbon fiber epoxy composites.

Experimental Investigation on the Influence of Fiber Path Curvature on the Mechanical Properties of Composites.

Automated fiber placement (AFP) has been widely used as an advanced manufacturing technology for large and complex composite parts and the trajectory planning of the laying path is the primary task of AFP technology. Proposed in this paper is an experimental study on the effect of several different path planning placements on the mechanical behavior of laminated materials. The prepreg selected for the experiment was high-strength toughened epoxy resin T300 carbon fiber prepreg UH3033-150. The composite laminates with variable angles were prepared by an eight-tow seven-axis linkage laying machine. After the curing process, the composite laminates were conducted by tensile and bending test separately. The test results show that there exists an optimal planning path among these for which the tensile strength of the laminated specimens decreases slightly by only 3.889%, while the bending strength increases greatly by 16.68%. It can be found that for the specific planning path placement, the bending strength of the composite laminates is significantly improved regardless of the little difference in tensile strength, which shows the importance of path planning and this may be used as a guideline for future AFP process.

Bulk factor characterization of heated debulked autoclave and out-of-autoclave carbon fibre prepregs

Tow impregnation during cure causes change in the laminate thickness, thus bulk factor, which causes variation in prepreg air permeability and large thickness deviations around corners. A noncontact eddy current thickness sensor monitored the laminate thickness throughout debulk and cure in an oven. Bulk factor values averaged to 1.1 for materials intended for autoclave use and 1.2 for out-of-autoclave, where a lower number is ideal for complex geometries. A heated debulk (HD) at around 48 °C for 2 h resulted in similar bulk factor values as a 16-h room temperature debulk (RTD), suggesting that this shorter cycle can be used as a replacement, resulting in a 26–71% cycle time reduction. For these thick sixteen ply laminates, up to six percent and five percent pore area can be expected of laminates processed RTD and HD, respectively. The highest short beam strength was achieved by a plain weave material intended for out-of-autoclave processing and lowest pore area was achieved by a 5-harness material intended for autoclave processing.

MCC develops highly heat- resistant and high-strength carbon fibre prepreg

MCC develops highly heat- resistant and high-strength carbon fibre prepreg

Quantifying inter- and intra-ply shear in the deformation of uncured composite laminates

Understanding the bending mechanics of uncured carbon fiber prepreg is vital for modeling forming processes and the formation of out-of-plane wrinkling defects. This article presents a modification of standard dynamic mechanical analysis (DMA) to characterize the viscoelastic bending mechanics of uncured carbon fiber prepreg using Timoshenko beam theory, along with an updated model describing inter-ply shear in uncured laminates. By post-processing DMA results, the analysis provides temperature and rate-dependent values of inter and intra-ply shear stiffness for a carbon fiber laminate and each individual ply with experimental results for AS4/8552 presented. The new methodology provides a means to parametrize process models, and also gives an indication of optimal manufacturing conditions to enable defect-free forming and consolidation processes.

Mechanical Properties of the Carbon Nanotube Modified Epoxy-Carbon Fiber Unidirectional Prepreg Laminates.

The effect of plasma treatment of the multi-walled carbon nanotube (MWCNT) surface on the fracture toughness of an aerospace grade epoxy resin and its unidirectional (UD) carbon fiber prepreg laminates has attracted scientific interest. A prepreg route eliminates the possible risk of carbon nanotube filtration by unidirectional carbon fibers. X-ray photoelectron spectroscopy results suggested that oxygen atom concentration at the nanotube surface was increased from 0.9% to 3.7% after plasma modification of the carbon nanotubes. A low number (up to 0.5 wt.%) of MWCNTs was added to epoxy resin and their carbon fiber prepreg laminates. Transmission electron micrographs revealed that the plasma treatment resulted in a better dispersion and distribution of MWCNTs in the epoxy resin. Plasma-treated MWCNTs resulted in a more pronounced resistance to the crack propagation of epoxy resin. During the production of the reference and nanotube-modified prepregs, a comparable prepreg quality was achieved. Neat nanotubes agglomerated strongly in the resin-rich regions of laminates lowering the interlaminar fracture toughness under mode I and mode II loading. However, plasma-treated nanotubes were found mostly as single particles in the resin-rich regions of laminates promoting higher energy dissipation during crack propagation via a CNT pull-out mechanism.

Investigation of Fire Protection Performance and Mechanical Properties of Thin-Ply Bio-Epoxy Composites

Hybrid composites composed of bio-based thin-ply carbon fibre prepreg and flame-retardant mats (E20MI) have been produced to investigate the effects of laminate design on their fire protection performance and mechanical properties. These flame-retardant mats rely primarily on expandable graphite, mineral wool and glass fibre to generate a thermal barrier that releases incombustible gasses and protects the underlying material. A flame retardant (FR) mat is incorporated into the carbon fibre bio-based polymeric laminate and the relationship between the fire protection properties and mechanical properties is investigated. Hybrid composite laminates containing FR mats either at the exterior surfaces or embedded 2-plies deep have been tested by the limited oxygen index (LOI), vertical burning test and cone calorimetry. The addition of the surface or embedded E20MI flame retardant mats resulted in an improvement from a base line of 33.1% to 47.5% and 45.8%, respectively. All laminates passed the vertical burning test standard of FAR 25.853. Cone calorimeter data revealed an increase in the time to ignition (TTI) for the hybrid composites containing the FR mat, while the peak of heat release rate (PHRR) and total heat release (TTR) were greatly reduced. Furthermore, the maximum average rate of heat emission (MARHE) values indicated that both composites with flame retardant mats had achieved the requirements of EN 45545-2. However, the tensile strengths of laminates with surface or embedded flame-retardant mats were reduced from 1215.94 MPa to 885.92 MPa and 975.48 MPa, respectively. Similarly, the bending strength was reduced from 836.41 MPa to 767.03 MPa and 811.36 MPa, respectively.

Improve durability and surface quality of additively manufactured molds using carbon fiber prepreg

AbstractHybrid tooling is an emerging concept introduced in the aerospace industries to reduce weight and cost of traditional tools. A hybrid tool features a skin, which provides desired surface quality, durability, and a low‐density substrate to reduce the weight of the mold. The big area additive manufacturing (BAAM) technology permits rapid production of thermoplastic polymer intensive large‐scale structures. The present study features a carbon fiber reinforced polyphenylene sulfide (CF‐PPS) substrate fabricated using Oak Ridge National Laboratory's BAAM system. Carbon fiber‐bismaleimide (CF‐BMI) prepreg skin was then bonded to the BAAM tool through high‐pressure autoclave molding. Process optimization was conducted to improve the bonding between CF‐PPS and CF‐BMI (transverse tensile strength increased from 0.54 to 4.8 MPa). Durability of the mold was demonstrated from fabricating seven (7) carbon fiber‐Huntsman epoxy hand lay‐up parts utilizing the mold.

Carbon/Epoxy Composites Fabricated by Vacuum Consolidation of the Interleaved Layup of Prepregs and Dry Fibers

The out-of-autoclave (OOA) or vacuum bag only (VBO) process uses partially impregnated prepregs for composite laminates, where gases and volatiles are removed by vacuum through the dry region of the prepregs during the consolidation. In this study, the fully impregnated carbon fiber prepregs and dry carbon fiber were laid up in an interleaved manner to form a hybrid laminate similar to the laminate with partially impregnated prepregs. By using the volumes of the fiber pore and resin in the hybrid laminate, we defined the saturation degree of a hybrid laminate. Three types of hybrid laminates were fabricated and they had different saturation conditions: over-saturation, saturation, and under-saturation. Tensile test was performed to find out how the saturation index affected the tensile properties of the composites. Also, the dual beam focus ion beam system (FIB) was used to observe the cross-section of the hybrid laminate. The result shows that if the saturation index is greater than one, the hybrid laminate will have competitive tensile properties as the composite manufactured by the conventional autoclave process.

Analysis of Impact Characteristics and Detection of Internal Defects for Unidirectional Carbon Composites with Respect to Fiber Orientation.

With the increasing use of carbon fiber reinforced plastics in various fields, carbon fiber composites based on prepregs have attracted attention in industries and academia research. However, prepreg manufacturing processes are costly, and the strength of structures varies depending on the orientation and defects (pores and delamination). For the non-contact evaluation of internal defects, the lock-in infrared thermography was proposed to investigate the defects in the composites subjected to the compression after impact test (CAI). The drop-weight impact test was conducted to study the impact behavior of the composites according to fibers orientation for composite fabricated using unidirectional (UD) carbon fiber prepregs. Using CAI tests, the residual compressive strengths were determined, and the damage modes were detected using a thermal camera. The results of the drop weight impact tests showed that the specimen laminated at 0° suffered the largest damage because of susceptibility of the resin to impact. The specimens with 0°/90° and +45°/−45° fibers orientation exhibited more than 90% of the impact energy absorption and good impact resistance. Furthermore, the specimens that underwent the impact tests were subjected to compressive test simultaneously with the lock-in thermography defects detection. The results showed that internal delamination, fibers splitting, and broken fibers occurred. The temperature differences in the residual compression tests were not significant.

Belt-Press Tape Forming of Carbon-Fiber-Reinforced Thermoplastic

A new tape placement device that incorporates the double belt press mechanism was developed for carbon-fiber-reinforced thermoplastic composites. A unidirectional carbon fiber prepreg tape, impregnated with PA6 at volume fraction fiber of 50%, was heated to the melting temperature by the heating roller, compressed on the base tape by the pressing roller, and cooled by the cooling roller. During this process, the prepreg tape was sandwiched between the base tape and the thin stainless belt surrounding the rollers. The combination of the pressing roller and the stainless belt provides a longer pressing and cooling region than that of the device without stainless belt. For the first trial of the device, a 10-layered ring with a diameter of 100 mm and a width of 18 mm was formed by applying a constant load using the six-axis robot. The specimen cut from the ring exhibited the flexural strength of 550 to 600 MPa and the good consolidation quality. For the second trial, a front heater was developed to elevate the temperature of the base tape, and a spiral tube was formed by manipulating the robot in the axial direction. The flexural strength was in the range of 500 to 600 MPa. The tape was compacted in width direction during the forming.

Non-contact ultrasonic inspection of carbon fiber prepregs for aviation applications in the manufacture of the layout

Non-contact ultrasonic inspection of carbon fiber prepregs for aviation applications in the manufacture of the layout

Comparison between honeycomb and composite corrugated cores in sandwich panels under compression loading

The study is to evaluate the compression properties of the polymeric composite corrugated-core sandwich structure against the honeycomb-core structure. The skin facings are from the prepreg carbon fibre composite laminate, while the core is made of different materials. Four core types are suggested; carbon fibre corrugated-core, fibreglass corrugated-core, Nomex honeycomb-core, and Kevlar honeycomb-core. The study is based on an experimental work of edgewise compression testing, and the comparison between alternatives are based on the specific properties-to-weight ratio. The analysed results prove there is superior compression capacity of the polymeric composite corrugated-core sandwich members to the honeycomb-core members, in particular in the nonlinear stage of compression test. The bonded surface between the honeycomb structure and the skins is often less than that of the corrugated profile for the same sandwich panel sizes. This contact area between the core and skin facings plays an important role in carrying load mechanism.

Determining process-window for manufacturing of continuous carbon fiber-reinforced composite Using 3D-printing

ABSTRACT Continuous carbon-fiber-reinforced acrylonitrile butadiene styrene (ABS) has been manufactured by a method based on fused deposition modeling (FDM). Before 3D printing, the carbon fibers pass through an ABS-acetone bath to prepare solution impregnated fibers (prepregs). Continuous fiber-reinforced thermoplastic composites (CFRTCs) were printed by feeding carbon fiber prepregs and ABS filament, simultaneously into a special single port nozzle. By varying print conditions such as nozzle diameter, layer height, and print speed, composite specimens were printed with different qualities. The visual evaluation of printed composites was used to determine a process window for stable or unstable CFRTC printing. In the obtained process window, four regions were observed including fiber fuzzing or tearing instability, fiber twisting instability, low quality stable print and high quality stable print. The optimum condition to print CFRTCs was found and then specimens were printed to investigate mechanical properties under the optimal printing condition. The mechanical and morphological properties of visual-optimized 3D-printed composites, without any fiber fuzzing, tearing or twisting were investigated. The results showed that tensile, flexural, and interlaminar shear strength of 3D-printed ABS-carbon CFRTCs have increased 313%, 121%, and 54%, respectively, when compared with the neat ABS 3D-printed samples.