Thermal Conductivity Of Carbon Fibers Research Articles

Cryogenic thermal conductivity of carbon fiber reinforced polymer composite laminates

Carbon fiber reinforced polymer (CFRP) composites with excellent mechanical properties and low thermal conductivity are promising materials for cryogenic facility support structures. However, the temperature dependence and stacking sequence dependence of the laminates’ thermal conductivities challenge their thermo-mechanical design. Previous work dealing with the cryogenic thermal conductivity of laminates was relatively inadequate, and the effect of stacking sequence has not been sufficiently clarified. Herein, the cryogenic thermal conductivity of CFRP composite was investigated, and a theoretical model for the out-of-plane thermal conductivity of laminate was developed. To this end, the thermal conductivities of epoxy resin and laminates were measured at temperatures from 20 K to 293 K. The cryogenic thermal conductivity of carbon fiber was then extrapolated. Subsequently, a theoretical model was developed based on the thermal-electrical analogy method to evaluate the effect of stacking sequence. The obtained model was then validated by numerical analysis and experimental work. Lastly, the effects of lay-up angles and component properties on out-of-plane conductivity were examined. The test results suggested longitudinal thermal conductivity of composites exhibiting significant temperature dependence, with a decreasing trend recorded from 6.317 Wm−1K−1 to 0.355 Wm−1K−1 and transverse thermal conductivity decline from 0.626 Wm−1K−1 to 0.156 Wm−1K−1. The theoretical analysis indicated that the stacking sequence could reduce the out-of-face thermal conductivity by up to approximately 6.5 %, while the lay-up angle did not show any influence. In sum, novel insights into the cryogenic thermal conductivity of CFRP composites were provided, with guidance for the design and analysis of CFRP composites in cryogenic applications.

A microstructure-based model for the thermal conductivity of carbon fibers

In this paper, a model is developed to predict the thermal conductivity of carbon fibers (CFs) based on the microstructure information and phase composition obtained experimentally. The microstructures of four different CFs are investigated by SEM and XRD. The contents of graphite crystallites, amorphous carbon, and microvoids are estimated by the internal standard method. Crystallinity, crystallite size, and the orientation of crystallite are considered in the model. The predicted thermal conductivities are in good agreement with the reported values. The contribution of the microstructural factors on the thermal conductivity is evaluated. It is revealed that crystallinity is the major factor that affects the thermal conductivity of CFs. Furthermore, the predictions of the presented model are also compared with the prediction of empirical models based on the measured electrical resistivity. The results show that the prediction of our model has a higher generality. The fundamental understanding on the thermal conductivity of CFs may benefit the development of high-performance CFs.

Computation of effective thermal conductivity of carbon fiber felts through numerical simulation and development of reduced order models

One of the major drivers of heat transfer within a spacecraft heatshield is the effective thermal conductivity of the thermal protection material. For carbon-based thermal protection materials, this quantity is strongly connected to the thermal conductivity of the carbon fiber felt (preform) used to create the final composite. Use of effective thermal conductivity data from experiments in volume averaged numerical models is complex because: i) they are carried out in different media than its actual application, ii) changes on geometry or material properties require repetition of the experiments. Simulation of effective thermal conductivity using high fidelity simulations can overcome those problems. In this work, we propose a synthetic model based of the carbon fiber felt of Calcarb® using Porous Microstructure Analysis (PuMA) software. This model is first validated with available experimental data and applied to new experiments and to study the effect of pyrolysis gas mixture on the effective property. Simplified correlations are then developed, which predict with remarkable accuracy the effective thermal conductivity of the Calcarb® material. The developed model can be used to explore and predict effective conductivity at different conditions. In addition, the simplified algebraic correlations can be easily implemented in volume averaged material response codes to account in a more appropriate way for the effect of the percolating pyrolysis/atmospheric gas.

Study on the effects of incremental curing on the thermal conductivity, insulation, and mechanical properties of thermal conductive silicone rubber

With the development of fields such as electronics and telecommunications, electronic devices are becoming more integrated and powerful. Therefore, there is an increasing demand for high thermal conductive and insulating flexible materials. Silicone rubber (SR), as an excellent flexible substrate, is often combined with various thermal conductive fillers to enhance its thermal conductivity (TC). Carbon materials are commonly used as thermally conductive fillers. To improve the insulation performance while maintaining the TC of the material, uncured SR filled with boron nitride (BN) is used as an insulating layer on the same substrate. The TC of the once-cured BN/SR composite and the incremental cured BN/SR composite as a coating are 0.492 W/(mK) and 0.484 W/(mK), respectively, with a BN content of 10 vol%. The TC of carbon fiber (CF)/SR composites before and after surface treatment with BN/SR are 1.760 W/(mK) and 1.682 W/(mK), respectively, with a CF content of 20 vol%. The volume resistivity of the former is less than 104 Ω cm, while the latter is greater than 1014 Ω cm.

Transferring heat accumulated by asphalt pavement from inside to outside through carbon fibers

On the Qinghai-Tibet Plateau, intense solar irradiation will cause serious heat accumulation in asphalt pavement. Downward heat transfer will disturb the permafrost under subgrade, thus leading to a series of subgrade and pavement diseases. This makes construction of asphalt pavement in the permafrost regions of the Qinghai-Tibet Plateau a world-class challenge. This paper proposes for the first time a transversal heat transfer channel in asphalt pavement, which can quickly transfer heat accumulated in pavement to road shoulders. Finite element software ABAQUS was used to simulate the rutting plate with high axial thermal conductivity carbon fibers inserted transversely. Under the constant heat load of 500 W/m2, the heat flux near the carbon fibers showed the characteristic of convergence. The maximum transverse heat flux in the carbon fibers reached 4.97×107W/m2, which was 14 times that in the asphalt mixture. Meanwhile, the maximum vertical heat flux in the carbon fibers reduced to 2.62×106W/m2, which was 12 % less than the asphalt mixture. The effective thermal conductivity of composite specimens with different carbon fiber parameters was studied through control experiments. When the axial thermal conductivity, volume fraction and number of carbon fiber bundles increased to 100 W/m·°C, 10.72 % and 4 bundles respectively, the transverse ETC of composite specimens increased to 4.05 W/m·°C, 7.09 W/m·°C and 16.18 W/m·°C respectively. They were 3.12 times, 5.45 times and 12.45 times of the control group. The radial thermal conductivity of carbon fibers has a significant effect on the vertical ETC. When it decreased to 0.2 W/m·°C, the vertical ETC decreased by 6.15 % compared with the control group. The temperature variation trend of specimens were measured by a laboratory irradiation experiment. The maximum temperature difference between the control group and the experimental group at 0 mm was 5.81 °C, and the average temperature difference within 2 h was 5.14 °C. The maximum temperature difference at 50 mm was 3.84 °C and the average temperature difference within 2 h was 3.24 °C. The results showed that the transverse heat transfer channel can reduce downward heat transfer. The application of the channels will enhance transverse heat release and relieve heat accumulation of asphalt pavement. This can create a low temperature state for pavement structure and has a positive effect on maintaining the stability of the permafrost regions on the Qinghai-Tibet Plateau.

Molecular dynamic study on modulating the interfacial thermal conductivity of carbon fiber/epoxy interfaces

Chemical functionalization of carbon fiber surface is a widely used strategy to improve the out-of-plane thermal conductivity of carbon fiber reinforced plastics (CFRPs) for structural and space applications. However, determining the ‘right ligand’ to achieve this objective is a difficult problem. Molecular dynamics (MD) simulations are performed in this study to characterize the effect of different chemical ligands on the interfacial thermal conductivity (Ki) of carbon fiber/epoxy composites. The carbon fiber is modeled as graphene layers, diglycidyl ether of bisphenol F (EPON862) and diethyl toluene diamine (DETDA) are used as epoxy and crosslinker in MD simulations. The carbon fiber is functionalized with different types of small (amine and carboxylic) and large (aniline, single-chain para-amine surface grafted molecules (SGM), and double-chain meta-amine SGM) functional groups with varying degrees of functionalization. When the carbon and the neighbouring epoxy molecules are bridged by relatively larger ligands, that are capable of large fluctuations in their end-to-end distances, we observe a very effective reduction in the thermal resistance that otherwise exists between base carbon and the epoxy matrix.

Significantly improving thermal conductivity of carbon fiber polymer composite by weaving highly conductive films

This paper significantly improved the transverse thermal conductivity (TC) of unidirectional carbon fiber reinforced polymer (CFRP) laminates by a simple and effective method of weaving highly conductive films (HCFs), including Copper (Cu) film and highly oriented graphite film (HOGF). The TC and interlaminar shear strength (ILSS) of HCF enhanced CFRP (HCF-CFRP) composite laminates were measured. The results show that the HCF-CFRP composite with a larger geometric undulation of HCF has a higher through-thickness TC. And the through-thickness and in-plane transverse TCs can be regulated by the undulation of HCF. The maximum through-thickness TCs of HCF-CFRPs are up to 49.19 W m−1 K−1 for HOGF-CFRP with 1.97 vol% HOGF, and up to 21.45 W m−1 K−1 for Cu-CFRP with 1.74 vol% Cu film, which are 11029% and 4753% higher than that of CFRP, respectively. Numerical simulation and infrared thermography demonstrate that the geometric undulation and ultrahigh in-plane TC of HOGF lead to the formation of a rapid through-thickness heat transfer path. In addition, the ILSSs of HOGF-CFRP and Cu-CFRP are 44.01 and 40.91 MPa, respectively, which are 13.76% and 19.77% lower than that of CFRP.

The role of impurities and degradation on the thermal conductivity of carbon fiber and amorphous carbon

Carbon microstructures evolve due to exposure to rapidly oxidizing environments. The evolution of these structures can fundamentally change intrinsic material properties and therefore performance. In this study, we use molecular dynamics to investigate the sensitivity of carbon fiber and amorphous carbon thermal conductivities to defects introduced as a consequence of these environmental factors. Pristine microstructures are first evaluated, followed by counterparts with the presence of impurities, oxygen, and etch pitting. Findings indicate diminished thermal transport capabilities of these materials for all defect types studied, and differences in conductivity of up to 50% as compared to pristine counterparts. We also conclude that etch pitting has a meaningful impact on these materials thermal response from the early stages of formation. Results found in this study advance our understanding of carbon fiber materials performance in extreme environments and serve as the basis for meso-scale simulations of effective material properties

Research progress on the quality and efficiency of carbon fiber reinforced thermoplastic polymer composites processed by laser

Carbon fiber reinforced plastics (CFRP) has been widely used in aerospace, military weapons, new energy and high-end vehicles due to its specific and superior strength, low density and long-lasting wear resistance. The processing of CFRP is very different from the traditional metal processing because of its heterogeneous structure, anisotropy and superior wear resistance of CFRP. Usually, CFRP has often various defects in mechanical processing and water jet processing, such as interlayer tearing, fiber pull-out, delamination, tool wear, and abrasive penetration. Through laser processing, the problems of CFRP materials existing in mechanical processing can be overcome. However, due to the huge differences in thermal physical properties such as thermal conductivity and vaporization temperature of carbon fiber and resin in CFRP, its laser processing also turns out to have some issues, such as heat-affected zone and fiber end expansion. This paper summarizes the research results of CFRP laser processing in China and internationally. Research progress was introduced in detail from various aspects including laser and material mechanism as well as laser processing parameters. It reports the experimental and theoretical studies covering the process accuracy in edge quality and the thermal characteristics in terms of heat-affected zone. Eliminating the heat-affected zone in the polymer matrix are considered the major obstacles of CFRP industrial applications. The methods of improving processing efficiency by increasing material removal rate and reducing processing time were reviewed. The influence of different thermal conductivity of carbon fiber and resin matrix in CFRP on the processing quality was discussed. Finally, the development trend and challenges of thermal conductivity of carbon fiber and resin in CFRP in theoretical modeling were proposed.

Hydrogenation Improving the Molecular Orientation of Coal Tar Pitch-Based Mesophase Pitch for Enhancing the Thermal Conductivity of Carbon Fibers

Hydrogenation Improving the Molecular Orientation of Coal Tar Pitch-Based Mesophase Pitch for Enhancing the Thermal Conductivity of Carbon Fibers

Radial thermal conductivity of a PAN type carbon fiber using the 3 omega method

The prediction of the effective thermal conductivity of composites filled with carbon fibers requires the knowledge of the microstructure and composition of the composite, the orientation of nonisometric filler, the thermal conductivities of both phases and the thermal contact resistances between fibers and also between fibers and matrix. Due to the anisotropy of carbon fibers, one should know both their axial and radial thermal conductivities. Contrary to the axial thermal conductivity of carbon fiber, there are not much work on the radial one. The present work describes the characterization of the thermal conductivity of carbon fiber in the radial direction using the 3 Ω method with a constant current source. One key point is the use of de-ionized water around the carbon fibers to enhance radial heat transfer. An appropriate thermal model is required in order to estimate the radial thermal conductivity. Therefore, analytical 1D and 2D thermal models are developed using quadrupole methods to describe heat transfer in the carbon fiber using periodic regime and are compared with a 2D numerical model. It appeared that the use of a 1D heat transfer model induces some bias until 50.3% on the estimation of the radial thermal conductivity showing that residual axial heat transfer still occurs. Therefore the 2D thermal model is more appropriate and is used with the experimental data to estimate the radial thermal conductivity. In addition, a detailed sensitivity analysis of the unknown parameter is performed that allows to find the best range of operating conditions especially the frequency range and the effect of the type of surrounding material. Measurements are performed with PAN type carbon fiber (FT300B) of 6–8 μm diameter and various lengths from 0.5 to 2.5 mm embedded in de-ionized water. Finally, radial thermal conductivity values are shown to be about 10 times smaller than the axial one, revealing strong anisotropy of the studied carbon fiber.

Atomistic calculations of thermal conductivity in films made from graphene sheets for electron emitter applications

Simulations for the thermal conductivity of carbon fibers (CFs) are carried out based on a molecular dynamics (MD) approach. Our calculations are geared toward providing a general trend for thermal conductivity and its dependence on sample length and to probe the suitability of this material for high power applications from the thermal management standpoint. Since abundant data are not available for carbon fibers, calculations are first carried out in silicon to validate the predictions. The MD results yield a bulk thermal conductivity of 148 W m−1 K−1 for silicon in good agreement with published reports. However, for CF, a much lower bulk value of ∼14 W m−1 K−1 is predicted. This suggests that thermal management would likely be an issue for this material and that CF emitters of lengths below 2 µm should be avoided. The predicted increases in thermal conductivity with temperature may help alleviate the issue to a minor degree. Carbon nanotubes would likely be a better alternative in this context of field emitter arrays.

Improving interfacial properties and thermal conductivity of carbon fiber/epoxy composites via the solvent-free GO@Fe3O4 nanofluid modified water-based sizing agent

In order to address the less-than-satisfactory interfacial properties and thermal conductivity of carbon fiber reinforced polymers (CFRPs), a general solvent-free GO@Fe3O4 nanofluid (GFNF) hybrid water-based sizing agent was prepared and applied for carbon fiber (CF) sizing. A discussion was conducted about the effects of different GFNF contents on the CF/epoxy composites (CF/EP) for their interfacial properties and thermal conductivity. In comparison with the composites made up of commercial CF and epoxy, the interfacial and thermal conductivities of the GFNFCF/EP composites were significantly improved. Notably, the increase in 2.5-GFNFCF/EP was most noticeable, with ILSS and flexural strength improved by 15% and 43.6%, respectively. This is attributed to the uniform adhesion of GFNF to the CF surface, which enhances the physical-chemical interaction of fiber with matrix, promotes the dispersion of stress, and prevents cracking from spreading. Also, the thermal conductivity was improved by 128.9% due to the formation of continuous thermal conduction pathways at the interface. The mechanism behind interface and thermal conductivity enhancement of the composites was proposed. This hybrid sizing agent contributed a different solution to improving the interfacial properties and thermal conductivity of CFRPs at the same time.

Opposed-flow flame spread over carbon fiber reinforced plastic under variable flow velocity and oxygen concentration: The effect of in-plane thermal isotropy and anisotropy

This work explores opposed-flow flame spread over carbon fiber reinforced plastics (CFRPs) with an emphasis on the in-plane thermal isotropy and anisotropy depending on carbon fiber (CF) orientation. CFRP sheets with different CF orientations were fabricated by laminating unidirectional prepregs in different directions and combusted via a chimney where flow velocity and oxygen concentration were variable. The limiting oxygen concentration (LOC) under buoyant flow significantly increased with CF orientation angle. At more than 45°, a flame did not spread at all but was extinguished immediately after ignition even at 60% O2. The flammability of CFRPs with CF orientation angles of 0°, 15°, and 30° was further investigated with varying opposed-flow velocities and oxygen concentrations. The LOC of CFRP was higher than that of polymethyl methacrylate (PMMA) over all tested opposed-flow velocities regardless of CF orientation. The response of LOC to opposed-flow velocity varied with CF orientation angle. At 0°, the LOC was not overly sensitive to opposed-flow velocity but almost constant at 31% O2. Meanwhile, the LOCs at 15° and 30° linearly decreased with increased opposed-flow velocity. Flame spread for CFRP was much faster than that for PMMA because of the high thermal conductivity of carbon fibers. The flame spread rate of CFRPs was affected by CF orientation and that at 0° was highest among the three tested CFRP sheets. IR images used to visualize the in-plane temperature distribution during flame spread showed that the preheat region was significantly varied according to CF orientation. Varying CF orientation, therefore, causes the in-plane thermal anisotropy, resulting in the differences in the LOC and flame spread rate. The findings from this work help us evaluate the fire risk and hazard of CFRP and serve to discuss flame spread behaviors of other anisotropic materials.

Study on Thermal Conductivity of Carbon Fiber / Resin Composite Modified with Graphene Nanoplatelets

A method for calculating thermal conductivity of graphene/carbon fiber reinforced resin composites (GnP-CFRP) was established basing on the Mori-Tanaka program in the DIGIMAT software. The influence of grapheme nanoplatelets (GnP) on the thermal conductivity of composites has been simulated and experimentally verified. The results show that the thermal conductivity of GnP-CFRP increased with the increase of GnP content, and when the GnP content is too high, the increasing rate of thermal conductivity decreases gradually. In addition, the maximum prediction error of the simulation calculation method in this paper is within 7.27%, which is in good agreement with the actual situation.

Correlating thermal conductivity of carbon fibers with mechanical and structural properties

Thermal conductivity of carbon fibers (CFs), being one of the important properties, is not easily quantified due to practical difficulties in measuring it. We suggest a universal correlation between the thermal conductivity of CFs and their electrical and mechanical properties in order to estimate it without direct measurement. Crystalline structural information did not show a clear correlation with thermal conductivity, especially for commercially available polyacrylonitrile- or isotropic pitch-based CFs that have less than a few nanometers of La and Lc. However, in a correlation between tensile modulus and thermal conductivity, there are three distinct regions and two properties increase with a different inclination in each region. We envisage tensile modulus to be utilized to estimate thermal conductivity without a direct measurement for all kinds of CFs.

Study on laser irradiation temperature field of carbon fiber reinforced plastic composites

Based on Abaqus software, the temperature profiles during laser heating CFRP materials in different fiber directions was investigated in this research. The 3D temperature distribution and temperature history of laminates with different ply directions were analyzed and compared through the homogenous model. It is found that the focusing characteristics of laser causes a large temperature gradient. Meanwhile, the temperature field of CFRP laminate extends toward the direction of fibers because of the large axial thermal conductivity of carbon fibers. The thermal conduction in the thickness direction is poor, so the lower layer will not reach the melting temperature. In order to verify the validity of the model, a real-time temperature field measurement device consisting of thermal imager and thermocouples was built. The results show that the model can effectively simulate the temperature field of composite materials irradiated by laser.

Measurement of intrinsic thermal conductivity of carbon fiber using direct electrical heating method.

It is usually very difficult to measure the intrinsic thermal conductivity of fibers using direct electrical heating method, due to the presence of lateral heat loss. In this study, we demonstrate that the intrinsic thermal conductivity and lateral heat transfer coefficient of fibers can be extracted simultaneously via multiple measurements on the same fiber. In our experiments, three samples of various lengths were prepared from an individual polyacrylonitrile-based carbon fiber of 5.6 µm in diameter and measured with the direct electrical heating method. From each sample, we can get a curve of thermal conductivity vs lateral heat transfer coefficient. We showed that the intrinsic thermal conductivity and lateral heat transfer coefficient can be extracted from the intersection of these curves. Our results also showed that ignoring the lateral heat loss can result in an overestimation in thermal conductivity of carbon fibers by more than 3 times.

Opto-thermal technique for measuring thermal conductivity of polyacrylonitrile based carbon fibers

Thermal conductivity of carbon fibers (CFs) is an important property because CFs are used as heat dissipation fillers in composites for aerospace and electronics applications. However, evaluating thermal conductivity of a single filament of CFs is an arduous task due to dimensional issue of specimens and limitations of conventional measurement system. Therefore, we suggest an opto-thermal technique using Raman spectroscopy to measure thermal conductivity of commercial polyacrylonitrile based CFs (T300, T700SC and T800H). The opto-thermal technique used that G band from Raman spectroscopy of carbon materials is shifted depending on temperature. For verifying an accuracy of the technique, the laser absorbance of CFs were estimated, and the thermal conductivity was measured depending on the length of CF. The measured data were reflected in the thermal conductivity calculation formula. It was demonstrated that the method provides more reasonable thermal conductivity values compare to a conventional Angstrom method. In addition, this simple technique confirmed that graphitic structure of CFs played a critical role in their thermal conductivity.

Transverse Thermal Conductivity of Epoxy Carbon Fiber Prepreg Laminates with a Graphite Filled Matrix

The thermal conductivity of carbon fiber reinforced polymers is crucial for new technologies and is used in cutting-edge technologies such as sensors, heated rollers and anti-icing of airplane wings. Researchers so far focused on coating conventional prepregs with thermally conductive materials to enhance the transversal conductivity. Another strategy is followed in this study: Thermally conductive matrices filled with graphite platelets were processed by a laboratory prepreg line. Laminates produced from this type of prepregs show an enhancement in thermal conductivity by 3.3 times with a 20 vol% filler content relative to the matrix, and a 55 vol% fiber volume content in the laminate. The research shows that the incorporation of conductive particles in the matrix is more effective for increasing the conductivity than previous methods.