Fiber Thermal Conductivity Research Articles

Stochastic mesoscale characterization of ablative materials for atmospheric entry

This study addresses the estimation of material properties at a mesoscopic level using the PuMA software from an uncertainty quantification perspective. Stochastic simulation with PuMA is primarily related to the random distribution of fibers, which is an intrinsic source of uncertainty. Additionally, the selection of certain physical parameters, such as the fiber's thermal conductivity, introduces further uncertainties. The first contribution of this study is to propose a low-cost surrogate-based methodology with an unequal allocation scheme, applied for the first time to the stochastic mesoscale characterization of ablative materials. The second contribution is a study on uncertainty propagation and sensitivity analysis of material properties, providing a systematic assessment of the choice of voxel resolution for both the fibers and the domain. Specifically, the convergence of quantities of interest can be monitored, thus identifying the minimal reference elementary volume.

A study on aramid nano-aerogel fiber and its fabric thermal conductivity

Aramid nano-aerogel represents an ideal structure for the fabrication of next-generation high-performance thermal insulation fibers and textiles. Single aramid nano-aerogel fiber can be achieved via wet spinning. The thermal conductivity of these fibers, a crucial determinant of textile insulation performance, remains under-explored in terms of numerical modeling. This research aims to establish a numerical inversion model to determine the thermal conductivity of single aramid nano-aerogel fiber. By simulating the three-dimensional geometry of plain fabric, the volume fraction of gas and solid within the fabrics are computed. Drawing from the law of energy conservation and Fourier's law of heat conduction, a relationship model is proposed between the thermal conductivity of single aramid nano-aerogel fiber and the overall thermal conductivity of the fabric. The finite difference method is employed to ascertain the thermal conductivity of single aramid nano-aerogel fiber. Furthermore, the influence of the geometric structure and the fiber diameter on the thermal insulation performance of the single-layer fabric is analyzed, which provides a feasible approach for the subsequent design of fabric structures with excellent thermal insulation properties.

Retracted: Investigation on Heat Deflection and Thermal Conductivity of Basalt Fiber Reinforced Composites Prepared by Hand Layup Method

Retracted: Investigation on Heat Deflection and Thermal Conductivity of Basalt Fiber Reinforced Composites Prepared by Hand Layup Method

In‐plane and in‐depth frontal polymerization behaviors of continuous fiber‐reinforced epoxy composites

AbstractFrontal polymerization (FP) is a self‐sustaining reaction that relies on polymerization exothermicity and heat transfer. This study explores the in‐plane and in‐depth FP mechanisms of continuous fiber‐reinforced epoxy composites. First, the effects of initiator and diluent concentrations on the FP behaviors of neat epoxy resins were examined. It was found that the frontal velocity and frontal temperature of the neat resins increase with an increase of either the initiator concentration or the diluent content, depending on the polymerization enthalpy and curing kinetics. Then, the FP behaviors of continuous carbon fiber and glass fiber‐reinforced epoxy woven composites were investigated. The results showed that the in‐plane FP behavior of the composites was primarily controlled by the thermal conductivity and specific heat capacity of the continuous fibers, whereas the in‐depth FP behavior mainly depended on the pores of the woven fabrics.Highlights Frontal velocity and temperature of neat resins are controlled by the polymerization enthalpy and curing kinetics. The in‐plane FP behavior of continuous fiber reinforced composites is dependent on the thermal conductivity and specific heat capacity of the fibers. The in‐depth FP behavior of composite is determined by both the thermal conductivity of fibers and the pores of fabrics.

Mathematical modelling and experimental validation of thermal conductivity of outer layer of fire protective clothing

Motivation for development of this mathematical model is the difficulties related to the experimental measurement of the thermal conductivity like frequent sample preparation, experimental setup availability and lack of easier methods for quick estimation of thermal conductivity of outer layer of fire protective clothing. Considering this, various studies were devoted in the past to determine the thermal conductivity of fabrics. Two mathematical approaches for prediction of thermal conductivity of woven outer layer have been presented in the present study. Series-parallel thermal resistance configuration has been used for prediction of effective thermal conductivity of the fabric. First approach uses input values of structural parameters and can be useful in the development of new woven fabrics for outer layer of fire protective clothing. Second approach uses fibre volume fraction and thermal conductivity of fibre and air. It is suitable for predicting thermal conductivity of finished fabrics. The values obtained from mathematical model were validated with experimental values.

Estimation of Effective Thermal Conductivity of Copper-Plated Carbon Fibers Reinforced Iron-Based Composites by 2D Image Analysis

Dies with high thermal conductivity (TC) can not only speed up heat transfer but also improve the production efficiency of parts and extend the life of the dies. Taking advantage of the high axial TC of carbon fibers (Cf), thermal channels are established in the composite. To protect Cf from being destroyed, Cf was electroless plated with Cu to form copper-plated Cf (Cf-Cu). Pores impede heat conduction, and the TC of the matrix is corrected by Bruggeman’s equation. Cf-Cu has high anisotropic, and its orientation can significantly affect the TC of iron-based composites. The mathematical equation between the orientation of Cf-Cu in the 3D model, the orientation of Cf-Cu on 2D cross-section, and the aspect ratio of an ellipse were obtained by Cf-Cu intersects with cross-section was determined by establishing a model of the orientation of Cf-Cu in 3D space. The simulated TC of the composite was calculated by 2D image analysis (finite element method). The effect of the orientation of Cf-Cu on the TC of composites with different Cf-Cu contents was investigated. When the volume fraction of Cf-Cu was 20%, the measured and simulated TC reached the maximum of 68.89 W m−1 K−1 and 71.02 W m−1 K−1, respectively. Before rolling, there is a significant difference between the simulated and measured TC. After rolling on the side surface of the rolling plane of the composite, both the simulated and measured TC on the rolling plane and its side surface show the same trend with the increasing of Cf-Cu content.

Thermal conductivity of single silk fibroin fibers measured from the 3ω method

Silkworm silk, a potential material used as the matrix of conductive fibers, has attracted extensive attention due to its excellent mechanical properties. However, researches on its thermal properties, especially in the axial direction of the single silk fibroin fiber are less. In this study, the axial thermal conductivity of a single silk fibroin fiber after coating a gold film on the surface is measured using the 3ω method. The effects of the radiation heat loss on the intrinsic thermal conductivity are eliminated by varying the length of the test samples. The results show that the thermal conductivity of the single silk fibroin fiber decreases slightly as the temperature increases from 260 to 300 K. The extracted intrinsic axial thermal conductivity is about 0.775 W/m-K at room temperature, an order of magnitude higher than most textile fibers. The method proposed in this study can be extended to accurately measure the thermal conductivity of the other non-conductive micro-fibers.

Investigation on Heat Deflection and Thermal Conductivity of Basalt Fiber Reinforced Composites Prepared by Hand Layup Method

Recent trends are shifting to the use of composite materials and their demands for making alternate materials to metals due to weight ratio, while the synthetic fiber composite also creates environmental hazards. To overcome these issues, composite materials with natural fiber reinforcement are being developed. The current work is concerned with the fabrication of composite laminates using the traditional hand layup method, with 40% reinforcement of basalt fiber mat and sawdust filler and 60% epoxy, with quantifying the thermal effects of composite laminates varying with four different weight fractions of basalt fiber and sawdust filler materials. The results revealed that maximum thermal conductance, heat deflection temperature, and coefficient of linear thermal expansion values are 0.254 W/mK, 95°C, and 2.9 × 10−5/°C, respectively, which increases sawdust filler loading resist the thermal effect compared to basalt fiber loading of hybrid composite.

Study on the Grooved Morphology of CMC-SiCf/SiC by Dual-Beam Coupling Nanosecond Laser

Due to the excellent properties of high hardness, oxidation resistance, and high-temperature resistance, silicon carbide fiber reinforced silicon carbide ceramic matrix composite (CMC-SiCf/SiC) is a typical difficult-to-process material. In this paper, according to the relationship between the spatial posture of dual beams and the direction of the machining path, two kinds of scanning methods were set up. The CMC-SiCf/SiC grooving experiments were carried out along different feeding directions (transverse scanning and longitudinal scanning) by using a novel dual-beam coupling nanosecond laser, and the characteristics of grooving morphology were observed by Laser Confocal Microscope, Scanning Electron Microscopy (SEM), and Energy Dispersive Spectrometer (EDS). The results show that the transverse scanning grooving section morphology is V shape, and the longitudinal scanning groove section morphology is W shape. The grooving surface depth and width of transverse scanning are larger and smaller than that of longitudinal scanning when the laser parameters are the same. The depth of the transverse grooving is greater than that of the longitudinal grooving when the laser beam is transverse and longitudinal scanning, the maximum grooving depth is approximately 145.39 μm when the laser energy density is 76.73 J/cm2, and the minimum grooving depth is approximately 83.76 μm when the laser energy density is about 29.59 J/cm2. The thermal conductivity of fiber has a significant effect on the local characteristics of the grooved morphology when using a medium energy density grooving. The obvious recasting layer is produced after the laser is applied to CMC-SiCf/SiC when using a high energy density laser grooving, which directly affects the grooved morphology.

Thermal Conductivity and Mechanical Characterization of Bamboo Fiber and Rice Husk/MWCNT Filler Epoxy Hybrid Composite

Recent trends utilizing recycled materials from around the world aim to improve a wide range of industrial and domestic applications. The natural fiber/filler matrix is used to evaluate the mechanical qualities of the hybrid nanocomposites. The specific concentration is dealing with a bidirectional bamboo fiber mat/rice husk particle/MWCNT blend with epoxy composite. The experimental work plan to execute with the three different proportional composites was as follows: bamboo fiber mat constant loading for all the specimens, but the filler particle ratio will be varied, prominently rice husk particle concentrated for all the three specimens: 5%, 10%, and 15%, and additionally, MWCNT drawn two specific specimens (2 and 3): 0.5% and 1% based on the fiber/filler concentration balanced the epoxy resin. The research presented here is hybrid nanocomposite experimented with thermal, mechanical, and morphological characterization. Thermal conductivity measured by Lee’s disc method is observed at 0.2577 W/mK for specimen 3. The tensile and flexural properties are higher for 0.5% MWCNT concentration (specimen 2): 42.66 MPa and 54.72 MPa, respectively. The maximum impact strength is reached at 1% MWCNT concentration (specimen 3). Bamboo fiber and rice husk filler matrix composite (specimen 1) reached extremities shore‐D hardness 84. Scanning electron microscopy was performed to examine the morphological characteristics of the tensile fractography specimen and analyzed the dispersion of the fiber/filler matrix adhesion of the surface. The bamboo fiber mat/rice husk/MWCNT (specimen 3) filler had better binding and observed fewer fiber pull‐out, fiber fracture, fiber extension, and voids. In the graphic comparison, 0.5% MWCNT achieved more mechanical properties than the other two combinations.

Influence of Solder Condition on Effective Thermal Conductivity of Two-Directional Random Fibres: Pore-Scale Simulation

Influence of Solder Condition on Effective Thermal Conductivity of Two-Directional Random Fibres: Pore-Scale Simulation

Thermal conductivity of hybrid fibre reinforced concrete under varying temperature

The Small closely spaced and uniformly dispersed fibres in concrete greatly improve its mechanical and fire-resistant properties. This paper deals with experimental investigation of the performance of Hybrid Fibre Reinforced Concrete (HFRC) with carbon and steel wool fibres under different elevated temperatures. Five different fibre volume fractions between 0 and 1% were selected. The concrete cube specimens were casted with five combinations of carbon fibre (CF) and steel wool fibre (SW) and cured. The concrete cube specimens were exposed to three different temperatures (400 °C, 600 °C, 800 °C) and the thermal conductivity of the concrete cube specimen were measured using K-type thermocouple. Temperature exposed specimens were tested for compressive strength and compared with control specimen. The compressive strength of temperature exposed HRFC cube specimens are reduced due to the degradation of the cube specimen. The compressive strength test results were compared with control specimen to find the optimum fibre proportion in HFRC.

Threshold properties of high modulus carbon fiber reinforced plastic composite with picosecond laser processing

The picosecond laser processing thresholds and morphology characteristics of polyacrylonitrile-based high modulus carbon fiber reinforced cyanate ester composite (M55/BS-4) and an asphalt-based high thermal conductivity carbon fiber reinforced plastic (K600/5418) were studied. Diameter-regression method was used to test and compare the ablation threshold, threshold incubation effect, and single-pulse thresholds for each composite were predicted. The influence of incident energy fluence (0.7-25 J/cm2) and beam scanning velocity (0.2-5 m/s) on the incision quality was analyzed. The results show that the great difference in the fiber thermal conductivity leads to significant quantitative difference in processing threshold and morphology. Using the highest scanning speed (5 m/s) available and fluence equivalent to 3.2 times the single-pulse threshold (i.e., about 8 J/cm2), carbon fiber and resin can be almost synergically removed, characterized by uniform slit inlet widths and neat cutting edge. The use of higher scanning speeds coupled with appropriate processing energy is expected to further improve the quality of processing.

Thermal Conductivity of Cellulose Fibers in Different Size Scales and Densities.

Considering the growing use of cellulose in various applications, knowledge and understanding of its physical properties become increasingly important. Thermal conductivity is a key property, but its variation with porosity and density is unknown, and it is not known if such a variation is affected by fiber size and temperature. Here, we determine the relationships by measurements of the thermal conductivity of cellulose fibers (CFs) and cellulose nanofibers (CNFs) derived from commercial birch pulp as a function of pressure and temperature. The results show that the thermal conductivity varies relatively weakly with density (ρsample = 1340–1560 kg m–3) and that its temperature dependence is independent of density, porosity, and fiber size for temperatures in the range 80–380 K. The universal temperature and density dependencies of the thermal conductivity of a random network of CNFs are described by a third-order polynomial function (SI-units): κCNF = (0.0787 + 2.73 × 10–3·T – 7.6749 × 10–6·T2 + 8.4637 × 10–9·T3)·(ρsample/ρ0)2, where ρ0 = 1340 kg m–3 and κCF = 1.065·κCNF. Despite a relatively high degree of crystallinity, both CF and CNF samples show amorphous-like thermal conductivity, that is, it increases with increasing temperature. This appears to be due to the nano-sized elementary fibrils of cellulose, which explains that the thermal conductivity of CNFs and CFs shows identical behavior and differs by only ca. 6%. The nano-sized fibrils effectively limit the phonon mean free path to a few nanometers for heat conduction across fibers, and it is only significantly longer for highly directed heat conduction along fibers. This feature of cellulose makes it easier to apply in applications that require low thermal conductivity combined with high strength; the weak density dependence of the thermal conductivity is a particularly useful property when the material is subjected to high loads. The results for thermal conductivity also suggest that the crystalline structures of cellulose remain stable up to at least 0.7 GPa.

Improvement of Thermal Conductivity for Carbon Fabric Composites Base on the Fabric Structure

This paper presents the development of methods for improving the thermal conductivity of fiber reinforcing materials based on the fabric structures. The thermal analysis of fabric structure in thermal load calculation is performed by Fourier’s Law of Thermal Conduction and Steady-State Thermal calculation in Siemens NX. This study leads to the development of thermal conductivity in manufacturing technology of fiber reinforcing materials. Keywords: Thermal conductivity, fabric structure, polymer composite materials

Numerical Investigation of Anisotropic Conductivity of Date Palm Fiber Bundle Composite

Date palm fiber bundle includes lumens in solid region, which present low thermal conductivity than that of fiber bundle. In this work, the transverse thermal conductivity of date palm fiber bundle was determined by numerical software to investigate the relation between the bundle fiber and the solid region thermophysical properties. Therefore, the results determined from the numerical investigation were compared to the analytical model to prove the numerical model developed in this study. In this context, numerical simulation of thermal conductivity was performed by the numerical finite element method by COMSOL software. To verify the developed models, the bundle fiber and solid region thermal conductivity relation were determined. Quadratic and Cubic polynomial expressions, were used to study the influence of the normalized conductivity of the bundle fiber and the solid region of the composite material and to evaluate the composites thermal conductivity. Influence of lumen on the thermal conductivity was also investigated in this work. The results indicate that the bundle fiber thermal conductivity is much less than that of the solid region thermal conductivity. This one depends on pore dimension, but not on distribution and shape of pore. The numerical results obtained from the model developed in this study are compared with analytical model to validate this model. Finally, a sensitivity analysis was conducted with the models to investigate how changes in the values of important variables, such as thermal conductivity and volume fraction of the constituent, can affect the effective thermal properties of the composite.

The effective thermal conductivity of coated/uncoated fiber-reinforced composites with different fiber arrangements

Fiber-reinforced composites are attractive for many applications in energy fields, such as thermal energy storage and building energy-saving. In these applications, their effective thermal conductivity is extremely important; however, research addressing the effect of various parameters on effective thermal conductivity is scarce. In this paper, the influences of different parameters, including volume fraction, aspect ratio, and orientation of fibers, and the thickness of coating layers on the effective thermal conductivity of fiber-reinforced composites, are numerically investigated by the Lattice Boltzmann method. Based on numerous numerical results, a correlation of the effective thermal conductivity is proposed for the composites with fibers randomly distributed in space. It is found that the thermal conductivity of fiber and coating layers are the two most dominant factors which influence the effective thermal conductivity of fiber-reinforced composites. The thickness of the coating layer affects the effective thermal conductivity of composites with fibers randomly distributed in space remarkably, while its effect on the effective thermal conductivity of composites with fibers arranged perpendicular to the heat transfer is negligible. The results of this work could provide important references for the process design and improvement of thermal performance of fiber-reinforced composites.

Structure and performance preparation on alginate-based fibrous aerogel with double network

To sodium alginate and acrylamide (AM) as raw material, using ammonium persulfate (APS) as initiator, N,N-methylene bisacrylamide (MBA) as crosslinking agent, SA/PAM-based fibrous aerogels are prepared by extrusion and freeze drying techniques based on dual network structure design. The results show that the best preparation process is one step molding, acrylamide 50 wt%, 1.2 mm spinneret pore size, 9 mm/min spinning rate, 3 wt% CaCl2 coagulation bath, 5 min coagulation time. The aerogels present a microscopic multi-layered pore structure with macroporous intervening mesopores and micropores, and rendered as macroscopic fibrous. The average pore size of macropores is 2093.70 nm, the specific surface area is 230.00 m2/g, the porosity is 72.10%. The average pore size of mesopores and micropores is 40.44 nm, the specific surface area is 18 m2/g and the thermal conductivity of fiber aerogels/epoxy composites is 0.1321 w/m·k.

High spatial resolution thermal conductivity mapping of SiC/SiC composites

Silicon carbide (SiC) ceramic matrix composites are being investigated as a new generation of fuel cladding materials due to its higher accident tolerance compared to Zircaloy. Characterization of the thermal conductivity of SiC constituents and their interfaces and interphases in SiC/SiC composites is needed as inputs to models of cladding performance. We used time-domain thermoreflectance (TDTR) to map the thermal conductivity with a spatial resolution of 2 µm. The SiC/SiC composite is comprised of Hi-Nicalon Type S fibers in a matrix made by chemical vapor infiltration (CVI matrix). The interphase material is a pyrolytic carbon/SiC multilayer. We report thermal conductivity maps of the SiC fiber and SiC matrix at temperatures of 25 °C, 90 °C, 164 °C, and 250 °C. The fiber has a uniform and isotropic thermal conductivity of 22 W m−1 K−1 at 25 °C; the thermal conductivity of fiber is approximately independent of temperature. The matrix thermal conductivity is not uniform and varies from 50 to 120 W m−1 K−1 at 25 °C; the thermal conductivity of the matrix scales approximately with the inverse of the square root of temperature, i.e., ∝ 1/T1/2. The thermal conductivity of the interphase at room temperature is 6 W m−1 K−1. The calculated spatially averaged thermal conductivity of this SiC/SiC composite at 1000°C is 29 W m−1 K−1.

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.