Uncoated Fibers Research Articles

Impact of Moisture Absorption on Optical Fiber Sensors: New Bragg Law Formulation for Monitoring Composite Structures

In recent decades, the aviation industry has increasingly adopted composite materials for various aircraft components, due to their high strength-to-weight ratio and durability. To ensure the safety and reliability of these structures, Health and Usage Monitoring Systems (HUMSs) based on fiber optics (FO), particularly Fiber Bragg Grating (FBG) sensors, have been developed. However, both composite materials and optical fibers are susceptible to environmental factors such as moisture, in addition to the well-known effects of mechanical stress and thermal loads. Moisture absorption can lead to the degradation of mechanical properties, posing a risk to the structural integrity of aircraft components. This research aims to quantify and monitor the impact of moisture on composite materials. A new formulation of the Bragg equation is introduced, incorporating mechanical strain, thermal expansion, and hygroscopic swelling to accurately measure Bragg wavelength variations. Experimental validation was performed using both uncoated and polyimide-coated optical fibers subjected to controlled hygrothermal conditions in a climate chamber. The results demonstrate that uncoated fibers are insensitive to humidity, whereas coated fibers exhibit measurable wavelength shifts due to moisture absorption. The proposed model effectively predicts these shifts, with errors consistently below 2.6%. This approach is crucial for improving the performance and reliability of HUMSs in monitoring composite structures, ensuring long-term safety in extreme environmental conditions.

Experimental investigation of field electron emission from uncoated and coated graphite fiber tips

Abstract This study investigates the field emission characteristics of coated and uncoated graphite fiber tips under high vacuum conditions in the pressure range of 10–6 Pa. A 2 M Sodium hydroxide (NaOH) solution was used in the electrochemical etching procedure to produce an uncoated etched graphite fiber emitter with a diameter of 436.5 nm. An epoxy coating 2301 dielectric material with a thickness of 61 ± 1 nm was used to coat the fiber tip. Field-emitter emission micrographs, current stability, and current-voltage (I-V) characteristics were recorded. Murphy’s Good plots were used to examine and analyse the I-V characteristics. An orthodoxy test was performed to evaluate the Murphy Good plots. In the reported results, at low applied voltages, the uncoated graphite fiber emitter passed orthodoxy tests, and generated a steady current with 0.03 µA uncertainty. However, the coated graphite fiber emitter showed an increase in the applied voltage and threshold voltages but had no impact on the sample emission characteristics.

Coating of Hemp Fibres with Hydrophobic Compounds Extracted from Pine Bark

Applying coatings of paraffins and other synthetic waxes is a common approach to impart hydrophobic properties to fibres and thus control their surface characteristics. Replacing these fossil-based products with alternatives derived from renewable resources can contribute to humankind’s transition to a sustainable bioeconomy. This study presents the coating of hemp fibres with waxes extracted from pine bark as an exemplar application. Two bio-based emulsifiers were used to prepare wax emulsions suitable for a dry blending process. The coatings on the fibres were characterised, quantified, and visualised using a combination of spectroscopic and microscopic techniques. Confocal fluorescence microscopy was an excellent tool to investigate the spatial distribution of the pine bark waxes on the fibre surfaces. While successful deposition was demonstrated for all tested formulations, coating homogeneity varied for different emulsifiers. Compounding the hemp fibres with a bio-based polyester resulted in the substantial improvement of the mechanical behaviour. However, the presence of a wax coating on the fibres did not lead to a significant change in mechanical properties compared to the controls with uncoated fibres. Optimising the composite chemistry or adjusting the processing conditions might improve the compatibility of the hemp fibres with the matrix material, resulting in enhanced mechanical performance.

Development and characterization of carbon fiber reinforcement in Aluminium metal matrix composites

Abstract Carbon fibers (CF) possess exceptional mechanical properties and the highest degree of chemical stability. However, carbon reinforcement in metal matrix composites is extremely scarce due to production difficulties, particularly in obtaining a uniform distribution. Carbon fiber reinforced composites are typically made using high temperature processing processes. However, the fibers must be coated with Ni or Cu in order to achieve effective particle dispersion; otherwise, there is a larger likelihood of intermetallic compound formation, which reduces the chances for enhanced properties. In this work, the metallurgical, mechanical, and tribological characteristics of the carbon fiber reinforcement in AA 7050 are examined. Uncoated carbon fibers are reinforced into the Aluminium matrix using a low temperature processing technique known as powder metallurgy. The AA 7050 matrix reinforced with carbon fibers at various weight percentages between 0 and 1.5. The samples undergone mechanical and metallurgical testing in accordance with ASTM guidelines. The findings indicate that the 0.25 weight percent carbon fiber reinforcement in the matrix increased the material’s hardness by 30% over the monolithic alloy, making it an excellent alternative for structural applications.

SYNCHROTRON BASED X-RAY ABSORPTION SPECTROSCOPY FOR STRUCTURAL ANALYSIS OF BASALT FIBERS

X-ray Absorption Near Edge Structure (XANES) spectroscopy at the Synchrotron Light Research Institute (Thailand) was used to investigate temperature related structural changes in basalt fibers. As a first step, XANES spectra of fiber samples cut from a basalt roving heated for 1 hour at 800 °C were recorded at the K absorption edges of three chemical elements and compared with the spectra of the untreated fibers. Silicon and calcium K-edge XANES spectra of the fibers were not affected by heating, whereas iron K-edge XANES spectra were significantly influenced by heating at 800 °C. The high iron content in basalt fibers has been attributed to their higher thermal stability compared to common natural or synthetic fibers. As a next step, iron K-edge XANES spectra of two types of fibers (basalt roving and uncoated chopped fibers) were recorded after heating at temperatures between 600 °C and 900 °C. In both cases, with increasing temperature the absorption edge shifts to higher energies, indicating progressing oxidation of the iron atoms in the fibers. These experiments demonstrate the potential of X-ray absorption spectroscopy as a powerful analytical tool to investigate structural changes in basalt fibers upon heating and to correlate them with changes in their mechanical properties.

The Impact of Liquids and Saturated Salt Solutions on Polymer-Coated Fiber Optic Sensors for Distributed Strain and Temperature Measurement.

The application of distributed fiber optic strain and temperature measurement can be utilized to address a multitude of measurement tasks across a diverse range of fields, particularly in the context of structural health monitoring in the domains of building construction, civil engineering, and special foundation engineering. However, a comprehensive understanding of the influences on the measurement method and the sensors is essential to prevent misinterpretations or measurement deviations. In this context, this study investigated the effects of moisture exposure, including various salt solutions and a high pH value, on a distributed strain measurement using Rayleigh backscattering. Three fiber optic sensors with different coating materials and one uncoated fiber were exposed to five different solutions for 24 h. The study revealed significant discrepancies (∼38%) in deformation between the three coating types depending on the surrounding solution. Furthermore, in contrast to the prevailing literature, which predominantly describes swelling effects, a negative deformation (∼-47 με) was observed in a magnesium chloride solution. The findings of this study indicate that corresponding effects can impact the precision of measurement, potentially leading to misinterpretations. Conversely, these effects could be used to conduct large-scale monitoring of chemical components using distributed fiber optic sensing.

Tribological performance of functional coated fiber reinforced additively manufactured polymer composite

Additive manufacturing has witnessed an upward trend in utilization across diverse industries in recent years. This study examines the tribological properties of polymer composites produced using additive manufacturing. The polymer composites were produced using the fusion deposition modeling process. Subsequently, they undergo thermal spray coating and spin coating processes that deposit hafnium carbide particles onto their surface. The wear test studies were conducted at three distinct temperature levels in accordance with the ASTM standard procedure. The findings demonstrated that the application of a ceramic particle coating led to a substantial decrease in the specific wear rates. Additionally, there were observed differences in the wear rates depending on the specific methods used for applying the coating. The application of thermal coating shown high efficacy in reducing wear rates and safeguarding the underlying materials against material loss. The uncoated carbon fiber reinforced polylactic acid (PLA-CF) material showed a slightly significant amount of material degradation as the test chamber temperature increased, in comparison to the coated specimens. The average specific wear rate of the thermally coated carbon fiber reinforced polylactic acid specimen at a temperature of 70 °C is 0.000156 kg Nm−1.

Enhancement of Flexural Strength in Fiber–Cement Composites through Modification of Sisal Fiber with Natural Rubber Latex and Expanded Perlite

This study presents a novel approach in enhancing the flexural strength of sisal fiber cement composites by employing a dual coating technique with natural rubber latex and expanded perlite to the sisal fibers. The effects of different fiber content (0.25, 0.5, 0.75, 1, 1.25, and 1.5 wt%) and fiber length (1, 2, and 3 cm) on the physical and mechanical properties of sisal fiber cement were also studied. The physical properties, including bulk density and water absorption, were evaluated via the Archimedes method. Flexural strength was measured using the 3-point bending method, and microstructure was observed using a scanning electron microscope (SEM) and an optical microscope (OM). As the fiber content and length increase, the bulk density of the sisal fiber cement decreases. However, composites utilizing coated fibers consistently exhibit a higher bulk density than those utilizing uncoated fibers, attributed to enhanced adhesion and reduced porosity. The water absorption of sisal fiber cement increases with fiber content, but it is mitigated by the natural rubber latex coating, which prevents fiber–water absorption, and by expanded perlite, which reduces voids in the matrix. Composites containing coated fibers consistently exhibit superior flexural strength compared to those with uncoated fibers. The highest flexural strength values of 5.58 MPa were observed in composites utilizing 3 cm of coated fiber with 0.25 wt% fiber content. Microstructure analysis reveals a well-bonded interface in coated fibers, emphasizing the positive impact of coating on mechanical performance. The incorporation of coated sisal fibers effectively improves adhesion, water resistance, and flexural strength, offering sustainable and durable construction materials. The achieved results can serve as the guidelines for the development of a high-performance bio-based construction materials with improved durability and reduced environmental impact.

Polydimethylsiloxane-coated Fiber Bragg Grating as a Bend Sensor

The fiber Bragg grating sensor is often demonstrated as a bend sensor. However, the demonstrated sensor in previous studies was limited to low sensitivity, thus reducing the sensing performance. Hence, this work demonstrated the polydimethylsiloxane-coated fiber Bragg grating sensor for sensitivity enhancement. The proposed sensor with a diameter of 5 cm was bent by adjusting the translation stage from 0.1 cm to 0.9 cm distance in forward and backward direction. The results showed that the Bragg wavelength shifted towards the longer wavelength region when the distance decreased. The polydimethylsiloxane-coated fiber Bragg grating sensor shows a sensitivity of 1743000 A.U, 8 times higher than the uncoated fiber Bragg sensor with a sensitivity of 284000 A.U. The presence of the polydimethylsiloxane layer has successfully improved the sensor performance.

Asbestos Bodies in Human Lung: Localization of Iron and Carbon in the Coating

Asbestos is a term that includes six fibrous mineral phases related to different lung diseases, including asbestosis, lung cancer, and Malignant Pleural Mesothelioma (MPM). Since the last century, these minerals have been widely studied under their mineralogical/chemical and physical aspects with in vivo and in vitro studies to understand the mechanisms of their carcinogenicity. There are several techniques described in the literature, as optical and electron microscopies, for the identification of coated (asbestos bodies, ABs) and uncoated fibers, but only micro-Raman spectroscopy permits a sure characterization of these minerals—and of the related phases—directly in the histological sections of pulmonary parenchyma without any manipulation. In this case, the risk of the loss of associated inorganic phases from asbestos bodies (ABs) and fibers (e.g.: iron or carbonaceous micro-particles) is avoided. Asbestos bodies are produced by the activity of alveolar macrophages with degradation/inactivation of asbestos fibers. Inside the alveolar macrophages, organic and inorganic material settles on the foreign fibers forming an iron-rich proteic and carbonaceous coating. In this study, Variable Pressure Scanning Electron Microscopy with annexed Electron Dispersive Spectroscopy (VP-SEM/EDS) and micro-Raman spectroscopy were applied to the characterization of the phases in the ABs. Characterization of carbonaceous materials (CMs), observed in pristine asbestos phases in previous works, was therefore performed, addressing the micro-Raman laser beam on different points of the asbestos bodies, and Raman mappings on ABs were carried out for the first time. Coupling the data obtained by VP-SEM/EDS and micro-Raman spectroscopy, it was possible to collect information about the iron and carbonaceous phases adhered to the fibers, probably lost during the classical tissue digestion procedures. Information about both mineral and carbonaceous components might be useful to understand the whole structure of “asbestos bodies” and the inflammogenic and carcinogenic effects of the asbestos phases coupled to CMs, that might derive from cigarette smoke or from environmental pollution; this study might be useful to deepen also the possible detrimental role of ABs in the tissues.

Impact of fiber coating with hydrophobic nanoparticles polymer on the physicomechanical properties of Pisum sativum L. fibers/ styrene butadiene rubber ecofriendly composites

Hydrophobic nanoparticle copolymers of vinyl acetate and different ratios of veova10 were used to coat Pisum sativum L. fibers (PSF). The impact of coating process on the reinforcement efficiency of PSF of styrene butadiene rubber (SBR) was investigated. The morphology study, indicated that, the coating with hydrophobic nanoparticle copolymers improved the interfacial adhesion between the PSF and SBR. The tensile strength (TS) of the composites containing coated fibers recorded the highest tensile properties, the lowest Mullins effect and the highest resistance to water absorption. The coating process improved the TS of PSF/SBR composite up to 35.3% after incorporation of 10 phr of coated PSF. The PSF/SBR composite containing 20 phr of coated fibers recorded water uptake of 14.18% compared to 23.24% for composites containing uncoated fibers. The PSF/SBR composites exhibited more biodegradation rate than that of neat SBR. The results indicated that the PSF coated with the prepared hydrophobic polymers had a beneficial impact on the physicomechanical properties of the PSF/SBR composites.

INVESTIGATION OF CARBON-ALUMINUM COMPOSITE WITH A BARRIER COATING ON CARBON FIBERS

Barrier SiO2 coatings on the surface of carbon fibers were deposited by the sol-gel solutions (dip coating) based on tertraethoxysilane Si(C2H5O)4. The average thickness of the barrier SiO2 coating on carbon fibers is 127 ± 30 nm. Carbon-aluminum composites were obtained by a type of liquid-phase infiltration — by the shell molding process. The components of the composite were placed in a steel hermetic shell, then after the shell evacuate and heat until the aluminum melts, the fibers were infiltrated by the melt under the external pressure, followed by cooling. Composites with SiO2 coating and without coating on carbon fibers were obtained. After extracting the composite from the metal shell, the structure, phase composition, and mechanical properties of the samples were studied. Studies of the structure of composites showed that the interfiber space is filled with aluminum melt, without porosity and macroscopic defects. The study of the phase composition of the composite reinforced with uncoated carbon fibers showed that aluminum carbide peaks are observed at the angles 2θ = 41°, 67°, 74°. Quantitative analysis carried out by the Rietveld method revealed that the amount of aluminum carbide in the composite is 12.0 ± 1.3 %. The deposition of a barrier SiO2 coating on carbon fibers leads to a decrease in the intensity of the main peaks of aluminum carbide, while the amount of Al4C3 decreases by 4 times, to 3.0 %. An analysis of the fracture surface of the samples after mechanical testing revealed that the fracture of the composite reinforced with uncoated carbon fibers is almost flat. No protrusions and relief are observed on the fracture surface. The fracture surface of a composite reinforced with coated carbon fibers has a relief surface, and separately sticking out fibers are observed. Mechanical tests of samples for three-point bending showed that the barrier coating on the fibers increases the strength to 520 ± 50 MPa, the strength of the uncoated composite is 350 ± 8 MPa. Barrier SiO2 coating applied to the surface of carbon fibers prevents the formation of aluminum carbide and fiber degradation in the carbon-aluminum composite.

Improved Thermal and Mechanical Properties of Kenaf Fiber/ABS Polymer Composites via Resin Coating Treatment

In developing natural fiber composites (biocomposites), compatibility between natural cellulosic fibers and polymers has always created serious challenges, reducing performance. This study focused on applying a novel approach using epoxy resin as a coating medium to enhance the properties of the fibers and the interface between the hydrophobic polymer and the hydrophilic natural fiber. 10 wt% of uncoated kenaf fibers (KF) and coated kenaf (CKF) fibers were compounded with acrylonitrile butadiene styrene (ABS) thermoplastic polymer in a twin-screw extruder at an optimized temperature of 220°C under the same processing conditions. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) examined the coated and uncoated fibers' physicochemical compositions and surface properties. The developed composites' thermal, mechanical, and microstructural characteristics were also examined, and the results revealed that the CKF/ABS composites had better interfacial bonding and mechanical characteristics than the uncoated KF/ABS composite. Coating natural fibers with epoxy resin is a novel technique for improving interfaces and developing environmentally friendly composites from natural sources.

Improving interfacial shear strength of fique fibres using an acrylic coating.

Natural fibres have proven to be a potential alternative to replace synthetic fibres in some composite materials applications. However, drawbacks such as impregnation difficulties and the poor fibre-matrix interface limit the use of natural fibres in high-performance applications. This work proposes using an acrylic resin to coat the fibre surface to enhance the interfacial compatibility among fique fibres and polyester resin. Pull-out tests revealed an improvement in the interfacial shear strength of about 110% for coated fibres. Furthermore, nanoindentation test, Micro Raman spectroscopy and scanning electronic microscopy indicated that the acrylic resin eliminates the gap at the fibre/matrix interface seen in the uncoated fibres. Observed behaviour could be attributed to a better chemical bonding between the fibre and matrix and is also hypothesised that the elastic characteristic of the coating helps to transfer loads effectively from the matrix to the fibre.

Influence of Adhesive Bonding on the Dynamic and Static Strain Transfers of Fibre Optic Sensors

The influence of the bonding procedure (the adhesive type, application procedure, etc.) on the static and dynamic strain transfers of bonded optical fibre sensors is studied theoretically and experimentally at room temperature. The achievable performances with four different types of adhesives (three urethane and one epoxy adhesive), and with different fibre types, are evaluated: acrylate-coated, polyimide-coated, and bare single-mode optical fibres. Static strain measurements, ranging from 20 to 200 µ strain, are performed using both fibre Bragg gratings (FBGs) and optical frequency domain reflectometry (OFDR), and are compared to reference strain-gauge measurements, and to the proposed analytical model, which is developed on the basis of stress equilibrium relations. This model is valid for bonding to all types of linear and elastic materials, as long as there is no sliding between the host material, the adhesive, and the optical fibre. The results agree between the analytical model and the experiments. Regarding the dynamic sinusoidal strain measurements, the studied dynamic range is from 10 to 100 Hz, and only the FBGs are tested. The results demonstrate that the sensitivities of strain sensors based on bonded uncoated fibres or bonded polyimide-coated fibres are comparable to those of strain gauges, and that it is possible to use bonded FBGs for precise dynamic strain measurements.

Development of Fiber-Bragg-Grating-Integrated Artificial Embedded Tendon for Multifunctional Assessment of Temperature, Strain, and Curvature.

This paper presents the development and application of an optical fiber-embedded tendon based on biomimetic multifunctional structures. The tendon was fabricated using a thermocure resin (polyurethane) and the three optical fibers with one fiber Bragg grating (FBG) inscribed in each fiber. The first step in the FBG-integrated artificial tendon analysis is the mechanical properties assessment through stress-strain curves, which indicated the customization of the proposed device, since it is possible to tailor the Young's modulus and strain limit of the tendon as a function of the integrated optical fibers, where the coated and uncoated fibers lead to differences in both parameters, i.e., strain limits and Young's modulus. Then, the artificial tendon integrated with FBG sensors undergoes three types of characterization, which assesses the influence of temperature, single-axis strain, and curvature. Results show similarities in the temperature responses in all analyzed FBGs, where the variations are related to the heterogeneity on the polyurethane matrix distribution. In contrast, the FBGs embedded in the tendon presented a reduction in the strain sensitivity when compared with the bare FBGs (i.e., without the integration in the artificial tendon). Such results demonstrated a reduction in the sensitivity as high as 77% when compared with the bare FBGs, which is related to strain field distributions in the FBGs when embedded in the tendon. In addition, the curvature tests indicated variations in both optical power and wavelength shift, where both parameters are used on the angle estimation using the proposed multifunctional artificial tendon. To that extent, root mean squared error of around 3.25° is obtained when both spectral features are considered. Therefore, the proposed approach indicates a suitable method for the development of smart structures in which the multifunctional capability of the device leads to the possibility of using not only as a structural element in tendon-driven actuators and devices, but also as a sensor element for the different structures.

Structure and properties of fine diameter continuous SiC ceramic fiber reinforced Al matrix composites

The polymer-derived-SiC ceramic fibers reinforced 7075 aluminum alloy composites were prepared by hot pressing method. The effect of an in-situ carbon coating on the fiber surface was investigated. The results showed that the uncoated SiC fibers reacted with the Al matrix after hot pressing at 630 °C for 6h. The interfacial bonding was too strong to deflect micro-cracks, leading to a pseudo-brittle fracture with a flexural strength of only 170.7 MPa. When an in-situ carbon coating of 400 nm was prepared on each SiC fiber, the carbon coating reacted with the Al matrix instead of the SiC fiber to form a complex multi-layer interface of 160 nm. The composite had an enhanced strength of 879 MPa. When heat treatment in air, the interfacial bonding strength of the two composites both gradually decreased, making the fracture mode and mechanical properties change finally.

Intrinsic MXene-Ti3C2Tx enhanced high sensitivity Mach-Zehnder interferometric microstructured optic fiber temperature sensor

A temperature sensing method with simple fabrication, real-time detection, and high sensitivity is proposed, and the feasibility of the method is experimentally verified. The sensing unit uses a single-no-multi-no-single (SNMNS) Mach-Zehnder Interferometric (MZI) structure to excite a stronger evanescent field and compares the effect of two different lengths of multimode fibers on the temperature sensing performance. To enhance the sensor sensitivity, a novel 2D material with superior photothermal, optoelectronic, and structural properties, MXene-Ti3C2Tx, was innovatively coated on the optical fiber surface. The intrinsic MXene-Ti3C2Tx material was prepared by the water bath method and characterized by scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD). The same temperature sensing experiments were carried out on uncoated and coated material fibers respectively, and the results showed that the temperature sensitivity improved from a minimum of 61.97 pm/℃ to 120.71 pm/℃ over the temperature range of 30℃∼80℃, an improvement of 94.7 % in sensitivity, with linearity all above 0.98. This paper combines for the first time the sensitive 2D material MXene-Ti3C2Tx with a microstructured fiber-optic temperature-sensing unit, providing a new way of thinking in the field of temperature detection and showing great promise in the field of fiber-optic sensing.

Unprecedented sensing of the twist level in fiber tows, as shown for carbon fiber by inductance-based self-sensing, which provides fast, low-cost and large-format sensing

Twisting is commonly imposed on fiber tows to improve the processability, as needed for manufacturing composites and other products. Twist level (number of twists per unit length) determination commonly involves visual inspection. This work provides a method of sensing the twist level, as shown for carbon fiber tows up to 4 twists/inch. This method involves measuring the inductance (0.5–2.0 kHz), which increases monotonically with the twist level, due to Faraday's Law. The method is fast, low-cost, high-durability and large-format (scanning not needed). Uncoated and nickel-coated carbon fiber tows (PAN-based, 12K) give similar fractional increases in the inductance (≤46%) due to twisting. Magnetic character (as provided by nickel) is not required. A larger tow (24K) increases the inductance, but reduces the fractional increase due to twisting. Increasing the voltage enhances the inductance, but the fractional increase due to twisting is not affected. An increase in frequency also enhances the inductance, but the fractional change in inductance due to the twisting is diminished. The resistance decreases monotonically with the twist level (≤14% and ≤4% decrease for uncoated and nickel-coated carbon fibers, respectively), due to the increasing number of fiber-fiber contacts, which enable current detour when defects are encountered. Inductance-based sensing is superior in twist-level sensitivity to resistance-based sensing. Both sensitivities decrease monotonically with increasing twist level, with highest sensitivity below 1 twist/inch. The lowest twist level with demonstrated sensing is 0.1 twist/inch. This work also provides the first report of inductance-based structural self-sensing, which differs from the widely reported resistance-based structural self-sensing.

Magnetic field enhancing preferred orientation of nickel-cobalt plated carbon fibers in cement paste, with relevance to compression self-sensing

The arrangement of carbon fibers in the cement matrix affects the stability and sensitivity of the composite. This study investigated the effects of bath pH and electroless plating time on the magnetic metallization (nickel coating, cobalt coating, and nickel-cobalt alloy coating) on carbon fibers and successfully prepared the CFRCs in which the metal-plated carbon fibers could be oriented by magnetic fields. The results showed that a pH of 10 and a plating time of 6 min were favorable for reaction kinetics, with the thickness gain, conductivity, and saturation magnetization of metal coatings all being the largest. The compressive strength of the prepared composites was increased by 26.5% by adding nickel-cobalt coated carbon fibers, which is attributed to the alignment of fibers refining pore structure. The resistivity of CFRCs with metal-plated carbon fibers is one order lower in magnitude than that with uncoated carbon fiber, due to that the alignment of fibers increases the conduction connectivity by decreasing the distance of fiber-fiber and the “quantum tunneling”. The cyclic compressive loading tests showed that the resistance changed reversibly with strain, such that the degree of reversibility is higher for CFRCs with pre-magnetic treatment than those without the treatment. The piezoresistivity (strain sensitivity) of CFRCs was stronger with magnetic field-induced orientation treatment, showing that the strain sensitivity increased by 114% after pre-magnetic treatment for CFRCs containing nickel-cobalt coating. This is attributed to that the well-aligned metal-plated carbon fibers form more conduction paths along the alignment direction, such that the resistivity along this direction is more sensitive to the compressive strain parallel to this direction.