Carbon Fiber Reinforced Polymer Substrate Research Articles

Morphological and mechanical studies of Al2O3-Na2SiO3 as a skin barrier coated with TiO2 for carbon fiber reinforced composite materials.

The utilization of adhesive compounds in bonding lightweight and high-performance composite structures, including carbon fiber reinforced polymer (CFRP) composites, has garnered significant attention from researchers. This study presents the novel application of Al2O3 coated with TiO2 as a thermal protective layer for CFRP substrate. Initially, the CFRP substrate underwent a protective treatment involving the application of Al2O3 as a middle coat, followed by a further protective layer consisting of TiO2 as a top coat. The deposition of TiO2 onto an Al2O3-based thermal barrier coating (TBC) was carried out utilizing the flame spray method. The use of a TiO2 coating as a top coat was employed to enhance protection and heat dispersion across the middle coat and substrate. In order to achieve sufficient adhesion between the CFRP substrate, an intermediate coat consisting of Al2O3 with a Na2SiO3 binder, the impact of varying nozzle distances on adhesion strength and pull-off test outcomes was investigated, with a nozzle distance of 180 mm yielding the highest adhesion strength. The thermal stability of a CFRP substrate was enhanced through the deposition of a layer of TiO2 on Al2O3. The surface and cross-sectional morphologies of the composite were analyzed using a Scanning Electron Microscope (SEM). It was observed that the presence of a TBC on the composite surface effectively reduced the amount of heat that was transferred to the composite material. In order to assess the effectiveness of TBC on CFRP substrates, a series of experiments involving thermal torch and conductivity tests were undertaken. The interaction between the top and middle coats of a composite material results in enhanced mechanical properties, hence improving its thermal insulation capabilities. The artificially produced TBC coatings have the potential to function as adhesive materials, ensuring the sustained high performance of CFRP substrates.

An investigation of bond behavior between composite materials (CFRP, GWMM, KPGC) and substrates (Brick and Concrete) for strengthening existing masonry structures

The use of novel composite materials to repair and upgrade existing masonry structures is a major research topic. The Rilem Technical Committee 250-CSM (Composites for the Sustainable Strengthening of Masonry) and Assocompositi (Italian Industry Association for Composite Materials) conducted a round robin test to study the properties of up to 25 types of composite materials in terms of direct tension and bonding behavior. These research results provide a more comprehensive understanding of the mechanical properties of fabric reinforced cementitious matrix (FRCM) reinforcement systems and further improve the standardization of testing procedures. However, owing to the diversity of composite materials and substrates, these results cannot be directly applied to strengthening existing masonry structures in China.In this study, we aimed to comprehensively investigate the bonding behavior between various commonly used composite materials and substrates. Three brick types commonly used in rural areas of China were selected as substrates, namely clay solid brick, shale perforated brick, and concrete hollow block, and three mainstream composite materials were selected as reinforcement materials, namely carbon fiber-reinforced polymer (CFRP), galvanized wire mesh mortar matrix (GWMM), and knitted polyester geogrid cementitious matrix (KPGC). It should be noted that both GWMM and KPGC can be viewed as FRCMs, because they comprise both a fabric and matrix. First, the mechanical properties of the composites were determined by unidirectional tensile tests. Second, single- and double-lap tests were conducted using a specially designed test setup. A comprehensive analysis of the experimental results was conducted, including failure modes, load-global slip curves, failure loads, peak stresses, and exploitation ratios. Finally, the prediction formula for the bonding load capacity of the composite materials mentioned above was explored using the experimental results recorded in this study and relevant literature. The results not only explain the bonding behavior among CFRP, GWMM, PGCM and different substrates, but also broaden the material selection scopes in the repair process of existing masonry structures in a large number of villages and towns in China.

An ultrathin polymer-derived UHTCs coating on CFRP substrate: Effective electromagnetic wave absorber

The utilization of carbon fiber-reinforced polymer (CFRP) materials in electronic equipment encounters notable challenges of electronic warfare operations and the risk of detection by various sensors. A novel ceramic coating comprising TiC/SiOC with added Al2O3 adhesive was formulated to address these issues. The TiC/SiOC-50 wt% Al2O3 coating demonstrated exceptional microwave-effective absorption bandwidth (EAB) of 13.5 GHz, effectively covering the entire Ka-band, while maintaining a thin thickness of 0.60 mm. The TiC/SiOC-80 wt% Al2O3 system exhibited remarkable EM characteristics, including a minimum reflection loss (RLmin) of −58.26 dB, an EAB of 10.74 GHz, and an ultra-thin thickness of 0.38 mm, which sets a new record as the thinnest reported coating in the existing literature. The outstanding electromagnetic performance, coupled with their lightweight and thin characteristics, positions these coatings as highly viable solutions for various electromagnetic shielding and absorption applications in extreme environments.

A Flexible Conformal Piezoresistive Sensor Based on Electrospinning for Deformation Monitoring of Carbon Fiber‐Reinforced Polymer

Carbon fiber‐reinforced polymer (CFRP) materials are widely applied in various areas as key structure components. The structural health monitoring of the CFRP components is crucial to prevent catastrophic failure. However, the nonplane surfaces of CFRP components hinder the attaching of monitoring sensors with hard substrates. Therefore, the substrate conditions for sensor preparation are mainly considered in this study. To adapt the proposed sensors to the curved substrate, including nondevelopable surfaces, electrospinning method is used to prepare conformal piezoresistive fiber films, in which polymethyl methacrylate is served as the matrix and carbon nanotubes are utilized as the conductive filler. The piezoresistive fibers covered on CFRP substrates have a gauge factor up to 207.95 and can response to the strain less than 0.05%. Moreover, the sensor also has high durability and the ability to follow the dynamic excitation signals with as high as 50 Hz.

A Lay-up-Oriented CFRP-Substrate Metamaterial Absorber with High Insensitivity to Polarization

Metamaterial absorbers with carbon fiber reinforced polymer (CFRP) substrates, which are called meta-CFRPs, have recently gained recognition for their excellent mechanical and electromagnetic performance. Different from traditional metamaterial absorbers with an isotropic substrate, meta-CFRPs with a highly anisotropic CFRP substrate are facing challenges in acquiring polarization-insensitive absorption. Here, a lay-up-oriented structure design method is proposed to solve this problem. Considering the lay-up configuration of CFRP laminates, metallic patterns are designed under corresponding polarization angles and then united together to form an integral structure. A meta-CFRP with a typical CFRP lay-up configuration([0°/45°/90°/−45°]3s ) is designed and tested. The experimental results exhibit over 99% microwave absorptivity at 2.44 GHz for all polarization angles. The maximum shift among the resonance peaks of the curves at all polarization angles is only 0.021 GHz. Further studies show that when there are cross-ply laminates in the first few layers of the CFRP substrate, the lay-up-oriented design method can be effectively simplified by ignoring the subsequent lay-up orientations after the first cross-ply layers. Our method can not only provide an effective way for acquiring polarization-insensitive microwave response on meta-CFRPs but also be expected to be promoted to metamaterial absorbers with other anisotropic materials.

Towards low-temperature laser paint stripping by photochemical mechanism on CFRP substrates

Multilayer paint on the surfaces of carbon fiber-reinforced polymer (CFRP) composites was cleaned using an ultraviolet picosecond laser (λ = 355 nm) under different parameters. The surface morphology of the composite after paint removal was investigated by scanning electron microscopy (SEM), chemical composition and functional group detection by energy dispersive spectroscopy (EDS) and FT-IR, while the sample temperature was monitored by an infrared thermal imager during cleaning. Additionally, CFRP performances were evaluated before and after paint removal. These results demonstrated that after three cleaning cycles with 12 W laser power, the paint layers on CFRP is removed, the surface epoxy resin is retained, and the carbon fiber does not have any morphological damage. At the same time, the surface after de-painting also met the re-painting conditions, and the tensile strength was not degraded compared with the original sample. It is noteworthy that the UV picosecond laser shows “low temperature cleaning”, which completely removes the paint layer on the CFRP surface at a temperature below 80 °C. This means that the paint stripping process will not cause potential thermal damage or degradation of mechanical properties for CFRP. Mechanism analysis indicated that the photochemical action led to the breaking of the chemical bond of the paint, thus achieving paint removal. This study demonstrates the feasibility of a laser cleaning process for de-painting from resin-based composite surfaces and guides the repair and maintenance of commercial aircraft.

Detection of Debonding Defects Between Radar Absorbing Material and CFRP Substrate by Microwave Thermography

Microwave thermography (MWT) is a non-destructive testing method based on the principle of microwave heating, which is widely used in the detection of debonding defects of various composite materials. Based on the principle of Microwave thermography (MWT), a resonant cavity microwave thermography detection system is proposed in this paper. The temperature variation characteristics of debonding defects in carbon Fiber Reinforced Polymer (CFRP) and radar absorbing material (RAM) are studied. This system consists of a resonator microwave source, an infrared thermal imager, a fan and two computers. This system successfully detects such defects at the pixel level by thermally loading the test piece, collecting the temperature change data of the test piece by the thermal imager, analyzing the temperature difference between the normal area and the defect area. In this paper, the advantages of microwave on the radar absorbing material (RAM) with large specific heat capacity and high thermal conductivity, high heating efficiency, large heating area and negligible damage to the radar absorbing material are verified, and the high performance of the detection system is verified. The experimental results show that microwave thermography can realize high-precision debonding detection and positioning of multilayer heterogeneous radar absorbing material (RAM).

MXene Reinforced Thermosetting Composite for Lightning Strike Protection of Carbon Fiber Reinforced Polymer

AbstractTi3C2 – a member of the MXenes (2D transition metal carbides and nitrides) family, is investigated as an effective filler to improve the electrical, mechanical, and thermal properties of divinylbenzene (DVB) thermosetting resin. Consequently, its performance as a lightning strike protection (LSP) coating for carbon fiber reinforced polymer (CFRP) is evaluated. Polyaniline (PANI) – dodecylbenzene sulfonic acid (DBSA) complex is used to cure the DVB resin. The synergic effect of MXenes (with surface that is negatively charged) with polyaniline (positive charge) shows electrostatic bonding and improved electrical conductivity in the composite. The addition of MXenes at 2 wt% into the PANI‐DVB composite shows ≈139%, 10%, and 9% improvement in electrical conductivity, flexural strength, and flexural modulus, respectively, compared to the neat PANI‐DVB composite. The composites are investigated using various material characterization techniques including Fourier transforms infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and scanning electron microscopy. Furthermore, MXenes‐DVB is utilized to create a conductive thermosetting coating on top of a CFRP substrate and tested against a lightning strike of 100 kA. CFRP with MXenes‐DVB coating reduced the surface damage from 40.61 cm2 (reference CFRP panel) to 13.29 cm2 (CFRP coated with MXenes‐DVB).

Effect of atmospheric pressure plasma treatment on surface physicochemical properties of carbon fiber reinforced polymer and its interfacial bonding strength with adhesive

To study the effect of surface physicochemical properties of carbon fiber reinforced polymer (CFRP) on its interfacial bonding strength with adhesive, atmospheric pressure plasma treatment (APPT) using three gases (i.e., argon (Ar), nitrogen (N2) and air (Air)) was conducted on surfaces of CFRP substrates. Atomic force microscope (AFM) observation indicates that APPT only changes the surface morphology of CFRP in a depth of tens of nanometers, and this minor change contributes little to the interfacial bonding strength of CFRP joints. X-ray photo electron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analyses reveal that the release agent (mainly the -Si-CH3 group) and other contaminations on CFRP substrate surfaces were effectively removed by APPT, which improves the shear strength of CFRP joints from 8.6 MPa to 23.1 MPa. In addition, polar chemical functional groups (i.e., –NH2, –OH, –COOH) were generated on the CFRP substrate surfaces after APPT when nitrogen and air were used as plasma gases, which not only enhances the surface free energy of CFRP substrate but also combines with adhesive molecules through the form of hydrogen bonds and covalent bonds. With this mechanism, the shear strength of CFRP joints increased further to 28.7 MPa and 31.5 MPa when nitrogen and air were used as the plasma gases, respectively. After a quantitative study, the interfacial bonding strength between CFRP substrate and adhesive is expressed as a function of the concentration of -Si-CH3, –NH2 and –OH groups.

Innovative conductive polymer composite coating for aircrafts lightning strike protection

ABSTRACTA new kind of high electrical conductive epoxy coating with low filler rate was investigated for lightning strike protection (LSP) of carbon fiber reinforced polymer (CFRP). The coating without CFRP substrate was firstly studied. The influence of silver submicronic wires (AgSWs) with a high aspect ratio on the electrical behavior is observed; that is, the electrical resistivity evolution, the current density value, and the electrical conduction mechanisms as function of temperature. The preponderant electrical conduction mechanism is an Ohmic behavior. The higher level of conductivity obtained is 5.5 × 105 S m−1 for 9% vol of AgSWs. Lightning strike tests were carried out on an epoxy/AgSWs coating filled with 8% in volume (74 gsm) and deposited on a CFRP. The ultrasonic testing after lightning strike on coated CFRP shows no structural delamination and demonstrates the interest of this new route for an efficient LSP. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48700.

Low-pressure plasma treatment of CFRP substrates for epoxy-adhesive bonding: an investigation of the effect of various process gases

This work reports a systematic and quantitative evaluation of the effects induced on the adhesive properties of carbon fiber reinforced polymer (CFRP) substrates by various vacuum cold-plasma treatments. In particular, surface activation of the CFRP substrates was performed using several combinations of exposure time, plasma power, and processing gas (air, O2, Ar and N2). By comparing these plasma treatments with conventional techniques of abrasion and peel ply, it was possible to substantially increase the performance of the adhesively bonded joints made by overlapping the CFRP substrates with a structural epoxy resin. On each differently treated surface, measurements of roughness and of wettability were performed, allowing the evaluation of the increase in surface energy after the plasma treatment. XPS analyses allowed the identification of the chemical state of the substrates and showed an in-depth functionalization of the outer layer of the CFRP material. The experimental results show that an engineered plasma treatment of the CFRP substrates allows one to modify the surface morphology and both wetting and chemical activation properties of the treated surfaces, resulting in an increased mechanical shear strength of the joints.

Effect of Atmospheric Pressure Plasma Treatment on Adhesive Bonding of Carbon Fiber Reinforced Polymer.

To improve the strength of the adhesive-bonded carbon fiber reinforced polymer (CFRP) joints, atmospheric pressure plasma treatment (APPT) was used to treat a CFRP substrate surface. This study investigated the effects of nozzle distance (i.e., the distance between plasma nozzle and CFRP substrate) and nozzle speed (i.e., the moving speed of plasma nozzle relative to CFRP substrate) of APPT on the lap-shear strength of adhesive-bonded CFRP joints. Results show that the lap-shear strength of plasma-treated CFRP joints increased to a peak value and then decreased as the nozzle distance increased, and the nozzle distance associated with the peaked joint strength depends on the applied nozzle speed. The lap-shear strength of plasma-treated adhesive-bonded CFRP joints reaches up to 31.6 MPa, compared to 8.6 MPa of the as-received adhesive-bonded CFRP joints. The surface morphology of plasma-treated CFRP substrates was investigated by scanning electron microscope observation, and the mechanism associated with the improved joint strength after applying APPT was revealed through surface chemistry analysis. It is found that APPT not only effectively removed the content of Si element and –CH3 (i.e., the main compositions of release agent) from the as-received CFRP substrate surface, but also generated many polar groups (i.e., –NH2, –OH, –COOH, etc.), which has a positive effect on increasing the wettability and interfacial bonding strength of CFRP substrates and consequently results in a significant improvement of lap-shear strength of plasma-treated CFRP joints. In addition, the result of differential scanning calorimetry (DSC) test shows that the surface temperature of CFRP substrate should not exceed 175.3 °C during APPT. In this study, an empirical model governing temperature, nozzle distance and nozzle speed was established to guide the selection of atmospheric pressure plasma treatment process parameters in industrial manufacture.

The effect of laser ablation treatment on the chemistry, morphology and bonding strength of CFRP joints

The strength of carbon fiber reinforced polymer (CFRP) adhesive-bonded joints can be greatly improved by laser ablation treatment, which modifies the surface physicochemical properties. This study investigated the effect of laser ablation treatment on the chemistry, morphology and resultant bonding strength of CFRP joints. It was found that laser ablation treatment improved the lap-shear strength of adhesive-bonded CFRP joints from 8.5 to 30.4 MPa when a laser energy density of 35.4 mJ/mm2 was applied. X-ray photo electron spectroscopy (XPS) analyses and contact angle measurements revealed that the laser ablation treatment not only removed the release agent but also enhanced the wettability of CFRP surface. Scanning electron microscope (SEM) observation indicated that the optimal laser ablation treatment merely removed a layer of epoxy resin above the carbon fibers and exposed the undamaged carbon fibers. The exposure of carbon fibers greatly increased the bonded area between the adhesive and the CFRP substrate, which acts as an additional mechanism of improving the lap-shear strength of adhesive-bonded CFRP joints.

In situ fabrication of copper electrodes on carbon-fiber-reinforced polymer (CFRP) for damage monitoring by printing and flash light sintering

The electrical resistance change method (ERCM) is a promising method for structural health monitoring (SHM) of composites. In this work, copper (Cu) nano-ink was printed and successfully sintered on carbon-fiber-reinforced polymer (CFRP) substrate for damage sensing via a flash light sintering method. Before printing, surface-polished CFRP substrate was flash light treated to remove remnant epoxy between carbon fibers. Then, Cu nano-ink was formulated and printed on the CFRP substrate, and the printed Cu nano-ink patterns were sintered within a few milliseconds using a range of flash light irradiation energies. A two-step flash light sintering method to reduce contact resistance between the Cu electrode and CFRP interface was further investigated. Fabricated Cu electrodes were characterized using scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Using a two-step sintering approach, we fabricated Cu electrodes on CFRP with low contact resistance (0.93 Ω), high durability, and no mechanical degradation of CFRP substrate.

Experimental Characterization of Unimorph Shape Memory Polymer Actuators Incorporating Transverse Curvature in the Substrate

Shape memory polymers (SMP) have the potential to be utilized as a lightweight, solid state actuator in modern reconfigurable structures including as a deployment system for satellite solar panels or morphing aircraft wings. This paper is primarily concerned with the use of Veriflex-S® shape memory polymer and bi-directional carbon-fiber-reinforced-polymer (CFRP) in a flexural unimorph actuator configuration. One of the major deficiencies of SMP unimorphs is the permanent set (unrecovered shape) after a single or multiple temperature cycle(s). The novel concept of incorporating transverse curvature in the CFRP substrate, similar to that of an extendable tape measurer, is proposed to improve the shape recovery by increasing the bending stiffness of the unimorph actuator to compensate for the lack of recovery of the SMP. A set of experiments was designed to investigate the influence of transverse curvature, the relative widths of SMP and CFRP substrates, and shape memory polymer thickness on actuator recoverability after multiple thermo-mechanical cycles. The performance of SMP unimorph actuators with varying degrees of transverse curvature were evaluated versus that of traditional SMP unimorphs incorporating a flat substrate. Digital image correlation was implemented to quantify the out-of-plane deflection of the unimorph composite actuators (UCAs) during the actuation cycle. Experimental results indicate that an actuator with transverse curvature significantly reduces the residual deformation by at least two orders of magnitude which could be further tailored to enhance the performance of shape memory polymers in reconfigurable arrangements.

The Effect of CFRP Surface Treatment on the Splat Morphology and Coating Adhesion Strength

Metallization of Carbon Fiber-Reinforced Polymer (CFRP) composites aggrandized their application to aircraft, automobile, and wind power industries. Recently, the metallization of CFRP surface using thermal spray technique, especially the cold spray, a solid state deposition technique, is a topic of research. However, a direct cold spray deposition on the CFRP substrate often imposes severe erosion on the surface owing to the high-impact energy of the sprayed particles. This urges the requirement of an interlayer on the CFRP surface. In the present study, the effect of surface treatment on the interlayer adhesion strength is evaluated. The CFRP samples were initially treated mechanically, chemically, and thermally and then an interlayer was developed by atmospheric plasma spray system. The quality of the coating is highly dependent on the splat taxonomy; therefore the present work also devoted to study the splat formation behavior using the splat-collection experiments, where the molten Cu particles impinged on the treated CFRP substrates. These results were correlated with the coating adhesion strength. The coating adhesion strength was measured by pull-out test. The results showed that the surface treatment, particularly the chemical treatment, was fairly successful in improving the adhesion strength.

Interaction between CFRP-repair and initial damage of wide-flange steel beams subjected to three-point bending

This paper presents the interaction between carbon fiber reinforced polymer (CFRP) composites and the level of damage in steel beams. An experimental program is conducted with three different sizes of notches at midspan of the beams to simulate initial damage prior to repair. A three-dimensional finite element analysis (FEA) is conducted to predict experimental behavior. Unlike existing predictive models that assume perfect bond between CFRP and steel substrate, the proposed modeling approach explicitly accounts for the bond–slip behavior of CFRP–steel interface. CFRP-repair improves the load-carrying capacity of damaged beams that have failed by crack propagation across the steel section with wide opening of the notch. For repaired beams; stress concentrations at a damage location result in local debonding of the CFRP sheet, followed by complete debonding failure of the sheet. These failure modes are found to be independent of the level of initial damage (notch depth). CFRP-repair delays crack-formation of the repaired beams; however, such an effect is not significant once a crack propagates towards the upper flange. The level of initial damage influences debonding propagation rates of the CFRP. Two distinct bond–slip responses of the CFRP–steel interface are experimentally observed.

Non-destructive ultrasonic evaluation of CFRP–concrete specimens subjected to accelerated aging conditions

The objective of this work is to utilize surface acoustic waves (SAWs) for non-destructive structural health monitoring of concrete specimens externally bonded with carbon fiber-reinforced polymer (CFRP) composites and subjected to accelerated aging conditions. Both experimental testing and signal processing schemes of ultrasonic wave propagation through the CFRP substrate are described. The surface waves are generated and received at the external face of the CFRP using narrow-band transducers with a 110-kHz center frequency. The received signals are filtered and amplified then digitized and processed to extract various parameters in both time and frequency domains including average power (PAvg), maximum amplitude (Vmax), and maximum power–frequency ratio ((P/F)max). Changes in these parameters due to water-immersion aging at different temperatures were monitored over 12 weeks. Results indicated a marked decrease in measured ultrasonic parameters over time, particularly after the first 2 weeks, indicating a possible debonding or deterioration in the samples. Ultrasonic results showed good agreement with the findings of a parallel destructive study on mode-II fracture loading of CFRP–concrete samples, tested to obtain fracture energy (Gf) and define traction–separation response under temperature and water-immersion aging effects. It was observed that all ultrasonic parameters exhibit good correlations (|r|>0.5, P<0.05) with the fracture energy at all temperatures. Moreover, when the measurements at all temperatures were incorporated and linear relationships between destructive and non-destructive parameters were assumed, correlations of r=0.84, 0.80, and 0.80 were found between Gf and PAvg, Vmax, and (P/F)max, respectively. This study paves the way for developing a non-destructive testing protocol for structural health monitoring of bridges and concrete structures undergoing repair and rehabilitation with CFRP composites.

Cost-effective bridge girder strengthening using vacuum-assisted resin transfer molding (VARTM)

The objective of this paper is to present the results of a demonstration project to apply externally bonded CFRP fabrics to retrofit a simple span prestressed concrete girder with improved repair and hardening techniques. The technique, Vacuum Assisted Resin Transfer Molding (VARTM), newly introduced to civil infrastructure was implemented in the field within two days without any traffic interruption. As an alternative to traditional hand lay up, VARTM has several processing advantages, like saving the processing time, uniform resin application, intimate contact between each layer of CFRP and concrete substrate ensuring good consolidation to remove void or dry spot, higher fiber volume fraction (about 70%) and greater wettability of the fiber, etc. The performance of the strengthened structures depends on the above potential factors to obtain high structural performance. VARTM uses single-sided molding technology to infuse resin over fabrics wrapping large structures such as bridge girders and saving tooling and processing time. Recently, the VARTM technique has been implemented in strengthening of an I-565 highway bridge girder in Huntsville, Alabama. Laboratory investigation included the construction of small concrete prisms to study the bonding behavior of Carbon Fiber Reinforced Polymer (CFRP) and strengthened concrete beams using VARTM to simulate the performance with and without strengthening. To the end, the process of field demonstration of this newly introduced technique to civil infrastructure has been presented.