Surface Of Carbon Fiber Reinforced Plastics Research Articles

Reducing the taper and the heat-affected zone of CFRP plate by Micro fluid assisted laser induced plasma micro-drilling

Carbon Fiber Reinforced Plastics (CFRP) with superior mechanical properties are widely used in aerospace, automotive, and medical fields. The characteristics of CFRP with anisotropy and inhomogeneous result in poor machining performances by conventional drilling techniques. Laser drilling is a non-contact high precision machining technique without tool wear but leads to a large heat-affected zone (HAZ) and taper. Although underwater laser drilling could reduce thermal damage on CFRP surface, bubbles produced in the machining process severely affect the machining stability and surface quality. In this study, a micro fluid-assisted laser-induced plasma drilling (MFA-LIPMD) method was proposed to relieve the negative effect of bubbles as well as reduce the taper and HAZ. A comprehensive analysis of hole surface quality, HAZ, taper, and mechanical properties was conducted, and MFA-LIPMD performed more advantages over laser in the air (LIA) and laser-induced plasma drilling (LIPMD). It was found that the taper of micro-holes was reduced by 42.8%–51.78%, and the thermal damage rate of micro holes processed by the MFA-LIPMD process was reduced by 65.3%–68.1% compared with the LIPMD process, and the maximum tensile load of samples was increased by about 7.68%. Therefore, MFA-LIPMD has great potential for machining high-quality micro holes of CFRP plates.

Surface modification of carbon-fiber-reinforced plastic by using photo-activated chlorine dioxide radicals as pretreatment of electroless plating

Carbon fiber reinforced plastic (CFRP) plays an important role in industrial fields of automobiles, aerospace transportations and astronautics on account of its high stiffness and light weight. To further expand its utilizations, coating with metals can provide with metallic appearance while improving water-resistance, durability and electric conductivity. In general, the composites of CFRP are hydrophobic and have low affinities to metals. Therefore, it requires the surface pretreatments to increase the wettability and surface energy for stronger adhesive properties with metals via enhancing both mechanical and chemical bonding. In this study, photo-oxidized chlorine dioxide radicals were used to introduce oxygen–containing functional groups on CFRP surface. The hydrophilicity and adhesion strength to metals were successfully improved by the introduction of oxygen functional groups via eco-friendly photo-oxidation by photo-activated ClO2• radicals. The improvement of hydrophilicity was determined by water contact angle measurement, and the incorporation of oxygen was confirmed by infrared (IR) and X-ray photoelectron spectroscopy (XPS) analysis. Scanning electron microscopy (SEM) observations revealed that the surface smoothness and structure of CFRP were maintained after pretreatment. Electroless plating of nickel and copper was then performed on both untreated and oxidized CFRP, demonstrating the enhanced adhesion properties of CFRP to both metals.

Comparison of the Electrochemical Response of Carbon-Fiber-Reinforced Plastic (CFRP), Glassy Carbon, and Highly Ordered Pyrolytic Graphite (HOPG) in Near-Neutral Aqueous Chloride Media

Carbon-fiber-reinforced polymers (CFRP), being conductive, are capable of supporting cathodic oxygen reduction reactions (ORR) and thus promote galvanic corrosion when coupled to many metallic materials. Hence, understanding cathodic processes at carbon surfaces is critical to developing new strategies for the corrosion protection of multi-material assemblies. In the present work, the electrochemical responses of CFRP, glassy carbon, and HOPG (Highly Ordered Pyrolytic Graphite) have been evaluated in a quiescent 50 mM NaCl solution, and their respective activities towards ORR have been ranked. Employing the averages of the specific charges (CFRP, 129.52 mC cm−2; glassy carbon, 89.95 mC cm−2; HOPG, 60.77 mC cm−2) passed during 1 h polarization of each of the 3 carbon surfaces at −1000 mVSCE in the test media as a ranking criterion, the propensities of the 3 carbon surfaces (CFRP, GC, and HOPG) to support cathodic activities that can lead to anodic metal dissolution on galvanic coupling to metallic materials are ranked thusly; CFRP > GC > HOPG. This ranking is consistent with the trend of capacitance values obtained in this work: CFRP (19.5 to 34.5 μF cm−2), glassy carbon (13.6 to 85.5 μF cm−2), and HOPG (1.4 to 1.8 μF cm−2). A comparison of electrochemical data at potentials relevant to galvanic coupling to metals indicated that at these cathodic potential(s) the CFRP surface is the most electrochemically active of the studied carbon surfaces. On the basis of the values and trends of the electrochemical parameters evaluated, it is postulated that the observed differences in the electrochemical responses of these 3 carbon-rich surfaces to ORR are significantly due to differences in the proportions of edge sites present on each carbon surface. These results could provide valuable insights on plausible strategies for designing carbon surfaces and carbon fiber composites with reduced activity toward ORR for corrosion protection applications or enhanced activity towards ORR for energy applications.

탄소섬유 강화플라스틱의 레이저 표면처리 적용에 의한 이종 접합부의 접합강도 개선에 관한 연구

The adhesive bonding technology of carbon fiber reinforced plastics (CFRP) and aluminum alloys, is one of the lightweight joining technologies for automobiles. The strength and properties of the bonded joint, depend on the surface of the bonded part that the adhesive touches. Thus, proper surface treatment is one of the most important steps in the bonding process. The laser surface treatment of carbon fiber composites is a new form of green and environmental surface treatment technology, which can effectively clean coatings and pollutants on the surface of materials. It is also possible to improve the bonding shear strength, by changing the microstructure and roughness of the material surface through laser micro texture processing, to form a mechanically interlocked structure. In this study, a pulsed laser was used to treat the surface of CFRP. By changing the scanning line spacing during laser micro texturing, the effect of laser micro texturing on the surface morphology of CFRP and the strength of aluminum alloy bonded joints was investigated. Results show that in the laser micro texturing process, when the scanning line spacing was 0.3 mm, the maximum tensile shear strength was 14.5 MPa, approximately 200% higher than that without laser treatment.

Passive Deicing CFRP Surfaces Enabled by Super-Hydrophobic Multi-Scale Micro-Nano Structures Fabricated via Femtosecond Laser Direct Writing.

Carbon fiber reinforced plastic (CFRP) is the main material of aircraft skin. Preparing superhydrophobic anti-icing/deicing surface on the CFRP is of great importance for aircraft flight safety. In this work, a variety of multi-scale micro-nano structures were imprinted on CFRP by femtosecond laser processing, and a transition from hydrophilic to superhydrophobic CFRP was realized. After being optimized by different geometries and laser conditions, the water contact angle, which is tested at 24.3 °C and 34% humidity, increased from 88 ± 2° (pristine) to 149 ± 3° (100 μm groove) and 153 ± 3° (80 μm grid). A further anti-icing test at −10 °C (measured on the cooling platform) and 28% humidity showed that the freezing time was increased from 78 ± 10 s (pristine) to 282 ± 25 s (80 μm grid). Most importantly, the tensile tests showed that the femtosecond laser processing method did not deteriorate the mechanical properties of CFRP. This work provides great significance for aircraft passive deicing technology.

Laser ablation of CFRP surfaces for improving the strength of bonded scarf composite joints

Repairing damaged composite parts using scarf technique requires a careful selection of treatment methods for composite surface. Laser treatment is one of the emerging techniques to treat the milled composite surface by unlocking various levels of morphological changes and, thus, optimizing joint strength. However, laser parameters, e.g., energy density (fluence), should be carefully determined to ensure the acceptable structural recovery. Here, the influence of CO2 laser with relatively high fluence (ablation effect) on the surface characteristics (roughness, morphology, wettability) and scarf joint strength with associated failure modes of unidirectional (UD) and quasi-isotropic (QI) carbon fiber-reinforced plastic (CFRP) laminates is studied. We found that the ablation effect using CO2 laser at 3.6 J/m2 was considered safe for UD laminates as their joint strength was comparable with that treated by manual sanding. The ablation at higher fluence (8.4 J/m2) reduced the joint strength in UD laminates due to severe damage occurred in 0∘ fibers that triggered adhesive failure. In QI laminates, 3.6 J/m2 laser fluence could improve joint strength since the cohesive failure was activated in off-axis plies (90∘, +45∘, −45∘).

Microstructural characteristics and mechanical properties of the laser cladded TC4+AlSi10Mg composite coating on carbon fiber reinforced plastic surface

Fabricating TC4 coatings on the carbon fiber reinforced plastic (CFRP) substrate surface will contribute to increasing the applicability of CFRP materials in the aerospace industry. However, chemical metallurgical bonding between the TC4 alloy and CFRP is crucial during the manufacturing process. Here, we studied the effect of Al powder content on the microstructural characteristics and mechanical properties of the laser cladded TC4+AlSi10Mg composite coating on the CFRP surface. Furthermore, the relationship between laser process parameters, interfacial morphologies, and mechanical properties is established. The amount of CFRP decomposed increases with a rise in the AlSi10Mg powder content, while augmenting the penetration of the transition layer into the CFRP material. Moreover, the TC4 coating with 10wt.% AlSi10Mg is composed of α′ martensite, TiC, Ti3Al, and Ti3AlC. The average nano-hardness of the TC4 coating increases from 6.00 to 6.86 GPa when the AlSi10Mg content rises from 5% to 20%. Meanwhile, the maximum shear strength of the CFRP/TC4 interface is 26.8 MPa. Based on the experimental observations and theoretical analysis, the interface reaction mechanism of the laser cladded TC4+AlSi10Mg composite coating on the CFRP surface is: Ti(s)+C(s)→TiC(s), Al(1)+3Ti(s)→Ti3Al(s).

Fabrication of Micro-Groove on the Surface of CFRP to Enhance the Connection Strength of Composite Part.

Carbon fiber-reinforced plastic (CFRP) has the advantages of being light weight, high strength, and corrosion resistant. At present, it is widely used in the lightweight design of automobile parts. The manufacturing of lightweight parts inevitably involves the connection between CFRP and the polymer material. The connection strength between CFRP and the polymer material significantly affects the service life of the composite parts. Taking CFRP and polyamide 6 (PA6) injection-molded composite parts as an example, this paper proposed a technological method to enhance the connection strength between CFRP and PA6. The proposed method was to fabricate micro-groove structures on the CFRP surface by compression molding. These micro-groove structures effectively increased the injection-molding area of the composite parts, thus enhancing the connection strength between CFRP and PA6. This paper presented a detailed study on the compression-molding process of micro-grooves on the CFRP surface, and successfully obtained the appropriate parameters. Finally, PA6 was used for injection molding on the CFRP with micro-grooves at an injection pressure of 8 MPa, an injection temperature of 240 °C, a holding pressure of 5 MPa, and a holding time of 2.5 s. The experimental results show that the micro-groove array structures on the CFRP surface could effectively improve the tensile strength of the connection interface in the composite parts. Compared with the composite part without micro-grooves, the tensile strength of the composite part with micro-grooves was increased by 80.93%. The composite parts prepared in this paper are mainly used in automobile interiors and the research results of this paper meet the actual needs of the enterprise.

Effect of cooling strategies on performance and mechanism of helical milling of CFRP/Ti-6Al-4 V stacks

Hole-making for Carbon Fiber Reinforced Plastics (CFRP)/Ti-6Al-4 V stacks is crucial for the assembling strength of aircraft structure parts. This work carried out experimental work for helical milling (HM) of the stacks with sustainable cooling/lubrication (dry, MQL and cryogenic) conditions. Cutting forces and temperatures at the CFRP layer, Ti-6Al-4 V layer and the interface of stacks were obtained by a developed measuring system. The temperatures in CFRP machining at cryogenic condition varied from −167 °C to −94 °C, which were much lower than those at dry and MQL conditions. The maximum temperature near the interface of stacks for the ninth hole was higher than 240 °C due to heat conduction from Ti-6Al-4 V layer. The hole quality, hole diameter and tool wear mechanism at different cooling/lubrication conditions were presented and discussed. MQL condition generated mainly extrusion fracture for the fibers, due to the reduced friction effect compared with dry condition. MQL was helpful to reduce the feed mark at the hole surface of Ti-6Al-4 V alloy. The flank wear of cutting edge at MQL condition was better than those at dry and cryogenic conditions. Cryogenic cooling contributed to better CFRP surface with smaller delamination and hole entrance damage due to the increased resin strength and fiber brittleness. The damage near the entrance of CFRP were analyzed by the contact state of cutting edges and fibers. Additionally, hole diameters near the exit of CFPR layer were larger than other test positions. This work provided feasible processes for improving hole quality and tool life in hole-making of CFRP/Ti-6Al-4 V stacks.

Adhesive strength analysis and real-scale simulation for smart curing in a large turbine blade with carbon fiber-reinforced plastic spar cap

Various approaches for the smart curing processes in the fabrication of large hybrid composite blades have been employed to determine whether smart curing, which has multiple heating and cooling processes during the total curing time, is applicable to the adhesive process between carbon fiber-reinforced plastic (CFRP) and glass fiber-reinforced plastic (GFRP). Therefore, investigating the adhesive strength and residual thermal stress between CFRP and GFRP is very important. In an experimental approach, the adhesive strengths of CFRP/GFRP single-lap joint specimens were compared according to surface treatment techniques and curing conditions. The proper roughness of the CFRP surface and the application of smart curing are very effective for the manufacture of CFRP spar cap wind turbines. The simulation results from the analytical approach demonstrated that when the final curing temperature was reduced by the smart curing process, the residual thermal stress and thermal shear stress in the blade were also reduced, resulting in an increased adhesive strength in the adhesive layers between the CFRP spar caps and GFRP skin. It was determined that large hybrid wind blades with CFRP spar caps could be efficiently manufactured using a smart curing process.

Formation of sub-wavelength laser induced periodic surface structure and wettability transformation of CFRP laminates using ultra-fast laser

Present work focuses on wettability transformation of carbon fiber reinforced plastic (CFRP) surface by generating micro/nano-structures using a femtosecond laser system. Laser induced periodic surface structures (LIPSS) were realized on carbon fiber (CF) surface at different defocus distances and pulse energies. The hydrophilic CFRP surface obtained just after the laser treatment progressively depicts hydrophobic behavior and further transforming to near superhydrophobic after cleaning followed by vacuum process for 4 h. Scanning electron microscopy (SEM) analysis was performed to capture the generated structure on the carbon fiber surface. Pulse fluence was effective parameters for transition of LSFL to HSFL. The lowest spatial period Λ ≈ 95 ± 6 nm and Λ ≈ 387 ± 15 nm was achieved for HSFL and LSFL, respectively, at 0.3 mJ.

Enhanced Surface Properties of Carbon Fiber Reinforced Plastic by Epoxy Modified Primer with Plasma for Automotive Applications.

Carbon fiber reinforced plastic (CFRP) is currently used as a lightweight material in various parts of automobiles. However, fiber reinforced plastic (FRP) material may be damaged at the time of joining via mechanical bonding; therefore, adhesion is important. When bonding is conducted without surface CFRP treatment, interfacial destruction occurs during which the adhesive falls off along with the CFRP. Mechanical strength and fracture shape were investigated depending on the surface treatment (pristine, plasma treatment times, and plasma treatment times plus epoxy modified primer coating). The plasma treatment effect was verified using the contact angle and X-ray photoelectron spectroscopy. The wettability of the epoxy modified primer (EMP) coating was confirmed through surface morphology analysis, followed by observation of mechanical properties and fracture shape. Based on test data collected from 10 instances of plasma treatment, the EMP coating showed 115% higher strength than that of pristine CFRP. The adhesive failure shape also changed from interfacial failure to mixed-mode failure. Thus, applying an EMP coating during the automotive parts stage enhances the effect of CFRP surface treatment.

Influence of surface treatment with infrared nanosecond laser on adhesion performance of adhesion-bonded carbon fiber/epoxy composite

The surface treatment of carbon fiber/epoxy composites with a pulsed infrared (1064 nm wavelength) nanosecond (7 ns pulse duration) laser has been investigated. It is found that single 1064 nm laser pulse can remove the polymer matrix from composite surface to expose the carbon fibers by expansion of the pyrolysis gas resulting from laser-induced polymer degradation. The influences of laser power density and scan strategy on matrix removal process have been studied. The bonding strength of laser processed, adhesion-bonded CFRP (carbon fiber reinforced plastic) increase with lower matrix residues on the fibers and a linear relation is found. The adhesion-bonding strength of CFRP surfaces, tested by lap-joint shear test, exceeds the strength measured for untreated and abrasion treated (SiC paper) samples. The main origin of fiber damage of the laser-treated surface is mechanical fracture rather than thermal damage as found by laser scanning confocal microscope and scanning electron microscope. The characteristic morphologies and failure modes of shear-tested surfaces are analyzed. The obvious improvement of adhesive strength is achieved by the laser-treated surfaces attributed to matrix removal and carbon fibers protruding. A 1 D model is established to describe temperature and internal gas pressure of the irradiated surface. The new laser treatment method needs less laser energy and low pulse numbers and prove the way to an efficient, low-cost surface treatment for preparation of high quality adhesion bonded CFRP components.

The effects of elliptical ultrasonic vibration in surface machining of CFRP composites using rotary ultrasonic machining

Compared with conventional surface grinding (CSG) process, surface machining of carbon fiber-reinforced plastic (CFRP) composites using rotary ultrasonic machining (RUM) with vertical ultrasonic vibration generates smaller cutting forces because of improved machining performance and more damages to the machined CFRP surface due to the intermittent knocking induced by vertical ultrasonic vibration. It is reported that surface quality can be improved when the ultrasonic vibration is parallel to the feeding direction. In addition, elliptical ultrasonic vibration can be formed by the combination of horizontal and vertical ultrasonic vibrations. However, the effects of elliptical ultrasonic vibration in RUM surface machining of CFRPs are still unknown. This paper will study the influences of elliptical ultrasonic vibration on the machining performance and machined surface quality in RUM surface machining of CFRPs. The comparisons of output variables (including cutting forces, surface roughness, and machined surface topography) between RUM surface machining with elliptical ultrasonic vibration and the CSG process as well as RUM surface machining with vertical ultrasonic vibration will be conducted under different levels of input variables (including depth of cut, feedrate, and tool rotation speed). The abrasive-grain trajectory and the tool-workpiece contacting modes in these three machining processes are analyzed. It is found that RUM surface machining with elliptical ultrasonic vibration produced smallest feeding-direction cutting force, smallest vertical-direction cutting force, best morphology of machined surface, and smallest surface roughness among these three kinds of machining processes.

Etching of Carbon Fiber-Reinforced Plastics to Increase Their Joint Strength

An original method to increase the mechanical strength of adhesively joined carbon fiber-reinforced plastics (CFRPs) and honeycomb CFRP sandwich structures by etching is proposed, based on sulfuric acid etching of the CFRP surface. Etched composites are joined by a novel phenolic resin-based adhesive and are cured, and their cross section is observed by FESEM. Etching of CFRP was aimed to obtain a “brush”-like composite to be infiltrated by the adhesive, giving a fiber-reinforced, stronger composite joint. This method gave a 100% increase in the lap shear strength for the adhesively joined etched CFRP, compared to the non-etched ones.

Enhancement of the bending strength of I-shaped cross-sectional beam of CFRP by dispersing cellulose nanofibers without hydrophobic treatment on the surface

Many researches on strengthening the matrix of Carbon Fiber Reinforced Plastic (CFRP) using cellulose nanofibers (CNFs) have been reported. However, hydrophobic treatment to modify the surface of CNFs is indispensable. Authors previously showed that the bending properties of CFRP were enhanced by CNF without hydrophobic treatment after the electro-activated deposition resin molding (ERM) method. CNF can be dispersed on the surface of CFRP since the electro-activated deposition solution is water based. In this study, first, it was confirmed that the tensile properties of CFRP could be enhanced by CNF dispersed on the surface after the ERM method. Also, the weight fraction of CNF was optimized to maximize the tensile properties. Second, the I-shaped cross-sectional beam (I-beam) was molded by laminating the CFRP with CNF dispersed on the surface. It was confirmed that the bending properties of the CFRP I-beam was enhanced by CNF, and the effect of CNF on the interlaminar strength was evaluated.

Sampling phased array technology for the detection of voids in carbon fiber-reinforced plastics

In the lightweight material industries, the current focus is on fiber-reinforced plastics, in particular on carbon fiber-reinforced plastics (CFRPs), since they offer higher relative specific tensile strength and stiffness as well as reduced weight compared to conventional metallic materials. Currently, the quality assurance of manufactured CFRP components represents a major challenge for CFRP manufacturers. Voids are generated during the infusion process of CFRPs, which in turn reduce the mechanical performance of CFRPs. This article presents the possibility to detect the distribution of voids across the surface of CFRPs by using a non-destructive testing method, the so-called sampling phased array ultrasound technology. Two types of CFRPs with six carbon layers in the same direction are fabricated by means of a vacuum-assisted resin infusion process. Voids in CFRPs are generated using a foaming agent during the impregnation process. The C-scan images produced through the sampling phased array technology are subsequently analyzed by the optical image analysis software in order to determine the amount of voids for each type of manufactured CFRP.

Failure mechanisms in carbon fiber reinforced plastics (CFRP) / aluminum (Al) adhesive bonds subjected to low-velocity transverse pre-impact following by axial post-tension

The present study aimed to explore the effects of impact surface and impact energy on the residual characteristics of the carbon fiber reinforced plastics (CFRP)/aluminum (Al) adhesive bonded joints. The adhesive specimens were manufactured in the hot pressing machine with specific curing temperature and curing pressure of the adhesive. In the experiments, a transverse low velocity pre-impact was carried out first and then followed by the axial (longitudinal) tensile test. The results divulged that CFRP, as an impact surface, could generate better structural integrity and decrease loss of joint strength in comparison with the aluminum impact surface. The mechanism for alternating residual tensile strength resulting from transverse impact load was the combined effect of both damage and mechanical interlocking effectiveness. The residual tensile strength and failure displacement decreased with increasing impact energy except for the joint strength impacted onto the aluminum surface at 10 J due to the prominent mechanical interlocking effect. The strain evolution paths in the adherends at the overlap region presented the different forms when impacted onto the different surfaces. In the tensile tests, the fracture surfaces for the joints with impacting on the aluminum surface can be classified as shear failure zone, annular failure zone and mixed failure zone, while the fracture surfaces for the joints with impacting onto the CFRP surface classified to be shear failure zone and crossed impact zone. This study is expected to provide systematic understanding on crashing behavior of adhesive joints with dissimilar materials for multiple impacts from different directions.

Scratching-induced surface characteristics and material removal mechanisms in rotary ultrasonic surface machining of CFRP

Rotary ultrasonic machining has been successfully explored in surface machining of carbon fiber reinforced plastic (CFRP) composites. It has been proven to be an effective and efficient CFRP machining method. Both theoretical and experimental investigations have been conducted with the assumption that the CFRP is removed by brittle fracture removal mode. However, in brittle material machining, ductile flow phenomenon still exists. Ductile scratching marks are also observed on the machined CFRP surfaces. It is still unknown that what actual material removal modes are under different machining variables. To investigate the material removal mechanisms in rotary ultrasonic surface machining (RUSM) of CFRP, single abrasive scratching tests were conducted. The scratching induced characteristics and scratching forces were analyzed. Both the ductile removal mode and the brittle fracture removal mode were observed and identified in both carbon fiber layers and epoxy resin layers on the machined marks by using scanning electron microscopy (SEM) imaging. With the increase of scratching depth, the material removal mode of CFRP was changed from the ductile removal mode to the brittle fracture mode. From the analysis of kinematic trajectory of diamond grain, the scratching cutting forces were decreased in the tests with the assistance of ultrasonic vibration under the same machining variables. The generation mechanisms of the delamination were analyzed and discussed.

Electroplating and brazing joining of 5083 aluminum alloy to CFRP

This study has analyzed the welding joint of carbon fiber reinforced plastics (CFRP) and aluminum alloys. The surface of CFRP and 5083 Al alloy was modified by electroplating with nickel at first. Then the effect of electroplating parameters on coating was explored. SEM images revealed that the coating gradually became well but then began to fall off with the current density and the plating time increased. CFRP and aluminum alloys were brazed at 285[Formula: see text]C and held for 20 s. Shear test was used to evaluate the strength of the joint and the strength was probably 7.56 MPa. SEM and EDS tests showed that there existed diffusion of the elements in the welding process and the joint reached the bonding of atomic or molecular sizes. Thus, this experiment achieved the tight brazing joining between thermoset CFRP and aluminum alloys providing the joining method of the application for CFRP.