Carbon Fiber Reinforced Polymer Surface Research Articles

Highly protective and functional strengthening strategies for 3D printed continuous carbon fiber reinforced polymer composites: manufacturing and properties

Carbon fiber-reinforced polymer (CFRP) composites have gradually emerged as a crucial material in the aerospace industry. However, inadequate impact resistance and thermal stability limit survival in extreme environments. Inspired by the specific functions of multiple layers of tissue, from bird feathers to the musculoskeletal system. We propose low-cost composite strengthening strategies and efficient novel three-dimensional graphene aerogel manufacturing methods. A novel graphene aerogel/carbon fiber reinforced polymer (GAC) composite prepared by in-situ laser-induced graphene (LIG) layers on the surface of 3D-printed CFRP. GAC composites enhance CFRP's impact protection, thermal insulation, and electromagnetic shielding capabilities. For protection, GAC composites reduce low-velocity impact damage by 26.2%. The graphene layer can increase the thermal buffering capacity of the material four times, and the long-term service temperature can be increased by 40% compared to traditional CFRP. For functionality, the composites enable electromagnetic interference (EMI) shielding effectiveness of up to 50.2 dB. Furthermore, it can achieve surface heating above 400 °C and rapid de-icing through electrothermal effects. The simple and efficient processing method of GAC composites and tunable functionalities holds promise for the development of highly protective and intelligent aircraft skins.

Fracture toughness in SPCC/CFRP hybrid laminates: Mode I and mode II perspectives

Hybrid composites using adhesive joints are gaining popularity in various industries as their various material combinations can create certain advantages. This research focuses on examining the mode I and mode II fracture toughness characteristics of the combined laminate between Steel Plate Cold Rolled Commercial (SPCC) metal and Carbon Fiber Reinforced Polymer (CFRP) composite processed using adhesive bonding. SPCC/CFRP hybrid laminate composites were manufactured with a variety of manufacturing options (A, B, and C) to find the most optimal method using two types of epoxy and cyanoacrylate adhesives, with two different bonding processes: secondary bonding and co-bonding. Fracture toughness values were measured through the Double Cantilever Beam (DCB) test for mode I and the End Notched Flexure (ENF) test for mode II. The test results showed that epoxy adhesives in the SPCC/CFRP adhesive joints provided better fracture toughness performance, especially when combined with the co-bonding technique. Specimens from manufacturing option C showed the highest GIC and GIIC values of 83.05 and 254.94 J/m2, respectively. These values increased by 58.98 % and 80.48 % compared to manufacturing options A and B in Mode I. Additionally, the GIIC value for manufacturing option C increased by 78.00 % and 66.76 % compared to manufacturing options A and B. The SPCC/CFRP hybrid laminates showed adhesive failure on the SPCC surface when using epoxy adhesive, whereas adhesive failure occurred on the CFRP surface with cyanoacrylate adhesive for the different manufacturing options.

CFRP surface ply-centric electrified spatiotemporal self-heating for anti-icing/de-icing

With the widespread application of carbon fiber reinforced polymer (CFRP) in engineering, the characteristics of uniformly carbon fiber (CF) orientation within a single-ply and laminated structure have inspired us to develop high-efficiency, low-consumption, manufacture-friendly, and non-destructive anti-icing/de-icing methods. Here, we propose a CFRP surface ply-centric electrified spatiotemporal self-heating (STSH) approach, which utilizes CFs in the surface ply as natural heating elements to achieve in-situ adaptable electrothermal anti-icing/de-icing. By adjusting the current waveform, the temporal heating profile can flexibly switch between a consistently stable temperature and periodically high peak temperatures, meeting the different heating characteristics required for anti-icing and de-icing, respectively. Simultaneously, the entangled CFs branch current, generating a spatial temperature gradient that enhances the design flexibility of temperature distribution. This enables energy concentration in icing-prone areas while maintaining a baseline temperature in less susceptible areas, thus reducing energy waste by up to 20%. Overall, this STSH approach is simple, efficient, and holds significant application potential, offering an innovative and feasible solution to long-standing challenges associated with anti-icing/de-icing.

Rapid surface patterning to strengthen adhesive bonding of carbon fiber reinforced polymer by spatial shaping femtosecond laser

Carbon fiber reinforced polymer (CFRP) have become gradually important in the aerospace industry due to their outstanding strength-to-weight ratio. However, traditional mechanical surface treatment methods are challenging to apply to CFRP because of their anisotropic and nonhomogeneous properties. Femtosecond laser offers unique advantages for surface treatment, as it allows processing with very low thermal load due to the extremely short interaction time. This study investigates the effect of different surface structures resulting from surface treatment using a femtosecond laser on adhesive properties of CFRP. The experimental results show that: 1) beam shaping can be realized by using the plano-convex cylindrical mirror, which improves the quality of laser processing and greatly improves processing efficiency. It only takes 20 s to complete the laser processing of a 1 cm*1 cm area, which increases the work efficiency by 49 times. 2) pre-bonding surface treatment significantly enhances the tensile shear strength of the single lap joint, and the shear strength of samples with low spatial frequency LIPSS (LSFL) (14.57 ± 1.58 MPa) is 2.96 times higher than that of the untreated sample (US) (4.92 ± 1.34 MPa). 3) LSFL structure exhibits the best results, because the surface of CFRP with LSFL exhibits a relatively higher surface polarity and surface energy. This study provides an efficient, high-precision, and low-damage surface treatment method for preparing CFRP for adhesive bonding, which may promote the application of femtosecond laser technology in difficult-to-process composite materials and provide new methods and technical support for its application in aerospace, vehicle manufacturing, and other fields.

Comprehensive investigation of bond properties of CFRP cables with concrete and mortar

This study investigated the bond properties of carbon fiber reinforced polymer (CFRP) cables with concrete and mortar. Analyses focused on the bond-slip behavior considering various factors, such as CFRP cable types (e.g., CFRP rod and strand), surface treatments, fixed end materials (e.g., concrete and mortar). Remarkably, the material type and compressive strength at the fixed end were found to have no discernible impact on bond-slip behavior. Conversely, the type of CFRP cable and its surface treatment emerged as pivotal factors influencing bonding strength outcomes. Employing the modified Bertero-Popov-Eligehanusen (BPE) model, a comparative evaluation was performed between experimental results and theoretical estimation of bond-slip behavior. Furthermore, image processing analysis revealed a similar bonding strength of CFRP cables with both concrete and mortar. This similarity can be attributed to the sparser distribution of coarse aggregates around cables in concrete samples, implying that the cementitious phase primarily governed the bond properties, resulting in consistent bonding strengths across different fixed end materials. Overall, this study sheds light on the intricate interplay between CFRP cable types, surface treatments, and material compositions, ultimately contributing to a deeper understanding of bond properties and their implications for various structural applications.

Optimization and Mechanism Study of Bonding Properties of CFRP/Al7075 Single-Lap Joints by Low-Temperature Plasma Surface Treatment

This paper studied favorable low-temperature plasma (LTP) surface treatment modes for Carbon Fiber Reinforced Polymer (CFRP)/Al7075 single-lap joints using complex experimental methods and analyzed the failure modes of the joints. The surface physicochemical properties of CFRP after LTP surface treatment were characterized using scanning electron microscopy (SEM), contact angle tests, and X-ray photoelectron spectroscopy (XPS). The influence mechanism of LTP surface treatment on the bonding properties of CFRP/Al7075 single-lap Joint was studied. The results of the complex experiment and range analysis showed that the favorable LTP surface treatment parameters were a speed of 10 mm/s, a distance of 10 mm, and three repeat scans. At these parameters, the shear strength of the joints reached 30.76 MPa, a 102.8% improvement compared to the untreated group. The failure mode of the joints shifted from interface failure to substrate failure. After low-temperature plasma surface treatment with favorable parameters, the CFRP surface exhibited gully like textures, which enhanced the mechanical interlocking between the CFRP surface and the adhesive. Additionally, the surface free energy of CFRP significantly increased, reaching a maximum of 78.77 mJ/m2. XPS results demonstrated that the low-temperature plasma surface treatment led to a significant increase in the content of oxygen-containing functional groups, such as C-O, C=O, and O-C=O, on the CFRP surface.

Comparative study of infrared nanosecond laser surface paint removal for carbon fiber reinforced polymer and glass fiber reinforced polymer

Carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) are widely used in aerospace applications due to their excellent properties. Green and efficient laser cleaning technology has a broad development prospect in the paint removal treatment of aerospace composites. However, the lack of theoretical analysis and guidance has prevented the industrial application of laser paint removal technology. An infrared nanosecond laser is used to clean the paint layer on the surface of CFRP and GFRP, and the best paint removal process parameters are explored. Surface micromorphology and 3D morphology of CFRP and GFRP after cleaning are observed to reveal the cleaning quality. The FTIR spectrum is used to verify the cleanliness of the paint layer. In addition, the contact angle and bonding force are tested, and the experimental results show that the surface wettability of both surfaces is enhanced after cleaning, and the paint adhesion of both surfaces is improved after repainting. Temperature monitoring, acoustic signal monitoring and high-speed photography monitoring are used to monitor the two cleaning processes respectively. The temperature, amplitude intensity, and plasma size of the two in the cleaning process are compared and analyzed. Based on the monitoring results, it is found that the cleaning mechanism of fiber-reinforced composites includes thermal ablation, vibration effect and plasma impact effect.

Mitigation of Galvanic Corrosion in CFRP-Metal Couples through Addressing the Carbon Surface

Carbon-based reinforcements are widely used in composite materials for a wide range of applications including wind energy and transportation. In the later, the carbon-fiber reinforced polymers (CFRP) components are often joined together with metallic parts creating conditions for galvanic corrosion. Therefore, a deeper understanding of the electrochemical processes occurring at the carbon surfaces is crucial for developing new approaches for the corrosion protection of multi-material assemblies.In the present work, the electrochemical performance of different types of carbons, namely HOPG (Highly Ordered Pyrolytic Graphite) glassy carbon (GC), and CFRP, have been investigated in neutral NaCl solutions under cathodic polarization. At the potentials relevant to galvanic coupling to metals the CFRP surface is the most electrochemically active of the studied carbon surfaces. The ranking of the studied surfaces in terms of supporting the oxygen reduction reaction was established as follows: CFRP > GC > HOPG. It was found that the observed differences in the electrochemical responses of these materials to ORR are correlated with the proportions of edge sites present on each carbon surface [1].Under galvanic coupling conditions in multi-material structures composed of CFRP and Al alloys or Zn, significant degradation of the composite surface occurs at the carbon/electrolyte interface and due to an attack on the epoxy of the matrix phase most probably resulting from nucleophilic attack by hydroxyl and perhydroxyl ions, formed as a result of the oxygen reduction reaction on carbon fiber. The obtained results demonstrate the intense electrochemical activity of CFRP even when slightly polarized cathodically with a concomitant sharp increase in the pH above its surface. Contrary to expectations, exposure of CFRP to degradative high pH media before galvanic coupling did not provoke accelerated galvanic corrosion of the coupled metal under bulk electrolyte immersion conditions [2].The use of the corrosion inhibition approach to suppress the degradation of CFRP and reduce its cathodic activity in the galvanic couples was also demonstrated. It was found that the presence of sodium dodecyl sulphate (SDS) in the electrolyte offers a clear inhibition effect. From the results, it is concluded that SDS interacts with CFRP surface resulting in the formation of a persistent adsorbed layer. Surface analysis by scanning electron microscopy confirms mitigation of the CFRP composite degradation under impressed cathodic polarization in the presence of SDS or after prior exposure to SDS-containing solution [3].[1] S.U. Ofoegbu, M.G.S. Ferreira, H.I.S.Nogueira, M.L. Zheludkevich, 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, C, 9 (2023) 7.[2] S.U. Ofoegbu, M.C. Quevedo, A.C. Bastos, M.G.S. Ferreira, M.L. Zheludkevich, Electrochemical characterization and degradation of carbon fibre reinforced polymer in quiescent near neutral chloride media, npj Materials Degradation, 6 (2022) 49.[3] S.U. Ofoegbu, K. Yasakau, S. Kallip, H.I.S.Nogueira, M.G.S. Ferreira, M.L. Zheludkevich, Modification of carbon fibre reinforced polymer (CFRP) surface with sodium dodecyl sulphate for mitigation of cathodic activity, Applied Surface Science, 478 (2019) 924-936.

Digital-image based performance analysis of CFRP–concrete interface bond under anchorage

This study investigated the bonding performance of Carbon fiber reinforced polymer (CFRP)-reinforced concrete interface under anchorage. The effect of positive compressive stress on the bonding performance of the interface was analysed using a single-sided shear test of the interface. The strain distribution on the CFRP surface during interface debonding was obtained using digital image technology. The shear-stress transfer law of the CFRP-concrete interface under anchorage was analyzed, and the bond-slip curve of the interface was obtained. Results showed that the increase in interfacial compressive stress improves the interfacial bearing capacity and slip behavior. After the interfacial compressive stress increases to a certain extent, the maximum strain of the CFRP specimens does not change with the positive stress. The principal model of bond slip in the anchorage zone under the anchoring action of the compressive steel plate was obtained; the models were tested and found to be consistent with the test results. The analytical solutions of the characteristic points of the interfacial load-slip curve in the anchorage zone under positive pressure were compared with the experimental values to prove the reliability of the fitted bond–slip intrinsic model.

Shape evolution and characteristics of carbon fiber reinforced polymer surface in laser ablation

Carbon fiber reinforced polymer (CFRP) has been far-ranging used for structural components in structural engineering. Laser paint removal is promising in the repair and maintenance of CFRP structural components. However, there are still many unknowns relating to laser paint removal, and the existing theory and practice are insufficient to guide the industrial application of laser paint removal from CFRP laminate. This paper uses nanosecond laser cleaning experiments on the paint of CFRP laminate surface to study the cleaning mechanism and cleaning effect of different process parameters for removing the paint. The surface morphology and three-dimension morphology of laser-cleaned samples are observed to reveal the cleaning quality. In addition, after laser paint removal, the nanostructures are generated on the carbon fibers (CFs) surface. The thermodynamic behavior of CFRP laminate during laser paint removal is discussed by the combination of experimental results and theoretical analysis. The contact angle measurements and single lap joints experiments demonstrate laser-cleaned surfaces present better wettability and higher tensile shear strength than other cleaning methods. This study provides a theoretical and experimental basis for the application of laser paint removal from CFRP laminate.

Interfacial enhancement of CFRP/titanium alloy bonding joint by constructing a 3D interconnected CNTs network

Carbon fiber-reinforced polymer (CFRP)/titanium alloy joints offer exceptionally lightweight, superior fatigue behavior and impact resistance for aerospace applications. Nevertheless, Fiber-tear failure manifestly occurs in the CFRP/metal bonded joints due to the stress concentration of carbon fiber (CF) surfaces, and the adhesive cannot develop its full shear strength capacity, resulting in low shear strength. This drawback has limited the reliability of CFRP in full-scale structures where adhesive bonding is essential. In this study, a three-dimensional (3D) interconnected carbon nanotubes (CNTs) network was constructed on the CFs on the surface of CFRP to release the stress concentration. Carboxyl functionalized CNTs were grown on the surface of CFs, and then the CNTs were arranged in the adhesive to form a 3D network using ultrasonic-powered adhesive injection (UPAI) process. The interfacial bonding strength can reach up to 29.51 MPa, increasing by 30.7%. The growth of CNTs was verified by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The ultrasonic process can effectively promote the construction of 3D coiled/entangled and vertically aligned CNT structures, providing a more complex crack propagation path for the energy dissipation capability. FESEM and energy dispersive spectroscopy (EDS) tests of the cross sections of CFRP/titanium (Ti) alloy joints revealed that the ultrasonic process promoted mechanical anchoring owing to improved wettability and increased acoustic pressure within the adhesive. These results provide insights into future high-performance CFRP/metal hybrid joining technology of lightweight structures.

Experimental study on structural adhesive properties of aluminum plate and carbon fiber-reinforced polymer heterogeneous materials

Structural adhesive bonding between aluminum and carbon fiber-reinforced polymer (CFRP) is an important part of the vehicle's lightweight design and must ensure high strength and durability during the life of the structural member. The paper presents a precise assessment scheme to accurately and reliably infer the performance of adhesive joints through a short-term experimental test method that focuses on intrinsic and extrinsic factors affecting bond strength. The experimental results show that the surface of CFRP is polished, which is beneficial to improve the bonding quality, and the damage type transitioned from adhesion damage to substrate or cohesion damage. Aluminum alloy electrophoresis and non-electrophoresis have no significant effect on the bonding performance. Secondly, the design of the bonding nodes should be considered to bring them into a state of shear stress and be able to withstand greater loads. Meanwhile, the moderate thickness of the adhesive layer and increased bonding area serve to enhance bond reliability. In addition, various environments can cause various physical and chemical changes within structural adhesives, which can reduce the cohesive strength and durability of adhesives. This experiment is designed to select process parameters and adhesive applications for structural adhesives, which are crucial in predicting and evaluating the performance of newly developed structural adhesives and bonded joints.

Review of the surface treatment process for the adhesive matrix of composite materials

To deepen the research on the surface treatment technology of bonding matrix of composite materials, carbon fiber reinforced polymer (CFRP) was selected as the research object, and the research status at home and abroad were reviewed from three aspects: matrix characteristics, durability and bonding and stripping effect before and after surface treatment. Because of the effects of existing surface treatments on the surface roughness, surface wettability, surface morphology, fatigue characteristics, shear strength, and tensile section morphology of CFRP, the influence mechanism of surface treatments on the bonding properties of CFRP was summarized, and the future research focus and direction prospected. The results show that the bonding effect depends on the good mechanical interlocking and adsorption/chemical bonding between the adhesive and CFRP surface. The surface treatment can remove the surface pollutants of CFRP, optimize the surface topography characteristics, and enhance the spreading ability of the adhesive on the substrate surface, thereby enhancing the bonding ability between CFRP and the adhesive. The combination of different surface treatments can significantly improve the preparation quality of the CFRP surface, and avoid the defects of the single surface treatment itself to a certain extent. The surface treatment technology of the bonding matrix is developing in the direction of precision, refinement, and accuracy.

Fatigue behavior of Al-CFRP spot-welded joints prepared by electromagnetic pulse welding

In this study, the fatigue performance of magnetic pulse welding (MPW) joints of AA5052 aluminum alloy and T300 carbon fiber reinforced polymer (CFRP) with sandwich structure was systematically investigated. Mechanical property tests and microscopic observations were used to evaluate joint performance and damage to the CFRP. The results showed that satisfactory tensile strength (up to 92.24% of the tensile strength of the base material) was obtained by optimization of discharge energy. However, the samples in the fatigue test exhibited more sensitive properties to the fatigue environment. The higher fatigue cycle life was demonstrated only when the stress amplitude Sa ≤ 20.41 MPa. The fatigue test data were analyzed by Weibull distribution to fit the S-N curves under different reliability levels, which can be used for reliability assessment and life prediction in practical applications. The CFRP surfaces in different states were studied by scanning electron microscope (SEM). It was found that MPW would not damage the surfaces, while delamination and cracking would gradually occur during the fatigue process.

Surface defect detection of CFRP materials based on infrared thermography and Attention U-Net algorithm

ABSTRACT Carbon fiber reinforced polymer (CFRP) materials have been widely used in aerospace and other fields because of their excellent properties such as high temperature resistance and corrosion resistance, so the nondestructive inspection technology for CFRP materials has become a hot research topic. In this paper, we propose a method based on infrared thermography and Attention U-Net algorithm to characterize the defect shape of CFRP material surface. Firstly, the CFRP surface is scanned by a line laser and the trend of its temperature distribution is recorded using an infrared thermography camera. Subsequently, temperature analysis and entropy value of image information are calculated for individual defect image blocks in order to select images with clear defect contours. Next, the Attention U-Net is used to segment the defect in the image blocks, and the defect shape is characterization. By calculating the evaluation indexes of image segmentation, the method in this paper can achieve 99.57% accuracy, 97.06% recall, 96.63% precision, and the processing time for a single image is 0.13s. Finally, the algorithm of this paper is compared with other algorithms to verify the advantages of this research in the task of detecting surface defects in CFRP materials with fast and high accuracy.

Effects of surface topography and specimen thickness on high-speed raindrop impact damage of CFRP laminates

Raindrop impact erosion has been observed since early days of aviation, and can be catastrophic for exposed materials during supersonic flight. A single impact waterjet apparatus is established for mimicking drop impacts at the velocities between 350 m/s and 620 m/s. Carbon Fiber Reinforced Polymer (CFRP) laminates with three different surface morphologies and specimen thicknesses are tested here. A central region with no visible damage has been noticed, surrounded by a “failure ring” with common damage patterns including resin removal, matrix cracking, fiber breakage and mass fiber loss. Asymmetric features are presented in the “failure ring” whose whole scope extends larger along the longitudinal direction than the transverse direction of the top layer. The mechanism of the resin removal is related to fiber–matrix debonding, and its onset and propagation can be facilitated by initial surface asperities with the shear action of the lateral jetting. In cases of multiple impact, good surface quality can slow down the evolution of resin removal and fiber exposure on the CFRP surface, reducing the erosion speed and delaying the occurrence of structural damages in the subsequent impacts. Rayleigh wave dominates the occurrence of matrix cracking on the CFRP surface, and subsequently, results in material loss and peeling of the top-layer because of lateral flow. With the increase of the specimen thickness, both the interlaminar and intralaminar failures decrease as the impact damage mechanism changes from plate bending stress to the reflection of stress waves.

Influence of joining temperature on damage of warm self-piercing riveted joints in carbon fiber reinforced polymer and aluminum alloy sheets

The deformation of and damage to carbon fiber reinforced polymer (CFRP) in warm self-piercing riveted (WSPR) joints with CFRP and AA5754 aluminum alloy are investigated. WSPR experiments were performed at different joining temperatures. A damage constitutive model for composite materials considering the shear effect and temperature effect was established to predict the mechanical properties of CFRP during the WSPR process. The simulation model of WSPR in CFRP and aluminum alloy was established, and the influence of the joining temperature on the delamination failure and macrocracks in the CFRP surface were analyzed by numerical simulations. The results show that the WSPR finite element model can accurately predict the forming section of the joints and the damage to CFRP. The propagation direction of the delamination damage crack is consistent with the laying direction of the underlying fiber. With an increase in joining temperature, the ductility of CFRP in the corresponding direction is enhanced, and the time of the rivet piercing the upper surface layer is delayed. When the forming temperature reaches the matrix glass transition temperature, the evolution trend of each damage mode changes.

Debonding detection of defected CFRP-concrete interface using active microwave thermography

This study presents an investigation of non-destructive evaluation (NDE) of carbon fiber reinforced polymer (CFRP)-concrete interfacial debonding using a novel technology referred to as active microwave thermography (AMT). AMT utilizes microwave energy as a heating excitation to the structure and captures the anomalies of temperature contrast (TC) at the structure surface using a thermal camera. In this study, AMT was used first as an inspection method of CFRP-concrete joints. Comparative tests on CFRP-concrete joints with and without an initial man-made defect showed AMT can detect initial defects at the CFRP-concrete interface in around 15 s. Then, AMT was used to monitor the time-history progressive interfacial debonding process of the CFRP-concrete joints tested in direct shear under monotonically increasing loading. The test results showed that: (i) the initial defect at the CFRP-concrete interface can be detected by AMT quickly; (ii) the presence of an initial defect at the CFRP-concrete interface can substantially decrease the load-carrying capacity of the CFRP-concrete joint; (iii) the initial defect can alter the interfacial debonding process and global load response; and (iv) significant load drops, indicative of interfacial damage formation, could be detected by a change of slope of the local CFRP surface TC determined by AMT.

Enhanced through-thickness electrical conductivity and lightning strike damage response of interleaved vertically aligned short carbon fiber composites

Through-thickness electrical conductivity of carbon fiber reinforced polymers (CFRPs) is a key characteristic that determines the severity of lighting strike-induced damage. Carbon Fibers (CFs) are inherently electrically conductive and therefore provide high conductivity in the direction of the fiber orientation. However, electrical conductivities through the thickness and orthogonal to the CF orientation in CFRPs are governed by the insulating polymer matrix present between CFs. In this work, through the thickness alignment of short CFs in between layers of CFRP laminates is demonstrated to improve the through-thickness electrical conductivity. Composites with interleaved vertically aligned short CF fibers (<150 μm) will be referred as V-fiber composites hereafter. The effect of the V-fiber on the lightning strike damage is evaluated against an artificial lightning strike of 100 kA (modified waveform A of SAE ARP-5412B standard). The improved through-thickness electrical conductivity of CFRP laminates (1.15 S/cm) through vertical alignment of short CFs was compared to reference CFRP laminates (0.13 S/cm) and was found to dissipate the artificial lightning strike current more efficiently. The surface damage after the artificial lightning strike in the V-fiber composites was reduced to 12.69 cm2 compared to the reference CFRP surface damage of 57.67 cm2, a 78% reduction. It was also demonstrated that Joule heat generated due to lightning strike on the composites was significantly less than the reference sample using infrared (IR) thermography. A high retention (up to 78%) of flexural properties (modulus and strength) was observed in V-fiber composites post lightning strike impact as compared to only 47% retention in the reference panel.

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.