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Carbon fiber reinforced plastics inevitably develop defects such as delamination, inclusions, and impacts during manufacturing and usage, which can adversely affect their performance. Ultrasonic phased array inspection is the most effective method for conducting nondestructive testing to ensure their quality. However, the diversity of defects within carbon fiber reinforced plastics makes it challenging for the current ultrasonic phased array inspection techniques to accurately identify these defects. Therefore, this paper presents a method for the ultrasonic phased array nondestructive testing and classification of various internal defects in carbon fiber reinforced plastics based on convolutional neural networks. We prepared an ultrasonic C-scan dataset containing multiple types of internal defects, analyzed the defect features in the ultrasonic C-scan images, and established an autoencoded classifier network to recognize manufacturing defects and impact defects of varying sizes. The experiments showed that the proposed method demonstrates superior defect feature extraction capabilities and can more accurately identify both impact and manufacturing defects. [ABSTRACT FROM AUTHOR]

In this study, we conducted an analysis and evaluation of the heat affected zone (HAZ), which serves as a measure of surface processing quality in laser machining of Carbon Fiber Reinforced Plastics (CFRP). Carbon fibers have two axes, horizontal or vertical, in the alignment direction of the fibers. When the optical energy of the laser is primarily conducted along the alignment direction of the carbon fibers and diffused into heat, the HAZ occurs on the surface of the CFRP, exhibiting anisotropic characteristics. In laser processing by pulse, the accumulation of residual heat energy within the carbon fibers induces evaporation and thermal deformation of the polymer at the carbon fiber boundaries, ultimately resulting in a permanent change in the properties of the CFRP, defined as the HAZ. To confirm the influence of process variables on HAZ formation in laser machining, ray tracing was applied to predict the thickness and length of the layer in which the laser beam is absorbed by the CFRP. Generally, it was confirmed that more than 90% of the laser beam is absorbed by three layers of fibers from the surface. Based on this, the temperature distribution of carbon fibers due to residual laser energy during laser machining was predicted. Through these results, the size of HAZ according to the arrangement direction of carbon fibers could be numerically predicted. Experimental results confirmed that process variables such as laser power density and scan speed affect the formation of HAZ. Additionally, the size of HAZ due to conduction along the arrangement direction of carbon fibers was experimentally verified, and quantitative comparison and analysis were conducted with numerical results from previous modeling. Through this analysis, it was possible to predict the size of HAZ affecting surface quality during laser machining of CFRP and validate optimized laser process variables. [ABSTRACT FROM AUTHOR]

Highlights In this paper, we created a new molded‐hole process to manufacture holes instead of drilling in unidirectional (UD) carbon fiber reinforced plastics avoid fiber discontinuity. Several open hole tensile (OHT) tests were carried out on specimens with Cross ply (CP) and Quasi‐isotropic (QI) stacking sequence with drilled holes and molded holes. At the same time, we established finite element analysis (FEA) models of drilled‐hole laminate and molded‐hole laminate to characterize the stress field around the hole. The numerical analysis results reveals that the max principal strain distribution around the molded hole has much higher coincidence with fiber axial direction than that in drilled‐hole laminate. Moreover, the OHT strength results of QI specimens indicate that the plates with molded holes were more 50% higher than those with drilled holes. This process will provide reference for molded UD CFRP structure holes. And the numerical model can help engineering designer make OHT strength prediction. A new molded‐hole process for unidirectional prepreg was created. Molded‐hole specimens have higher open hole tensile strength than drilled‐hole pieces. The simulation results were close to the experimental results. [ABSTRACT FROM AUTHOR]

Increasing the size of radio frequency (RF) reflectors in space can enhance gain and spatial resolution in applications such as space-based communication and remote sensing. The size of current passive deployable reflectors is limited by a tradeoff between diameter and surface precision, which causes RF performance to degrade as size increases. A promising approach to overcome this tradeoff is to combine in-space manufacturing, which enables large structures, with distributed embedded actuation, which enables precise control over the reflector surface. Here we demonstrate a reflector antenna system that integrates these two technologies, using a candidate in-space manufacturing process, termed "Bend-Forming," with embedded electrostatic actuators. We design and fabricate a 1-m-diam prototype of an electrostatically actuated X-band reflector with a knitted gold-molybdenum mesh as the reflector surface, carbon-fiber-reinforced plastic booms as electrodes, and a truss support structure fabricated with Bend-Forming. We characterize the RF performance of this reflector, successfully demonstrating i) control over a wide range of focal lengths by suppressing a pull-in instability and ii) beam steering over an angular range of 4.2° via asymmetric electrostatic actuation. This work lays the foundation for future space communication and remote sensing technologies, offering a scalable solution to enhance RF performance through in-space manufacturing and precision control. [ABSTRACT FROM AUTHOR]

Fracture processes in carbon fiber reinforced plastics significantly depend on the architecture of the laminate reinforcement. For ± 45° angle-ply laminates of carbon fiber reinforced plastics, mechanical loading is accompanied by pseudo-ductility. This mechanism is characterized by the nonlinear stress-strain behavior under unidirectional loads. Bending stress combines compressive and tensile stresses. A transition between them is not linear, and destruction processes in carbon fiber reinforced plastic structure having layers angled at ± 45°, are interesting and not completely understood. The paper presents the experimental results of bending damage of a laminate with stacking sequences of [(± 45°)2/0°]S and [(± 45°)2/90°]S. High-frequency acoustic microscopy is used to visualize the bending damage development. Layer-by-layer ultrasound imaging shows localization of fiber fractures, microcrack nucleation, growth and association with interlayer delamination. [ABSTRACT FROM AUTHOR]

This paper investigated the mechanical performance, progressive failure process, and failure modes of riveted joints, bonded joints, and hybrid joints with different adhesive layer thicknesses connecting carbon-fiber-reinforced plastic (CFRP) and aluminum alloy subjected to quasi-static tensile loading. The 2D digital image correlation technique was used to record the deformation and strain of the overlap area. The results show that the thickness of the adhesive layer had a negative effect on the mechanical properties of the hybrid joints, and when the thickness of the adhesive layer was increased from 0.2 to 0.8 mm, the peak load and the energy absorption (EA) values of the hybrid joints were reduced by 14.38 and 23.22%, respectively. Compared with the bonded and riveted joints, hybrid joints showed better performances in peak load and EA values, and rivets were able to continue carrying loads when the adhesive layer failed. The typical failure modes of the hybrid joints included CFRP compressive failure, adhesive failure, fiber-tear failure, and light-fiber-tear failure. It was further found that the adhesive could disperse the stress around the rivet holes and effectively reduce the stress concentration around the rivet holes. [ABSTRACT FROM AUTHOR]

An experimental assessment results of residual stresses magnitude, which was carried out using the cantilever method using plates made of carbon, glass, and basalt plastics as elastic substrates, are presented. The same type of epoxy binder was used in the fabrication of samples and in the fabrication of an elastic substrates. This work shows the dependence of the residual stress values on the curing mode. It was found that the residual stresses for basalt plastics are lower than those for glass and carbon plastics and that they are characterized by a lower relaxation rate. [ABSTRACT FROM AUTHOR]

It has been established that exposure to a microwave electromagnetic field with an energy flux density that is rational for each type of composite (carbon-, glass-, organoplastic) contributes to an increase in the specific work of delamination by 18.6, 12 and 20%, respectively, which satisfactorily correlates with an increase in strength of these materials under three-point bending and interlaminar shear. [ABSTRACT FROM AUTHOR]

In this study, the influence of four different process parameters on hot gas welding of CF/epoxy fiber composites functionalized with a PA6 thermoplastic film is investigated. Additional experiments are carried out on specimens adorned with triangular beads of coupling material that are printed onto the plates, ensuring extra material within the joining zone. This approach offers a great advantage for compensating geometric tolerances. The parameters considered are common process parameters for regular two-step processes: Heating element temperature (THE), heating time (HT), welding force (F) and welding time (HTF). The design of experiments (DoE) is planned according to the Taguchi method. An orthogonal array is used to set up the experimental plan. Three factor levels of each welding parameter are considered. The test series are carried out with two sample variants. In the second sample variant, additional thermoplastic material is placed in the joining zone. The strength of the welded joints is investigated by tensile shear tests according to DIN EN 1465. The results show that the welding force has the greatest influence on the welding strength. Heating times of 20 s were found to be optimal. Within the first sample variant, a saturation behavior of the welding force can be observed at 500 N. Higher heating element temperatures (500 °C) and welding forces (1165 N) are advantageous using additional material. High welding temperatures result in a negative effect on the interdiffusivity of the polymer chains. [ABSTRACT FROM AUTHOR]

The accelerated testing methodology (ATM) developed by the authors is the methodology for predicting statistically long-term life of CFRP structures based on the viscoelasticity including the time-temperature superposition principle for matrix resin. The formulae of ATM are expressed as the product of static strength at room temperature, its dispersion, and the viscoelastic parameter of matrix resin that changes with time and temperature history. This methodology ATM was applied to the prediction of long-term creep failure life for unidirectional CFRP with heat-resistant epoxy resin as matrix under heat degradation in this study. Resin impregnated CFRP strands with heat-resistant epoxy resin were molded using a filament winding system as virgin specimens of unidirectional CFRP. Then, heat-degraded specimens were prepared by exposing the virgin specimens under acceleration conditions determined based on the time-temperature superposition principle for chemical deterioration assuming the condition of practical temperature 110°C and period 10 years. Second, the creep strengths of virgin and heat-degraded CFRP strands were statistically predicted based on ATM and the effect of heat degradation on the long-term life of CFRP strands was evaluated. As results, it was cleared that when the creep strength of CFRP strands undergoes thermal aging at the practical condition, in addition to the strength decrease to time due to the viscoelasticity of the resin, a comparable decrease in static strength and increase in this scatter occur. [ABSTRACT FROM AUTHOR]

Self- piercing riveting (SPR) is an advanced process of the mechanical joining of two or more sheet metals by piercing a rivet into the sheets. SPR has been widely applied to join dissimilar materials that are difficult to join, such as aluminum alloys and steels, especially in automobile industries. In the present work, the Carbon Fiber Reinforced Plastics (CFRP) with thickness of 1.3 mm to SPFC 590DP steel with thickness of 1.2 mm was mechanical joined in lap configuration by the SPR process, and the effect of process parameters of force and shape of rivets on joints were investigated. The integrity of the joints was estimated by quality criteria in terms of the gap between the rivet head and the upper plate, remaining thickness of bottom plate and the length of interlock between the rivet and bottom plate. Furthermore, the tensile shear load, fatigue load and the fracture mode characteristics were investigated. From the result, maximum tensile-shear load of 1.94 kN was obtained at a force of 29 kN, which showed separation of CFRP due to fiber split phenomenon on interface of CFRP side in joints. [ABSTRACT FROM AUTHOR]

The accelerated testing methodology (ATM) for the statistical life prediction of carbon fiber reinforced plastics (CFRP) under creep and fatigue loads based on the viscoelasticity of matrix resin has been proposed by authors. This method has been successfully applied to the life predictions of unidirectional CFRP with thermosetting epoxy resin as the matrix under tensile and flexural loads. In this paper, this method was applied to the fatigue life prediction of unidirectional CFRP (CF/PP laminates) with thermoplastic polypropylene (PP) as the matrix under tensile and flexural loads, and the effect of matrix viscoelasticity and load cycles on the fatigue behavior of CF/PP laminates were discussed under tensile and flexural loads. First, the viscoelasticity of matrix PP was measured. Second, the static and fatigue strengths of CF/PP laminates were statistically measured at various temperatures and frequencies under tensile and flexural loads. Third, all of material parameters in the fatigue strength formulation in ATM were determined using measured data, and the statistical long-term fatigue strengths of CF/PP laminates were predicted under tensile and flexural loads. As results, comparison with tension and bending test results clarified that the long-term tensile fatigue strength of CF/PP laminates decreases at an accelerated rate as the number of cycles increases, and that the flexural fatigue strength is affected by temperature and frequency rather than by the number of cycles to failure. [ABSTRACT FROM AUTHOR]

Self-commitments and increasing legal requirements lead to the compulsion to reduce carbon dioxide emissions in commercial aerospace. One viable approach is the reduction of structural mass, that would reduce emissions for every flight. This is especially true for high cadence singe aisle aircrafts. However, high quantities are required in this segment. To achieve these goals the newly developed low-melt Poly-Aryl-Ether-Ketone (LM-PAEK), a high-performance carbon fiber-reinforced thermoplastic composite was chosen to build a full-scale multi-functional fuselage demonstrator (MFFD) in order to delevelop an automated process that shows these savings. Single-step automated Fiber Placement (AFP) with in-situ consolidation offers distinct advantages in this field with its short curing times and especially by eliminating high amounts of waste otherwise caused by vacuum bagging and related tasks for post-consolidation in an autoclave. In order to ready this technology for future aircraft production this paper demonstrates how the processing window for LM-PAEK tape (TC1225) provided by TORAY was established. By closely linking robot and end-effector data with positionally accurate thermocouple measurements, the determined mechanical properties at coupon level and micro-sections of the manufactured specimens can be precisely correlated. This holistic approach is independent of the placement equipment and may enable global comparability within the community working in the field of thermoplastic AFP. In conclusion the procedure is evaluated and possible simplifications are discussed. [ABSTRACT FROM AUTHOR]

Heat resistant thermoplastic matrices offer potential advantages over thermoset polymers and represent a promising alternative in advanced composite applications. In the present work, the properties of carbon fiber reinforced plastics (CFRPs) based on the developed semicrystalline polyimide R‐BAPB were studied and compared with those of highly heat‐resistant thermoplastic polymers such as amorphous polyetherimide Ultem‐1000 and semicrystalline polyetherketone PEEK. To obtain CFRP, an approach was used basing on the uniform distribution of polymer powders on continuous carbon fibers by electrostatic spraying followed by their impregnation in heated calenders and hot pressing. The thermal and thermomechanical properties of CFRPs based on mentioned above polymers were studied. The effect of temperature on the mechanical behavior of CFRPs, including flexural properties and interlaminar fracture toughness G1C, was investigated as well. CFRPs based on PEEK and R‐BAPB are found to have the highest thermal stability and heat resistance. The maximum flexural strength, which practically does not change in a wide temperature range from −50 to 180°C, is observed for CFRP based on R‐BAPB polyimide. Among the investigated CFRPs, the highest value of interlaminar fracture toughness is shown by CFRPs based on semicrystalline R‐BAPB. [ABSTRACT FROM AUTHOR]

The physical-mechanical properties of epoxy matrices modified with polyethersulfone (PES) and unidirectional glass- and carbon-fiber-reinforced plastics (GFRP and CFRP) based on them were investigated. The fracture toughness of epoxy matrices modified with 20 wt% PES, increased by 4.3 times. The delamination energy of GFRP and CFRP with this content of PES in the matrix increases by 50 and 65%, respectively. A correlation between the fracture toughness of modified matrices and the delamination toughness of GFRP and CFRP was established, and the influence of structure of the matrices on the fracture toughness of the reinforced plastics was demonstrated. A significant increase in the fracture toughness of the matrices and reinforced plastics was also observed during the formation of extended phases enriched with PES. [ABSTRACT FROM AUTHOR]

In recent years, carbon fiber reinforced plastics (CFRP) have attracted widespread attention in many industrial fields such as aerospace, automobiles, and high-speed railways. It has become a trend to replace traditional aluminum alloys and steels with CFRP in certain key components in order to achieve a better lightweight effect. However, due to the huge difference in the performance of metal materials and CFRP, problems such as unreasonable structural design and insufficient weight reduction may occur during the material replacement process. In order to solve the above problems, a progressive optimization method was proposed by this article. This progressive optimization method includes the conceptual design stage and the detailed design stage. The conceptual design stage includes modal analysis and topography optimization. The detailed design stage involves the weight reduction analysis of components, including the optimization of fiber layup angle, stacking sequence, and thickness. This article takes a CFRP key component as an example to verify the feasibility of the optimization method. Compared with the traditional method, using the optimization method, the structural stability of key components is improved. The weight reduction ratio of key components reaches 61.1%. Finally, a test sample was manufactured according to the optimized results by molding and RTM molding process, the actual weight reduction ratio is 57%, and the sample successfully passed the tests required by the relevant standards. These results indicate that the proposed progressive optimization method has great application potential in the design of CFRP lightweight structures in the aerospace field.

Carbon fiber reinforced plastics (CFRP) composites are the most widespread advanced composite materials. Still, machining with traditional tools quickly generates defects such as high cutting forces and severe subsurface damage, while micro-textured tools can improve CFRP machining performance. Therefore, to reveal the cutting mechanism of CFRP processing by micro-textured tools and guide the tool design, macroscopic and microscopic orthogonal cutting models were established in this study, which compared and analyzed the material removal process and the indicated topography of unidirectional CFRP with different fiber orientations (0°, 45°, 90°, and 135°) by traditional tools and micro-textured tools, and the accuracy of the models was verified with experiments. Compared with traditional tools, micro-textured tools reduce cutting forces by minimizing the tool-chip contact length to reduce friction and converting the fiber failure form from crush failure to shear failure. Meanwhile, the texture on the rake face enables cutting burrs, effectively improving the surface quality of the workpiece and suppressing the depth of subsurface damage. In addition, the influence of different texture parameters on the machining quality of the workpiece was analyzed. [ABSTRACT FROM AUTHOR]

In this study, we aim to investigate the effect of galvanic corrosion on the mechanical properties of aluminum-CFRP adhesive joints. Aluminum-CFRP, aluminum-aluminum, and CFRP-CFRP adhesive joint specimens were prepared. Subsequently, the specimens were subjected to accelerated aging treatment in a salt spray environment, and the tensile shear adhesive strength, the transition of the failure surface and the deposition state and the components of corrosion products with aging time were quantitatively evaluated. As a result, in aluminum-CFRP adhesive joints under the salt spray, galvanic corrosion of the aluminum substrate occurred within 24 hours, and the adhesive-adherend interfacial strength decreased significantly compared to aluminum-aluminum and CFRP-CFRP adhesive joints. In addition, the failure mode of aluminum-CFRP adhesive joints changed from the mixed failure of interfacial failure, cohesive failure, and fiber tear failure to interfacial failure. Furthermore, it was found that the deposition amount of Al2O3 increased under the influence of the salt spray environment.

Carbon fiber reinforced plastics (CFRPs) are widely used in the aerospace, automotive, and construction industries. CFRP prepregs (intermediate products) are generally used in CFRP production, with a large number of prepreg cut‐offs being discarded during cutting processes. There is strong demand for a method for recycling carbon fiber prepreg cut‐offs. This paper proposes a method for recycling such material, which is characterized by low cost and high added value, in order to foster the development of a recycling‐oriented society. We prepare carbon tapes (CTs) by cutting discarded cut‐offs according to their size so as to maximize fiber length. Using a simple water CT dispersion method, we fabricate uniform CT sheets and mold a recycled CT‐reinforced composite (R‐CT‐RC). Sample prototyping and mechanical characteristic testing indicate that this R‐CT‐RC is characterized by low recycling cost and desirable mechanical properties. Recycled CT‐reinforced composite with thermoplastic (R‐CT‐RC/TP), which is prepared by adding thermoplastic resin between CTs, can be re‐molded and therefore readily re‐recycled. [ABSTRACT FROM AUTHOR]

• Based on the principle of superposition, the proposed method provides the displacements as the measured displacements. • The strain distributions are obtained from measured displacements without errors due to numerical differentiation. • The strains near the fiber-matrix interface are evaluated compensating for the insufficient resolution of microscope images. A DIC-FEM hybrid method is proposed to capture micro-scale deformation behavior near the fiber-matrix interface by combining displacement distributions measured using digital image correlation (DIC) with finite element method (FEM) analysis. Images of CFRP cross section with fine random pattern before and after deformation are taken with a laser microscope. The in-plane displacement components near the interface of fiber and matrix are obtained using digital image correlation and they are used as the input of the hybrid method. Not only the displacement distributions but the strain fields are determined using the proposed hybrid method, based on the superposition principle, so that the same distributions are obtained as those obtained by the measurement. The proposed DIC-FEM hybrid provides the strains near the interface between fiber and matrix, compensating for the insufficient resolution of microscope images. [ABSTRACT FROM AUTHOR]

• A bio-inspired CFRP tube was designed by mimicking the ceiba pentandra. • Quasi-static and dynamic axial crushing responses were studied. • Mesoscale failure mechanisms were explored by the scanning electron microscope. • Bio-inspired tube exhibited superior quasi-static and dynamic SEA than square tube. The multi-corner design approach can effectively enhance the energy absorption capacity of thin-walled metallic tubes under axial quasi-static and dynamic loading conditions. However, its efficacy in augmenting the crashworthiness performance of carbon fiber reinforced plastic (CFRP) tubes remains inconclusive, particularly due to the different failure mechanisms and pronounced strain rate effects inherent to CFRP materials compared to their metallic counterparts. Therefore, a type of bio-inspired multi-corner CFRP tube structure was designed by mimicking the non-convex cross-sectional shape of the root of ceiba pentandra tree, and its axial crushing responses were studied experimentally and numerically. Quasi-static compression and dynamic impact tests were conducted to compare the energy absorption capabilities of square and bio-inspired tubes with the same mass. The results showed that the specific energy absorption (S E A) of the square CFRP tube increased after adopting the bio-inspired design; however, different percentages of increase in S E A values were found under quasi-static and dynamic crush conditions, 13.5 % and 4 %, respectively. With the aid of finite element analysis and electron scanning technologies, the energy absorption mechanisms of bio-inspired tubes were further studied. It was found that the increase in S E A values was attributable to the increased number of axial splitting and secondary squeezing effects between internal fronds in the crushed tubes. Moreover, most of the fibers at the corner in a tube failed in tensile fracture mode during quasi-static testing, whereas they failed in both tensile and shearing fracture mode in dynamic testing, thereby leading to a reduction of energy absorption. Finally, two novel multi-corner tubes based on bio-inspired design and corner fractal design methods were proposed and they showed higher SEA values than initial one under dynamic impact. [ABSTRACT FROM AUTHOR]

Developing high‐performance polymer (HPP) with improved properties by green processing method is one of the core parts of HPP research. In this paper, a new monomer (4,4′‐((propane‐2,2‐diylbis(4,1‐phenylene))bis(oxy))dibenzaldehyde (PBhDCI)) of high‐performance aromatic nitrile‐based (AN) resins with good solubility in ethanol was designed. The rheological analysis showed that PBhDCI is suitable for the processing by laminating process. The cured resins and the corresponding carbon fiber reinforced plastics (CFRP) showed outstanding thermal and mechanical properties. The thermal decomposition temperature (T5%) of the cured PBhDCI under nitrogen up to 510°C, the glass transition temperature (Tg) of both resin matrix and CFRP exceeds 500°C, and the flexural strength and modulus of CFRP were 507 ± 5 MPa and 59 ± 2 GPa. This work will offer some guidance for the preparation of high‐performance resins and corresponding CFRP with a green processing and high thermal and mechanical properties. [ABSTRACT FROM AUTHOR]

Vibration of manufacturing machine parts can be reduced by applying CFRP to precision machines. Recently, the use of 3D printers in manufacturing has increased. However, there are few studies on the vibration characteristics of 3D printed composite materials. The objective of this study is to analyze the vibration reduction effect of a 3D printed composite material used as a CFRP chuck adapter. The existing chuck adapter is made of steel. In this study, the vibration values for three types of CFRP, steel, and CFRP with steel chuck adapters are compared. The products were rotated at 10, 500, and 1000 rpm, and the vibration velocity and displacement were calculated as an average value after repeating each measurement 5 times. Vibration velocity was improved by up to 64% and displacement by up to 31.1%. These results can be usefully applied to other mechanical parts requiring vibration damping. [ABSTRACT FROM AUTHOR]

A composite laminate with high conductivity and high mode I fracture toughness was prepared by using a silver-plated nylon mesh as the interleaf. Through in-depth comparison with the silver-plated non-woven veil interleaved composites, the mechanisms of the conductivity improvement and interlaminar toughening were discussed. The conductivities along the fiber direction, in transverse to fiber direction and through thickness direction reached 739 S/cm, 734 S/cm, and 5.4 S/cm, respectively, which increased by 196%, 344,500%, and 4326%, respectively, and are much higher than these of the other modified systems. At the same time, the mode I interlaminar fracture toughness increased by 112%. Mechanism study shows that the conductivities along the fiber direction and in transverse to fiber direction are greatly affected by the interleaf conductivity, while the conductivity through thickness direction is little affected. The toughening mechanism of the plain or silver-plated nylon mesh is much different from that of the non-woven veils. Both of the composites interleaved with the plain or silver-plated nylon mesh have higher mode I interlaminar fracture toughness, but less improved mode II toughness. The effect of silver-plating on the mode I and mode II fracture toughness was studied. [ABSTRACT FROM AUTHOR]

Carbon fiber‐reinforced polymers are one of the lightweight materials used in structural design due to their exceptional mechanical performances. The drilling operation is indispensable as it facilitates the assembling of various manufactured components. However, drilling of fibrous laminates is deemed difficult in comparison to the traditional metals because of the anisotropic and non‐homogeneous nature. The present work addresses the parametric effect on the drilled hole delamination and further reduces it with an optimal combination of parameters for multi‐objectives using different multi‐criterion decision‐making techniques. Initially, the response surface‐based regression model of delamination as a function of three static inputs has been developed, further revised with induced thrust as well as mean torque for the improvisation of the prediction capability. Finally, for the overall improvement, a decision‐making model has been used that includes grey relation analysis, technique for order performance by similarity to ideal solution, and VIšekriterijumsko Kompromisno Rangiranje method. The delamination was found to be minimum at a low drill point angle (100°), high spindle rotation (2150 min−1), and low feed rate (0.025 mm/rev) due to reduced thrust force. The mean absolute prediction error was significantly improved considering root mean square torque rather than axial thrust with process variables. [ABSTRACT FROM AUTHOR]

In this work, a numerical simulation was carried out to analyze the influence of contact points as well as fibers breakage on the transverse conductivity of unidirectional (UD) carbon fiber reinforced plastics (CFRP). The analysis is based on the calculation of the distribution of the electric scalar potential on a geometry inspired by a cross‐section along the axis of the fibers taken by scanning electron microscopy (SEM) on a CFRP. The observation of the cross‐section allows us to capture the microstructure of the material which served as a basis for our model, in which numerical analysis using the finite element method (FEM) was performed. This simulation allows us to highlight the electric current pathways and evaluate their influence on both longitudinal and transversal electric conductivity. The obtained results give a good agreement with those found in the literature. [ABSTRACT FROM AUTHOR]

Carbon fiber is an ideal candidate for preparing electrode of structural supercapacitors, while its low specific surface area is a vital factor which restricts energy storage performance. In this study, MnOOH nanowires (MnOOH‐NWs) are in‐situ deposited onto the woven carbon fiber fabric (WCF) surface through an effective one‐step hydrothermal treatment to prepare MnOOH‐NWs modified WCF (MnOOH‐NWs@WCF) structural supercapacitor with appreciable electrochemical performance. The areal capacitance of MnOOH‐NWs@WCF structural supercapacitor reaches 77.1 mF/cm2, which is two orders of magnitude higher than that made from neat WCF electrode. The increase in areal capacitance is primarily due to the presence of conductive networks and abundant ion storage sites constructed by the MnOOH‐NWs. Meanwhile, flexural strength and modulus of the MnOOH‐NWs@WCF structural supercapacitor are 30.3 MPa and 1.8 GPa, respectively. Interestingly, the resultant structural supercapacitor also enables electromagnetic interference (EMI) shielding based on the conductive networks constructed by the WCF and MnOOH‐NWs, and the maximum EMI‐shielding effectiveness (EMI‐SE) is 59.1 dB. Consequently, a highly integrated multi‐functional structural supercapacitor is developed, which cannot only be applied as energy storage module and load bearing component but can also be adopted to protect electronic devices from the electromagnetic pollution. [ABSTRACT FROM AUTHOR]

Delamination in carbon fiber reinforced polymer (CFRP) composite structures plays a significant role in reducing the stiffness and strength of the structure, thus downgrading the integrity and reliability of the system. Aiming at the problem that traditional linear Lamb wave technology is not sensitive to the layered defects of composite materials and the existing nonlinear Lamb wave method is difficult to locate and detect damage, this paper proposes an ultrasonic tomography method based on Lamb waves to detect and reconstruct the delamination defects in CFRP plate. The dynamic finite element analysis method is used to simulate the propagation process of A0 mode Lamb waves in the 14-layer cross-layer CFRP defect plate. Sixty-four sensors perform fan-beam scanning on the composite plate in an equal-angle arrangement to obtain time-of-flight data corresponding to the sensing path. The layered defects of the composite material are imaged and evaluated by the filtered back-projection method. The experimental results show that this method can obtain high-quality reconstructed images of layered defects. [ABSTRACT FROM AUTHOR]

Al/FeCoNiCrMo high-entropy alloy (HEA) coatings were prepared on the surface of carbon fiber reinforced plastic using plasma spraying technology. The microstructure of the HEA coatings was characterized under different spraying currents, and the hardness, interfacial bonding, corrosion resistance and friction and wear properties of the coatings were tested. The results showed that with the increase of the current, the unfused particles in the coatings decreased, and the coating porosity and thickness also decreased gradually; the hardness, corrosion resistance and friction and wear resistance properties increased with the increase of the current, in which the maximum hardness was 740.3 HV 0.1 , and the minimum self-corrosion current was 1.21 × 10−5 A·cm−2, and the minimum volumetric wear rate was 7.66 × 10−5 mm3·N−1·m−1. • Preparation of FeCoNiCrMo coatings with special properties on CFRP surfaces using plasma spraying technology. • Preparation of Al transition coating on CFRP to improve the interfacial properties between the coating and substrate. • FeCoNiCrMo coatings prepared with different spraying currents were studied. [ABSTRACT FROM AUTHOR]

This paper describes the age-related warp of carbon fiber reinforced plastic (CFRP) asymmetric laminated beams due to the viscoelasticity, anisotropy, and nonhomogeneity of CFRP laminates. Asymmetric orthogonally laminated CFRP beams held at a high curing temperature were cooled at various rates with and without constraints against warping during cooling. Furthermore, the warping of CFRP beams with the constraint lifted after cooling was measured during the aging processes. The age-related warping generated under various conditions was predicted using the viscoelastic and thermal properties of the CFRP laminates. The results were compared with measured data. The results were interpreted as follows. The age-related warping of CFRP beams depends strongly on the process conditions of the cooling rate and constraint, and the thermal and physical age-related shrinkage and viscoelasticity in the transverse direction of unidirectional CFRP affect the age-related warp of CFRP beams. Thermoviscoelastic analysis with physical age-related shrinkage is effective for this prediction. [ABSTRACT FROM AUTHOR]

To explore the method of low-damage gas-assisted laser processing of carbon fiber reinforced plastics, using QCW450 quasi-continuous fiber laser cutting machine (maximum peak power 4500 W), and laser scribing carbon fiber reinforced plastics with three gas-assisted methods: coaxial nitrogen, coaxial oxygen, and coaxial oxygen paraxial nitrogen compound gas-assisted, and study the influence of the three on cutting quality. At the same time, the single factor experiment method is used to study the impact of laser peak power, scanning speed, and gas pressure on processing quality, mainly analyzing the size of the heat-affected zone of the cutting section, the cutting depth, and the width of the upper slit, and analyze the action mechanism of gas-assisted laser processing of carbon fiber reinforced plastics. The experimental results show that nitrogen can bring a certain cooling effect during high-power and high-speed processing. Oxidation exothermic effect of oxygen can promote the removal of thermal melting of materials, and high-pressure airflow can take away a part of the excess heat and erosion of the residual kerf. Meanwhile, the nitrogen and oxygen mixed gas assists comprehensively in reducing thermal damage and improving the feasibility of etching. The greater the laser peak power, the deeper the etching depth, and the greater the width of the heat-affected zone, the higher the cutting speed, the width of the heat-affected zone, and the cutting depth will decrease. Too much or too little gas pressure is not conducive to improving quality. This research provides a reference for low-damage gas laser processing carbon fiber reinforced plastics. [ABSTRACT FROM AUTHOR]

In order to meet the hydrogen storage requirements of fuel cell vehicles, and improve the storage density of hydrogen, a cryo-compressed hydrogen storage method was proposed. The performance of cryo-compressed hydrogen storage vessel was analyzed in this paper. Based on the classical laminate theory and heat transfer solution, the stress and displacement of carbon fiber were precisely calculated to guarantee the cryo-compressed vessel severing in the cryogenic condition. Subsequently, the Tsai-Wu failure criterion was used to judge the failure of carbon fiber reinforced plastics layers. The stacking sequence, winding angle, comparison of the vessel's performance at room temperature and low temperature were conducted. The numerical results showed that the properties of storage vessel decreased at cryogenic condition, and the thickness of carbon fiber at cryogenic temperature at least increased by 47.06% than that at the room temperature. Mainly influence of low temperature on the cryo-compressed vessel were concentrated on the hoop stress of helical winding and the axial stress of hoop winding. For the vessel design, it is achievable to increase these two parts by using higher strength resin materials. • A method to design CcH 2 storage vessel was developed for vehicle applications. • Distributions of stress, strain and deformation of CcH 2 vessel were calculated. • Normal compressed vessel failed under cryogenic situation unless thickening. • Influence of low temperature can also be reduced by higher strength resin materials. [ABSTRACT FROM AUTHOR]

The mode-I and mode-II interlaminar fracture properties of high modulus pitch-based carbon fiber reinforced polymers (CFRPs) (fiber: K13C; resin: EX-1515 cyanate ester) modified with 20–30 nm β-SiC nanoparticles or multiwalled-carbon nanotubes (MWCNTs) were investigated. Different volume fractions of both the β-SiC nanoparticles (1, 2, 5, and 10 vol%) and MWCNTs (1, 3, 5, and 7 vol%) were tested. The values of the mode-I and mode-II interlaminar fracture toughness of the CFRPs containing the lowest volume fractions of these nanostructures were larger compared with the unfilled composite but decreased with increasing the volume fraction of the inclusions. No differences in mechanical properties were observed among the different nanostructure types. [ABSTRACT FROM AUTHOR]

Among advanced cutting methods, High Speed Milling (HSM) is often recommended to improve the productivity and to reduce the costs of machining parts. As every cutting process, HSM is characterized by some defects like surface roughness and delamination are the main defects generated in composite materials. The aim of this experimental work is the studying of the machining quality of woven Carbon fiber reinforced plastics (CFRP) using the HSM technology. Experiments were done using different machining parameters combinations to make opened holes in CFRP laminates. This study investigated the effect of cutting speed, orbital feed speed, hole diameter on the delamination defect and surface roughness responses generated in the drilled holes. The design of experimental tests was generated using the approach of Central Composite Design (CCD). The characterization of these responses was treated with the Analysis of variance (ANOVA) and Response surface methodology (RSM). Results showed that the surface roughness is highly affected by the orbital feed speed (F) with contribution of 22.45%. The delamination factor at entry and exit of holes is strongly influenced by the hole diameter D (25.97% and 57.43%) respectively. The developed model equations gave a good correlation between the empirical and predicted results. The optimization of the milling parameters was treated using desirability function to minimize the surface roughness (Ra) and the delamination factor simultaneously. [ABSTRACT FROM AUTHOR]

This paper aims to study the evolution of cutting edge geometry due to tool wear and discuss its impact on the hole quality of a carbon fiber reinforced plastic (CFRP) laminate. A drilling experiment was conducted using three types of twist drills: uncoated, BAM (AlMgB14) coated, and (AlCrSi/Ti)N nanocomposite coated tungsten carbide tools. After generating 120 holes, the uncoated drill had the largest cutting edge radius (∼36 µm), while the BAM coated drill had the most extensive flank wear (∼287 µm) among the three drills. This relatively rapid tool wear results in a reduction of average hole size and a considerable variation on the hole profiles. The worn drills with the cutting edge radius greater than 19.3 µm form the fiber pull-outs in not only the 135° plies but also the adjacent 45° and 90° plies from the cutting direction, creating deep void networks. This type of networked fiber pull-out damage was observed with the holes machined by the uncoated and BAM coated drills. The (AlCrSi/Ti)N coated drill, which experienced the least amount of flank wear and the least increase of cutting edge radius, generated consistently sized holes up to 120 holes. However, the relatively sharp (AlCrSi/Ti)N coated tool results in the higher arithmetic roughness average (Ra) and the maximum roughness height (Rz) values than the other tools due to the localized fiber pull-outs and the absence of severe matrix smearing. [ABSTRACT FROM AUTHOR]

One of the crack resistance characteristics of carbon fiber reinforced plastics (CFRPs) is fracture toughness, which is the change in the elastic deformation energy of the structural element upon the increase in the crack area by unity at the crack onset. By studying fracture toughness, the position of the front of the crack is determined: both initial and during its growth. Currently existing test standards (STO TsAGI, ASTM D7905) determine fracture toughness by the GIIc shear mode on the samples with a crack initiator. However, the method does not reflect the real conditions of crack initiation in structures of CFRPs and can lead to a decrease in the accuracy of determining the load of crack onset. A new technique of fracture toughness determination of CFRPs in the GIIc shear mode on samples free of the standard delamination initiator has been developed at TsAGI. The aim of this work is to perform studies for developing the proposed technique. The GIIc values were determined for a shear crack that occurred under three-point bending conditions after wedging. To determine the position and shape of the crack front, as well as to estimate the dynamics of its propagation under subsequent loads, we used ultrasonic methods: ultrasonic flaw detection (ultrasonic NDT) and acoustic microscopy. It is shown that acoustic microscopy at a frequency of 50 MHz makes it possible to determine the crack front position in CFRP samples at a depth of 3.0–3.5 mm with a high resolution of about 100 μm. The features of the crack growth under shear conditions are discussed. The results of the study show that high accuracy of acoustic microscopy in comparison with conventional ultrasonic testing is eagerly sought for determining the crack shape, as well as for analyzing the dynamics of crack growth and revealing the mechanisms of interlaminar crack propagation in a composite material. [ABSTRACT FROM AUTHOR]

The influence of technologies of preliminary treatment of carbon fibers by various electromagnetic methods, namely, cold plasma and ultraviolet radiation, on their mechanical characteristics is considered. The purpose of this treatment is to increase the adhesive strength of a metal coating with a fiber to produce carbon fiber plastics with a high interlayer shear strength. The use of plasma treatment is experimentally found to be most effective. The interlayer shear strengths are presented for the manufacture of carbon fiber plastics from carbon fabrics and tapes after their preliminary treatment and the subsequent deposition of a copper coating onto their surface. [ABSTRACT FROM AUTHOR]

Vibration of manufacturing machine parts can be reduced by applying CFRP to precision machines. Recently, the use of 3D printers in manufacturing has increased. However, there are few studies on the vibration characteristics of 3D printed composite materials. The objective of this study is to analyze the vibration reduction effect of a 3D printed composite material used as a CFRP chuck adapter. The existing chuck adapter is made of steel. In this study, the vibration values for three types of CFRP, steel, and CFRP with steel chuck adapters are compared. The products were rotated at 10, 500, and 1000 rpm, and the vibration velocity and displacement were calculated as an average value after repeating each measurement 5 times. Vibration velocity was improved by up to 64% and displacement by up to 31.1%. These results can be usefully applied to other mechanical parts requiring vibration damping.

Background: The tensile strength along the longitudinal direction of unidirectional carbon fiber reinforced plastics (CFRPs) constitutes important data for the reliable design of CFRP structures. Our earlier reports proposed the formulations for the statistical static, creep, and fatigue strengths of CFRP based on Christensen's model of the viscoelastic crack kinetics. Objective: This study is concerned with the statistical assessment of the tensile static, creep, and fatigue strengths of unidirectional CFRPs by using the proposed formulations and the characterization of the long-term strengths of unidirectional CFRPs. Method: First, the proposed formulations for the time-dependent and temperature-dependent statistical static, creep, and fatigue strengths of CFRP are introduced. Second, the tensile static, creep and fatigue strengths of unidirectional CFRP are measured statistically at various temperatures using resin-impregnated CFRP strands as tensile test specimens by measuring the viscoelasticity of the matrix resin. Finally, the master curves showing the long-term life of these strengths are constructed by substituting these measured data into the formulations. Results: The results clarify that the formulations are applicable with high reliability over wide ranges of time and temperature for the statistical tensile static, creep and fatigue strengths of unidirectional CFRP except above the glass transition temperature of the matrix resin. Therefore, the fatigue strength degradation phenomena of unidirectional CFRPs can be expressed by the time- and temperature-dependent part due to the viscoelastic behavior of the matrix resin and the number of load cycle-dependent parts. Conclusions: The long-term life prediction of unidirectional CFRPs under static, creep and fatigue tension loadings can be determined by ascertaining the mechanical properties of the CFRP and matrix resin in the proposed formulations. [ABSTRACT FROM AUTHOR]

This study investigates the effect of composite material stiffness on the accuracy of drilled holes and delamination in the drilling process. Two types of composite materials were tested: glass fiber reinforced plastic (GFRP) and carbon fiber reinforced plastic (CFRP). The drilling process was performed using dedicated drill bits. Samples were clamped in a vice of the Avia-VMC 800 HS vertical machining center. Drilling parameters were maintained constant but unsupported element length was changed. The unsupported element length was defined as an unsupported distance between the drilled hole axis and the sample attachment location. The maximum feed force Ff was determined in the experiments. The accuracy of drilled holes was estimated by optical microscopy. Diameters of the drilled holes were measured. Results made it possible to determine the recommended unsupported element length at which the hole dimensions were within the dimensional tolerance. The study showed a clear decrease in the drilled hole quality and a significant increase in the feed force, especially in the area of tool exit from the workpiece. In addition, the number of delaminated fibers increased with unsupported element length was determined in the study. [ABSTRACT FROM AUTHOR]

Carbon-fiber-reinforced plastics (CFRPs) are used as structural materials in the aircraft and automotive industries owing to their lightweight and high strength. With increasing global demand for CRFPs, their application as an alternative to metals is expected to expand to several other fields. Consequently, carbon fiber (CF) products, such as CFRPs, have been attracting attention, and are used worldwide. However, there is little scientific evidence on the safety of CFs. In addition, problems similar to those caused by microplastics will ultimately arise if milled CFs or CF dust are released into the aquatic environment. Therefore, on the basis of existing microplastics studies, we conducted a CF ecotoxicity experiment using Japanese medaka and confirmed that the medaka were harmed by fine CF particles in an aquatic environment under static conditions, such as stagnant water, although the CFs themselves did not exhibit notable toxicity. It is possible that the rate of infection by microorganisms increased as a result. [ABSTRACT FROM AUTHOR]

A new strategy of recycling and reusing abandoned carbon fiber reinforced plastics (CFRP) is proposed: CFRPs are first fully carbonized to CF reinforced carbon (C/C) preforms, and then are manufactured into high value-added C/C composites. The results showed that the carbon residue rate of epoxy-resin (EP) matrix was fully recovered as the decomposition route of EP matrix was changed by charring agent. The recycled CF (rCF) was not markedly oxidized or thermally damaged, and possessed comparable properties with those of the virgin CF (vCF) after pyrolysis. The pyrolytic char had no obvious negative effect on the densification efficiency of the rCF reinforced carbon (rCF/C) composites. Both of the rCF/C and vCF reinforced carbon (vCF/C) composite bodies were quite dense, and exhibited almost no difference in their microstructures. The rCF/C and vCF/C composites therefore had quite close interface bonding strength (12.6 MPa and 13.0 MPa, respectively), and bending strength (106.4 MPa and 111.5 MPa, respectively). Furthermore, the rCF/C composites possessed comparable ablative rate with that of the vCF/C composites. The rCF/C composites derived from abandoned CF/EP composites present a great potential to be used as substitutes for vCF/C composites owing to their indistinguishable properties. [ABSTRACT FROM AUTHOR]

Drilling high quality holes is a necessary prerequisite to ensure efficient and accurate connection and assembly of CFRP components. In addition to cutting force, cutting heat is another important factor affecting the quality of CFRP drilling. In this paper, a drilling experiment of CFRP laminate is carried out, and the method of prefabricating thermocouple holes on the edge of the test-hole is used to study the influence of fiber direction and processing parameters on the drilling temperature. Results show that when drilling along the fiber direction of 0°, the heat conduction in the edge area of test-hole wall is better than that of drilling along the fiber direction of 90°. Accordingly, the drilling temperature is obviously higher. Under this experimental condition, the temperature difference of the edge area of test-hole caused by the fiber direction is as high as 44 °C. At the feed rate of 0.04 mm/rev, when the speed increases from 1500 rpm to 4500 rpm, the axial force decreases by 13.9 %, and the peak temperature at p1 and v1 increase by 63.2 % and 22.2 %, respectively. At the spindle speed of 3000 rpm, when the feed rate increases from 0.02 mm/rev to 0.06 mm/rev, the drilling axial force increases by 35.0 %, and the peak temperature at p1 and v1 decreases by 31.1 % and 30.0 %, respectively. [ABSTRACT FROM AUTHOR]