Carbon Fiber Reinforced Polymer Research Articles

Enhancing Carbon Fiber-Reinforced Polymers’ Performance and Reparability Through Core–Shell Rubber Modification and Patch Repair Techniques

Carbon fiber-reinforced polymers (CFRPs) are widely used in high-performance applications, but their inherent brittleness and susceptibility to impact damage remain critical challenges. This study investigated the effect of core–shell rubber (CSR) particles as impact modifiers on the mechanical properties of CFRPs and evaluated patch repair techniques for damaged CFRP panels. Mechanical tests, including flexural, tensile, short-beam, fracture toughness, and impact tests, were conducted on reference and CSR-modified specimens to assess their structural performance. The CSR-modified samples demonstrated significant improvements in energy absorption and fracture toughness, with a 50% increase in impact strength and up to 181% improvement in absorbed energy during Mode I fracture testing. However, slight reductions in flexural and tensile strengths were observed due to the softening effect of CSR particles. Fracture surface analysis revealed distinct failure mechanisms, with Scanning Electron Microscopy imaging showing consistent fiber pull-out behavior in tensile and flexural tests, but more stable delamination propagation in CSR-modified specimens during short-beam shear tests. Patch repair effectiveness was assessed through drop-weight impact tests on damaged panels repaired with patches containing CSRs of two thicknesses. Patches of equal thickness to the damaged panel successfully restored structural integrity and enhanced energy absorption by 37% compared with the reference samples, while thinner patches (as a suggestion to reduce production costs) failed to withstand impact loads effectively. Non-destructive testing (NDT) via ultrasonic C-scans confirmed reduced delamination and damage depth in CSR-modified repaired panels, validating the toughening effect of CSR particles. These findings demonstrate the potential of CSR-modified resins to improve CFRPs’ performance and provide effective repair solutions for extending the service life of damaged composite structures, rendering them especially suitable for applications demanding high damage tolerance and durability, including aerospace structures, automotive body panels, and energy-absorbing crash components.

Multiple Regression Analysis and Non-Dominated Sorting Genetic Algorithm II Optimization of Machining Carbon-Fiber-Reinforced Polyethylene Terephthalate Glycol Parts Fabricated via Additive Manufacturing Under Dry and Lubricated Conditions

The present research deals with the processing of the additively manufactured Carbon-Fiber-Reinforced Polymer (CFRP) under dry and lubricated cutting conditions, focusing on the generated surface roughness. The cutting speed, feed, and depth of cut were selected as the continuous variables. A comparison between the generated surface roughness of the dry and the lubricated cuts revealed that the presence of coolant contributed towards reducing surface roughness by more than 20% in most cases. Next, a regression analysis was performed with the obtained measurements, yielding a robust prediction model, with the determination coefficient R2 being equal to 94.65%. It was determined that feed and the corresponding interactions contributed more than 45% to the model’s R2, followed by the depth of cut and the machining condition. In addition, the cutting speed was the variable with the least effect on the response. The Non-Dominated Sorting Genetic Algorithm 2 (NSGA-II) was employed to identify the front of optimal solutions that consider both minimizing surface roughness and maximizing Material Removal Rate (MRR). Finally, a set of extra experiments proved the validity of the model by exhibiting relative error values, between the measured and predicted roughness, below 10%.

Performance of circular CFST columns strengthened with CFRP grid-reinforced ECC under axial compression: Numerical modelling and design

This paper describes a detailed numerical investigation using finite element models validated against test results from an experimental investigation on concrete-filled steel tubular (CFST) columns strengthened with carbon fiber-reinforced polymer (CFRP) textile grid-reinforced engineered cementitious composite (ECC). The three-dimensional model incorporates the confinement effects provided by the ECC, CFRP grid layers, and the circular tube. The validated model is used to evaluate the performance of strengthened CFST short columns through parametric assessments covering different geometric and material properties. Range analysis is applied in an orthogonal design to evaluate the relative significance of key parameters influencing the ultimate axial strength of the column member. The findings reveal a nearly 24 % increase in ultimate strength and over a 42 % enhancement in the residual strength of the concrete core due to the strengthening configuration. Additionally, the composite action of the CFRP grid-reinforced ECC leads to a 13 % increase in ultimate axial strength and over a 28 % improvement in the residual strength of the CFST column. The tube diameter is shown to have the greatest impact on the column axial resistance, followed by ECC thickness, ECC compressive strength, core concrete compressive strength, tube yield strength, tube thickness, and the number of CFRP grid layers. Finally, a simplified design model, which is supported by the experimental and numerical results, is introduced for the prediction of the compressive capacity of strengthened circular CFST columns.

Electrical discharge-mechanical hybrid drilling of micro-holes in carbon fibre-reinforced polymers

Electrical discharge-mechanical hybrid drilling of micro-holes in carbon fibre-reinforced polymers

Experimental Study on Bond Fatigue Between Carbon Fiber-Reinforced Polymer Bars and Seawater–Sea Sand Concrete Under Seawater Immersion and Dry–Wet Cycle Conditions

The durability of carbon fiber-reinforced polymer (CFRP) bars in marine environments is essential for their application in seawater–sea sand concrete (SWSSC), especially under cyclic loading conditions. While previous studies primarily focused on static bonding performance, the effects of seawater immersion and dry–wet cycles on bond fatigue behavior at CFRP–SWSSC interfaces remain underexplored. This study investigated the bond fatigue performance of CFRP bars and SWSSC under seawater immersion and dry–wet cycling conditions. Eighteen CFRP bar-SWSSC bond specimens were divided into three categories and prepared for static and fatigue pull-out tests. The effects of varying stress levels (fatigue upper load/static bond ultimate load) after seawater immersion and dry–wet cycling on fatigue failure modes, bond–slip behavior, and fatigue characteristics were evaluated. The results show that seawater immersion and dry–wet cycling significantly degrade the performance of bonds between CFRP bars and SWSSC, with an average bond strength reduction of 10.31%. These conditions reduce fatigue cycles and stiffness while increasing bond–slip (relative displacement at the bar–concrete interface) and residual–slip (displacement after unloading). Moreover, dry–wet cycling has a greater negative impact on fatigue bond performance than seawater immersion. Higher fatigue stress levels exacerbate damage and crack propagation at the CFRP–SWSSC interface, leading to significant increases in both bond–slip and residual-slip. Under similar conditions, higher stress levels enhance bond stiffness. However, excessively high stresses may lead to bond fatigue failures. Using experimental data and existing fatigue bond–slip constitutive models, a customized model for CFRP bars in SWSSC was developed. These findings highlight that marine environments and fatigue loading severely impair bond performance, thereby emphasizing the importance of careful design for marine applications. The proposed model offers a reliable framework for predicting bond–slip behavior under fatigue conditions, enhancing the understanding of CFRP–SWSSC interactions and supporting the design of durable marine infrastructure.

The Role of Advanced Materials in the Optimization of Wind Energy Systems: A Physics Based Approach

The transition towards renewable energy sources is essential for addressing climate change and reducing greenhouse gas emissions, positioning wind energy as a vital component of sustainable power generation. This paper investigates the pivotal role of advanced materials in optimizing the efficiency and reliability of wind energy systems through a physics-based approach. Recent advancements in material science including carbon fiber reinforced polymers (CFRPs), glass fiber reinforced polymers (GFRPs), and nanomaterials such as graphene and carbon nanotubes are evaluated for their potential to significantly enhance mechanical properties, reduce weight, and improve energy conversion efficiencies of wind turbines. A comprehensive review of the literature reveals the historical context of wind turbine materials and emphasizes the transition from traditional construction methods using steel and wood to innovative composite materials. The study introduces a novel methodology for the integration of advanced materials into turbine design, supported by numerical simulations and experimental validations. The impact of these materials on key operational performance metrics, including power output, structural integrity, and aerodynamic efficiency, is quantified. Moreover, the application of smart materials for real time structural health monitoring is explored, highlighting the potential for predictive maintenance that can prolong the lifespan of wind turbines. The findings suggest that although the initial costs of advanced materials may be higher, their superior performance characteristics offer significant long-term economic benefits and sustainability advantages. The discussion concludes with recommendations for future research directions, including the optimization of hybrid material systems, advancements in manufacturing techniques, and comprehensive long-term durability assessments. This study underscores the critical necessity for continued innovation in materials science to enhance the resilience and environmental efficiency of wind energy systems, thereby contributing positively to the global transition towards sustainable energy solutions.

Mitigation of Fiber Print-Through During Replication of Carbon Fiber-Reinforced Polymer Mirrors

Aiming at the phenomenon of fiber print-through (FPT) during the curing process of carbon fiber-reinforced polymer (CFRP) mirrors, this paper effectively mitigates FPT by improving the replication technique. This paper simulates and analyzes the causes of FPT generation and then improves the replication technique based on multiple explorations of the replication process. In the improved replication technique, a mold is designed to assist in the curing process of the mirrors and to further suppress the FPT on the surface by applying pressure during the curing process. In addition, the layup method, resin matrix, and curing equipment are also optimized and improved. The surface roughness of the CFRP mirrors before and after the process improvement is measured using an optical surface profilometer, and the roughness parameters such as the arithmetic average deviation, root mean square error, and maximum height are obtained. Measurement results show that the improved replication technique effectively mitigates FPT, the surface of the obtained CFRP mirror is smoother, and the application of pressure during curing can further reduce the roughness of the mirror surface.

Machinability optimization of carbon fiber reinforced polymer composites for aviation manufacturing parts

PurposeSurface roughness and delamination during the milling of carbon fiber reinforced polymer (CFRP) composite parts in aviation can lead to component rejection. This article aims to optimize cutting conditions to reduce these failures while ensuring compliance with aviation standards. By improving machinability, the goal is to minimize part rejection rates and scrap, optimizing costs and increasing safety.Design/methodology/approachFull factorial experimental design and response surface methodology (RSM) were used to establish relationships between the cutting parameters and the cutting force, delamination and surface roughness. To validate the model and identify significant parameters, analysis of variance (ANOVA) was performed. The cutting parameters were optimized to reduce cutting force and improve surface quality using ANOVA and RSM.FindingsThe lowest response values can be achieved with a cutting speed of 285.35 m/min and a feed of 358.57 mm/min using the Aluminum Chromium Nitride (AlCrN)-coated tool. Accordingly, the optimum cutting force was obtained as 190.97 N, delamination depth as 1.562 mm and surface roughness as 1.431 µm. It has been seen that the obtained surface roughness and delamination values are consistent with aviation literature studies, sectoral data and standards.Originality/valueThis study uniquely examines cutting force, surface roughness and delamination using Titanium Aluminum Nitride (TiAlN)- and AlCrN-coated tools instead of traditional Poly Cyristaline Diamond (PCD) tools. It employs a two-stage experimental framework, starting with a full factorial design followed by RSM. The initial data have been used as inputs for optimization in the second stage to achieve more accurate results.

Mechanical anchorage system in retrofitting of RC slabs using CFRP rods and concrete jacket

Over the past few decades, the demand for retrofitting reinforced concrete members has risen dramatically. Retrofitting reinforced concrete slabs with carbon-fiber-reinforced polymer (CFRP) rods and ultra-high-performance-fiber-reinforced-concrete (UHPFRC) jackets is the one of significantly effective techniques. However, the main challenge of employing CFRP rods and UHPFRC jackets technique to strengthen existing reinforced concrete members is the efficiency of using CFRP rods and the debonding issue between old and fresh new concrete jacketing. Debonding mostly occurs between CFRP rods and old concrete, as well as the surfaces of old and new concrete, and is especially prevalent when the slab is subjected to daily repetitive loads such as cyclic loads. In this study, a new retrofitting system utilizing a mechanical anchor system was proposed to improve the bond between the UHPFRC layer and existing slab. This mechanical system incorporates an expandable anchorage bolt and steel plates. Therefore, a benchmark RC slab and two retrofitted RC slabs were experimentally tested under a five-point incremental repeated load (cyclic load) employing the dynamic actuator. The influence of embedded CFRP rods into the jacket of UHPFRC on the performance of system were studied. The experimental results showed that the newly proposed approach was significantly effective in preventing early debonding. In addition, the mechanical system played an essential role by improving the attachment between the jacket and the slab, ensuring better load transfer. A new proposed retrofitting technique improved the capacity of slabs from 164 to 298kN, illustrating an improvement of over 82%. On the other hand, the FE models have been developed to provide both practical validation and deeper analytical insights, ensuring a comprehensive evaluation of the proposed retrofitting system. Experimental data were used to validate the results of the finite-element models, which showed good agreement and high accuracy. Finally, a parametric study was executed to evaluate the impact of various parameters on the performance and efficacy of the new suggested strengthening technique, and to optimize the proposed system parameters, including the diameter of bolts, a normal strength concrete (NSC) jacket with various grades rather than the UHPFRC, applying the proposed retrofitting technique on a compressive side instead of a tension zone, and rebar steel of varying diameters in the jacket instead of CFRP rods. Findings indicated (parametric study) that using anchor bolts with a diameter greater than 12 mm improved the slabs’ ultimate load capacity.

Mechanical Properties and Vibrational Behavior of 3D-Printed Carbon Fiber-Reinforced Polyphenylene Sulfide and Polyamide-6 Composites with Different Infill Types

The aim of the present study is to investigate the performance of two carbon fiber-reinforced composite polymers used to manufacture end-use parts via the fused filament fabrication (FFF) method. The materials under investigation were carbon fiber-reinforced Polyamide-6 (PA6-CF15) and carbon fiber-reinforced polyphenylene sulfide (PPS-CF15). To evaluate their mechanical properties and vibrational behavior, specimens were fabricated with four distinct infill patterns: grid, gyroid, triangle and hexagon. In particular, the vibrational behavior of the 3D-printed composites was determined by conducting cyclic compression testing, as well as modal tests. Additionally, the mechanical behavior of the reinforced polymers was determined by conducting both uniaxial tensile and compression tests, as well as three-point bending tests. The results of the mechanical experiments revealed that the grid pattern exhibited the best overall performance, while the gyroid pattern exhibited the greatest strength-to-weight ratio, making it the most durable infill for use with composite filaments. In vibration experiments, PA6-CF15 structures exhibited higher damping ratios than PPS-CF15, indicating superior damping capacity. Among the infill patterns, the hexagon pattern provided the greatest vibration isolation performance.

Surface treatment of carbon fiber reinforced polymer for adhesive bonding with pioneer epoxy using atmospheric pressure plasma jet

A recent technique used in surface preparation for adhesive bonding is plasma treatment. In the Philippines, one of the most accessible brands of adhesive is Pioneer epoxy adhesive and, currently, there has been no existing research on the effect of plasma treatment with this adhesive. Thus, this research aims to investigate the effects of plasma pretreatment on the adhesive bonding of carbon fiber-reinforced epoxy adherents with the Pioneer epoxy adhesive. To achieve this, carbon fiber-reinforced polymers (CFRPs) samples were first plasma treated using an atmospheric pressure plasma jet (APPJ) for 0, 1, 2, and 3 min. Then, these were used to form the joint systems with three different adherent combinations. The samples were characterized using the lap shear test, contact angle measurements, optical microscope, laser microscope, and Raman spectroscopy. The result shows that the surface free energy and roughness of the CFRP increase with increasing plasma treatment time. However, the roughness is contributed by the introduction of impurities, which can weaken the bonding. Thus, when the CFRP has adhered using Pioneer epoxy adhesive, the lap shear stress (LSS) of the treated CFRP proves to be lower than that of untreated samples, with a statistically significant p-value of 0.0069. From Tukey’s honestly significant difference (HSD) test, it is concluded that plasma treating the adherent weakens the adhesive bonding of the CFRP and Pioneer adhesive joint system instead of improving it. Potential explanations for this result include the introduction of impurities by the APPJ and the presence of Mercaptan polymer in the epoxy.

Effect of Fiber Architecture on the Physical and Mechanical Properties of Carbon Fiber-Reinforced Polymer Composites

Effect of Fiber Architecture on the Physical and Mechanical Properties of Carbon Fiber-Reinforced Polymer Composites

Spatial and temporal deep learning algorithms for defect segmentation in infrared thermographic imaging of carbon fibre-reinforced polymers

ABSTRACT For non-destructive evaluation, the segmentation of infrared thermographic images of carbon fibre composites is a critical task in material characterisation and quality assessment. This paper presents a study on the application of image processing techniques, particularly adaptive thresholding, and advanced neural network models, including U-Net, DeepLabv3, and BiLSTM, for the segmentation of infrared images. This work introduces the innovative combination of DeepLabv3 and BiLSTM applied in infrared images of carbon fibre-reinforced polymer samples for the first time, proposing it as a novel approach for enhancing the accuracy of segmentation tasks. An experimental comparison of these models was conducted to assess their effectiveness in identifying artificial defects in these images. The performance of each model was evaluated using the F1-Score and Intersection over Union (IoU) metrics. The results demonstrate that the proposed combination of DeepLabv3 and BiLSTM outperforms other methods, achieving an F1-Score of 0.96 and an IoU of 0.83, showcasing its potential for advanced material analysis and quality control.

Enhancing CFRP damping with graphene nanoplatelets: experiments versus finite element analysis

This study investigates the enhancement of damping properties in carbon fiber-reinforced polymer (CFRP) composites by incorporating graphene nanoplatelets (GNPs) into the epoxy matrix. Epoxy and CFRP specimens with varying GNP concentrations, were developed and tested through free vibration experiments to measure damping ratios. Additionally, a computational model based on the finite element method was developed to simulate the damping behavior of these hybrid nanocomposites. Using periodic representative volume elements under sinusoidal axial loads, the model accurately predicted damping performance by calculating the time lag between applied loads and resulting deformations. Comparison of numerical results with experimental data revealed a strong correlation, confirming the model's effectiveness in capturing the influence of GNP mass fraction on damping enhancement.

Compression behavior of the CFRP square tubes after low‐velocity impact

AbstractThis work investigates the impact resistance and compression after impact (CAI) strength of carbon fiber‐reinforced polymer (CFRP) square tubes with varying wall thicknesses and diameters. Low‐velocity impact (LVI) tests are conducted on CFRP square tubes with three wall thicknesses and diameters at four incident energy levels, followed by compression tests on the impacted specimens. The results, including impact response history and failure morphology captured by the digital image correlation (DIC) technology, reveal that augmenting the wall thickness of CFRP square tubes substantially boosts their impact resistance and load‐bearing capabilities, evidenced by a remarkable 176.17% enhancement in CAI strength when the wall thickness is increased from 1.5 to 2.5 mm under a 20 J impact energy. Conversely, enlarging the diameter tends to diminish rigidity and impact resistance; however, it marginally augments CAI strength and residual strength.Highlights CAI strength of CFRP square tubes with varying geometries was investigated. DIC graph providing a comprehensive understanding of failure mechanisms. Failure mode was distinguished based on the low‐velocity characterization.

Impact of fiber orientation and stacking sequence on the severity of drilling induced delamination in carbon fiber reinforced polymer (CFRP) laminates

Impact of fiber orientation and stacking sequence on the severity of drilling induced delamination in carbon fiber reinforced polymer (CFRP) laminates

Evaluation of tensile strength variability in fiber reinforced composite rods using statistical distributions

Fiber Reinforced Polymer (FRP) composites are known for their exceptional resistance to harsh conditions, impressive durability, and high tensile strength, making them increasingly popular in structural applications. However, the inherent variability of composite materials poses a critical challenge, particularly in tensile strength, which directly impacts the safety and durability of structures. This study evaluated the tensile strength of 395 specimens, including 103 carbon fiber-reinforced polymer (CFRP) rods and 293 hybrid glass-carbon FRP (HFRP) rods, tested according to the GB 30022–2013 standard. To analyze the data, four statistical distributions—normal, lognormal, Weibull, and Gamma—were applied, and a goodness-of-fit test identified the Weibull distribution as the most suitable model. The study further proposed standardized tensile strength values of 2,912.40 MPa for 5 mm CFRP rods and 2,230.98 MPa, 2,385.12 MPa, and 2,517.44 MPa for 6, 7, and 8 mm HFRP rods, respectively. These findings provide valuable insights into the tensile performance of FRP rods, contributing to enhanced design and safety standards for FRP-based structural elements and offering practical references for mitigating material variability in construction applications.

Experimental and Numerical Investigation on Strengthening Techniques for Double-Wythe Stone Masonry Walls

Masonry structures represent the architectural and cultural heritage of great historical importance. They have been used for public and residential buildings for several thousand years. Many well-preserved old masonry structures still exist, proving that this construction can overcome loads and environmental impact. These structures have been exposed to lateral and vertical loads and atmospheric influences throughout their lives. In masonry structures, undesirable damage, cracks, and voids may occur due to environmental factors or various natural disasters, such as earthquakes, which may cause the structure to collapse. Different conventional strengthening techniques are available depending on the purpose required for stone masonry walls. This study aims to evaluate the structural behavior of double-wythe travertine stone masonry walls strengthened by carbon fiber reinforced polymer (CFRP). For this purpose, two masonry stone walls, which are made of saw-cut travertine stones and constructed with English bond, a pattern formed by laying alternate courses of stretchers and headers, were constructed and tested under in-plane monotonic lateral load and constant axial load. Lateral load-displacement relations and failure mechanisms were discussed. In addition, triaxial compression tests of stone, mortar, grout, and stone-mortar composite materials were performed to determine constitutive relationships. Furthermore, three-dimensional (3D) nonlinear finite element analysis (NLFEA) of stone masonry walls using the Drucker-Prager (DP) yield criterion was performed for unstrengthened stone masonry walls and strengthened ones with grout injection and CFRP. The study findings revealed that the proposed numerical modeling approach can accurately predict the experimental lateral load-displacement behavior of both strengthened and unstrengthened specimens subjected to in-plane combined axial loading and shear. Additionally, the model demonstrated its capability to simulate the experimental load-displacement and cracking patterns effectively.

Selective processing of CFRP by two-color double-pulse femtosecond laser.

This paper employed a two-color double-pulse femtosecond laser (TDFL) technology for surface processing of carbon fiber reinforced polymers (CFRP). By exploring the changes in ablation thresholds for resin and carbon fiber under varying wavelengths and pulse numbers, optimal wavelength combinations were identified. Adjustments to processing parameters and pulse delay enabled precise removal of the CFRP surface, targeting resin while causing no damage to the underlying carbon fibers. After laser treatment, the CFRP surface showed modifications in surface roughness and wettability, improving adhesive bonding with binders or coatings.

Interfacial Interlocking of Carbon Fiber-Reinforced Polymer Composites: A Short Review

The mechanical properties of the carbon fiber-reinforced polymer composites (CFRPs) are dependent on the interfacial interaction and adhesion between carbon fibers (CFs) and polymer matrices. Therefore, it is crucial to understand how modifying the CFs can influence the properties of these composites. This review outlines recent research progress with a focus on the relationship between the interfacial and mechanical properties of CFRPs and provides a systematic summary of state-of-the-art surface modification techniques. These techniques are divided into four categories: (i) wet, (ii) electrochemical, (iii) dry, and (iv) polymer matrix modifications. Several strategies for enhancing the interfacial interactions and adhesion of CFRPs are discussed, providing insights for future trends.