Carbon Fiber Reinforced Plastic Research Articles

Functional-gradient carbon fiber-reinforced plastic based on epoxy matrix modified with thermoplastic elastoplast

Modification of epoxy binders with butadiene-styrene thermoplastic elastomers was used to obtain functional-gradient carbon plastics with increased impact resistance. Samples were made and comparative tests of carbon fiber-reinforced plastics for resistance to impact loads and compression after impact were carried out. It is shown that smooth change of modifier concentration at transition from the external surface of the part to the internal one allows to increase effectively the impact strength of carbon fiber-reinforced plastic while maintaining the rigidity of the composite material.

Transferability of the Structure–Property Relationships from Laser-Pretreated Metal–Polymer Joints to Aluminum–CFRP Hybrid Joints

The transferability of structure–property relationships for laser-pretreated metal adhesive joints to laser-pretreated metal–carbon-fiber-reinforced plastic (CFRP) bonds was investigated. Single-lap shear tests were performed on hybrid AW 6082-T6–CFRP specimens pretreated with the same pulsed laser surface parameter sets on the metal surface as previously tested, AW 6082-T6–E320 metal adhesive joints. The fracture surfaces were characterized to determine the type of failure and elucidate differences and commonalities in the link between surface structures and single-lap shear strengths. Digital image analyses of the hybrid specimens’ fractured surfaces were used to quantify remaining CFRP fragments on the metallic joint side. The results indicate that high surface enlargements and the presence of undercut structures lead to single-lap shear strengths exceeding 40 MPa and 35 MPa for unaged and aged hybrid specimens, respectively. Whereas for the metal–polymer joints, the trend from high strength to weakly bonded specimens is largely continuous with the degree of surface structuring, hybrid metal–CFRP joints exhibit a drastic drop in joint performance after aging if the laser-generated surface structures are less pronounced with low surface enlargements and crater depths. Surface features and hydrothermal aging determine whether the specimens fail cohesively or adhesively.

Damage and failure mechanisms of CFRP due to manufacturing induced wrinkling defects

Out-of-plane wrinkling is a typical defect in the manufacturing process of carbon fiber reinforced plastics (CFRP). The cross-ply composite laminates containing various wrinkles were designed and prepared based on a hybrid generation method of gaps and transverse strips. An analytical model based on the sine function was proposed to characterize the shape of wrinkles, and the severity of the defect was characterized by the wrinkle angle. With the aim to investigate the compression and out-of-plane shear failure performance of CFRP with wrinkles, experimental and numerical studies were conducted. Results show that the existence of wrinkled zone can significantly reduce the compressive strength of laminates and exacerbate delamination during compression failure, a maximum of 26.9% and 2.8% drop in the compressive and interlaminar shear strength was reported in the most severe experimental conditions. Meanwhile, it is indicated that wrinkles have little effect on interlaminar shear strength, but it can change the location and severity of the delamination failure. In addition, the failure mechanism of several models with different levels of wrinkling defects was studied through numerical analysis techniques. It is confirmed that the numerical model can effectively predict the failure intensity and failure modes. These findings are of great significance for the accurate evaluation of the mechanical properties of composites containing wrinkling defects.

Interface engineering of carbon fiber composites using CNT: A review

AbstractThis paper aims to explore the potential of carbon nanotubes (CNTs) in enhancing the structural capability and multifunctionality of carbon fiber composites in aerospace applications, primarily by focusing on interfacial applications. The conventional method of dispersing CNTs in a matrix is not fully efficient in exploiting the mechanical and multifunctional performance of CNTs. Hence, the use of CNTs at the interface or as a coating on the surface of carbon fibers has been suggested as a means of achieving multifunctionality, in addition to enhanced mechanical performance. The paper presents an overview of the various processes for growing CNTs on carbon fiber surfaces and examines the effects of CNT geometry and growth parameters on the properties of grafted fibers and their composites. Furthermore, it discusses the potential improvements in thermal and electrical conductivity achievable by incorporating CNTs at the interface, as well as the benefits of using CNTs as a sizing layer for carbon fibers, including enhanced fracture toughness and resistance to delamination.Highlights Comprehensive study of interface engineering in carbon fibers and Carbon Fibre Reinforced Plastic (CFRPs) using carbon nanotubes (CNTs). Improved transverse mechanical properties and overall thermal and electrical properties. Multifunctional applications possible with the use of CNT. Both experimental and numerical studies reviewed.

Temperature-dependent cutting physics in orthogonal cutting of carbon fibre reinforced thermoplastic (CFRTP) composite

The global commitment towards reducing carbon emissions drives the implementation of sustainable carbon-fibre-reinforced-thermoplastic composites (CFRTPs). However, the machining of CFRTPs presents challenges due to the material’s ductile–brittle composition and sensitivity to machining-induced high temperatures. For the first time, we conducted temperature-controlled orthogonal cutting of CFRTP (using CF/PEKK as a demonstrator) to unveil its temperature-dependent cutting physics. Three representative cutting temperatures, 23 ℃ (ambient temperature),100 ℃ (<PEKK’s glass transition temperature (Tg)) and 200 ℃ (>Tg) and four typical fibre cutting orientations (0°, 45°, 90°, and 135°) have been investigated. The evolution of chip microstructural morphology and surface/subsurface damage have been analysed by advanced microscopy to reveal temperature-dependent material removal mechanisms. The experimental results were elucidated through a novel microscale finite-element-analysis (FEA) model considering thermal softening of the matrix and interface. Results show the transition of the cutting physics with increasing temperature is associated to the degradation of the thermoplastic matrix stiffness/ultimate strength and interface bonding strength and fracture toughness, especially when > Tg.

Estimation of axial compressive strength of unidirectional carbon fiber-reinforced plastic considering the variability of fiber misalignment

The analytical method to calculate the axial compressive stress–strain relation of a unidirectional carbon fiber-reinforced plastic (UD CFRP) was presented considering the variability of the fiber misalignment angle. Because the compressive load-bearing capability of fibers surrounded by a matrix was different depending on the fiber misalignment angle, fibers were grouped based on the misalignment angle. The contribution to the load bearing was calculated and summed based on the area ratio of the fiber groups. All fibers supported a compressive load in the initial loading. However, with increased loading, the load-bearing capabilities of the different fiber groups decreased more dramatically with greater misalignment angles. The fibers with a misalignment angle of 0.5° showed a large load drop after their maximum loading, which triggered the ultimate failure. The variability of the fiber misalignment angle was indispensable to determining the axial compressive strength under the assumption of zero mean fiber misalignment angle.

A Review of the Network Arch Bridge

The network arch bridge (NAB) is a new structural form of arch bridge that was devised 60 years ago by the Norwegian engineer Per Tveit, who is now prof. dr. docent emeritus at the University of Agder, Norway. The network arch is a tied-arch (also known as a bowstring-arch) bridge that combines the benefits of tied-arch bridges and trusses in a single system. While in a classical tied arch, the hangers are vertical, in a network arch, the suspension of the deck to the arch is ensured through a network of inclined hangers that intersect each other at least twice. Thus, the core of the NAB is the hanger arrangement that minimizes the bending moment in the arch to very small values, leading to compression in the arch. Compression with only small bending leads to very slender cross-sections for the elements of the bridge, and deep reductions in terms of materials used and economic and environmental costs. This paper reviews the research into the structural form proposed by Per Tveit and extended by researchers and engineers worldwide. The research methodology included bibliometric literature research, obtained by interrogating the ISI Web of Science (WoS) database and the cited references from the articles on WoS. While the first structural form of a network arch is still in use today and it has proven to be a good idea for spans around 100–120 m, engineers worldwide devised new bridge cross-sections. A brief view of the types of bridge cross-section in use today is given, with details about the bridges chosen as representative. Using analysis of Prof. Tveit’s map, Structurae database and literature review, a database of the network arches around the world was created, emphasizing the development of network arches from the perspectives of continental distribution, opening year, number of structures in different structural forms, and bridge purposes. The structural form was assessed from the perspective of materials used for the arch and the tie, span, purpose and number of lanes, the presence/absence of upper wind-bracings and arch disposition in the vertical plane. In the last part of this review, the newest research into the development of the network arch is discussed. In the past 15 years we have seen an acceleration in network arch development from multiple perspectives: new materials used, such as glulam for the arch or carbon fiber-reinforced plastic for the hangers; span lengths of 250 m and 380 m for large bridge widths; architectural constraints that lead to the outward inclination of the arch, that is pleasing to the eye, but difficult to address from an engineering perspective; the most slender arch bridge in the world, with very slender cross-sections for the arch and the tie.

Numerical modeling of the carbonization of polyimide fibers in a cylindrical furnace

Carbon fiber is widely used as a reinforcing material in polymer composite such as carbon fiber reinforced plastic (CFRP) due to its high specific strength, elastic modulus and lightweight. The majority of the industrial carbon fiber is produced from synthetic precursor polymer such as polyacrylonitrile (PAN), pitch and polyimide. While relatively many studies have been published for the carbonization of PAN, little studies have been found on the heat transfer during carbonization of polyimide precursors. In this study, we numerically analyzed the carbonization process of a polyimide (PI) precursor for carbon fibers in a lab-scale cylindrical furnace. Gas flow, temperature distribution and concentration profiles including the off-gases from the precursor fibers were included in the analyses. First, we established mathematical models for the off-gases behavior from the precursor fibers. The models were incorporated into computational fluid dynamics in order to find behavior of the mixture gas of the working nitrogen gas and the off-gases. And then, numerical simulation results using the model were obtained and compared to the experimental results to verify the model. Finally, we evaluated the application scalability of the established numerical model through changes in wall temperature and precursor fiber moving speed. The results showed that the model can be used to study the PI carbonization process in the industrial size carbonization furnace.

Superaligned carbon nanotube film/quartz fiber composites towards advanced lightweight lightning strike protection

Due to poor electrical conductivity, carbon fiber-reinforced plastic (CFRP) is easily damaged by lightning strikes. In this paper, highly conductive superaligned carbon nanotube films (SA-CNTFs) and new isolation layers (quartz fibers) were combined to fabricate advanced lightweight lightning strike protection (LSP) composites. We verified that the isolation layer indeed has an LSP effect and demonstrated for the first time that quartz fibers are a better alternative isolation layer material candidate than conventional glass fibers due to their high thermal resistance. The “complementary effect” between the conductive layer and the isolation layer is revealed. The preliminarily optimized laminate composites made of SA-CNTF/quartz fiber can sustain 100 kA simulated lightning strike. Compared with typical CNT-based LSP laminate samples made of buckypaper/Boron Nitride/epoxy layer or SA-CNTF/glass fiber, the weight can be reduced by at least ∼30% and ∼38%, respectively.

Reinforcement of columns using different composite materials

The adoption in construction of composite materials made by combining two or more materials to produce a material with improved properties over the separate components has been steadily increasing over the past decades. In the past few years there have been advances in composite manufacturing technology, increased demand for sustainable and eco-friendly building materials, and the need for materials that are lightweight and easy for transportation. For these reason, architects and civil engineers incorporate composites into structural elements to achieve these desired goals and optimize the cost of construction. One of the most common composite materials that was introduced to the industry is fiber reinforced polymer (FRP), produced by combining fibers (carbon, glass, or aramid) with a polymer matrix (epoxy or polyester). FRP materials are lightweight, durable and corrosion resistant, which makes them ideal for use in a wide range of construction applications. This study aims to propose a comparison between four different methods as a viable solution to strengthen and reinforce column structures. The structural behavior of three different composite materials was investigated. One traditional concrete-steel column was tested in the experiment for comparison. The other three columns were reinforced using carbon fiber reinforced plastic (CFRP), glass fiber reinforced plastic (GFRP) and stainless steel respectively. The obtained experimental results were analyzed, and comparison of three different systems of reinforcement for strengthening columns with composite materials was performed.

Multi-Objective Optimization of Process Parameters in Longitudinal-Torsional Ultrasonic Vibration Face Grinding CFRP

Due to its superior characteristics, carbon fiber reinforced plastics (CFRP) have been widely used in aerospace and other fields. However, their effective and economical processing remains a challenge. The purpose of this paper was to experimentally investigate the influence of several machining parameters, namely spindle speed, cutting depth, feed rate, and grit size on different machining performances, i.e., grinding force, and surface roughness through longitudinal-torsional (L&amp;T) ultrasonic vibration grinding CFRP. The response surface methodology with a Box—Behnken design was used to create the experiments. The fitting mathematical models of grinding force and surface roughness were established separately to explore the interaction between the machining parameters and the impact on machining results. With the purpose of improving the surface quality and reducing the grinding force, the NSGA-II was used for multi-objective optimization to obtain the Pareto optimal solution. Compared with the initial experimental parameters, the optimized results can significantly improve the surface roughness and reduce the cutting force.

Fatigue behavior of single-lap adhesive joints with similar and dissimilar adherends under cyclic loading: A combined experimental and simulation study

This study aims to research the fatigue behavior and reveal the failure mechanism of the adhesive joints with similar and dissimilar adherends, which made of the aluminum alloys (Al) and carbon fiber reinforced plastics (CFRP). Firstly, the electronic universal testing machine and fatigue testing machine were used to obtained the failure strength and fatigue life of the joints. Secondly, the joints were modeled by cyclic cohesive zone model (CCZM) to obtained the damage evolution process of the joint. Finally, the fatigue failure mechanism of the joint was analyzed based on the experimental failure mode and microscopic morphology. The results showed that in the fatigue process, the damage in CFRP-Al joints extends from the CFRP end to the Al end and eventually fractures near the Al end, while the damage in CFRP-CFRP and Al-Al joints are symmetrically distributed along the central axis of the lap area. In addition, the failure characteristics of the joints are mainly affected by the peel stress, and compared to differences in substrate stiffness (the cause of peel stress in joints with dissimilar adherends), the differences in the strength of the substrate-adhesive connection (the cause of peel stress in joints with similar adherends) plays a greater role in the generation of peel stress.

Optimization of friction lap joining parameters and exploration connection mechanism of CFRPA6/6061-T6 aluminum alloy hybrid structures

Carbon-fiber-reinforced thermoplastics (CFRTP) and lightweight-metal hybrid structures have been applied in the automotive and aerospace industries. Nonetheless, due to the enormous differences in physical and chemical properties of materials, the stability of the CFRTP and the lightweight-metal hybrid joint interface is challenging to ensure. In current work, the influence of welding parameters (rotational speed, welding speed, and plunge depth) on the stability of friction lap joining (FLJ) hybrid joints between carbon-fiber reinforced polyamide6 (CFRPA6) and 6061-T6 aluminum alloy (6061) was studied. The analysis of variance (ANOVA) showed that the rotational speed was the greatest factor affecting joint strength. By optimizing the welding parameters, a high-strength hybrid joint with a maximum tensile force of 2.5 kN was obtained. To further understand the mechanism of interface connection, experimental methods and density functional theory (DFT) calculations were systemically performed. The results show that the nitrogen and oxygen atoms in CFRPA6 will bond with aluminum on the 6061 surfaces to produce the interfacial Al-N and Al-O covalencies due to the p-orbital hybridization between bonding atoms.

Study on pure-torsional size effect of CFRP-strengthened RC beams using a 3D meso-scale numerical model

In this paper, a 3D meso-scale numerical model for pure-torsional failure analysis of carbon fiber reinforced plastic (CFRP)-strengthened reinforced concrete (RC) beams is established. Three main aspects regarding the establishment of the numerical model are thoroughly considered, including the heterogeneity of concrete, the bond-slip relationship between steel bars and concrete, and the nonlinear interaction between CFRP and concrete. Effects of CFRP fiber ratio and span-height ratio on pure-torsional performances and size effect behaviors of CFRP-strengthened RC beams are analyzed. With the increase of CFRP fiber ratio, the cracks spacing decreases, the number of cracks increases, and the strain of CFRP decreases. With the increase of the span-height ratio, the inclination angle of the oblique crack decreases, and the strain of CFRP increases. It is found that CFRP-strengthened RC beams have an obvious torsional size effect. Furthermore, CFRP fiber ratio and span-height ratio not only have a coupling enhancement effect on the nominal torsional strength, but also have a coupling weakening effect on the size effect behavior. Based on the simulation results, a CFRP-related Torsional size effect law (SEL), which can quantitatively describe the influences of CFRP fiber ratio and span-height ratio on the size effect of nominal torsional strength of CFRP-strengthened RC beams, is established.

Effects of fiber orientations on fracture mechanisms in rotary ultrasonic drilling of carbon fiber reinforced plastic laminates

The fracture mechanisms of the carbon fibers seriously depend on fiber orientations which significantly influence the surface quality of carbon fiber reinforced plastics (CFRPs). Rotary ultrasonic drilling (RUD), possessing some excellent characteristics including the superior sidewall quality and high cylindricity error, offers a possibility for the efficient drilling of the CFRP components. In contrast, the effects of fiber orientations on fiber fracture mechanisms are still not fully recognized in RUD of CFRP composites. Incorporated with kinematic characteristics of the abrasive, a novel theoretical model was developed to quantitatively describe the effective orientation of the fiber. Afterwards, the drilling experiments with and without ultrasonic were conducted under the same parameters. The surface topographies of the hole sidewalls at various orientations were comparatively characterized to explore the fiber fracture mechanisms. Subsequently, the influences of these mechanisms and the drilling parameters the surface qualities were also investigated. Moreover, the bending failure mechanisms of the carbon fibers were explored through theoretical analysis. As a result, another fiber fracture mechanism, bending failure, was identified with the smooth fracture and micro-fragmentation topographies at upwind and leeward parts of the fiber cross-section, respectively. Ultrasonic superimposition by means of the immense inertia force of the abrasive promoted the micro-fracture of the carbon fiber. The weaker sustainment from the back-up materials brought about the serious bending failure of fiber oriented at 135°, while the axial load component aggravated the tensile fracture of the carbon fiber with the effective orientation of 45°. The critical moment of the fiber bending failure was also established, by incorporating the beam theory and linear elastic fracture mechanics. The fundamental investigation provided a favorable foundation for further optimizing the parameters to improve the drilling quality and efficiency in formal RUD of CFRP composites.

Finite Element Simulation and Experimental Assessment of Laser Cutting Unidirectional CFRP at Cutting Angles of 45° and 90°.

Laser cutting of carbon fibre-reinforced plastics (CFRP) is a promising alternative to traditional manufacturing methods due to its non-contact nature and high automation potential. To establish the process for an industrial application, it is necessary to predict the temperature fields arising as a result of the laser energy input. Elevated temperatures during the cutting process can lead to damage in the composite's matrix material, resulting in local changes in the structural properties and reduced material strength. To address this, a three-dimensional finite element model is developed to predict the temporal and spatial temperature evolution during laser cutting. Experimental values are compared with simulated temperatures, and the cutting kerf geometry is examined. Experiments are conducted at 45° and 90° cutting angles relative to the main fibre orientation using a 1.1 mm thick epoxy-based laminate. The simulation accurately captures the overall temperature field expansion caused by multiple laser beam passes over the workpiece. The influence of fibre orientation is evident, with deviations in specific temperature data indicating differences between the estimated and real material properties. The model tends to overestimate the ablation rate in the kerf geometry, attributed to mesh resolution limitations. Within the parameters investigated, hardly any expansion of a heat affected zone (HAZ) is visible, which is confirmed by the simulation results.

STUDY OF PREPREGS LIFETIME BASED ON EPOXY RESIN WITH AROMATIC AMINE HARDENER

Today, there is a steady trend in the use of carbon fiber-reinforced plastics in the aerospace and defense industries, mainly based on using pre-impregnated semi-finished products - prepregs. Producing carbon fiber parts from prepregs often requires a long manufacturing time, during which the prepreg must maintain its performance properties. Therefore, one of the main characteristics of prepreg is its viability. This work developed a suitable resin composition with optimized properties and a methodology for studying the viability of prepreg samples, based on determining the stickiness and degree of curing of the prepreg depending on storage time. The influence of prepreg storage time on the strength characteristics of cured laminates was studied. Prepreg samples with long-term viability of up to 60 days were obtained. The experimental data obtained are of practical significance in the industrial production of carbon fiber products, as they establish a connection between the performance properties of the prepreg and storage time.

Precision and Dimensional Stability of Bonded Joints of Carbon-Fibre-Reinforced Polymers Parts

This article aims to investigate the accuracy and dimensional stability of bonded metal and CFRP (Carbon Fibre Reinforced Plastic) adherends. The motivation behind this study was to assess the suitability of CFRP for optical devices through the evaluation of precision bonding technology. A binocular was selected as a reference optical device. A technological sample was designed, with required total runout of key dimensions 0.05 mm. The sample underwent testing according to ISO 9022-1. The total runout was evaluated after production and environmental tests. Eight out of 15 samples were turned after gluing due to insufficient accuracy. None of the turned samples exceeded the total runout deviation of 0.01 mm, and the average value of the maximal deviation was 0.0041 mm. The noncalibrated samples performed significantly worse with the average value of the maximal deviation of 0.0164 mm. The measurements during the climatic tests showed that the largest deviation (on average 77.6% of the maximum achieved deviation) occurs at the first temperature loading. Subsequent temperature cycles caused lower deviations. The results highlight the significance of addressing deformations resulting from adhesive volume shrinkage-induced stress as a crucial factor in precision bonding technology.

On adhesively bonded joints with a mixed failure mode—An experimental and numerical study

Cohesive zone model (CZM) has been extensively used to study interfacial failure behaviors such as fracture of adhesively bonded joints (ABJs). Accurate and efficient identification of traction–separation law (TSL) in CZM signifies an important issue for design and analysis of adhesive structures. In this study, a modified Arcan fixture was developed and employed to investigate the mixed mode failure behaviors of ABJs for carbon fiber reinforced plastic (CFRP) substrates under a tensile-shear coupling load, in which the double cantilever beam (DCB) test was carried out to characterize fracture toughness for benchmark data. With the help of digital image correlation (DIC) technique, the interfacial displacement field was obtained. The virtual crack closure technique (VCCT) was adopted to decouple the mode mixture at different tension-shear angles of the Arcan specimens. Based on the traction–separation law for each mixed ratio of failure mode, a refined CZM was established. In this study, the Arcan and DCB specimens bonded with a flexible adhesive of 3M DP190 were prepared and tested. The experiments were carried out for the ABJs with two adhesive layer thicknesses of 0.3 mm and 1 mm, respectively, to investigate the influence of bonding thickness. Based on the extracted CZM parameters, a finite element (FE) analysis model was developed and validated with the experimental results. Unlike the traditional predetermined damage evolution law, a new CZM was established without a priori cohesive damage evolution; and the effectiveness of the proposed model for the TSL extraction was verified. By using this method, the mechanical response of the bonding interface under complex stress state was well predicted and the FE modeling of ABJ’s fracture was accurately achieved. The study is anticipated to gain new understanding and fundamental data on mixed failure mode, thereby enabling better design of ABJs for engineering applications.

Influences of Main Machining Process Parameters and Tool Wear on The Machining Damage Generated During Edge Milling CFRP Composites

Machining Carbon Fibre Reinforced Plastics (CFRPs) composites are typically accompanied by the appearance of machining damage which strongly impacts the structural integrity of composite parts during their service lives. Studying the correlation between machining damage and its affected factors has still been an open issue. Hence, it is necessary to do more research. This study focuses on investigating the influences of main process parameters and tool wear phenomenon in terms of machining length on the machining quality which was characterized by the surface roughness criterion, the ten-point max, Rz. A full factorial design of experiments was conducted including three levels of feed speed and two degrees of spindle speed. The results revealed that machining damage was mainly influenced by process parameters at a small machining distance, whereas at a longer machining distance, tool wear had a dominant effect on the machining quality than machining parameters. These findings could provide guidelines for selecting suitable machining parameters to enhance the machining quality of CFRP.