Carbon Fiber Reinforced Polymer Composites Research Articles

Progress on Microwave Absorption Performance of Carbon Fiber Reinforced Composites

AbstractThe current electromagnetic environment exhibits a growing demand for efficient microwave‐absorbing materials. Developing multifunctional and efficient wave‐absorbing materials poses a challenging research hotspot. Numerous researchers have dedicated their efforts to developing high‐performance broadband wave‐absorbing materials with outstanding mechanical properties. Utilizing carbon fiber‐reinforced polymer composites (CFRP) for electromagnetic wave absorption (EMA) is a rapidly evolving field. Carbon fiber‐based EMA composites are characterized by high dielectric loss, high thermal stability, and low density, enabling them to achieve EMA properties while meeting mechanical property requirements. This review summarizes the principles of electromagnetic EMA, focusing on dielectric and magnetic losses, the preparation methods of CFRP, such as organic polymer synthesis, chemical vapor deposition, and vacuum forming processes, as well as their underlying principles. It also evaluates the research progress on the EMA properties of CFRP composites, particularly highlighting CFRP matrix modification and coating treatment. Finally, the challenges of CFRP EMA and potential future development directions are discussed. This analysis offers multiple recommendations for future researchers.

Comparison of Mechanical Property Simulations with Results of Limited Flexural Tests of Different Multi-Layer Carbon Fiber-Reinforced Polymer Composites.

This article is focused on the experimental study of flexural properties in different multi-layer carbon fiber-reinforced polymer (CFRP) composites and correlations with the results of finite element method (FEM) simulations of mechanical properties. The comparison of the results shows the possibility of reducing the number of experimental specimens for testing. The experimental study of flexural properties for four types of carbon fiber-reinforced polymer matrix composites with twill weaves (2 × 2) was carried out. As input materials, pre-impregnated carbon laminate GG 204 T and GG 630 T (prepreg) and two types of carbon fiber fabrics (GG 285 T and GG 300 T (fabric)) were used. Multi-layer samples were manufactured from two types of prepregs and two types of fabrics, which were hand-impregnated during sample preparation. The layers were stacked using same orientation. All specimens for flexural test were cut with the longer side in the weft direction. Pre-impregnated carbon laminates were further impregnated with resin DT 121H. Carbon fabrics were hand-impregnated with epoxy matrix LG 120 and hardener HG 700. To fulfill the aim of this research, finite element method (FEM)-based simulations of mechanical properties were performed. The FEM simulations and analysis were conducted in Hexagon's MSC Marc Mentat 2022.3 and Digimat 2022.4 software. This paper presents the results of actual experimental bending tests and the results of simulations of bending tests for different composite materials (mentioned previously). We created material models for simulations based on two methods-MF (Mean Field) and FE (Finite Element), and the comparative results show better agreement with the MF model. The composites (GG 285 T and GG 300 T) showed better flexural results than composites made from pre-impregnated carbon laminates (GG 204 T and GG 630 T). The difference in results for the hand-impregnated laminates was about 15% higher than for prepregs, but this is still within an acceptable tolerance as per the reported literature. The highest percentage difference of 14.25% between the simulation and the real experiment was found for the software tool Digimat FE 2022.4-GG 630 T composite. The lowest difference of 0.5% was found for the software tool Digimat MF 2022.4-GG 204 T composite. By comparing the results of the software tools with the results of the experimental measurements, it was found that the Digimat MF 2022.4 tool is closer to the results of the experimental measurements than the Digimat FE 2022.4 tool.

Real-Time Phased Array Ultrasonic Monitoring of Debonding Growth Under Cycling Loading in CFRP

Carbon Fibre Reinforced Polymer (CFRP) composites are widely employed in diverse industries due to their specific stiffness and strength, and corrosion resistance. However, over time, service-induced damage can initiate a failure that can threaten the operation’s safety and reliability, especially in critical industries like aerospace applications. The challenge lies in identifying and monitoring the defects before they escalate into serious issues. Non-Destructive Testing (NDT) methods play a pivotal role in this scenario, aiming to detect and evaluate defects without causing harm to the material. Detecting flaws in composite materials such as CFRP remains a complex task. Traditional NDT methods often struggle to effectively pinpoint and assess defects within these intricate structures. However, recent advancements in ultrasonic testing, especially Phased Array Ultrasonic Testing (PAUT), show promise in examining the internal composition of CFRP composites with higher accuracy and reliability. This study aims to demonstrate the applicability of PAUT for real-time monitoring of debond growth under dynamic loading. The loading was applied to the test specimens up to one million cycles, and 64 elements 2 MHz linear phased array probe was attached to the specimen. The acquired signals were analyzed and could also be recorded for offline processing or archiving. To validate the credibility of the findings, the performance of PAUT was compared to Acoustic Emission (AE), a well-established method for detecting and analysing high-frequency signals emitted by materials undergoing deformation or damage. Encouragingly, both methods exhibited similar trends in capturing the growth of debond. Furthermore, to verify the final defect lengths, post-test ultrasonic C-Scans utilizing the through transmission technique were conducted, complemented by visual inspections. These assessments served to confirm the accuracy and reliability of the results obtained through Phased Array Ultrasonic Testing. Real-time monitoring of composite structures using phased array technology comprises a valuable tool for real- time assessment of debonding in the composite. As industries continue to rely on Carbon Fibre Reinforced Polymer composites for multifaceted applications, the utilization of advanced Non-Destructive Testing methodologies like Phased Array Ultrasonic Testing emerges as a cornerstone in guaranteeing their continued integrity and performance.

Simultaneously improving interfacial adhesion and toughness of carbon fiber reinforced epoxy composites by grafting polyethyleneimine on the carbon fiber surface to construct a rigid‐flexible interface

AbstractChemical grafting is commonly employed to functionalize carbon fiber (CF) surface to enhance the interfacial properties of CF reinforced polymer composites (CFRP) by forming a robust interface. However, an overly rigid interface layer can result in relatively poor interface toughness. To balance interfacial strength and toughness, this paper proposes an effective method to simultaneously strengthen and toughen the interface of CF/epoxy composites by grafting branched polyethyleneimine (PEI) on CF surface using hexachlorophosphazene (HCCP) as active intermediate, which features a rigid ring structure and six active P‐Cl groups. The introduction of PEI provided a large number of amine and imine groups on CF surfaces, which were contributive to improving surface wettability and reactivity of CF, thus resulting in strong chemical bonding between CF and epoxy matrix. Additionally, the long and flexible molecular skeleton of PEI constructed a rigid‐flexible composite interface, which could effectively reduce stress concentration and absorb impact energy. After surface modification with PEI, the interfacial shear strength and fracture toughness of CF/epoxy composite were increased to 89.9 MPa and 200.3 J m−2, by 64.3% and 149.7%, respectively, in compared with desized CF reinforced epoxy composites.Highlights A rigid‐flexible interface was constructed between CF and epoxy resin. The interfacial strength and toughness of CFRP were synergistically improved. IFSS and interfacial toughness increased by 64.3% and 149.7%, respectively.

A coupled FEM-FFT concurrent multiscale method for the deformation simulation of CFRPs laminate

Carbon fiber reinforced polymer composites (CFRPs) laminate is increasingly used in aircraft structures and its assembly deformation has great influence on the aircraft aerodynamic profile and mechanical performance. Due to the inherent multiscale nature of CFRPs, the traditional macroscopic models are unable to incorporate their true microstructural details, resulting in them being unable to provide both the macro and micro deformations simultaneously. To address this issue, this work proposed a coupled FEM-FFT concurrent multiscale method for the deformation simulation of CFRPs laminate, where the mechanical response of each macro point of CFRPs laminate was from the corresponding unidirectional representative volume element (UD RVE). The FEM (Finite Element Method) was used for the analysis at the macroscopic scale, while the FFT (Fast Fourier Transform) based method was employed in the UD RVE to speed up the calculation. The elastoplastic behavior of resin matrix in the UD RVE was modelled with the parabolic yield criterion. The proposed concurrent multiscale method was validated respectively by the tension, compression and shearing experiments of CFRPs laminate. The results show that there is a good agreement both for the full strain field and load–displacement curve, demonstrating the effectiveness of the proposed concurrent multiscale method.

In situ interlaminar shear behavior of carbon fibers reinforced polymer composites exposed to severe thermal aggressions: PPS versus epoxy laminates

This study investigates the influence of a combined thermal heat flux and a flexural loading on the interlaminar shear behavior of quasi-isotropic carbon fibers reinforced PPS and Epoxy laminates. Regardless the intensity of the heat flux (ranging from 20 to 50 kW/m2), the maximum surface temperature is higher than the onset of thermal decomposition [Formula: see text] in C/Epoxy laminates ([Formula: see text]) whereas the thermal decomposition is reached only for 40-50 kW/m2 heat fluxes in C/PPS laminates ([Formula: see text]). A mechanical bench was specifically designed to study the interlaminar shear behavior of polymer-based laminates during the thermal aggression (imposed by a cone calorimeter). In C/PPS laminates, with respect to the reference values (as received state), the flexural modulus and the apparent ILSS (under 50 kW/m2) decreases by about 80%. In C/Epoxy laminates, with respect to the reference values (as received or virgin state), the flexural modulus and the apparent ILSS (under 50 kW/m2) decreases by about 20% and 50%, respectively. In carbon fiber-reinforced polymer materials, the matrix state is crucial for preserving the cohesion of the fibers network and the bonding of the plies together, a role that seems compromised in C/Epoxy and C/PPS laminates under high heat flux conditions, once the pyrolysis of the matrix has severely degraded the interlaminar properties of the material.

Does hygrothermal degradation of Mode I fatigue delamination resistance in carbon fibre reinforced polymer laminates depend on the ageing conditions?

Hygrothermal ageing has detrimental effect of the fatigue delamination growth (FDG) in carbon fibre reinforced polymer laminates, and may increase the crack growth rate by a factor of ∼5. The paper examines, how this degradation for Mode I fatigue delamination is affected by the severity of the ageing conditions. Fatigue delamination tests for R = 0.1 and R = 0.5 are conducted after ageing (1) at 70 °C 85 % relative humidity (RH) and (2) immersion in 70 °C water bath (WB). Paris-type FDG characterisation is derived, in the form, which accounts for the effect of fibre bridging. It is demonstrated that parameters of FDG degradation do not differ for these two types of hygrothermal ageing. The physical reasons for this are examined using dynamic mechanical thermal analysis (DMTA) and fractographic analysis, which revealed similar irreversible degradation of the material near the fibre/matrix interface and in the matrix itself, and the similar damage mechanisms in fatigue delamination. Furthermore, this study can highlight the importance of obeying similitude principles in FDG characterisation, and provide extra information for the ISO standard development for mode I fatigue delamination in unidirectional carbon fibre reinforced polymer composites.

Investigation and selection of optimistic material for two wheeler brake disc: An experimental and finite element approach

The brake disc is a vital component in the braking system of the automobile which helps in reducing the speed or stopping the vehicle whenever required. Whereas, increasing the effectiveness of the braking system is highly challenging for the researchers to ensure safe driving by minimizing the stopping distance of the vehicle during braking. However, the performance of the braking system mainly relies on the brake disc material utilized in the braking system. In the current trend, the usage of alternate materials with a high strength-to-weight ratio is in practice to reduce the fuel consumption of the automobile. Hence, researchers concentrate on Fiber Reinforced Polymer Composites and Metal Matrix Composites to manufacture automotive components. In this research work, the performance of the existing mild steel brake rotor is correlated with brake discs fabricated using different materials such as zirconium-coated steel, AA7075+nSiCp, AA6061+nano Rice Husk Ash particles, Glass Fiber Reinforced Polymer composite, and Carbon Fiber Reinforced Polymer composites. The effectiveness of a two-wheeler braking system is reported concerning the stopping distance, disc weight, friction coefficient, and wear resistance properties of the brake disc material. Moreover, a 3D Finite Element Model (3D FEM) is also developed and the braking mechanism is simulated. The experimental and FEA results reveal that SiC reinforced AA7075 composite shows compromising properties as required such as maximum stress of 558 MPa, excellent wear resistance, good friction coefficient of 0.40, good temperature dissipation property, and effective stopping distance of 81 m.

Adjusting the pH of sizing agents to achieve superior interfacial and mechanical properties of carbon fiber reinforced epoxy composites

Interfacial properties were crucial in determining the mechanical properties of carbon fiber reinforced polymer composites (CFRPs). Applying appropriate sizing agents could effectively improve the interfacial properties of CFRPs. However, the influence of the pH of the sizing agents on the interfacial properties of CFRPs was still unclear. In this work, the above issues were elucidated by adjusting the pH of the diethanolamine-modified E51 (E51@DEA) sizing agent to investigate its impact on the interfacial properties of CFRPs. The molecular weight and emulsion particle diameter of E51@DEA increased with increasing pH of the sizing agent, despite the presence of identical chemical functional groups. E51@DEA-pH 7 showed the best interfacial enhancement. It exhibited ILSS and IFSS values of 102.24 and 113.45 MPa, respectively. This showed an increase of 76 % and 37 % when compared with T700. Additionally, the compressive and tensile strength of T700/E51@DEA-pH 7 also improved by approximately 13 % and 30 %, respectively. The suitable molecular chain length of the sizing agent and the high roughness of the surface of CFs were regarded as the contributing factors. This work further provided an effective and simple strategy for adjusting sizing agents to better improve the interfacial properties of CFRPs.

Mechanical characterization of 3D-Printed carbon fiber-reinforced polymer composites and pure polymers: Tensile and compressive behavior analysis

AbstractFused deposition modeling (FDM) 3D printing is widely utilized for producing thermoplastic components with functional purposes. However, the inherent mechanical limitations of pure thermoplastic materials necessitate enhancements in their mechanical characteristics when employed in certain applications. One strategy for addressing this challenge involves the incorporation of reinforcement materials, such as carbon fiber (CF), within the thermoplastic matrix. This approach leads to the creation of carbon fiber-reinforced polymer composites (CFRPs) suitable for engineering applications. The utilization of CFRPs in 3D printing amalgamates the benefits of additive manufacturing, including customization, cost-effectiveness, reduced waste, swift prototyping, and accelerated production, with the remarkable specific strength of carbon fiber. This study encompasses tensile and compressive testing of distinct material compositions: recycled polylactic acid (rPLA), PLA enriched with 10 wt.% carbon fiber, pristine polyethylene terephthalate glycol (PETG), and PETG bolstered with 10 wt.% carbon fiber. Tensile tests adhere to the ASTM D3039 standard for specimens of rectangular shape, while the ASTM D695 standard governs the compressive testing procedures. Additionally, an inquiry into the influence of the primary 3D printing build orientation parameter on the tensile and compressive strengths of diverse materials was conducted. The outcomes reveal that rPLA exhibits superior mechanical properties in both tensile and compressive tests, irrespective of flat or on-edge build orientations. In the context of tensile strength analysis, it is noteworthy that rPLA demonstrated a superior performance, surpassing CFPLA by 30% in flat orientation and exhibiting a remarkable 39.2% advantage in on-edge orientation. Moreover, PLA reinforced with carbon fiber exhibits superior tensile and compressive properties compared to its PETG counterpart. A comparative analysis between CFPLA and CF-PETG indicates that CF-PLA demonstrates higher tensile strengths, with increases of 26.6 and 27.6% for flat and on-edge orientations, respectively. In the context of compressive strength analysis, rPLA surpassed CFPLA, PETG, and CF-PETG by 23.7, 53, and 67%, respectively. Intriguingly, the findings indicate that the incorporation of 10 wt.% carbon fiber diminishes the tensile and compressive properties in comparison to pure PETG.

Mechanical recycling process: An alternative for a viable disposal of carbon fiber‐reinforced thermoplastic waste

AbstractConcern for the environment has increased the interest of the automotive and aerospace industries in evaluating the feasibility of mechanical recycling of waste carbon‐fiber‐reinforced polymer composites (CFRP) and waste from protective films used during the transport and storage of thermosetting composites, which are removed and discarded during manufacturing. Therefore, this work aimed to develop a recyclable composite from protective film waste by incorporating carbon fiber/poly(aryl ether ketone) (CF/PAEK) composite particles obtained through grinding in knife mills, followed by an analysis of the particle size distribution. Protective film residues (PEres) were cut to facilitate processing. A mixture of low‐density polyethylene and PEres (50/50) was used as the composite matrix, and 5, 10, 15, and 20 wt% CF/PAEK composite particles were added as the reinforcing agents. Then, these recycled composites were prepared by melt mixing using a twin‐screw extruder and injection molding to obtain standardized samples. Mechanical, thermal, electrical, and electromagnetic properties were evaluated. It was possible to observe that the increase in the addition of CF/PAEK composite particles contributed to a 290% increase in elastic modulus values and a 9.1% increase in Shore D hardness, electrical conductivity, and attenuation of the electromagnetic wave. Furthermore, satisfactory adhesion between filler and matrix contributed to a good interface and reinforcement of the final material.Highlights Mechanical recycling by extrusion of waste from the automotive and aerospace sectors Grinding of carbon fiber/poly(aryl ether ketone) composite waste to be used as filler Protective film waste used as matrix Composites developed with waste with good electrical and electromagnetic properties The addition of thermoplastic composite residues does not affect thermal and mechanical properties

Noncontact visualization of multiscale defects in CFRP composites using eddy current testing with T-R probe

Carbon fiber reinforced polymer (CFRP) is widely used in modern industries, and damages may occur from manufacturing to utilization, highlighting the importance of CFRP detection. As being a multi-phase structural material, the CFRP's mesostructural features contained in eddy current signals can obscure macroscopic defect characteristics. Phase rotation is a common method for eddy current signal processing, but the specific criteria for evaluation of processing effect are lacking. This paper proposes three reliable criteria for assessment of the phase rotation processing effects of Transmitter-Receiver (T-R) probe signals, namely: signal overlap ratio (SOR), signal-to-noise ratio (SNR), and image average gradient (IAG). To begin, the SOR serves as a crucial indicator for assessing signal similarity and the degree of overlap, with a low SOR indicating the method's effectiveness in distinguishing defect characteristics. Subsequently, by comparing the SNRs of images, the clarity of defects under different rotation angles can be effectively quantified. Finally, a novel criterion, i.e. the IAG, is introduced. What distinguishes this criterion is its higher degree of automation, facilitating a comprehensive evaluation of processing effects without excessive subjective intervention. After analyzing these criteria, it is clear that the IAG criterion excels in automation and objectivity for evaluating eddy current signal processing effects.

Mechanical Recycling of Carbon Fiber-Reinforced Polymer in a Circular Economy.

This review thoroughly investigates the mechanical recycling of carbon fiber-reinforced polymer composites (CFRPCs), a critical area for sustainable material management. With CFRPC widely used in high-performance areas like aerospace, transportation, and energy, developing effective recycling methods is essential for tackling environmental and economic issues. Mechanical recycling stands out for its low energy consumption and minimal environmental impact. This paper reviews current mechanical recycling techniques, highlighting their benefits in terms of energy efficiency and material recovery, but also points out their challenges, such as the degradation of mechanical properties due to fiber damage and difficulties in achieving strong interfacial adhesion in recycled composites. A novel part of this review is the use of finite element analysis (FEA) to predict the behavior of recycled CFRPCs, showing the potential of recycled fibers to preserve structural integrity and performance. This review also emphasizes the need for more research to develop standardized mechanical recycling protocols for CFRPCs that enhance material properties, optimize recycling processes, and assess environmental impacts thoroughly. By combining experimental and numerical studies, this review identifies knowledge gaps and suggests future research directions. It aims to advance the development of sustainable, efficient, and economically viable CFRPC recycling methods. The insights from this review could significantly benefit the circular economy by reducing waste and enabling the reuse of valuable carbon fibers in new composite materials.

Biotribological properties of 3D printed high-oriented short carbon fiber reinforced polymer composites for artificial joints

Short carbon fiber (SCF) reinforced polymer composites are expected to possess outstanding biotribological and mechanical properties in certain direction, while the non-oriented SCF weakens its reinforcing effect in the matrix. In this work, high-oriented SCF was achieved during nozzle extrusion, and then SCF reinforced polyether-ether-ketone (PEEK) composites were fabricated by fused deposition modeling (FDM). The concrete orientation process of SCF was theoretically simulated, and significant shear stress difference was generated at both ends of SCF. As a result, the SCF was distributed in the matrix in a hierarchical structure, containing surface layer I, II and core layer. Moreover, the SCF was oriented highly along the printing direction and demonstrated a more competitive orientation distribution compared to other studies. The SCF/PEEK composites showed a considerable improvement in wear resistance by 44 % due to self-lubricating and load-bearing capability of SCF. Besides, it demonstrated enhancements in Brinell hardness, compressive and impact strength by 48.52 %, 16.42 % and 53.64 %, respectively. In addition, SCF/PEEK composites also showed good cytocompatibility. The findings gained herein are useful for developing the high-oriented SCF reinforced polymer composites with superior biotribological and mechanical properties for artificial joints.

High stiffness 3D-printed continuous pitch carbon fiber reinforced polymer composites

This study presents a method for 3D printing very high stiffness pitch-based carbon fiber (CF) reinforced polylactic acid (PLA) composites using a modified open-source 3D printer. The fused filament fabrication (FFF) technique was used to fabricate the samples with alternating layers of PLA and PLA-coated pitch CF. The tensile Young’s modulus of the 3D-printed composite samples was measured to characterize the effect of different grades and volume fractions of pitch CF on the behaviour of the printed composites. Three grades of pitch CF which have different Young’s modulus were used with volume fractions ranging from 2.4 to 8.4%. Tensile tests showed that the K1392U CF reinforced composite with a 7.3% volume fraction demonstrated the highest improvement in Young’s modulus of 850% compared to neat 3D-printed PLA. This improvement is notably higher than any previous 3D-printed carbon-based composites at a relatively low volume fraction of CF. Statistical analysis showed increased Young’s modulus in all of 3D-printed composite samples tested. The experimental values were compared to the Halpin-Tsai model and suggest that some degree of fibre breakage occurred during the 3D printing process owing to the relative stiffness of the pitch-based fibers. Future directions and suggestions for process improvements are discussed.

Influence of Milled carbon fiber MCF on mechanical and dynamic mechanical behaviour of carbon fiber fabric reinforced polymer composites

Carbon fiber reinforced polymer (CFRP) composites are widely used in engineering applications. Better understanding about the thermo mechanical properties of CFRP composites are essential for their development. Static and dynamic mechanical properties of CFRP composites can be modified by the filler materials loaded on it. This study investigates the effect of Milled Carbon Fiber (MCF) filler reinforcement on flexural and thermo-mechanical properties of CFRP composites. Fabricated composites are quasi isotropic laminates with unidirectional carbon fibers. The composite laminates were fabricated by hand lay-up technique. XRD analysis illustrates that all the processed specimens are in non-crystalline nature. Three-point bending mode is followed to evaluate the flexural and Dynamic Mechanical Analysis (DMA) tests. MCF fillers are loaded at 6 wt%, 8 wt%, 10 wt%, 12 wt% to evaluate above mentioned properties, i.e, Flexural Strength and Break strain were found from flexural analysis. Storage Modulus (E'), Loss Modulus(E’'), under varying temperature and glass transition temperature (Tg) were determined from DMA. The test results indicated that, 8 wt% of MCF filler loading improves the static and dynamic mechanical properties of CFRP composites when compared to 10 wt% and 12 wt% of MCF content.

Mechanical behavior of nacre-inspired CFRP composites by 3D printing

High-performance carbon fiber reinforced polymer (CFRP) composites are essential for many structural applications, however, properties such as strength and toughness are often considered mutually exclusive in CFRP composites. Inspired by the biological structure of nacre, this study offers a new 3D printing strategy for manufacturing nacre-inspired CFRP composites, aiming to overcome the limitations of traditional materials. The geometric parameters of the nacre-inspired brick composites, including waviness angle and aspect ratio were considered to systematically investigate their respective roles in achieving both strength and toughness and reveal the failure and deformation mechanisms through tensile and three-point bending tests. The results indicated the interlocking and appropriate aspect ratio nacre-inspired CFRP composites provides distinct advantages in enhancing both the overall strength and toughness of the structure under tensile loading. It is further shown that the bending property exhibited a significant sensitivity to the waviness angle. As the waviness angle gradually increases from negative to positive, the bending resistance of the sample decreases. The findings regarding deformation, failure modes, and toughening mechanisms shed light on how geometric parameters affect the mechanical performance of the nacre-inspired CFRP composites.

Quantification of the out-of-plane loading fatigue response of bistable CFRP laminates using a machine learning approach

This study proposes data-driven machine learning models to predict the nonlinear load-displacement response in constant amplitude high-cycle fatigue loading of unsymmetric, cross-ply bistable carbon fiber reinforced polymer composites. Four selected ML models are trained on experimental fatigue data with eleven unique frequency, temperature, and boundary conditions combinations. Stiffness and damage index values, which serve as additional evaluation metrics, are calculated using the predicted load data. The models capture the nonlinear load response with acceptable error for in-domain experimental conditions. Model expandability demonstrates the sensitivity of machine learning models to training features but suggests an economical alternative to extensive fatigue experiments.

Experimental investigation on tensile behavior of CFRP bolted joints subjected to hydrothermal aging

Abstract With the help of bolted joints to assemble a complex structure, carbon fiber reinforced polymer composite (CFRP) is widely used in various fields. However, stress concentration around holes at the bolted joints leads to a decrease in bearing capacity. Composites often result in mechanical degradation subjected to a complex hydrothermal environment. Therefore, to study the tensile behavior of CFRP bolted joints subjected to hydrothermal aging, the tensile tests are conducted carefully. The influence of aging time and temperature on tensile strength is investigated based on the response history, strain contour, and failure morphology. The failure mechanism is revealed via digital image correlation technology. Finally, the experimental results demonstrate that the bearing capacity of the structure in hydrothermal aging decreases significantly. Compared with the unaged specimens, the peak force of the specimens aged for 6 weeks at 25°C and 65°C is reduced by 22.79% and 35.63%, respectively. Under both the unaged and aged, the same bearing failure is found in the tensile tests of CFRP single-bolt single-lap joints.

A Multi-Scale Analysis of Unidirectional Carbon Fiber-Reinforced Polymer Composite

In this paper, a multi-scale computational analysis is conducted based on representative volume element (RVE) modeling and molecular dynamics (MD) simulation of a carbon fiber-reinforced polymer composite micropillar. The fiber distribution in the micropillar was obtained from a specimen manufactured for real micropillar mechanical testing. Based on the failure modes directly observed from the micropillar testing, the RVE model aims to capture the major failure mechanism, which is the fiber/matrix interface failure of the composite. In the finite element model, the properties of each individual phase, namely, the fiber and the matrix are first identified. Then, cohesive elements are incorporated into the interphase region between the fiber and matrix to capture the interphase debonding. Finally, the global stress–strain relation of the composites is obtained and compared to experimental results. A good correlation was found. Due to convergence difficulties associated with stiffness degradation, the simulation was performed in the commercial software ABAQUS/Explicit. A Molecular dynamics simulation is performed to investigate the stress–strain relation and shear strength of carbon fiber-reinforced polymer composites at nanoscale. The compressive strength and stiffness obtained from MD simulation were lower than that observed from experiments. Interface debonding is a critical failure mode, of which the failure strength is determined from fiber pull-out simulation. The results can be used in RVE simulation to deduce the interphase properties. The modeling method allows the detailed failure mechanisms of the composite microstructure to be captured and a correlation between the micro-properties and macro-properties of the material to be established.