Search Results (56)

Solvent-free, continuous manufacture of carbon-fiber/poly(ether ether ketone) (CF/PEEK) towpregs via fluidized-bed powder coating requires stable powder fluidization together with controllable coating residence time. A laboratory-scale continuous coating line comprising a creel, guiding/tension rollers, a vibrated fluidized-bed coater, as well as a take-up unit was designed and commissioned. Subsequently, a two-stage optimization and modeling framework was developed. First, PEEK powder fluidization was optimized using a Taguchi L9 design, varying air pressure ($P$), powder weight ($W$), and vibration frequency ($f$); bed expansion ratio ($\epsilon$) and average surface bubble diameter ${(D}_b)$ were measured and ANOVA identified air pressure as the primary contributor to $\epsilon$ (83.4%), establishing a stable operating window. Second, within this window, coating performance was assessed by varying line speed ($V_{line}$) and coating-roller position ($H_r$) in 12 runs and combining them into a geometry-based residence time ($R_t$) for simplified control. Coating quality was quantified based on fiber volume fraction ($Vf$) and composite tensile strength (${\mathsf{\sigma }}_c$) after consolidation. The best condition in the tested range was $Hr=0.5 \mathrm{c}\mathrm{m}$ and $V_{line}=1.5 \mathrm{m}/\mathrm{m}\mathrm{i}\mathrm{n}$ ($R_t=0.54 \mathrm{s}$), achieving 61.5% $Vf$ and 1800.5 MPa tensile strength. The resulting mathematical models predicted $Vf$ and ${\mathsf{\sigma }}_c$ with good accuracy ($R^2\ge 0.92$), supporting parameter selection and process optimization for continuous CF/PEEK towpreg production. Full article

Carbon fiber-reinforced polyetheretherketone (CF/PEEK) thermoplastic composites are increasingly applied in aerospace structures due to their outstanding mechanical and thermal properties. However, their strengthening mechanism and damage evolution under repeated low-velocity impacts remains inadequately explored. This study systematically investigates the mechanical response and failure mechanisms of CF/PEEK laminates subjected to sequential single and second impacts at energy levels of 10 J, 20 J, and 30 J. Through comprehensive analysis of impact parameters (peak load, energy absorption, residual displacement), optical microscopy and ultrasonic C-scan, this study reveals that the load-bearing increase under repeated low-velocity impacts results from the combined effects of multiple mechanisms, including matrix plastic deformation, local compaction, matrix damage, and interlaminar failure. Under initial impacts, laminates exhibit high load-bearing capacity and energy dissipation, which are dominated by plastic deformation and matrix failure at 10 J and 20 J, whereas the 30 J impact causes pronounced fiber failure. An anomalous increase in peak load is observed during secondary impacts, which is attributed to matrix compaction-induced strengthening resulting from the initial impact. Optical microscopy and C-scan quantification demonstrate that, while the initial impact induces compaction-related strengthening, it also causes internal damage, which leads to aggravated damage evolution during the subsequent impact. The findings provide fundamental insights into damage accumulation in thermoplastic composites and directly inform impact-resistant design strategies. Full article

Carbon fiber-reinforced thermoplastic composites (CFRTP) are widely used in automotive, aerospace, and other industries due to their lightweight, high specific strength, recyclability, and superior thermal properties. However, their non-homogeneity and anisotropy present challenging machining characteristics, often leading to damage that deteriorates component performance. It is imperative to conduct numerical simulation and experimental studies on CFRTP to systematically analyze the relationship between cutting mechanisms and the surface integrity of CFRTP. This study aimed to establish an innovative three-dimensional micro-scale cutting numerical model that integrates the differentiated constitutive behaviors and damage criteria of carbon fibers, matrices, and fiber–matrix interfaces—enabling precise characterization of micro-scale damage evolution during cutting. By combining simulation with experimental verification, it unveils the material removal mechanisms and processing damage causes of CF/PEEK, and further pioneers the quantification of the gradient correlation between fiber orientations (0°, 45°, 90°, and 135°) and fracture modes, cutting forces, and surface integrity, thereby addressing the gap of micro-mechanism and quantitative analysis in CFRTP machining. The micro-scale damage mechanisms revealed by the model directly reflect the intrinsic response of individual fibers in the tow, and the collective effect of these micro-behaviors determines the macro-scale machining performance observed in the experiments. A right-angle cutting experiment was conducted to validate the accuracy of the micro-scale numerical model. The mechanisms of fiber fracture, damage patterns, and chip morphology were systematically compared. The experimental results demonstrate good agreement with the outcomes of the numerical simulations. This study aims to bridge the gap between theoretical understanding and practical application of the cutting mechanisms in CFRTP, providing valuable insights for advancements in manufacturing processes. Full article

On-orbit cutting is a critical process for the on-orbit manufacturing of carbon fiber reinforced polyetheretherketone composites (CF/PEEK) truss structures, with pulsed laser cutting serving as one of the feasible methods. Achieving high-quality cutting of CF/PEEK remains a major challenge for on-orbit manufacturing. Therefore, the cutting process of CF/PEEK prepreg tape was studied by an ultraviolet (UV) nanosecond laser. A three-factor, five-level orthogonal experiment was carried out to analyze the influence of laser repetition rate (LRR), laser cutting speed (LCS), and laser scanning times (LCTs) on cutting quality. The ablation mechanism dominated by the photothermal effect between the UV nanosecond laser and CF/PEEK was analyzed, and the by-products in the cutting process were explored. Finally, the optimal cutting quality (the width of slit (W_s) = 41.69 ± 3.54 μm, the heat-affected zone (HAZ) = 87.27 ± 7.30 μm) was obtained under the process conditions of LRR 50 kHz-LCS 50 mm/s-LCT 16 times. The findings show that the W_S and HAZ increase with the increase in LRR and LCT and the decrease in LCS, and the carbon fiber decomposes and escapes due to the photothermal effect. Full article

Polyetheretherketone (PEEK) is a high-performance engineering plastic widely used in aerospace, automotive, and other industries due to its heat resistance and mechanical strength. However, its high friction coefficient and low thermal conductivity limit its use in heavy-load environments. Existing studies have extensively explored the individual effects of thermal processing or irradiation on PEEK. However, the synergistic mechanism between the initial microstructure formed by mold temperature and subsequent irradiation modification remains unclear. This paper investigates the coupled effects of injection molding temperature and electron beam irradiation on the tribology of carbon fiber-reinforced PEEK composites, with the aim of identifying process conditions that improve friction and wear performance under high load by controlling the crystal morphology and cross-linking network. Carbon fiber (CF) particles were mixed with PEEK particles at a 1:2 mass ratio, and specimens were prepared at injection molding temperatures of 150 °C, 175 °C, and 200 °C. Some specimens were irradiated with an electron beam dose of 200 kGy. The friction coefficient, wear rate, surface shape, and crystallinity of the material were obtained using friction and wear tests, white-light topography, SEM, and XRD. The results show that the injection molding temperature of the material influences the friction performance. Optimal performance is obtained at 175 °C with a friction coefficient of 0.12 and wear rate of 9.722 × 10⁻⁶ mm³/(N·m). After irradiation modification, the friction coefficient decreases to 0.10. This improvement is due to the moderate melt fluidity, adequate fiber infiltration, and dense crystallization at this temperature. In addition, cross-linking of chains occurs, and surface transfer films are created at this temperature. However, irradiation leads to a slight increase in wear rate to 1.013 × 10⁻⁵ mm³/(N·m), suggesting that chain segment fracture and embrittlement effects are enhanced at this dose. At 150 °C, there is weak interfacial bonding and microcrack development. At 200 °C, excessive thermal motion reduces crystallinity and adds residual stress, increasing wear sensitivity. Overall, while irradiation reduces the friction coefficient, the wear rate is affected by the initial microstructure at molding. At non-optimal temperatures, embrittlement tends to dominate the wear mode. This study uncovers the synergistic and competitive dynamics between the injection molding process and irradiation modification, offering an operational framework and a mechanistic foundation for applying CF/PEEK under heavy-load conditions. The present approach can be extended in future work to other reinforcement systems or variable-dose irradiation schemes to further optimize overall tribological performance. Full article

Poly(ether ether ketone)/carbon-fiber (PEEK/CF) composites possess excellent mechanical and thermal stability but exhibit inadequate friction and wear resistance for demanding tribological applications. In this study, femtosecond laser texturing was used to generate sinusoidal–circular hybrid microtextures on PEEK/CF surfaces, and the effects of laser power and geometric parameters were systematically evaluated through a Taguchi L9 design. The optimal laser power of 0.85 W produced the highest machining quality factor (MQF = 0.968). The textures caused a hydrophilic-to-hydrophobic transition, increasing the static contact angle from 43° to 96.2°. Under boundary lubrication, all textured specimens exhibited reduced steady-state friction compared with the untreated surface. Among them, specimen L7—corresponding to the largest amplitude (A) and wavelength (B) levels in the orthogonal design—achieved the lowest average coefficient of friction (≈0.12) and generated the narrowest wear track. These results demonstrate that femtosecond-laser-fabricated hybrid microtextures effectively enhance lubricant retention and improve the tribological performance of PEEK/CF composites. Full article

This study focuses on the synthesis of two new bisphenol-based polyimide (PI) sizing agents to improve the fiber–matrix interface of carbon fiber-reinforced poly (ether ether ketone) (CF/PEEK) composites. One of the synthesized polyimides contains bisphenol A (BPA) monomer, while the other has bisphenol S (BPS) monomer. The produced polyimide precursor resins were coated with carbon fibers by thermal imidization. The thermal, thermomechanical, and mechanical properties of the CF/PEEK composites produced by the autoclave process were investigated. According to the mechanical test results, there was a balanced performance between the BPS-containing polyimide-coated composites (CF-PEEK-PI-S) and the BPA-containing polyimide-coated composites (CF-PEEK-PI-A). While tensile strength is 291 MPa and interlaminar shear (ILSS) strength is 119 MPa, the CF-PEEK-PI-A sample showed superior mechanical properties in flexural (92.1 MPa) and compressive strength (54.9 MPa). As a result, it was concluded that bisphenol-based polyimide coatings significantly improve the interfacial interactions in CF/PEEK composites, which have great potential in aerospace, automotive and advanced engineering applications. Full article

Static and dynamic uniaxial tensile responses were investigated to accurately characterize and predict the mechanical properties of PEEK (polyether-ether-ketone) at strain rates ranging from 10⁻³ s⁻¹ to 200 s⁻¹ and temperatures ranging from 23 °C to 110 °C. The tensile responses showed dependences on the strain rate and temperature, and the dependences of the yield strength and elastic modulus on the temperature and strain rate were studied. A modified phenomenological Sherwood–Frost constitutive model considering a wide range of strain rates and temperatures was established to characterize the tensile mechanical response of PEEK material before yielding based on the experimental data. The results indicate that the model can accurately describe the pre-yield behavior of PEEK under different temperature and strain rate conditions, thus reducing the dependency on experimental data for subsequent researchers, thereby providing a theoretical foundation and modeling framework for the design and performance evaluation of CF/PEEK composite structures. Full article

Fused filament fabrication of thermoplastic composites, despite its recyclability, increased strength, and efficiency, faces structural limitations under elevated temperatures. The literature on heat treatments for improving the thermal resilience of accessible 3D printed composites is limited. Therefore, this study comprehensively presents the efficacy of annealing on carbon fiber reinforced polyamide (PAHT-CF). The methodology includes uniaxial tensile testing of 200 samples across a wide temperature range (25–150 °C) and five different infill orientations, annealed as per the Technical Data Sheet (80 °C, 12 h). Scanning electron microscopy (SEM) of the fracture surfaces revealed the microstructural changes responsible for the improved properties after annealing. At 25 °C, annealing led to a 50% strength increase (63.88 MPa) and a 70% lower strain (2.65%). At 150 °C, the material maintained a 17.5% strength advantage (23.62 MPa) and a 17.5% reduction in strain (12.67%). The 0°, 90°, and 0/90° orientations exhibited the highest improvements, while the remainder displayed lower strengths and higher deformation beyond the glass transition temperature (70 °C). Overall, annealed PAHT-CF demonstrates high-temperature resilience, comparable to previously analyzed materials like carbon fiber reinforced polyether–ether–ketone (PEEK-CF). This makes it a potentially accessible alternative for the aerospace and automotive sectors. However, practical applications must consider the trade-off between its enhanced mechanical properties and the increased lead time from annealing. Full article

This study proposes a novel algorithm for generating representative volume elements which mitigate microstructural inhomogeneities in fiber-reinforced composites. The algorithm integrates void characteristics obtained from micro-computed tomography to more accurate microstructure models. Based on these models, the effects of void content, spatial distribution, and void diameter on the mechanical behavior of CF/PEEK composites are systematically evaluated using finite element analysis and experimental validation. The results reveal that void content significantly reduces transverse tensile strength and ductility, while void size further accelerates failure and enhances brittleness. In contrast, void distribution has minimal influence on the transverse mechanical response. These findings not only offer qualitative insights into void-induced damage mechanisms but also provide a theoretical basis for optimizing microstructures to enhance the mechanical performance of CF/PEEK and similar composite systems. Finally, the limitations of this study have been discussed, and directions for future research are proposed. Full article

Designing thermoplastic composites for particular uses requires understanding their dynamic mechanical behaviour, which affects how well they operate in practical settings. The Split Hopkinson pressure bar (SHPB) test allows for evaluating these materials’ responses to high strain rates. In this study, an in-situ laser-assisted fibre placement (LAFP) machine has been utilised to produce laminate composites with varied designs, i.e., different angles of layers [0/45/–45/90]_4s, using three types of thermoplastic tapes (UD-CF/PPS, UD-CF/PEEK, and UD-CF/PEKK). Using a servo-hydraulic testing machine and SHPB apparatus, we have examined the dynamic compressive behaviour of thermoplastic laminate composites with various matrices (PPS, PEEK, and PEKK) in in-plane directions and at strain rates of approx. 0.001, 0.1, 10, 800, 1800/s. Experimental results indicate that the type of thermoplastic matrix and strain rate significantly affect how the laminate composites behave. The in-plane compressive strength and modulus increase approximately linearly with the strain rate. According to the fracture of morphological pictures, the main failure mechanism of all three types of specimens is shear failure under in-plane compression loads, which is followed by delamination and burst. Full article

Polyether ether ketone (PEEK) is a high-performance thermoplastic widely used in aerospace, automotive, and medical applications due to its exceptional strength, heat resistance, and chemical stability. However, warpage and mechanical property variations remain significant challenges in 3D printing PEEK parts. This study investigates the effect of key printing parameters, including nozzle temperature, layer thickness, platform temperature, and infill rate, on the mechanical properties and warpage of 3D-printed PEEK components. By systematically analyzing tensile and compressive loading conditions, this research aims to optimize printing settings to improve dimensional accuracy and structural integrity. The experimental results indicate that mechanical properties, such as tensile and compressive stress at break, vary significantly with printing conditions. The highest tensile strength and compressive strength achieved were 71.4 MPa and 167 MPa, respectively. Meanwhile, the lowest tensile (45.36 MPa) and compressive strengths (72.5 MPa) were also recorded. Higher nozzle and platform temperatures, coupled with increased infill rates, enhance layer adhesion, leading to improved tensile and compressive strength. However, a nozzle temperature of 400 °C, platform temperature of 130 °C, and 60% infill rate lead to optimal bonding between layers and thus a reduction in warpage. Considering warpage in all four corners and mechanical properties, a 400 °C nozzle temperature, 0.16 mm layer thickness, and 130 °C platform temperature, coupled with a 60% infill rate, provide optimal printing conditions. The 10% carbon fiber-reinforced PEEK composites exhibit an improved tensile strength that is 1.68 times higher compared to pure PEEK. To emphasize the importance of thermal and structural settings, the findings highlight the crucial role of printing parameters in minimizing warpage and enhancing mechanical properties in 3D-printed PEEK parts, which were analyzed by the multi-objective optimization method. Scanning electron microscopy analyses were carried out to analyze fracture morphology and printing layer orientation. Full article

This paper performs orthotropic constitutive modeling for short carbon fiber-reinforced polyetheretherketone (CF-PEEK) composites fabricated using material extrusion 3D printing technology. A variety of specimens for tensile, compressive, and shear tests are 3D printed under different deposition path patterns. The related experimental results disclose the strong directional mechanical properties, including tensile/compressive modulus and strength. The Tsai–Wu failure criterion is also developed based on the experimental data. The tensile–compressive behavior models of different orthotropic materials were constructed by importing the experimental data into COMSOL, followed by a compression simulation of the S-shaped specimen. The experimental results of the S-shaped compression test were compared with the COMSOL-based simulation analysis, which validated the effectiveness of the Tsai–Wu failure prediction. The predicted failure timings, locations and load–displacement curves all show a good agreement with experimental observations. Furthermore, the Tsai–Wu failure index is incorporated as a stress constraint in structural topology optimization, showing the effect of significantly reduced stress concentration. These findings and data will be supportive for the design and optimization of 3D printed CF-PEEK composites. Full article

Carbon-fiber-reinforced polyetheretherketone (CF/PEEK) composites are being increasingly used in aerospace, biomedical, and other industries due to their superior mechanical properties. However, CF/PEEK structural components require secondary processing after curing and molding to meet connection and assembly precision requirements. This process, however, often results in defects such as burrs and pits, which significantly compromise the mechanical performance and assembly quality of the structural components. This study first employed finite element simulations to analyze the laser-assisted milling of CF/PEEK composites, investigating the material removal mechanism under thermal coupling, which was then experimentally validated. Variations in the cutting force, cutting heat, surface damage, and fiber fracture mechanisms during milling were investigated. During laser-assisted milling, the fibers fractured mainly in bending at a cutting angle of 0°, in bending shear at a cutting angle of 45°, in compression at a cutting angle of 90°, and in compression shear at a cutting angle of 135°. The experimental findings were generally consistent with the simulation results. In addition, laser-assisted milling effectively reduced the cutting forces, cutting temperatures, and surface damage compared to conventional milling; laser-assisted milling reduced the cutting forces in the 90° fiber direction by 24.8% (total cutting forces) and 16.3% (feed-cutting forces). The fiber integrity was further increased with increasing spindle speed. Full article

Carbon fiber/polyether ether ketone (CF/PEEK) is widely used in aerospace, transportation, and other high-end industries for its light weight, high strength, and recyclability. However, its inherently brittle–ductile two-phase structure presents challenges in processing CF/PEEK. This paper introduces a laser-assisted milling method, wherein four types of CF/PEEK unidirectional plates (0°, 45°, 90°, and 135°) are milled under varying laser powers and spindle speeds. The results are compared with conventional milling (CM) techniques, based on cutting forces, temperatures, surface roughness, and damage defects. The cutting force, temperature, and surface quality were optimal at a fiber direction of 0° and were least favorable at 90° under identical machining conditions. When the fiber direction was 90°, the milling temperatures at 400 W and 500 W laser power decreased by 19.8% and 7.9%, respectively, while the average values of Fx and Fy decreased by 20.5% and 9.55%, compared to conventional milling. Furthermore, the laser-assisted milling method significantly reduces surface defects and improves surface roughness. In CF/PEEK composites, brittle fracture is the primary material removal mechanism, with damage characteristics such as fiber fracture, fiber pullout, and fiber/matrix debonding. The optimal parameter combination is a 0° fiber orientation, 400 W laser power, and a spindle speed of 4000 rpm. This study provides theoretical and technical support for the high-quality processing of CF/PEEK composites. Full article