Drilling of carbon fiber reinforced polyetheretherketone (CF/PEEK) is prone to burr and delamination damage due to coupled thermal-mechanical effects. A double-angle drill featuring a double-top angle and an outer-edge tip is developed based on cutting-edge decomposition to mitigate such damage. The drilling process of this drill is analyzed, and drilling experiments are conducted on CF/PEEK composites. Results demonstrated that the double-angle drill demonstrated the best cutting performance. In comparison with the traditional twist drill, the double-angle drill reduces the average thrust force and drilling temperature by 45.09% and 10.54%, respectively. This reduction is attributed to the shortened contact length between the cutting edge and chips, as well as the progressive cutting achieved by multiple cutting edges. Moreover, the double-angle drill generated a lower delamination and burr factor, which can be attributed to its independent cutting tips. This design minimizes extrusion and thermal effects during the formation of the machined surface, thereby reducing hole-making damage. This study presents a new methodology for improving the drilling quality of CF/PEEK composite.

The geometry of cutting tools has a critical impact on the hole-making quality of carbon fiber-reinforced polyetheretherketone (CF/PEEK), which in turn significantly influences the mechanical properties and service life of connected components. Based on the cutting-edge decomposition, a double-angle drill with a double-top angle and an outer-edge tip is proposed. A comparative study is performed to evaluate the static tensile performance of drilled thermoplastic CF/PEEK using conventional twist and double-angle drills. The complex strain distribution around the hole edges is examined using the digital image correlation (DIC). The findings indicated that compared with the twist drill, CF/PEEK laminates drilled with the double-angle drill exhibit superior tensile performance, consistent with the lower degree of drilling-induced damage. Furthermore, drilling-induced damage is found to influence the surface strain distribution around the holes. Observed fiber fracture and crack propagation corresponded well with high-strain zones identified via DIC around the hole periphery. These findings provide useful guidance for evaluating machining quality and achieving low-damage drilling of thermoplastic composites.

Glass fiber reinforced polyether ether ketone (GF/PEEK) composites have been widely used in engineering manufacturing fields due to their excellent mechanical and thermal properties as well as recyclability. This study aims to investigate the drilling quality of GF/PEEK composites under varying machining conditions. Drilling experiments were carried out using twist drill and double-angle-tip drill to evaluate the effects of drilling parameters and drill geometry on drilling temperature, thrust force, as well as exit and hole wall morphology. The results show that compared with the twist drill, the thrust force and drilling temperature generated by double-angle-tip drill were reduced by 32% and 15%, respectively. The double-angle and outer-edge drill tip of the double-angle-tip drill resulted in less delamination and burr formation. SEM analysis further revealed that the double-angle-tip drill produced finer and smoother hole wall than the twist drill. These experimental findings provide valuable guidance for achieving low-damage drilling of thermoplastic composites.

Due to their lightweight and high-strength characteristics, composite fasteners have become one of the focal points in the field of composite material connections. This paper establishes progressive damage models for specimens with different connection methods. Through the implementation of the VUMAT subroutine based on the Hashin failure criteria, the single shear performance and damage processes of GFRP fasteners in bolt, screw, and stud connections are analyzed. The results indicate that bolts exhibit the highest single shear strength, followed by screws, with studs being the weakest, which is related to the structure of the specimens. The relative errors between the ultimate loads predicted by the finite element model and those obtained from experiments are 3.28%, 3.34%, and 5.49%, respectively. Bolts tend to approximate planar fracture characteristics, screw fracture surfaces show a pointed apex shape, while studs display stepped cracks. These findings align well with experimental results, verifying the reliability of the model.

Thermoplastic carbon fiber reinforced polyetheretherketone (CF/PEEK) composite materials have broad application prospects in the aerospace field due to their unique recyclability and reusability. This paper proposes a novel heat treatment method aimed at enhancing the tensile properties of drilled CF/PEEK composite laminates based on crystallinity control. The crystallinity of the thermoplastic CF/PEEK composite plays a pivotal role in determining its mechanical properties. The nonisothermal crystallization kinetics of the CF/PEEK composite indicate that the composites have the longest crystallization time and the highest crystallinity at a cooling rate of 2 degrees C/min, which provides a basis for the selection of furnace cooling for heat treatment. The combined heat treatment conducted at 320 degrees C can increase the tensile load of the laminate by up to 25.68%. Digital image correlation technology is used to track the deformation and strain distribution in drilled CF/PEEK samples during the tensile process. Investigation of the tensile failure modes of the drilled laminate indicates fiber fracture and intralaminar failure as the primary mechanisms, with heat treatment effectively strengthening the polymer matrix and, consequently, enhancing the overall tensile performance of the laminates. This research provides valuable insights and practical guidance for optimizing the drilled thermoplastic composites in various industrial applications.

For the first time, this paper proposes a new strategy based on crystallinity control in enhancing the flexural strength of drilled carbon fiber reinforced polyetheretherketone (CF/PEEK) composite laminate. The high-positive correlation between the unique crystalline characteristic of the CF/PEEK composite and its flexural strength is introduced into the strategy, and the superposition of pre-heat treatment, intermediate-heat treatment, and post-heat treatment is carried out to increase the crystallinity. The optimal heat treatment temperature of 320 degrees C is identified through in situ X-ray Diffraction (XRD) patterns. The results show that the proposed strategy effectively increased the crystallinity by 21.70%, leading in turn to an increase the flexural strength of the CF/PEEK by 19.56%. The heat treatment compacts the molecular chains, enhancing the intermolecular interactions, which in turn result in increased thrust force in the drilled laminate. Four-point flexural loading experiments of the open-hole laminate reveal that CF/PEEK generates compression and tension failures at the macroscopic level and interlaminar and intralaminar failure at the microscopic level. Finally, the enhancement mechanism is elucidated, in which the transcrystallization of the matrix PEEK caused by heat treatment results in stronger bonding strength between the fiber and matrix, ultimately leading to an improved flexural strength of the drilled CF/PEEK laminate. Highlights Novel strategy enhances CF/PEEK flexural strength via crystallinity control. 21.70% crystallinity increase boosts CF/PEEK flexural strength by 19.56%. Optimal heat treatment at 320 degrees C is identified for CF/PEEK composites. Flexural tests reveal compression, tension, and interlaminar failures in CF/PEEK. Heat treatment fosters crystallization, improving CF/PEEK flexural strength.

Carbon fiber reinforced polyetheretherketone (CF/PEEK) is widely used in the aviation industry due to its high performance and ease of recycling and repair. The PEEK matrix is easy to soften when heated, which causes serious tool wear and affects machining quality and efficiency. However, tool wear mechanisms in drilling CF/PEEK composites are still unclear and there is a lack of research on the relationship between tool wear and drilling performance. This is the first study presents a comprehensive comparative analysis of tool wear mechanisms and their influence on drilling temperature, cutting forces, and hole-making quality between thermoplastic CF/PEEK and thermoset CF/epoxy composites. The results indicate that the primary wear mechanism for drilling thermoset CF/epoxy is abrasive wear, while adhesion wear dominates in thermoplastic CF/PEEK. The drilling thrust force and temperature in CF/PEEK exhibit significantly higher sensitivity to the progression of tool wear. As the number of drilled holes increases, the hole-making quality of CF/PEEK exhibits a more pronounced deterioration compared to that of CF/epoxy. This study provides valuable insights into the distinct wear mechanisms and performance differences between thermoplastic and thermoset composites during drilling processes.

To enhance the strength of screwed connections, three types of threaded joints-internal threaded joints, insert threaded joints, and adhesively bonded insert threaded joints-were fabricated on the surface of carbon fiber metal laminate (CFM) composites. The study investigates the influence of laminate stacking sequence and joint type on the tensile properties and failure behavior of the composites. Tensile tests were conducted on CFM specimens with different laminate stacking sequences and threaded joint types. Additionally, the digital image correlation (DIC) technique was employed to capture the tensile deformation process in real time. The results indicate that when the laminate stacking sequence of the joint is Al-CFRP, the load-bearing capacity of the same type of threaded joint is significantly higher compared to the CFRP-Al sequence, with improvements of 9.5 %, 9.0 %, and 12.1 %. In addition, under the Al-CFRP stacking sequence, the ultimate load-bearing capacity of the improved adhesively bonded insert threaded joint was 11.05 kN, which represents an increase of 38.3 % and 18.8 % compared to the internal threaded joint and the insert threaded joint. Additionally, as the screw inclination angle increases, the failure mode of the specimen transitions from extrusion failure to a combination of extrusion and shear-out failure, with the surface of the specimen progressively exhibiting more severe damage. The strain distribution and out-of-plane displacement at the ultimate load confirmed the aforementioned failure modes. This study provides important insights for the optimization design of CFM threaded joints.

In this paper, experimental hole-making tests were conducted on CFRP/Al stacks. The effects of different stacking sequences (CFRP, CFRP/Al, Al/CFRP) on drilling temperature, thrust force, and hole-making quality were studied. The influence of hole-making damage on the residual tensile strength and strain distributions of open-hole laminates were investigated by digital image correlation and mechanical experiments. The results indicate that the drilling temperature and thrust force of laminates can be increased by adding aluminum metal layers in the process of hole-making. Compared with CFRP laminates without aluminum metal layers, the hole-making damage of CFRP/Al lamination at the exit of CFRP holes is less, and the tensile strength of the open-hole CFRP increased by 3.03

Composite bolts have become one of the research focuses in screw threads joints due to their lightweight, high-strength, and wave transmission properties. We elucidate the differences in tensile properties, damage processes, and tensile failure forms between two types of layered woven GFRP composite bolts through tests and numerical simulations. It was found that the tensile strength of layered plain woven bolts is 40% higher than layered twill woven bolts. The failure forms of both types of bolts are related to their layered woven structure. The fracture surface of plain bolts is planar, while the fracture surface of twill bolts is apex shaped. Subsequently, a refined thread stretching model was established to study the effect of loading speed on the tensile property of screw threads. It was found that the tensile strength of plain woven screw threads and twill woven screw threads at a loading speed of 1 mm/min was 11% and 6% higher than that at 3 mm/min, respectively. The results show that the bolts and screw threads with layered plain woven have stronger tensile strength than those with layered twill woven, and a decrease in loading speed within a certain range can improve the tensile strength of the screw threads.

Remelting and remolding characteristics of thermoplastic resin make the carbon fiber-reinforced polyether-ether-ketone (CF/PEEK) composite process unique recyclability and reusability, while thermal characteristics play the crucial mechanism. This paper presents a comprehensive investigation on thermal characteristics of CF/PEEK drilling in terms of the heat transfer mechanism, crystallinity, and hole making performance. Crystallinity is introduced to quantitatively evaluate the change of material performance for CF/PEEK drilling where the crystallinity is positively correlated with tensile strength. Parameter analysis shows that the increased spindle speed leads to the increase of drilling temperature, crystallinity, and slightly deduces the tensile strength of CF/PEEK. The heat transfer curve of CF/PEEK drilling was first obtained and it is found that the heat transfer experiences three stages, namely steady rising, slow falling, and fast falling stage. Crystallinity comparative analysis between the hole wall and chips reveal that heat transfer effect dramatically affects the crystallinity when the drilling temperature exceeds the glass transition temperature (142 °C). Further, high temperature-induced PEEK smearing effect reduces the fiber exposure and surface roughness of hole wall but increases the crack appearance. The work provides important guidance for the high quality drilling of CF/PEEK composites from the point of view of the thermal characteristics.

Thermoplastic carbon fiber reinforced polyetheretherkrtone (CF/PEEK) and thermoset carbon fiber reinforced epoxy (CF/epoxy) composites are being widely applied in aviation and aerospace fields for their excellent performance. To compare the drilling characteristics of two typical carbon fiber reinforced composites under varying feed speeds, drilling experiments were carried out using three different special drills involving twist, brad, and dagger drills. The drilling performance of CF/epoxy and CF/PEEK composites was analyzed in terms of chip morphology, drilling temperature, thrust force, delamination damage, and surface morphology. The results show that CF/PEEK composites produced continuous chips, so that CF/PEEK composites generated higher drilling temperature and thrust force than that of CF/epoxy composites. CF/epoxy composites showed larger delamination damage and poorer machined surface than CF/PEEK composite due to its poor interlaminar toughness. Burrs produced agglomeration and crimping at the hole edges of the CF/PEEK composites due to PEEK resin is softened by heat, matrix plastic deformation. Brad drill revealed fewer burrs and merely a tearing damage at the exit. Dagger drill showed more burrs. The hole wall damage is minimal for brad drill. The results provide guidance for drilling of high quality thermoset and thermoplastic composites.

This paper comprehensively investigated the effect of the tool geometries on heat transfer and special crystallization characteristics in the drilling of carbon fiber-reinforced polyetheretherketone (CF/PEEK) composite for the first time. Three tools with different geometries (twist, brad, and dagger drill) are carried out on CF/PEEK drilling experiments, and temperature, as well as crystallinity and surface roughness, are introduced to make a comparative evaluation on the effect of the tool geometries. The results show that the drilling temperature is determined by the contact length of the profile between the drill and the material. Correspondingly, better surface quality with lower surface roughness and smoother surface is obtained by using a twist drill due to the heat-induced PEEK smearing effect. Further, in situ XRD and differential scanning calorimeter (DSC) were used to characterize the crystallization characteristics where crystal phase transformation at different temperatures was measured. The occurring temperature of the strongest crystallization characteristics for CF/PEEK is basically not affected by tool geometries, all at 300 degrees C, and the limiting crystallization temperature is 344.5 +/- 0.7 degrees C. The crystallinity is found to be affected by drilling temperature and cooling rate and gradually decreases along the heat transfer direction. This work provides a new sight into the improvement of CF/PEEK drilling. Highlights The effect of tool geometries on thermal and crystallization for CF/PEEK is provided. In situ XRD and DSC are used to characterize crystallization characteristics. The drilling temperature and cooling rate are both determinants of crystallinity. The limiting crystallization temperature of the CF/PEEK composite is 344.5 +/- 0.7 degrees C. Heat-induced PEEK smearing effect improves the surface quality of CF/PEEK drilling.

Vibration-assisted cutting (VAC) is an effective way of improving machining quality. Through vibration-assisted cutting experiments, the cutting mechanism of carbon fiber-reinforced polyetheretherketone (CF/PEEK) composites during vibration-assisted cutting and the influencing factors on the quality of machined surfaces were investigated. The effect of cutting-directional vibration-assisted (CDVA) and normal-directional vibration-assisted (NDVA) on cutting force, cutting temperature evolution, chip and surface morphology were analyzed. The experimental results demonstrate that compared with the traditional cutting (TC), the cutting ability of the tool in VAC was enhanced. When the fiber orientation is 0°, 45°, 90° and 135°, the maximum reduction of cutting force in CDVA is 36.48

Removable joint technology is commonly used in composite laminates for various load-bearing structures. However, existing research primarily focuses on bolted joints, there is relatively limited research on screwed joints in composite materials. This study investigates the influence of connected layer thickness and hole diameter on the tensile behavior of threaded joints in carbon fiber-reinforced polymer (CFRP) laminates. After fabricating different CFRP screwed joint specimens, tensile tests were conducted. The digital image correlation (DIC) technique captured the deformation process. The experiment results indicate a significant increase in load-bearing capacity with the increase in diameter. For instance, joints with an 8 mm diameter exhibited a load-bearing capacity of 10.82 kN. The increase in the connected layer thickness correspondingly enhanced the load-bearing capacity of the joint. The joint with a thickness of 7 mm had the highest load-bearing capacity of 8.83 kN. Besides, with the increase in the thickness of the connected layer, the failure mode transitioned from shear failure in the connected layer to screw pull-out. The tilt angle of the screw during the pull-out process also decreases with the increase in the connected layer thickness. Strain and out-of-plane displacement measurements under ultimate load conditions verify these observations.

Carbon fibre reinforced thermoplastic (CFRTP) has emerged as a sustainable alternative to carbon fibre reinforced plastic (CFRP) due to its improved reparability and recyclability. CFRTP, particularly carbon fibre reinforced polyetheretherketone (CF/PEEK), is a high-performance material known for its excellent mechanical, thermal, and corrosion resistance properties, making it well-suited for extreme environments in civil aviation equipment. However, machining processes such as milling often result in defects due to the material’s high toughness and anisotropic nature. This study aims to investigate the material removal mechanism in ultrasonic-assisted milling (UAM) of CF/PEEK and compare the effects of fibre cutting angle ( θ ) and milling processes on milling performance. To simulate the fibre fracture mechanisms under different θ , finite element analysis (FEA) is employed. The results reveal different fracture modes, including bending, bending-shear, compression, and compression-shear, at various θ . Additionally, UAM demonstrates lower cutting forces and temperatures compared to conventional milling (CM). Notably, UAM greatly improves surface quality by reducing burr height and facilitating chip evacuation, while also enhancing surface integrity by minimizing cavity defects and fibre pull-out phenomena. These findings contribute to the development of low-damage machining methods that aim to achieve higher accuracy in CFRTP.

Tool geometry can significantly influence hole quality during drilling of CFRP laminates, which has impact on mechanical properties. In this paper, drilling experiments with different drill bit geometries (twist, brad and dagger drill) are carried out on carbon fiber reinforced polyetheretherketone (CF/PEEK) composites. The influence of tool geometry on drilling temperature, thrust force, and hole-making quality are analyzed. The effect of machining-induced damage on the tensile properties of CF/PEEK composites with machined hole are investigated. The strain distributions around the holes were measured using digital image correlation (DIC). The results indicate that PEEK is softened by heat, the matrix is plastically deformed, and the edge burrs of the hole are curled and agglomerated. The best hole-making quality is obtained by brad drill. Compared to the tensile strength of undrilled laminates, the tensile strength of the laminates drilled with brad, dagger and twist drills decreases by 51.47%, 53.99% and 56.09%, respectively. The strain distribution of open-hole laminates with different machining-induced damage shows obvious difference. The fracture mode of matrix cracking, fiber splitting, delamination, fiber pull-out and debonding are mainly observed. The research results in this paper can provide reference for the optimization of CF/PEEK composites drilling process.

Carbon fiber-reinforced polyetheretherketone (CF/PEEK) composites are being widely applied in aviation and aerospace fields for excellent performance. Ultrasonic-assisted drilling (UAD) is a processing method that combines the conventional drilling (CD) with ultrasonic vibration. In this study, comparative experiments were conducted to investigate the drilling of CF/PEEK composites with CD and UAD. The effects on thrust force, machining temperature, the delamination at the exit, surface topography and roughness were analyzed. The experimental results demonstrate that compared with the CD process, the cutting ability of the drill bit in UAD was enhanced. The maximum drilling thrust force was reduced, and the maximum machining temperature was increased in UAD with a maximum decrement and increment of 12.87 and 6.42%, respectively. Meanwhile, the delamination, burr and surface roughness were effectively suppressed, and the surface integrity was improved in UAD. The research in this paper indicates that the UAD process can be used for machining of CF/PEEK composite hole for achieving low damage.

Rotation axes have been proven to be the greatest factor leading to machine tool errors, which seriously affect the machining accuracy. Therefore, it is imperative to identify the geometric errors of the rotation axes. This research focuses on how to identify the critical geometric errors of the rotation axes, so that the coupling effect of geometric errors which seriously affects the identification of geometric errors of the rotation axes can be examined. To achieve this goal, this paper proposes a global quantitative sensitivity analysis method based on homogeneous transformation matrix (HTM) theory and Sobol sensitivity analysis method. The size and randomness of geometric errors are taken into consideration and the specific indexing angles of the rotation axes are introduced to identify the critical geometric errors of the five-axis machine tool. Based on this analysis method, each geometric error components and the coupling effect between different error sources are evaluated under different indexing angles. The variation of the coupling effect of each error components within the traverse of the rotation axes is explored. The geometric error measurement experiment is established and the results are compared with the simulation results. The simulation results and experimental results reveal that the critical geometric errors that affect the machining accuracy and the variation of the geometric errors coupling effect, which provides useful guidance for the manufacturers and users of five-axis machine tools.

为了研究胶接修复对碳纤维复合材料层合板弯曲挠度的影响,试验设置了阶梯搭接和斜面搭接两种搭接方式,通过三点弯曲实验和数字图像相关技术(DIC)来研究胶接接头的弯曲变形情况.结果表明,在相同搭接长度下,阶梯搭接试件的失效载荷和弯曲强度均低于斜面搭接试件;试件的弯曲挠度与强度和搭接长度有关,搭接长度越长,弯曲强度越高,而弯曲挠度越小.由此表明,搭接长度越长,胶接层合板的强度越高,但不利于层合板的柔性变形.