Fiber Placement Research Articles

Effect of Processing Parameters on Bonding Performance of a Carbon Fiber/Polyetheretherketone Thermoplastic Composite Prepared by Induction Welding.

Among the various welding techniques used to bond thermoplastic composites, induction welding stands out as a fast, clean, and contact-free process that shortens the welding time and prevents the weight increase of mechanical fastening, such as rivets and bolts. In this study, we manufactured polyetheretherketone (PEEK)-resin-based thermoplastic carbon fiber (CF) composite materials at different automated fiber placement laser powers (3569, 4576, and 5034 W) and investigated their bonding and mechanical characteristics after induction welding. The quality of the composite was evaluating using various techniques, including optical microscopy, C-scanning, and mechanical strength measurements, and a thermal imaging camera was used to monitor the surface temperature of the specimen during its processing. The results revealed that the preparation conditions of the polymer/carbon fiber composites, such as the laser power and surface temperature, significantly affect the quality and performance of the induction-welding-bonded composites. A lower laser power during preparation resulted in weaker bonding between components of the composite and yielded samples with a lower shear stress.

An experimental implication of long‐term hot‐wet‐aged carbon fiber/polyether ketone ketone composites: The impact of automated fiber placement process parameters and process‐induced defects

AbstractDuring the service life of aerospace‐grade composites, process parameters and process‐induced defects may become crucial. Most studies in this field have mainly focused on the relationship between process‐induced defects and mechanical performance. However, the potential impact of process parameters and process‐induced defects on the service life of composites serving under severe service conditions has received little attention. In this work, the effects of hydrothermal conditioning on the mechanical performance of carbon fiber/polyether ketone ketone (CF/PEKK) composites are examined, along with the correlation between automated fiber placement (AFP) process parameters and process‐induced defects. For this, gap and overlap defects integrated CF/PEKK laminates were exposed to a long‐term (90 days) hot‐wet aging environment to simulate the actual service conditions. Defect‐induced composite samples reached saturation point at the end of 30 days with a mass gain of 0.2 wt%. The aging process resulted in an increase in the degree of crystallization by almost 14% without a change in the chemical structure, indicating the postcrystallization of the PEKK matrix. Even though the thermo‐mechanical performance diminished (~25%) with the aging process, storage modulus was slightly affected by process parameters and process‐induced defects. Considering the flexural and shear test results after the aging process, the impact of gap and overlap defects on the service life of AFP composites can be minimized with higher compaction forces (600 N) and lower lay‐up speeds (0.1 m/s).

A novel hand-eye semi-automatic calibration process for laser profilometers using machine learning

Hand-eye calibration is a vital step in the laser profilometer integrated measurement system. However, the widely applied standard sphere calibration process requires extensive laborious human work and expertise. To standardize and streamline the hand-eye calibration process for Industry 4.0, a semi-automatic calibration process was proposed, containing a calibration postures generation model and an intelligent circle detection method based on machine learning. With the proposed process, the measurement system can collect required data with minimal human participation and automatically processes them, which can significantly improve hand-eye calibration accuracy and efficiency. Additionally, an exhaustive study of the influence of the number of postures on the calibration accuracy of the industrial robot and automated fibre placement (AFP) machine demonstrates the proposed model’s effectiveness. Moreover, the current study’s results can also be excellent tools for further hand-eye calibration research. Our code and dataset are made publicly at: https://github.com/tangyipeng100/hand_eye_cali_circle_segmentation.

Smart Roller: Soft Sensor Array for Automated Fiber Placement

AbstractRollers and wheels are widely used in industry and transportation, but there is seldom direct information about contact forces. A smart roller is introduced which provides real‐time pressure measurements from a soft, elastomer‐coated cylinder. The roller is designed for automated fiber placement (AFP) machines, which are widely used in the aerospace industry to manufacture complex composite parts. For optimum process performance, real‐time feedback is highly desirable for detecting flaws during manufacturing. The sensor replaces the elastomer outer layer of a standard roller with 4 by 13 tactile pixels (taxels) of soft capacitive sensors, which provide more than 1 pF of change in capacitance per taxel over a pressure range of 1 MPa. Sensors are made of silicone and mounted on a flexible printed circuit board on which a microcontroller with Bluetooth‐Low‐Energy collects and transmits capacitance data. The sensor dielectric layer is composed of pillars that increase layer compliance and sensitivity while also providing the stiffness of typical industrial rollers. The ability of the roller to measure real‐time local compaction pressure at typical manufacturing speeds enables the monitoring of spatially‐resolved pressure‐time curves, which can be used to predict and control adhesion.

Effect of gap and overlap on mode II interlaminar fracture toughness of automated fiber placement prepreg laminates

Automated Fiber Placement (AFP) technology facilitates the manufacturing process of composite structures with complex geometry owing to its high efficiency and accuracy. However, the unavoidable imperfections induced by the automated layup method bring challenges to the stability of the final mechanical properties of composites. The influence of AFP-induced gaps and overlaps on the mode II interlaminar fracture process of oven-cured laminates is experimentally investigated and explicitly revealed. End-Notched Flexure (ENF) tests were performed to measure the interlaminar fracture toughness of unidirectional laminates under three different defect configurations, namely “Gap” “Overlap” and “Gap & Overlap”. A marginal decline (about –1.2% in non-precracked tests, –5.1% in precracked tests) and an obvious increase (about 15.2% in non-precracked tests, 5.2% in precracked tests) in fracture toughness were observed for the “Gap” group and the “Overlap” group, respectively. Fractographic studies which involve the metallographic observation and Scanning Electron Microscopy (SEM) observation revealed that the increases in fracture area and crack length helped improve the fracture toughness of the “Overlap” group. However, the resin-rich area with high porosity induced by gaps was detrimental to the delamination resistance. To capture the interlaminar stress distribution local to imperfections, a three-dimensional numerical model was established. Gap defects facilitate the local delamination process, and the overlap defect postpones the damage onset and the propagation.

Accuracy of robot-assisted stereotactic MRI-guided laser ablation in children with epilepsy.

Robot-assisted (RA) stereotactic MRI-guided laser ablation has been reported to be a safe and effective technique for the treatment of epileptogenic foci in children and adults. In this study the authors aimed to assess the accuracy of RA stereotactic MRI-guided laser fiber placement in children and to identify factors that might increase the risk of misplacement. A retrospective single-institution review of all children from 2019 to 2022 who underwent RA stereotactic MRI-guided laser ablation for epilepsy was undertaken. Placement error was calculated at the target by measuring the Euclidean distance between the implanted laser fiber position and the preoperatively planned position. Collected data included age at surgery, sex, pathology, date of robot calibration, number of catheters, entry position, entry angle, extracranial soft-tissue thickness, bone thickness, and intracranial catheter length. A systematic review of the literature was also performed using Ovid Medline, Ovid Embase, and the Cochrane Central Register of Controlled Trials. In 28 children with epilepsy, the authors assessed 35 RA stereotactic MRI-guided laser ablation fiber placements. Twenty (71.4%) children had undergone ablation for hypothalamic hamartoma, 7 children (25.0%) for presumed insular focal cortical dysplasia, and 1 patient (3.6%) for periventricular nodular heterotopia. Nineteen children were male (67.9.%) and 9 were female (32.1%). The median age at the time of the procedure was 7.67 years (IQR 4.58-12.26 years). The median target point localization error (TPLE) was 1.27 mm (IQR 0.76-1.71 mm). The median offset error between the planned and actual trajectories was 1.04° (IQR 0.73°-1.46°). Patient age, sex, pathology and the time interval between date of surgery and robot calibration, entry position, entry angle, soft-tissue thickness, bone thickness, and intracranial length were not associated with the placement accuracy of the implanted laser fibers. However, the number of catheters placed did correlate with the offset angle error on univariate analysis (ρ = 0.387, p = 0.022). There were no immediate surgical complications. Meta-analysis indicated that the overall pooled mean TPLE was 1.46 mm (95% CI -0.58 to 3.49 mm). RA stereotactic MRI-guided laser ablation for epilepsy in children is highly accurate. These data will aid surgical planning.

Automatic process control of an automated fibre placement machine

Automatic process control of an automated fibre placement machine

Enhanced ductility in in-layer glass-carbon fiber/epoxy hybrid composites produced via tailored fiber placement

Enhanced ductility in in-layer glass-carbon fiber/epoxy hybrid composites produced via tailored fiber placement

Impedance Analysis of Three-Dimensional Continuous Carbon Filament Embroidered Electrodes in Large 300 cm2 Redox Flow Cells

The paper investigates the use of three-dimensional (3D) continuous carbon filament electrodes prepared using tailored fiber placement (i.e. embroidered electrodes) in a 300 cm2 redox flow cell with 50% state-of-charge (SOC) ferro/ferricyanide redox couple as the probe electrolyte. Electrochemical impedance spectroscopy (EIS) was conducted to identify the different resistance contributions, and thus voltage losses of the electrodes. The findings indicate that: (1) achievingh high frequency resistance values comparable to the felts is possible through side contacting of continuous filament electrodes to the graphite plates, eliminating the need to press the entire electrode structure. (2) The embroidered electrodes can minimize pressure drop, regardless of the electrode thickness, due to the parallel orientation of the carbon filaments to the electrolyte flow, resulting in reduced hydraulic resistance. (3) To reduce charge-transfer resistances, an oxidation treatment is required to improve the wettability of the electrodes, and the duration of the activation treatment must be optimized to avoid filament breakage due to etching. (4) Embroidered electrodes exhibit higher mass transfer coefficients thanfelts, which is attributed to the perpendicular orientation of the carbon filaments to the electrolyte flow. The paper provides avenues for further development of 3D carbon fiber electrodes.

Improved fibre placement in filament-based 3D printing of continuous carbon fibre reinforced thermoplastic composites

This study investigates the mechanism of fibre deposition in conventional 3D printing and presents an aligned fibre deposition (AFD) method to improve the fibre placement. The deposition mechanism reveals that the cracking of the filament in the transition zone and the torsional deformation during the steering path are the main cause of the defects in the conventional printing process. The AFD method is shown to reduce and mitigate the fibre waviness and twisting, hence producing smooth filament deformation, introducing less air voids and fibre breakage during printing. It is found that the AFD method improves the fibre alignment angle from ±25° to ±12° and reduces the void content to 0.27 % during straight-line deposition. During curved-line printing at a large radius of curvature, tow shearing instead of fibre folding is produced by AFD method, resulting in smooth edges with less fibre breakage.

Redundancy resolution of 9-DOF machine through synthesized global and local performance indices

The 9-degrees-of-freedom (DOF) machine is used to lay the rotating mold driven by the positioner. In order to reduce the 9-DOF machine to a 6-DOF non-redundant structure, this paper proposes a redundancy resolution method based on synthesized global and local performance indices. Since the number of non-redundant machine types is enormous, all non-redundant machines are divided into six classes depending on the redundant joints, called axis assignment schemes. After defining the global and the local performance indices of the non-redundant machine, the redundancy resolution method is proposed. It consists of three parts: Firstly, refine the machine types of each axis assignment scheme based on the average global indices. Then, select the best axis assignment scheme by comparing the scheme’s local indices for a given mold. Finally, optimize the non-redundant machine type contained in the optimal scheme with the objective of superior local indices and continuous positioner rotation space. In the experiment, using the air-inlet as an example, two motion planning methods gave different motion trajectories for the 7-DOF layup system. The effectiveness of the proposed method was verified analytically by comparing the joint motion and fiber placement speed of the optimal machine type with other types.

Numerical and experimental study of the viscosity and mechanical parameters effect on tow feeding quality during automated fiber placement

For automated fiber placement (AFP), it is crucial to research the contact characteristics between tow and roller during the tow feeding process. However, it has not been widely explored. In this paper, a theoretical model of contact characteristics for the tow feeding process is established by analyzing the distribution of normal stress, tangential stress, adhesion zone, and slip zone, respectively. The model proposed a numerical algorithm for calculating the contact characteristic. Then the contact characteristic of the tow feeding system can be acquired and validated by the experiment and finite element method. The model that provides theoretical support for AFP optimization. Furthermore, proper pressure (P = 0.6Mpa) and tension (T = 3 N) for towpreg feeding under experimental conditions were obtained.

Analysis of roller compaction pressure distribution in automated dry fibre placement

Automated Dry Fibre Placement (ADFP) is a version of Automated Fibre Placement (AFP) where prepreg tapes are substituted with dry fibre tapes. In this process, a uniform compaction pressure applied by a compaction roller is required to manufacture preforms with consistent quality. In this paper, a finite element model is developed to analyse the roller-applied pressure on the fibrous reinforcement bed. The model has been validated by using a pressure sensitive film. The influence of roller material, tool curvature and substrate thickness on the pressure distribution are investigated. Increasing tool curvature leads to a decrease in compaction pressure uniformity using the same compaction force. Force input target bounds for different rollers on tools with different curvatures are determined using the model. It is found that softer rollers show large force control window and suitability for tools with higher curvature. Thick substrates exhibit large deformation which could increase complexity for force control strategies.

Thermal analysis for in-situ consolidation in the AFP process

An analytical approach was developed for assessing the thermal history of thermoplastic composites during tape placement for in-situ consolidation of the automated fiber placement (AFP) technique. In this study, the heat-conduction equation is developed and solved for internal energy instead of temperature because the diffusivity does not significantly change over a wide range of temperatures in the AFP process, despite the significant change in the specific heat and conductivity. The three-dimensional internal energy history is derived in an integrated form using the Green function technique. The temperature field obtained from the internal energy field agreed with the finite element solution, where the temperature-dependent thermal properties were considered. The effects of manufacturing parameters, such as the placement speed and thickness of the placed laminates, on the thermal history of laminated composites during AFP are discussed using the present approach and finite element analysiss.

Discrete path planning of carbon fiber patch placement with complex surface

At present, carbon fiber automatic placement technology is mainly applicable to the preform of large and complex components, while the preform of small size and large curvature carbon fiber components mainly relies on manual placement, which has the problems of high labor cost, slow speed, and low repeatability. In order to realize the automatic placement of carbon fiber components with large curvature and small size, this article adopts the carbon fiber patch placement method to make the preforms. By combining the surface subdivision method and the finite element optimization method of carbon fiber patch placement angle, a discrete path planning method of robotic carbon fiber patch is proposed. This method divides the complex surface into surface fragments with similar curvature and normal angle, which can effectively reduce the wrinkles in the process of carbon fiber patch placement and improve the utilization of carbon fiber patch. At the same time, the stiffness optimization design of carbon fiber patch composite preforming is realized by combining the finite element optimization method of placement angle. The helmet surface was selected as the research object of carbon fiber placement path planning, and the path planning of helmet surface placement was carried out, and the simulation tests of helmet placement in different regions and overall placement were compared. It was found that the stiffness of carbon fiber patches placed in different regions of the helmet surface was better than that of the overall placement.

Morphing characteristics and damage analysis of 3D printing variable stiffness bistable laminates based on continuous fiber thermosetting composites

The morphing characteristics and damage analysis of variable stiffness bistable laminate fabricated by continuous fiber 3D printing technology are systematically studied. Conventionally, bistable structures used in morphing applications are achieved with straight fibers. With the application of fiber placement technology, it is now possible to prepare variable stiffness laminates with different directions and layup angles of fibers. Moreover, the structure will be damaged with the increase in deformation times. How to effectively suppress the failure of laminates is also a highlight for this composite structure. In this paper, three curvilinear fiber paths are designed and compared. And a semi-analytical model based on the Rayleigh-Ritz method is used to predict the curvature of stable configuration. In particular, continuous fiber thermosetting resin matrix composites 3D printing technology is proposed for preparing variable stiffness laminates, which has several advantages compared to other traditional preparation methods of variable stiffness laminates. The corresponding finite element model is also developed to investigate the bistable behavior and damage analysis. In addition, the influence of different angle parameters and fiber paths on the stable configuration and the snap-load are also discussed. Finally, the damage evolution and mechanical properties of straight-fiber laminates and variable stiffness laminates in tension and compression are carried out based on the Hashin failure criteria.

Placement defects in thermoset‐impregnated rovings deposited along curved paths

AbstractWet Fiber Placement (WFP) is a novel process for manufacturing complex shaped parts from continuous fiber‐reinforced polymers without semi‐finished products. Here, dry fiber bundles (rovings) are in‐line impregnated with a thermoset resin, followed by almost tension‐free deposition. The freshly impregnated and limp rovings allow for placement in radii. Due to the lack of compression in deposition, subsequent consolidation, for example, via vacuum bagging, is required. However, this consolidation cannot compensate for defects already present in the deposited lay‐up as they will typically occur when depositing rovings along curved paths. In this study, we deposited two carbon fiber rovings in radii between 5 and 2000 mm by WFP. The occurring defects were visually evaluated. Three main defects were observed: Fiber waviness, up‐folding and twists. The extent of the defects was evaluated using image analysis techniques. Results show, that up‐folding and twists are dominant for radii <100 mm, while for greater radii fiber waviness is the main defect. Up‐folding and twists almost completely disappear for radii >500 mm, but a slight waviness is still observed. However, the effect of fiber waviness on the longitudinal stiffness is estimated to be small for radii >500 mm and perhaps acceptable for some applications.

Combining filament winding with tailored fiber placement in composite cylinders locally reinforced with fibrous patches

In this paper, a novel hybrid manufacturing process that combines filament winding (FW) and tailored fiber placement (TFP) is introduced. The main idea is to place a TFP patch in between two filament wound layers aiming at maximizing the load transfer between the parts. To assess its feasibility, physical properties, such as density, fiber volume fraction and void content, and also the hybrid process kinematics and error propagation are evaluated. Furthermore, to determine the mechanical performance of this novel procedure, axial compression tests are carried out considering several unidirectional TFP patches. Key results show low-void content and good cross-section quality, demonstrating the feasibility of the process. In addition, mass–normalized load peaks as high as 394% with respect to the reference (non-patched) cylinder were obtained.

Micro Computed Tomography based stochastic design and flow analysis of dry fiber preforms manufactured by automated fiber placement

The effective design of channels in dry tape preforms is crucial for achieving desired preform permeability for successful resin injection for composites manufacturing using Automated Fiber Placement (AFP) process. Achieving target gaps and their locations in the AFP layup is extremely challenging. This work investigates the correlation between the spatial variability of the preforms and the in-plane permeability using an X-ray Computed Tomography (XCT) based characterization framework. The tomographic images of two different dry carbon tape preforms with different tape widths were used to generate realistic and XCT based stochastic models to be used for numerical permeability predictions. The variability in the tape placement by the robotic head and its effect on preform permeability was also examined through stochastic geometric modeling of the laid preform. A benchmark transient permeability measurement set-up was utilized to obtain experimental in-plane preform permeability through 2D radial mold filling. The in-plane numerical permeability values showed significant scatter, with a coefficient of variance of 75%–130%, which deviated from the experimental measurements by approximately one order of magnitude. These findings strongly re-affirm that the experimental permeability measurement technique based on transient mold filling of dry fiber AFP preforms is complex however, the XCT based stochastic modeling technique is an effective way to estimate the permeability of dry fiber AFP preforms virtually.

Impact damage assessment of thin defective composite laminates manufactured by Automated Fiber Placement technique

Fiber tow-gap is a composite defect that occurs during fiber deposition using Automated Fiber Placement technique. This defect resulting from the inherent gap between the adjacent fiber tows causes local thickness consolidation. It creates relatively large resin pockets that can affect the impact response and residual compressive strength of composite structures. Although the tow-gap effect on the in-plane response of composite laminates has been widely studied, there is still a lack of knowledge in damage assessment of defective composite plates subjected to Low-Velocity Impact (LVI) loading. In this study, a series of experimental Compression After Impact (CAI) tests are carried out on the standard carbon/epoxy composite plates subjected to impact loads to investigate the combined effect of impact damage and gap defect on the residual compressive strength reduction. Effect of the curing process on the gap formation is evaluated by measuring the Induced Gap Shrinkage Factor (IGSF) using microscopic observation. This factor is used for numerical simulation of the defective composite plates. Digital Image Correlation (DIC) technique is also used to measure the in-plane strains of the specimen under compressive loading. Furthermore, a numerical investigation is carried out by implementing the Induced Defect Layer Method (IDLM) model. The numerical studies contain both LVI and CAI results, including the impact response, impact damage, and final failure of impacted specimens under compressive loading. Results show that the induced gaps play a significant role in the residual strength reduction of thin composite plates, which is significant in low-velocity impact loading. It is also shown that IDLM is a robust meso-macro damage method for damage analysis of the composite laminates with manufacturing-induced gaps.