Automated Fiber Placement Research Articles

Composite materials, technologies and manufacturing: current scenario of European Union shipyards

ABSTRACT This paper provides the results and the analysis of a study conducted on the processes and technologies currently used by European Union shipyards, and their potential interest in new advanced composite construction technologies, including Adaptive Moulds, Automated Tape Laying, Automated Fibre Placement, Curved Pultruded Profiles, Additive Manufacturing, Hot Stamping, Modular and Serialised Shipbuilding and Digitisation of Production. A new set of indexes are also introduced with the objective of facilitating the evaluation of the technological level of the shipyard, thereby allowing the understanding of the shipyard's interest in new developments. The analysis of the survey conducted shows that almost the 95% of shipyards either currently use or plan to use composite materials, being the composites made of fibreglass and polyester resin the most used. These composites are mainly manufactured by manual lamination and vacuum infusion techniques. The survey has also shown that there is a high interest in the shipyard digitisation and the use of new technologies in the shipbuilding industry, especially for new construction shipyards. The study shows that despite shipyards want to adopt digitisation in engineering and design processes, implementation of new technologies and concepts is being held back by financial cost and uncertainty regarding outcomes such as improved operational efficiency of vessels. The shipyards that do not use composites are less technologically advanced than those that use them, according to the analysis of the technological indexes. This analysis has also shown that the shipyards with a high technological index have a more varied potential market offer.

Effect of atmospheric plasma treatment on Mode-I and Mode-II fracture toughness properties of adhesively bonded carbon fiber/PEKK composite joints

This study aims to assess the influence of peel-ply (PP), mechanical abrasion (MA), and atmospheric plasma activation (APA) treatments on Mode-I and Mode-II fracture toughness of carbon fiber/ poly-ether-ketone-ketone (CF/PEKK) composite joints. A comprehensive examination of the topography and wettability of the adherend surfaces is conducted using various methods. The CF/PEKK adherends are produced through an automated fiber placement (AFP) process, and the CF/PEKK bonded joints are prepared using two different structural adhesive films, one of which has a lower strength, while the other has a higher strength. To evaluate their fracture toughness properties, double cantilever beam (DCB) and end-notched flexure (ENF) tests are carried out in accordance with ASTM standards. Acoustic emission sensors are used to monitor the test specimens during DCB tests, allowing for an in-depth evaluation of the failure modes and damage propagations in the joints. The results show that the GIC and GIIC values of the APA-treated CF/PEKK bonded joints are remarkably higher than those of the untreated ones, with a range of improvement of 34.0–84.8 times and 7.5–17.4 times, respectively. Adhesive failure is the dominant failure mode on the surfaces of non-treated (NT) and PP samples, while cohesive failure is more prominent in those treated with MA and APA. The failure modes of the treated samples varied depending on the adhesive used, with APA-treated samples always exhibiting a cohesive failure. It is observed that the AE counts increase more slowly in APA-treated samples compared to MA-treated joints as delamination progresses more slowly with cohesive failure dominant, which leads to a lower release of AE energy.

In-plane and out-of-plane deformations in automated fiber placement employing micromechanics method

In-plane and out-of-plane deformations in automated fiber placement employing micromechanics method

Mapping of multimodality data for manufacturing analyses in automated fiber placement

Automated Fiber Placement (AFP) is an advanced composites manufacturing technique utilized for industrial scale structures. During this process, data is collected from a multitude of modalities spanning numerical analysis of processing parameters to inspection techniques. With data collection existing both in-situ and ex-situ. To ensure interoperability of multimodality data, a mapping is necessary to understand the relationship between these various conditions, and the positioning on the tool surface. This paper defines a mapping technique which enables the evaluation of spatial data from many different sources within the AFP process. Through these mapping techniques, a global array of data is generated that includes all aspects of AFP manufacturing. The developed methodologies are applied to the manufacturing of a doubly curved part. Results showcase the ability to map multimodality data into a uniform format. With the uniform format of the data, further steps can be made to the improvement of fiber paths and processing parameters.

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.

Automatic process control of an automated fibre placement machine

Automatic process control of an automated fibre placement machine

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.

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.

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.

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.

Layup time for an Automated Fibre Placement process in the framework of a detailed sizing optimisation

Automatic Fibre Placement manufacturing processes have become the aerospace industry standard for the production of large-scale composite components. Besides the challenges linked with the manufacturing of such components, their design process is also complicated leading to the two mainly being treated as different subjects. In this work, the aspect of the layup time required to manufacture the composite component is introduced as an objective function in a detailed sizing optimisation process. The methodology presented is able to identify how the material is going to be laid on the tool, using the sizing information available via a zone-based modelling of the thickness and stiffness properties of the structure. The method is applied to the skin of an aircraft wing and a trade-off between the structural weight and layup time is observed. Results demonstrate that the bi-objective optimisation is a promising tool for reducing the structural mass, while keeping the layup time to acceptable levels by benefiting from a more detailed structural modelling.

Modeling of tow tension fluctuations and parameter optimization during the stable transfer phase for automated fiber placement

The fluctuation in tow tension is critical for Automated Fiber Placement (AFP). However, it has not been widely studied. In this paper, a tension variation equation was developed to represent the tension fluctuation during AFP, and experiments were used to demonstrate the validity of the equation. According to the equation, the degree of bending rigidity, power-law friction, and extensibility influence on the tension change was obtained. Additionally, the effects of bending rigidity and extensibility can be disregarded during AFP. Moreover, automatic wire feeding and laying trials were carried out separately, and proper tensions (T = 3 N) for wire feeding and layup under experimental conditions were obtained. Therefore, the equation provides theoretical support for the structural and parameter optimization of the AFP.

Modeling the effect of automated fiber placement induced gaps based on serial layer scanned point clouds

The gap is one of the most common defects during the AFP process, which has a nonnegligible impact on the mechanical properties of laminates. This paper proposes a novel three-dimension reconstructive gap model based on the in-process serial layer scanned point clouds, which can characterizes the gap features inside the laminate and pre-determine the mechanical performance before the subsequent procedures. The measured point cloud will be transformed into eligible and processible formats and then be used to generate a finite element grid using the element-based material property assignment method. The local material properties and fiber orientation are defined by previously assigned classes and grid geometries respectively. The effect of gap size on the in-plane tensile strength and damage evolution of laminates is investigated and both the experimental and simulation results find that the ultimate strength and stiffness show a significant decrease with the increase of gap size.

Probabilistic analysis of composite stiffened panels including random AFP-produced defects towards enhanced design allowables

Automated fiber placement introduces defects such as gaps and overlaps during production, which add uncertainty to the mechanical behavior of composite parts. This study describes a probabilistic methodology which allows the direct introduction of random defects to the composite part and the calculation of the allowable design values through probabilistic virtual testing. The method is applied on a stiffened panel and is based on measurements regarding the random defect magnitude. An offline database of knock-down factors for stiffness and strength properties is first generated via detailed defected FE models. The factors are then assigned to the panel FE model accordingly, and via a Monte Carlo procedure the statistical response sample of the part is calculated. The process is further accelerated by a machine learning technique able to emulate the relationship between the random input and the selected responses. Several parametric analyses reveal that the number of defects on the panel is often more sensitive than the defect size, while the intensity of the defect at the through-the-thickness direction and the affected plies have a rather strong effect. Moreover, the conservatism of the deterministic design approach based on safety factors is proven by a direct comparison to the described probabilistic approach.

A study of post-processing for AFP-fabricated thermoplastic composites with void content and air permeability characterization

Improving the quality of fiber-reinforced composite laminates using out-of-autoclave techniques has been a challenge for a long time. The recent trends toward the replacement of autoclave processes with out-of-autoclave processes for thermoplastic composites still lack a compressive recipe. This study first develops an understanding of the integrated effect of the automated fiber placement (AFP) lay-up process parameters (compaction force and lay-up velocity) and the type of post-processing: i) autoclave and ii) vacuum bag only (VBO) processing with two vacuum hold times, 2 and 24 h. The void content results highlight the potential of the VBO process to replace the autoclave with an improved void content of VBO with 24 vacuum hold times. Then, this result has been correlated with the morphology of voids after the AFP lay-up as isolated or connected via air permeability characterization. This study reveals that the high air permeability to effective porosity ratio of samples after AFP lay-up which is achievable with low compaction force facilitates the air removal mechanism during the VBO process with sufficient vacuum hold times.