Automated Fiber Placement Research Articles

Influence of fiber cutting at the composite grid intersection on the compressive performance of laminate

For thick composite grid structure, automated fiber placement (AFP) must be adopted to alternating cut fiber at the composite grid intersection to avoid out-of-plane fiber bending. In the present work, an experimental and numerical study has been carried out to understand and predict the influence of different cutting methods at the composite grid intersection on the compressive failure performance of laminate. Five kinds of test specimens with different cutting ratios were firstly manufactured and tested. A maximum of 67% drop in the compressive strength was recorded for the most severe cutting ratio. A High-speed camera was used to clarify the compressive failure progress of cut specimens. The dominant failure mechanism was classified into fiber fracture failure and inter-ply delamination. Further, numerical simulations were carried out to inform the deformation and failure mechanism of cut specimens. The FEM results correlated well with experimentsin terms of location of dominant failure mode and strength knockdown for five different cutting configurations. These findings offered certain practical reference for the design and manufacture of thick AFP composite grid structures.

Adaptive surrogate-based harmony search algorithm for design optimization of variable stiffness composite materials

Having the advancement in automated fiber placement (AFP) and three-dimensional (3D) printing, fabricating novel composites reinforced with curvilinear fibers, namely variable stiffness composites (VSCs), have gradually become feasible. Contrasted to the traditional straight fiber-reinforced composites, VSCs possess significantly enhanced mechanical properties and increased mechanical performance. However, the optimization of a VSC panel is still a challenging problem, which can be attributed to the high non-convexity of the feasible design space and highly involved computation resources. To accelerate the design and optimization of VSC structures, in this study, we propose an effective and efficient adaptive surrogate-based harmony search algorithm (ASBHSA). The VSC is modeled using the fiber path methodology through which the fiber trajectory is generated by a mathematical formulation. In addition, the manufacturability and quality of the product are guaranteed by considering the curvature constraint. For the ASBHSA, a distance-based infill criterion in combination with a radial basis function (RBF) is proposed to guide the adaptive sampling. The global best harmony search (GHS) with a good ability to find the global minimum is integrated into the developed optimization framework. After solving some popular benchmark optimization problems as well as making comparisons of the optimal designs of VSCs with those in published works, the proposed optimization framework is demonstrated being able to effectively and efficiently find the global minimum. Then, a series of designs and optimizations of laminated VSC plates under various boundary conditions and different loading conditions are carried out systematically. The reported interesting findings may provide some insights and guidance in the design of laminated VSC composites. Moreover, our proposed optimization model provides a useful tool for solving various kinds of optimization problems.

Robotic automated fiber placement of carbon fiber towpregs

ABSTRACT Robotic Automated Fiber Placement (R-AFP) technology was developed to manufacture composite laminates by placing carbon fiber thermoset towpregs, obtained by impregnating 12 K high-strength grade carbon fibers in an epoxy resin system. In order to avoid placement induced defects, a thermographic scanning technique was implemented for on-line quality monitoring of the R-AFP process. The thermal analysis proved to be an effective and quick approach for the real-time detection of deposition defects generated during. The R-AFP process was performed by applying a constant pressure through the compaction roller; different pressure values were investigated. The effect of the resin weight fraction and compaction pressure on the mechanical properties applied by the deposition head during R-AFP of cross-ply laminates was studied. The reduction of the tensile strength and the increase of the elastic modulus with decreasing pressure of the compaction roller was observed. Furthermore, the values of ultimate tensile strength and elastic modulus decrease as the resin content increases. Finally, the three-dimensional topography of surface fracture of tensile samples was investigated by means of the optical and scanning electron microscopy.

Automated fibre placement process for a new hybrid material: A numerical tool for predicting an efficient heating law

An innovative hybrid thermoplastic manufacturing process has been investigated, which consists in carbon fibres reinforced poly(ether-ether-ketone) (PEEK) prepreg sandwiched between two amorphous polyetherimide (PEI) films. By using a laser-assisted automated fibre placement (AFP), a laminate is produced by the deposition of hybrid prepreg tapes, layer-by-layer without using autoclave. The temperature history control is required to ensure good consolidation throughout the part. This depends on the optical behaviour of the hybrid material, which is also subjected to the influence of process parameters. Before determining the optical properties of the new hybrid material, the correlation between these process parameters has been established based on the interaction of laser spot with PEI film and PEEK/carbon fibres tape. Then, the thermal distribution in the laminate is obtained via an optico-thermal model and validated with experimental results. Finally, a heating law for the AFP process is established using iterative numerical simulations.

Effect of gap on strengths of automated fiber placement manufactured laminates

Tensile and compressive tests of automated fiber placement (AFP) manufactured quasi-isotropic laminates with repeating embedded gaps or overlaps are conducted and reveal significantly lower tensile and compressive strengths compared to those of normal laminates in spite that the gaps and overlaps cut no fiber. The reduction in tensile strength is greater than that of the compressive strength. A two-dimensional mechanical model of the quasi-isotropic laminates with an arbitrary inclined gap is proposed and analytically solved using a super-position technique as the sum of a global uniform stress field that satisfies equilibrium and compatibility conditions by applying a virtual force at both ends of the gap and a local stress field caused by the virtual force. The local problem is approximately solved using a Green function technique. The stress and strain fields under a unidirectional load are obtained in a closed-form expression in which the effect of the tapered portions typically observed at both sides of the gap is incorporated. The present analytical solution agrees with the finite element solution. The derived expression shows that significant stress concentration occurs at the end portion of the gap.

Moderation of thermoplastic composite crystallinity and mechanical properties through in situ manufacturing and post-manufacturing tempering: Part 1 – Mechanical characterisation

This study presents an investigation into the sensitivity of CF-PPS thermoplastic composite material to automated fibre placement process parameters: specifically the surface temperature of the layup tool and the addition of simple tempering post-manufacturing. The impact of both are investigated using DSC and mechanical tests, with a thermal analysis of the as-delivered material acting as a reference. Reference material measurements show that secondary crystallinity can be produced by exposing the material to temperatures above the cold (heating) crystallisation temperature. This secondary crystallinity begins to dominate the polymer-inherent crystallinity as the tempering conditions begin to approach the material melting temperature. At the maximum temperature tested (260°C), secondary crystallinity accounts for over 70% of the total. Laminates produced using heated tools show a significant increase in both inter-laminar shear and perpendicular tensile properties with increasing temperature. Additionally, tempering samples is able to increase the polymer tensile strength by up to 32%.

Enhancement in Interply Toughness of BMI Composites Using Micro-Thin Films

Nowadays, laminated composites are widely used in the aerospace sector. All laminates have interply/interlaminar interfaces even if they are made using automated processes. The interfaces act as the areas of weaknesses and the potential crack initiation regions. Hence, any enhancement in the crack initiation and propagation resistance is always sought after. Usage of polymeric thin films is one of the promising and viable ways to achieve this. It is also easy to incorporate micro-thin films into any automation process. In the present study, different customized thin films that are compatible with Glass/BMI composites are fabricated. Fracture toughness tests in Mode I (opening mode), Mode II (sliding mode) and Mixed Mode I/II are conducted respectively using Double Cantilever Beam (DCB), End Notch Flexure (ENF) and Mixed Mode Bending (MMB) test specimens. This paper discusses the manufacturing of compatible micro-thin films. The various challenges faced during the manufacturing and incorporation of thin films are presented. The results of the various fracture toughness tests are examined. Mechanisms through which the different films help in resisting the crack initiation and propagation are deliberated and discussed. The incorporation of this technique in Automated Fiber Placement (AFP) is also discussed.

Synthetic image data augmentation for fibre layup inspection processes: Techniques to enhance the data set

In the aerospace industry, the Automated Fiber Placement process is an established method for producing composite parts. Nowadays the required visual inspection, subsequent to this process, typically takes up to 50% of the total manufacturing time and the inspection quality strongly depends on the inspector. A Deep Learning based classification of manufacturing defects is a possibility to improve the process efficiency and accuracy. However, these techniques require several hundreds or thousands of training data samples. Acquiring this huge amount of data is difficult and time consuming in a real world manufacturing process. Thus, an approach for augmenting a smaller number of defect images for the training of a neural network classifier is presented. Five traditional methods and eight deep learning approaches are theoretically assessed according to the literature. The selected conditional Deep Convolutional Generative Adversarial Network and Geometrical Transformation techniques are investigated in detail, with regard to the diversity and realism of the synthetic images. Between 22 and 166 laser line scan sensor images per defect class from six common fiber placement inspection cases are utilised for tests. The GAN-Train GAN-Test method was applied for the validation. The studies demonstrated that a conditional Deep Convolutional Generative Adversarial Network combined with a previous Geometrical Transformation is well suited to generate a large realistic data set from less than 50 actual input images. The presented network architecture and the associated training weights can serve as a basis for applying the demonstrated approach to other fibre layup inspection images.

Placement suitability analysis of automated fiber placement on curved surfaces considering the influence of prepreg tow, roller and AFP machine

Automated fiber placement (AFP) is an important process used for fabrication of composite structures. Path planning is one of the important steps in the process of AFP. The rationality of the path is directly related to the quality of the composites component. However, the generation of the placement path is constrained by a variety of factors, including geometry characteristics of curved surface, prepreg tow deformation performance, compaction roller deformation characteristics and capabilities of AFP machine. Unreasonable planning parameters selection will lead to local placement path failure or even entire path planning failure. Thus, this paper deals with making some necessary analysis about the placement suitability before path planning and then selecting the appropriate parameters, including the tow width series, compaction roller specifications and AFP machine type. The selection of suitable planning parameters can reduce the unreasonable risk of path planning and then improve the efficiency of path planning.

Experimental investigation of prepreg tackiness in automated fiber placement

Automated fiber placement (AFP) is widely used to manufacture composite lightweight structures in different industries, including aerospace. Prepreg tackiness plays an important role in the AFP process. This study aims to measure the prepreg tackiness at different AFP processing conditions and predict the optimum parameters for high tackiness levels. Two in-house setups were developed for layup and to measure tackiness. The first setup was designed to simulate the AFP process and precisely control layup speed, compaction force, and temperature. It is used to layup the prepreg under different conditions and with different rollers. The second setup performs a peel-off test to measure the sample’s tackiness. The Taguchi method is applied to optimize the layup process parameters and find the optimal combination for high resultant tackiness. It is also applied to study the effect of the placing roller. Analysis of results shows that prepreg tack is affected by the interaction among the process parameters rather than the individual effect of these parameters. The study shows that the Taguchi method is suitable to solve the stated problem with a minimum number of trials as its results are experimentally validated.

Tensile strength of CFRP with curvilinearly arranged carbon fiber along the principal stress direction fabricated by the electrodeposition resin molding

To strengthen carbon fiber reinforced plastics (CFRPs), fiber placement along the principal stress directions have been studied as a promising approach. However, a method to sufficiently impregnate a resin between the curved carbon fibers has not established thus far, although arbitrary arrangement of carbon fibers is feasible using the automated fiber placement (AFP) machine. Previously, the authors had developed an electrodeposition resin molding method based on electrophoresis. In this method, the carbon fiber preforms sewn by the AFP machine is immersed in the electrodeposition solution containing polymers with epoxy groups, and optimal current is applied to impregnate resin between carbon fibers. In this study, we showed that a CFRP specimen could be fabricated with arranging the carbon fibers along the principal stress direction, resulting in approximately 10% higher tensile strength than that of the specimen with unidirectional carbon fibers.

Micro-CT analysis of process-induced defects in composite laminates using AFP

ABSTRACT Carbon fiber reinforced polymer (CFRP) composites have been gathering a lot of interest in several engineering applications because of their favorable properties including lightweight and ease of manufacturing. Robotic manufacturing techniques using automated fiber placement (AFP) for aerospace and automotive applications present a growing trend toward error-free manufacturing. AFP manufactured laminates can be prone to internal flaws due to improper selection of manufacturing process parameters. Additionally, internal damage in composite laminates can occur during the operational service of the laminate due to fatigue or foreign object impacts. Identifying and characterizing at the microscopic level may allow optimization of process parameters, leading to higher quality laminates. In this paper, a direct 3D imaging approach to characterize global and local deformation-induced defects in AFP manufactured CFRP laminates using X-ray CT techniques is presented. The investigations are conducted on two sets of thermoplastic PEEK composite laminates (undeformed and deformed) manufactured using a set of processing conditions. The presented approach to quantify the defects provides local and global statistics including the evolution of local 3D fiber orientation as a methodology to detect the degree of deformation.

Machine learning-based inverse predictive model for AFP based thermoplastic composites

Manufacturing of thermoplastic composites using automated fibre placement (AFP) machine with specific characteristics is a challenging task due to the interdependence of various processing conditions and variables. It is of interest to know the accurate value of different input variables which would give the desired characteristics (outputs) of the laminates. This problem comes under the framework of inverse identification and is often ill-posed and its solution becomes increasingly difficult when the available data samples are very less. The present study develops a neural network-based inverse predictive model for AFP based manufacturing process using virtual sample generation (VSG) techniques. The efficacy of the developed predictive inverse model has been established considering varieties of experimental data. The proposed approach can be applied to a large class of manufacturing processes to determine the input conditions to a get product with desired characteristics.

Determination of convective heat transfer coefficient for hot gas torch (HGT)-assisted automated fiber placement (AFP) for thermoplastic composites

In-situ manufacturing of thermoplastic composites using the automated fiber placement (AFP) process consists of heating, consolidation and solidification steps. During the heating step using hot gas torch (HGT) as a moving heat source, the incoming tape and the substrate are heated up to a temperature above the melting point of the thermoplastic matrix. The convective heat transfer occurs between the hot gas flow and the composites in which the convective heat transfer coefficient h plays an important role in the heat transfer mechanism which in turn significantly affects temperature distribution along the length, width and through the thickness of the deposited layers. Temperature is the most important process parameter in AFP in-situ consolidation that affects bonding quality, crystallization and consolidation. Although it is well known the convective heat transfer coefficient h is not constant and has a distribution, most studies have assumed a constant value for h for heat transfer analysis which leads to discrepancy between numerical and experimental results. In this study a new function is proposed to approximate the distribution of the convective heat transfer coefficient h in the vicinity of the nip point. Using the proposed convective heat transfer coefficient distribution, a three-dimensional finite element transient heat transfer analysis is performed to predict temperature distribution in the composite parts. An optimization loop is employed to find the free parameters of the distribution function so that the predicted temperature match experimental data. It is shown that, unlike other studies assuming constant h value, not only maximum temperature can be well predicted, but also predicted heating and cooling curves agree well with experimental results. The cooling rate is of significant importance in crystallization behavior and residual stress calculation.

Multiphase Flow Coupling Behavior of Bubbles Based on Computational Fluid Dynamics during AFP Process: The Behavior Characteristics of Bubbles during AFP Process

To investigate the mechanism of the effect of process parameters on bubble flow behavior during automated fiber placement (AFP) and the relationship between the bubble and voids, mechanical properties of laminates, this paper analyzes the multiphase flow coupling behavior of the bubble and fiber formation using computational fluid dynamics (CFD) and finite element (FE) method under different AFP process parameters. The effects of AFP process parameters on bubble characteristics and fiber deformation are then discussed, respectively, including bubble displacement, maximum cross‐sectional area, the lowest internal temperature of the bubble, bubble breakup, and maximum deformation of the fiber. Furthermore, the AFP and corresponding test experiments are performed to investigate the relationships between different bubble characteristics and void content, mechanical properties, mainly interlaminar shear strength (ILSS) and flexural strength (FS). The results show that the maximum cross‐sectional area of bubbles is closely related to the AFP process parameters. The FS and ILSS are positively correlated with the maximum cross‐sectional area. With the increase of bubble displacement and fiber maximum deformation, FS and ILSS are first increased and then decreased.

РАЗВИТИЕ АВТОМАТИЗИРОВАННОЙ ВЫКЛАДКИ: ОТ ИСТОКОВ ДО НАШИХ ДНЕЙ (обзор) Часть 3. Сравнение технологий ATL и AFP. Гибридная технология ATL/AFP

Automated tape laying (ATL) has found application in the production of simple parts: wing skins and flaps, vertical and horizontal tail panels. For laying out, tapes with a width of 75; 150 and 300 mm are used. Automated fiber placement (AFP) is used to produce complex structures with great visuals: fuselage and other contour structures. For laying, bundles with a width of 3,2; 6,35 and 12,7 mm are used. Presents a comparison of ATL and AFP equipment, including robotic hybrids ATL/AFP-machines.

РАЗВИТИЕ АВТОМАТИЗИРОВАННОЙ ВЫКЛАДКИ: ОТ ИСТОКОВ ДО НАШИХ ДНЕЙ (обзор) Часть 2. Автоматизированная выкладка волокон (AFP)

Automated Fiber Placement is one of the main technologies used today for manufacturing of modern composite materials from narrow bundles of 3.2; 6.35 and 12.7 mm wide, which are usually stacked in one sequence using a special head. AFP allows you to lay out parts with complex geometry. The second part considers the development of technology from its origination to the present day and provides the description of the laying process and modern equipment on the market.

Multi-objective design exploration using self-organization map for composite structures made by automated fiber placement

In this study, we apply the sequential approximate multi-objective optimization (SAMOO) to an open-hole laminated plate with partially different lay-up configurations for assuming fabrication by the AFP equipment. The SAMOO is a method to search for the optimal design with a small number of evaluations of the objective function while adding appropriate sample points to the response surface. When the optimization problem deals with many objective functions, it becomes difficult to visualize the design candidates and to understand the relationship between the objective functions. Thus, the self-organizing map (SOM) which displays multi-dimensional data in two dimensions is employed for visualization and clustering of obtained non-dominated solutions. Numerical results showed that the trade-off relationships among the three objectives were clarified and design alternatives could be explored according to the design tastes, and it was confirmed that the SOM was effective for the present optimization problem.

РОБОТИЗИРОВАННАЯ ВЫКЛАДКА ПРЕПРЕГА КАК АЛЬТЕРНАТИВА ТЕХНОЛОГИЯМ ATL И AFP (обзор)

With the growing use of composite materials, the automated production of parts using prepreg is gaining increasing interest. There are two main types of prepreg laying automation: Automated Tape Laying (ATL) and Automated Fiber placement (AFP). Both of these technologies are not always cost effective for all types of parts, and manual labor tends to be used to make complex parts with low production volumes. As an alternative to these two dominant automation solutions, there are 4 options for automated laying with manipulators.

Investigation of asymmetrical fiber metal hybrids used as load introduction element for thin-walled CFRP structures

Due to the industrial success of fiber reinforced plastic (FRP) light-weight components, the demand for joining methods suitable for FRP increases as well. Conventional joining elements like rivets and screws or simple clamping are designed for an application in conventional isotropic materials such as steel or aluminum. Therefore, by design these joining elements do not consider characteristic FRP properties such as the orthotropic (fiber) or the setting behavior of matrix materials that are subjected to a constant load. Thus, without any FRP specific adjustments, conventional joining elements will, in most cases, lead to poor results and an inferior joint. Hence, this investigation presents the concept of a layered local metal-hybrid area that can be used as a load introduction element, the “Multilayer-Insert”. The design aspects of the hybrid area are discussed for several stacking options. Furthermore, the sensitivity to geometrical design variables and asymmetrical stackings are investigated by a simplified two-dimensional finite element model. The deduced parameter relations are discussed in the context of an application in an automated fiber placement process in order to formulate recommendations for the geometrical parameters.