Fiber Path Research Articles

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.

Optimization with manufacturing constraints for composite laminates reinforced by curvilinear fibers through a parametric level set method

This paper presents the design optimization with manufacturing constraints for composite laminates reinforced by curvilinear fibers by using a parametric level set method. In each layer of the composite laminate, a level set function is defined by using the compactly supported radial basis functions (CS-RBFs), and the iso-contours of each level set function represent the fiber paths in one layer of the laminate. By this means, the fiber orientation at an arbitrary point in a layer can be computed by the orientation of the tangent vector of the iso-contour passing through this point. To avoid structure defects (such as gap/overlap, wrinkling and delamination) that would arise if the fiber paths are not parallel or their curvature is too large, the gradient norm and contour curvature radius of the level set functions are considered as constraints in the design optimization. The p-norm method is used to aggregate the constraints to improve the optimization efficiency. The coefficients of CS-RBFs are considered as design variables. Several numerical examples of compliance minimization and eigen-frequency maximization are investigated to verify the proposed method.

Maximisation of Bending and Membrane Frequencies of Vibration of Variable Stiffness Composite Laminated Plates by a Genetic Algorithm

PurposeIn comparison to traditional, constant stiffness laminates, variable stiffness composite laminates (VSCL) with curvilinear fibres represent an extra analysis effort. It is the purpose of this work to present and test a relatively simple optimisation procedure, in order to find the maximum fundamental frequency of vibration in bending and in in-plane vibrations. It is also intended to explain why certain fibre paths lead to higher frequencies.MethodsThe optimisation is performed using a genetic algorithm (GA), which is described in detail. The bending and the in-plane plate models are based on the p-version Finite Element Method. Each model requires a small number of degrees of freedom, an important feature because applying the GA involves the solution of a large number of eigenvalue problems. In order to support the physical interpretation of the optimal designs, mode shapes and stress fields corresponding to some optimal solutions are illustrated.ResultsSingle- and multi-layer plates with different boundary conditions and fibre path types are studied. Fibre paths that lead to maximum fundamental frequencies are found and justified. The consequences that maximising the first frequency has on the higher-order modes of vibration are studied.ConclusionThe proposed optimisation and modelling methods are effective. Curvilinear fibres with the characteristics considered led to the maximum first natural frequency of vibration in a few cases, but not all. Particularly in in-plane vibrations, curvilinear fibres can provide major gains in comparison to straight fibres. The increase in the vibration frequency is accompanied by, overall, larger stresses.

BIO13: Effect of Artificial Lung Fiber Bundle Geometric Design on Micro- and Macro-scale Clot Formation

Purpose of Study: The hollow fiber membrane bundle is the functional component of artificial lungs, transferring oxygen and carbon dioxide to and from the blood. It is also the primary location of blood clot formation and propagation in these devices. The geometric design of fiber bundles is defined by a narrow range of parameters that determine gas exchange efficiency and blood flow resistance, such as fiber packing density, path length, and frontal area. However, these parameters also affect thrombosis. Methodology: This study investigated the effect of these parameters on clot formation using 3-D printed flow chambers that mimic the geometry and blood flow patterns of fiber bundles. Hollow fibers were represented by an array of vertical micro-rods (380 micron diameter) arranged with varying packing densities (40, 50, and 60%) and path lengths (2 and 4 cm), all of which are fiber bundle parameters in commercially available artificial lung devices. Blood was pumped through the device corresponding to three mean blood flow velocities (16, 20, and 25 cm/min), which were scaled from 4 L/min flowrates in an Adult Quadrox oxygenator. Results: Results showed that (1) clot formation decreases dramatically with decreasing packing density and increasing blood flow velocity, (2) clot formation at the outlet of fiber bundle enhances deposition upstream, and consequently (3) greater path length provides more clot-free fiber surface area for gas exchange than a shorter path length. Summary: These results can be used to create less thrombogenic, more efficient artificial lung designs.Figure 1. a) The experimental flow chamber was designed to be 2 or 4 cm and with a packing density of 60%, 50% or 40% rods to simulate the flow path of blood through an artificial lung hollow fiber bundle. (b) The flow circuit involved one-way flow from a syringe pump, connected to the flow chamber and then to a waste container. A manometer measured the pressure drop across each experimental device. (c) The averaged clot volumes from the microCT scans show more clot (red) at the outlets of all devices. There was also less clot in the chambers with a longer path length device, faster flow rate, and less density.

Spatially optimised fibre-reinforced composites with isosurface-controlled additive manufacturing constraints

A design approach accounting for manufacturing constraints is described for spatially optimised fibre-reinforced composites. The approach is based on the optimisation of local fibre orientation, the fibre volume fraction and density-based topology optimisation to determine the optimal design. A continuity equation is adopted to constrain the fibre orientation and ensure continuous fibres within the bounds of realistic fibre volume fractions. This results in a fibre orientation with a corresponding and controllable variation of the fibre volume fraction. In order to ensure the continuous fibre can be deposited, the manufacturability of the optimised results is ensured by introducing constraints controlled with two scalar fields to reconstruct fibre paths which are able to provide sufficient information to generate printer toolpaths. A cantilever beam problem is solved to show the advantage of the fibre reinforcement, the inclusion of manufacturing constraints and the penalty in compliance due to the application of the manufacturing constraints. The results show that the presented approach successfully guarantees the manufacturability with minimal loss of performance.

Optimization design of variable stiffness composite cylinders based on non-uniform rational B-spline curve/surface

Compared with a constant stiffness (CS) composite structure of traditional straight fiber path, a variable stiffness (VS) composite structure of curvilinear fiber path has a broader design space. Taking the performance of a CS cylinder as the baseline, two curved fiber formats of VS cylinders are investigated. One is that the fiber angle varies in circumferential direction (i.e., circumferential stiffness variation, VS-C), the other is that the fiber angle varies in both circumferential and axial directions (i.e., circumferential and axial stiffness variation,VS-CA). Non-uniform rational B-spline curve/surface is used to define the continuously varying fiber orientation angle, making the VS design come true. This paper focuses on the maximum buckling capacity of VS composite cylinders under two kinds of loading cases (pure bending moment at both ends, concentrated force at the middle of the axis), and the optimal fiber angles of VS-C and VS-CA cylinders are obtained. In order to improve the computational efficiency, the adaptive Kriging surrogate model is integrated with genetic algorithm to solve the above optimization problems. The results show that the anti-buckling performance of VS-CA structure is always better or close to VS-C structure under different loading conditions, and all are better than that of CS structure.

Designs of lattice truss core sandwich structures with improved compressive strength and stiffness

Lattice truss core sandwich composite (LTCSC) panels can exhibit high compressive performance until failure is caused by compressive fracture of the composite strut. Early failure of the core-facesheet and central nodes, as well as fiber misalignment, can hinder the full potential of an LTCSC. This study aimed at improving the compressive stiffness and strength of LTCSC panels through minimizing the fiber misalignment and fabrication issues, while strengthening the central and core-facesheet nodes. The lost-molding technique was used to fabricate LTCSC panels, which were then subjected to quasi-static flatwise compression testing. Relative positioning of neighboring composite struts, modification of the carbon fiber path, and strengthening of the core-facesheet node significantly improved the compressive performance of the panels. Based on the findings, compressive strength and stiffness of LTCSC panels can be improved about 100% and 300%, respectively, with minimal increase in weight. Fabricated LTCSC panels were found to demonstrate competitive specific compressive properties in comparison with conventional core materials.

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.

Thermal buckling analysis of laminated plates with variable angle fiber orientation

The thermal buckling response of square plates with variable angle tows under simply supported conditions is modeled numerically. The path of variable angle tow is modeled as a function of lateral location. The classical lamination theory utilizes fiber paths to calculate thermal loads and stiffness matrices. Using Kirchhoff plate theory and finite element theory, the global material stiffness matrix and the global geometric stiffness matrix of the plate under thermal buckling loads are obtained. By using these matrices, eigenvalues or critical buckling temperature is obtained and the buckling response of the plate is examined. The theoretical results are validated by studies in the literature and finite element models. It has been seen even in an unoptimized span of a sample composite material, variable angle tows (VATs) were 8,60% more resistant to thermal buckling than common composite lay-ups.

Fluid-structure interaction analysis of nonlinear flapping dynamic behaviors of variable stiffness composite laminated plates in viscous flows

This paper is concerned with the development of a numerical model for the analysis of nonlinear fluid–structure interaction problems of large-deformable curvilinear fiber-reinforced composite laminated plates in viscous flows. A higher-order shear deformation zig-zag theory in conjunction with nonlinear von Kármán strains is employed to accommodate the large deformations of variable stiffness composite laminated plates. An implicit partitioned fluid–structure interaction method based on an arbitrary Lagrangian-Eulerian framework is adopted for dealing with the coupling of the large-deformable plate and the viscous flow. The validity of the proposed model and method is confirmed by comparing the computed results of a two-layered plate with those available solutions in the literature. Effects of material properties and fiber paths of composite plates on the periodic limit cycle oscillation and the wake-flow vortices are examined. It is found that symmetrical lay-ups of the constant stiffness composite laminated plates can produce asymmetrical flapping shapes, resulting in asymmetrical hairpin vortex structures in the wake flow. For a variable stiffness composite laminated plate, the flexibility of the leading or trailing sections can be adjusted by the curved fiber path, which in turn leads to changes in the plate flapping shapes.

Analysis of vibration characteristics based on variable‐angle hybrid laminates

AbstractComposite laminates are widely used in the aerospace field. Aircraft wings are subject to strong aerodynamic interference, which produces resonance, instability and other phenomena. To avoid this resonance and reduce the vibration of laminates it is essential to adopt a variable‐stiffness laminate. Methods for changing the stiffness include designing the fiber path and inserting a damping layer. The former can increase the natural frequency but does not improve the damping performance. Here we demonstrate how, depending on the resin's agglomeration, variable‐angle hybrid laminates made of carbon fiber and Kevlar fiber increase the damping performance. By using a short beam shear test we found that sandwich hybrid samples with a hybrid ratio of 50% performed better than inter‐laminar hybrid samples, which increased by 19.5%. Based on the results of interlayer properties, 8 layers of pure carbon fiber (CF) laminates and carbon fiber‐kevlar fiber (CF‐KF) hybrid laminates with variable angles were manufactured. Modal tests demonstrated that the change in fiber angle had a greater impact on the natural frequency, the maximum result of which was seen at an angle of <60|75>. By inserting, the KF layer the damping ratio of the <15|30> hybrid laminate increased by 5.45% more than pure CF laminates. These results can be referenced to improve the damping parameters of variable‐angle laminates.

Supersonic flutter of variable stiffness circular cylindrical shells

Curvilinear reinforcement fibres allow to tailor the elastic properties of composite laminates in space, leading to Variable Stiffness Composite Laminates (VSCL). In this work, the aeroelastic stability of VSCL cylindrical shells under a supersonic airflow along the axial direction is analysed in order to verify if curvilinear fibres can be used to increase the flutter speed. A linear mathematical model for thin circular cylindrical VSCL shells is developed for that purpose. The aerodynamic pressure caused by the supersonic airflow is modelled recurring to the linearised piston theory. The p-version of the finite element method is used to transform the differential equations of motion from partial to ordinary. Using the latter, eigenvalue problems are defined to obtain the natural frequencies and mode shapes of vibration, and the critical flutter conditions. Various types of curvilinear fibre paths are explored, to find paths that result in higher values of critical flutter free stream pressure. The values are compared with the ones of conventional, constant stiffness, composite laminated shells.

Eigenfrequency optimization of variable stiffness manufacturable laminates using spectral Chebyshev approach and lamination parameters

This study presents a meshless modeling approach to design variable-stiffness laminates considering manufacturing constraints. The governing equations are derived using lamination parameters and first-order shear deformation theory. The solution approach uses Chebyshev polynomials and Galerkin’s method to obtain the discretized equations of motion. The developed framework was used to maximize the fundamental frequency of composite plates. The variable-stiffness designs provided up to 28.4% higher frequencies compared to optimum constant-stiffness laminates, although the actual level of improvement depends on the number of layers. Finally, manufacturable fiber paths were obtained considering the allowed fiber curvature, which can also reduce the frequency values.

A partition of unity level set method with moving knot CS-RBFs for optimizing variable stiffness composites

A partition of unity level set method with moving knot Compactly Supported Radial Basis Functions (CS-RBFs) is proposed for optimizing variable stiffness composite structures. The iso-contours of a level set function are utilized to represent the curved fiber paths, and the tangent vector of the iso-contour defines the orientation of fiber. The level set function of the full design domain is constructed according to the Partition of Unity (POU) method by a set of local level set functions defined on an array of overlapping subdomains, and they are constructed by using the CS-RBFs. The positions of knots are iteratively changed during the optimization to improve the performance of composite structures. Several examples of compliance minimization are presented.

Manufacturing-oriented topological design of CFRC structures with variable fiber volume and orientation

Allowing freely steering fiber orientation, curvilinear fiber reinforced composite has much better load-bearing capacities than conventional straight-fiber composites. However, the uneven distribution of the fiber and the manufacturability are often ignored while designing variable stiffness composite structures. In this paper, a manufacturing-oriented topology optimization method is proposed for designing continuous fiber reinforced composite (CFRC) structures, in which the fiber content as well as the fiber orientation are concurrently optimized with topology variables. The smooth design with explicit boundary is achieved by the floating projection topology optimization (FPTO) method, in which the implicit floating projection constraint is employed to simulate 0/1 constraints of topology design variables. In order to improve the manufacturability of the design, the fiber placement path fitting method based on the potential flow theory is proposed and embedded in the optimization procedure. By analogy with the streamlines, the fiber path would be placed continuously without any crossing and overlap, meanwhile the fiber content could be adjusted optimally according to the stress distribution. Numerical examples are presented to demonstrate the effectiveness of the proposed method.

Progressive concurrent topological optimization with variable fiber orientation and content for 3D printed continuous fiber reinforced polymer composites

In this paper, a multidisciplinary framework to design and produce a topological structure with inhomogeneous distributions of fiber orientation and content for 3D printed continuous fiber reinforced polymer composites (CFRPCs) was proposed to maximize load and fiber utilization efficiency. The combination of optimization design and 3D printing for composites with curvilinear fiber was achieved that the fiber orientation and content were progressively designed in the two-stage procedure. The fiber orientation and topological structure were concurrently optimized firstly. Then, the fiber content was designed through finite element analysis (FEA) and realized by changing continuous fiber path with a hierarchical structure design method. Based on this, the topological beam has been additively manufactured and experimentally investigated, showing 38.55% and 25.40% in stiffness and peak load enhancement compared with the original CFRPCs design, while 264.39% and 165.84% increments compared with pure polymer design. The proposed approach has widened design freedom of CFRPCs 3D printing, possessing potential application to solve engineering problem in aerospace, automotive and other fields.

Development of an automated fibre placement-based hybrid composite wheel for a solar-powered car

Substantial range, handling and acceleration improvements in high-performance vehicles can be achieved by weight reduction. An important area for weight reduction on a car is the wheels. A novel prototype carbon fibre/epoxy wheel has been developed using a combination of automated fibre placement (AFP) and hand layup for the Sunswift 7 solar car. A three-piece wheel design that utilises each process where best suited has been analysed and optimised using the ANSYS ACP PrepPost suite, manufactured, and mechanically tested. The wheel disc was produced using AFP and featured selective reinforcement in the form of spokes. The AFP fibre paths for the disc have been optimised using CGTech’s VERICUT VCP and VCS to minimise gaps and overlaps, resulting in a 98.9% reduction in overlaps when compared with the unoptimised layup. The rim and tyre mounting region of the wheel have been manufactured using hand layup and adhesively bonded to the disc. This hybrid manufacturing approach has demonstrated an advancement in the feasibility of combining traditional and automated composite manufacturing. The final wheel weighed 3352 g, and the wheel deflection under a compressive load has been experimentally verified within 3% of the theoretical value.

Revealing the shallow soil structure of the Yigong Lake in the Tibetan Plateau using a portable distributed acoustic sensing interrogator

The harsh and extreme environmental and near surface conditions of the Tibetan Plateau have limited the conventional electrical-based seismic instruments from obtaining high-quality seismic data through long-term and continuous observations, setting challenges for environmental seismology study and natural hazard monitoring in this area. Distributed acoustic sensing (DAS) is an emerging technique based on optical fiber communication and sensing. It provides a possible solution for subsurface imaging in extreme conditions at high spatiotemporal resolution by converting fiber-optic cables into dense seismic strainmeters. We deploy two survey lines with armored optical fiber cables in the Yigong Lake area, Southeastern Tibetan Plateau, to record ambient noise for a week. The DAS interrogator is specifically designed in a portable size with very low power consumption (25 W/h). Hence, we can use a 12V-DC battery for power supply to adjust the power limitation during the field recording. Ambient noise interferometry and multichannel analysis of surface waves are used to get 2D shear wave velocity profiles along the fiber paths. The results highlight the great potential of DAS for dynamic monitoring of the geological evolution of lakes and rivers in areas of extreme environments as in the Tibetan Plateau.

GoodFibes: An R Package for The Detection of Muscle Fibers from diceCT Scans.

Contrast enhanced computed-tomography imaging like diffusible iodine-based contrast-enhanced computed tomography (diceCT) can provide detailed information on muscle architecture important to comparative analyses of functional morphology, using non-destructive approaches. However, manual segmentation of muscle fascicles/fibers is time-consuming, and automated approaches are at times inaccessible and unaffordable. Here, we introduce GoodFibes, an R package for reconstructing muscle architecture in 3D from diceCT image stacks. GoodFibes uses textural analysis of image grayscale values to track straight or curved fiber paths through a muscle image stack. Accessory functions provide quality checking, fiber merging, and 3D visualization and export capabilities. We demonstrate the utility and effectiveness of GoodFibes using two datasets, from an ant and bat diceCT scans. In both cases, GoodFibes provides reliable measurements of mean fiber length compared to traditional approaches, and is as effective as currently available software packages. This open-source, free to use software package will help to improve access to tools in the analysis of muscle fiber anatomy using diceCT scans. The flexible and transparent R-language environment allows other users to build on the functions described here and permits direct statistical analysis of the resulting fiber metrics. We hope that this will increase the number of comparative and evolutionary studies incorporating these rich and functionally important datasets.

Generation of Ultra-High Signal to Noise Ratio Harmonics in an All-Polarization-Maintaining Fiber Laser

Harmonic mode locking (HML) was proved to be an effectively technique for generating high repetition rate ultrafast pulses. However, none of the various research methods currently used could improve the defects of HML's low signal to noise ratio (SNR), mostly less than 40 dB, limiting its further application. Using the self-made single walled carbon nanotubes (SWCNTs) as saturable absorber (SA) in an erbium-doped fiber laser to obtain HML pulses with an ultra-high SNR (>62 dB) was reported here. A series of harmonics from fundamental frequency to sixth orders could be observed by simply increasing the pump power, and the all-polarization-maintaining (PM) fiber path ensured time domain frequency stability. Moreover, by adjusting the polarization direction of the directional SA, a stable traditional soliton pulse was obtained. In this mode, the repetition frequency no longer split with the increase of pump power, and the SNR was as high as 83 dB. Such an environmentally stable, all-PM fiber, versatile operations laser could not only expand the industrial application prospects of high repetition frequency HML pulses, but also be an excellent seed source for ultra-high-power lasers research.