Fiber Placement Research Articles

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.

A general method of trajectory generation based on point-cloud structures in automatic fibre placement

In the process of manufacturing fibre reinforced composite components with automatic fibre placement(AFP), trajectory generation is the core technology that determines the quality and efficiency of fibre placement and the performance of formed components. This study overcome the limitation that traditional algorithms only consider parameter surfaces or mesh surfaces and study a general method of AFP trajectory generation based on point-cloud structures. Firstly, we proposed a directed projection providing a theoretical guarantee for the subsequent trajectory generation on moulds represented by point-clouds; Secondly, we provided two different solvers named numerical and direct approach to generate initial trajectories and subsequent offsetting trajectories. Our numerical simulations and error analyses show that proposed tactics are well suitable for point-cloud structures and could generate full coverage trajectories within a tiny error without gaps and overlaps. The proposed method is absolutely different from the traditional method and does not need to mesh or reconstruct the point-cloud, but it can directly generate trajectories on point-clouds, thus avoid errors in surface reconstruction and reduce processes of AFP trajectory generation.

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.

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.

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.

3D printing of continuous carbon fibre reinforced polymer composites with optimised structural topology and fibre orientation

This study presents a sequentially coupled optimisation of structural topology and fibre orientation for 3D printing of continuous carbon fibre reinforced polymer composites. Topology optimisation was first performed to obtain the geometry of the structure under a specific load, and then continuous fibres were placed along the identified principal stress trajectories. Composite preforms were 3D printed by a material extrusion-based technique followed by post-processing with vacuum bagging using epoxy for infusion. The case of Messerschmitt-Bolkow-Blohm (MBB) beam under three-point bending test was studied and a path-based model was also built to analyse the effect of customised fibre placement and their lightweight performance. Experimental results showed that 3D printed composites with optimised fibre orientation achieved 305% and 256% higher strength and stiffness than Markforged® printed composites. By comparing with the traditionally-manufactured composites and aerospace-grade aluminium alloy, this study demonstrated the potential of manufacturing ultra-lightweight composite structures via 3D printing and the benefits of fibre orientation optimisation in lightweight design of composites with topology optimisation.

Effect of Roller Pressure and Base Prepreg Layer on Tensile and Flexural Properties of CFRP Laminates Fabricated Using Automated Fiber Placement

Composites can be manufactured in numerous ways. Among the available methods, Automated Fiber Placement (AFP) is the most advanced and latest technology utilized by companies for aerospace and other projects. Although it offers many benefits, it has unique manufacturing challenges and quality issues. The presence of tow placement defects such as tow gaps, tow overlaps, twisted tows, incomplete tows, and missing tows in the AFP process are causes for concern as these lead to a decrease in the mechanical performance of the fabricated parts. Although it is not possible to completely avoid the occurrence of defects, optimizing key process parameters is a possible way to minimize them. Roller pressure is one such parameter. If it is too high, it can lead to wider and thinner tows and if it is too low, the towpreg may not stick properly to the substrate and hence, not conform to curvatures. In this work, test layups of different configurations using carbon (T700SC-24K-50C) towpreg with epoxy (UF 3376-100) as the matrix system were prepared at different compaction roller pressures (2 bar, 3.5 bar, and 5 bar), with and without the presence of base prepreg layers. Tensile and bending tests were respectively carried out according to ASTM D3039 and ASTM D7264 to study the effects of these process parameters on the layup defects. From the test results, it is found that using a compaction roller pressure of 3.5 bar and a base prepreg layer of the same material as the towpreg, leads to minimum defects, and hence, to the best tensile and bending properties.

Experimental study on the influence of lamination parameters on the vibration characteristics of variable stiffness composite laminates

In this study, the vibration characteristics of composite laminated plates with variable stiffness were studied using a modal analysis experiment based on the hammering method and a free vibration attenuation experiment. Twenty-five variable stiffness laminates fabricated from carbon fiber-reinforced resin matrix composite prepregs were manufactured via an automated fiber placement process. By varying the parameters, such as the fiber angle (<0°|15°>, <15°|30°>, <30°|45°>, <45°|60°>, <60°|75°>, <74°|89°>), curve ply ratio (0, 0.5, 1), and the number of layers (8, 12, 16), these laminates were tested in a dynamic signal analyzer to obtain their modal frequency and modal damping. These parameters were observed to significantly affect the modal parameters. As experimental investigations on the vibration characteristics of variable stiffness composite laminates are very rare, this study can be considered a reference for future work.

Pseudo-ductile fracture in grid stiffened structure by automated fibre placement

Pseudo-ductile fracture in grid stiffened structure by automated fibre placement

Light-trapping carbon nanotube forests in glass fibre-reinforced thermoplastic prepregs for efficient laser-assisted automated fibre placement

Laser-assisted automated fibre placement (LATP) is an emerging technology for manufacturing thermoplastic composite components. However, major challenges are still encountered for the LAFP process for glass fibre (GF) reinforced composites due to the high near-infrared (NIR) laser reflectance and transmission as well as resulting poor absorption of prepreg constituents. Inspired by the efficient light-trapping and photothermal characteristics of carbon nanotube (CNT) forest, we fabricate CNT forest onto the GF surface by rapid and low‐cost flame synthesis method, to enhance the photothermal conversion efficiency of poly-ether-ether-ketone (PEEK)/GF prepregs during LAFP process. CNT forests with different lengths, alignments and densities were produced by changing flame synthesis parameters. The spectroscopy results show that CNT forest suppresses transmission and reflection from GF and crystals in GF/PEEK prepreg within the NIR wavelength range at near normal incidence, decreasing transmission and reflectance to 0.3% and 7.9%, respectively, and increasing absorption to 91.8% at 1080 nm wavelength. Furthermore, CNTs forest improves the heating rate of GF/PEEK prepreg by more than 700% for a wide range of incident angles. Consequently, CNT forest enables a 400% increase in placement speed and a 79% reduction in energy consumption during LAFP process, while making negligible voids in the interlayer.

Application of tailored fiber placement to fabricate automotive composite components with complex geometries

Fabrication of continuous carbon fiber composite components with complex geometries has traditionally been a challenge, yet automotive components are rarely simple in design or loading. Unidirectional and woven fabrics dominate the industry but are limited to generally homogenous microstructure across a layer. Tailored fiber placement (TFP) is a relatively new composite preforming technology that provides a means to address this limitation. In TFP, tows of fibers are positioned by a robotic gantry and stitched in place. This process affords unmatched control over the local fiber orientation. In this study, we design, fabricate, and test a simplified carbon fiber composite connecting rod for an internal combustion engine. Design is aided by performance simulation using the finite element BSAM program. The connecting rods are tested in monotonic compression, monotonic tension, and fatigue. Results show that the TFP process is able to successfully fabricate a high strength carbon fiber composite component featuring a complex structure. Discussion focuses on evaluating achieved performance relative to design targets, correlation between simulated predictions and test results, and evaluation of failure modes from post-failure analysis. The TFP process could be useful to many automotive applications, including seat frames, chassis components, and electric propulsion system components.

Additive manufacturing of fiber-reinforced polymer composites: A technical review and status of design methodologies

Additive manufacturing (AM) of fiber-reinforced composites is gaining traction as an important manufacturing technology to produce complex, highly customized structures. AM processes enable the fabrication of complex 3D structures with control over fiber position and orientation, offering tremendous design freedom. Although the use of AM to fabricate fiber-reinforced composites is promising, various design difficulties remain. These include consideration of structural performance subject to manufacturing constraints on fiber placement, orientation, bend radius, and other relevant limitations. Design engineers will have to consider these limitations to be able to reap the full benefits of AM to fabricate fiber-reinforced polymer composites. This paper aims to provide a survey on the advances in multi-scale topology optimization, fiber orientation parameterization, micromechanics of fiber-matrix interactions and process planning specific for the AM of complex fiber reinforced composites. The status of recent research is summarized, and future directions outlined.

Thermally conditioned aerospace‐grade carbon fiber reinforced polyether ketone ketone composites: Structure, impact response, and thermomechanical performance

AbstractCarbon fiber‐reinforced high‐performance thermoplastic composites have recently become an efficient alternative for aerospace engineering applications. However, the temperature sensitivity of semi‐crystalline carbon fiber/polyether‐ketone‐ketone (CF/PEKK) polymers revealed the necessity of investigating their performance in service conditions. This study aims to evaluate the effect of extreme service conditions on thermomechanical performance and fracture characteristics of CF/PEKK composite laminates. For this, aerospace‐grade composite laminates were manufactured with the automated fiber placement process and were exposed to extreme service temperatures of −50°C (Conditioned I), 180°C (Conditioned II), and initially 180°C following −50°C (Conditioned III), simulating critical service temperature ranges in aerospace applications. According to impact tests, the energy absorbance of CF/PEKK composites decreased in all thermal conditioning scenarios by up to 25%. Additionally, Conditioned I samples represented relatively low glass transition temperature and degree of crystallinity compared to the control samples; however, Conditioned II and Conditioned III samples exhibited an opposite behavior. Dynamic mechanical analysis (DMA) investigations revealed a 13% reduction in the storage modulus for all thermal conditionings. While CF/PEKK composites represented ductile/brittle behavior at room temperature and high/low conditioning temperatures, their brittleness increased at −50°C, and the structure became ductile at 180°C. This study confirms that DMA is a powerful tool for determining the glass transition temperature for fiber‐reinforced composites with higher sensitivity and accuracy than DSC.

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.

Research on the method of improving the laying accuracy of automated fiber placement

Research on the method of improving the laying accuracy of automated fiber placement

Load-bearing composite fracture-fixation devices with tailored fibre placement for toy-breed dogs

Fibre reinforced composites are attractive materials for hard tissue reconstructions, due to the high strength and low flexural modulus. However, lack of contourability in the operation theatre inhibits their clinical applications.The study presents a novel in situ contourable composite implant system for load-bearing conditions. The implant system consists of a thin bioresorbable shell with several cavities, much like bubble-wrap. The central cavity contains a semi-flexible glass fibre preform prepared using Tailored Fibre Placement method. The preform is either pre-impregnated with a light curable resin, or the resin is injected into the cavity during the surgical procedure, followed by light curing. The semi-flexible glass fibre preforms were also examined as separate devices, “miniplates”. Two types of miniplates were scrutinized, a simplified pilot design and a spatially refined, “optimized” design. The optimized miniplates were implemented as biostable and bioresorbable versions.The feasibility of the in situ contourable composite implant system was demonstrated. The potential of Tailored Fibre Placement for the semi-flexible glass fibre preforms and miniplates was confirmed in a series of biomechanical tests. However, structural optimization is required. Antebrachial fractures in toy-breeds of dogs are exemplar veterinary applications of the devices; further applications in veterinary and human patients are foreseen.

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.

To Study Fracture Resistance of Interligtm Glass Fiber Orientation and Placement on Large Class II Cavities in Maxillary Premolars: An in Vitro Study

To examine &amp; assess how varied InterligTM glass fibre placement &amp; orientation affect fracture resistance of large class II cavities in maxillary premolars -An In Vitro study. Class II (MOD) cavities were organized with uniform dimensions on 50 extracted human maxillary premolars, and samples were erratically distributed into 5 groups (n = 10 each) as follows: Group I contains composite materials; Group II contains composite + horizontal Interlig placement on the gingival &amp; pulpal floors; Group III contains composite + horizontal Interlig placement only on the pulpal floors; Group IV contains composite + vertical Interlig placement on the gingival &amp; pulpal floors; and Group V contains composite + Interlig chips. Fracture resistance of all samples was tested using universal testing machine following restorations and the thermocycling process. Under a stereomicroscope, the fracture modes were examined. One-way ANOVA &amp; Tukey test were used to analyse data, with significance values of P 0.05. The fracture strength of control group was 736.8640 N while it was 1233.4480 N for group 2, 1223.2260 N for group 3, 1185.0440 N for group 4 and 797.5600 N for group 5. Fracture strength of group 5 was more than other groups except for group 1, there was no statistically substantial modifications. Fortification of composite with fiber does upsurge fracture resistance of wide Class II mesio-occluso-distal premolars cavities significantly.

Shape and topology optimization method for fiber placement design of CFRP plate and shell structures

In this study, we present a novel non-parametric shape-topology optimization method for fiber placement and orientation design, aiming at controlling the stiffness of CFRP (Carbon Fiber Reinforced Plastics) shell structures. The sum of squared error norm for achieving the target displacements on the arbitrarily specified position is minimized under the length constraints as a design problem. A simultaneous shape and topology optimization problem is formulated as a distributed-parameter optimization problem based on the variational method. The shape gradient function and the density gradient for this design optimization problem are theoretically derived with the Lagrange multiplier method, the material derivative method and the adjoint variable method. The solid isotropic material with penalization (SIMP) method is employed for topology optimization. The gradient functions derived are applied to the H1 gradient method for fibers to determine the optimal shape and topology. With the present method, the optimal fiber placement and orientation can be obtained without any parameterization. Numerical examples are solved to show the validity of the proposed method and the results are discussed.