14:30
Session 6: Automated Fiber Placement
14:30
20 mins
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Fiber Steering, Waviness and Strength: Correlating Z-Deviation with Tensile Strain Fields in Automated Fiber Placement
Kevin Scheiterlein, Noah Möller, Julian Schuster
Abstract: Automated Fiber Placement (AFP) represents a cutting-edge manufacturing process that enables the precise and automated production of fiber-reinforced plastic composite structures. The possibility of curvilinear layup paths, designated as "fiber steering", facilitate the placement of fibers along load-optimized trajectories. This gives the opportunity for the fabrication of mechanically demanding components that are difficult or impossible to achieve using conventional manufacturing methods as hand layup.
However, the introduction of steering introduces challenges within the layup quality, most notably in-plane and out-of-plane effects leading to fiber waviness, which form microscopic angular deviations functioning as a mechanical weak point. Out-of-plane defects have been shown to induce interlaminar effects, thereby resulting in z-deviation. Conversely, in-plane defects have been observed to modify the fiber orientation exclusively within the plane.
The present study investigates the effects of steering on the mechanical behavior of the laminate. First the steering behavior across a range of machine and tooling configurations was evaluated. This aimed to generate a qualitative value indicating the impact of process parameters employed on the used thermoset material. With this information two parameter windows are defined for the manufacturing of steering integrated coupon laminates used for tensile testing: one with induced out-of-plane effects and the other with in-plane effects. The objective was to evaluate the impact of varying degrees of fiber waviness. The evaluation was conducted using a novel methodology, which was specifically developed for this purpose. The method employs 3D scanning, using a machine integrated laser light section sensor, to detect steering induced surface deviations, identified with a defined z-threshold from the laminate plane. The resulting defects are then correlated with strain and failure patterns obtained through Digital Image Correlation (DIC) during the tensile testing of the specimens. This enables the establishment of relationships and conclusions about their mechanical impact.
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14:50
20 mins
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Thermal Analysis of Incoming Tape during In-Situ Consolidation by Automated Fiber Placement Using a Novel Experimental Measurement Technique and Conjugate FVM Simulation
Mahmoud Fereidouni, Suong Hoa
Abstract: The temperature field of the incoming tape, particularly around the deposition region, governs the mechanisms of melting, consolidation, and crystallization during automated fiber placement (AFP) of thermoplastic composites. However, direct measurement of the internal temperature distribution within the incoming tape has remained elusive due to limitations of infrared thermography and the impracticality of conventional thermocouple placement.
To address this limitation, a new experimental technology was developed to monitor the internal temperature of the incoming tape during AFP. A specially engineered sensor tape was fabricated to replicate the geometry and material of the actual thermoplastic tape while embedding a fast-response fine thermocouple at mid-thickness. The sensor tape was fed through the AFP head, enabling direct measurement of the temperature profile along its complete trajectory, from pre-heating to consolidation and subsequent cooling. This technique provides, for the first time, reliable access to temperature data within the most critical and previously unmeasurable regions of the AFP process.
Complementing the experiments, a three-dimensional conjugate heat transfer model was established using the finite volume method. The model incorporates the coupled thermal interactions among the impinging hot gas flow and solid domains including incoming tape, composite laminate, and compaction roller, and employs the SST k-ω turbulence formulation to resolve detailed convective heat-transfer dynamics. Model predictions were compared with experimental results, demonstrating good agreement across the heating and cooling zones.
Finally, a computationally efficient data-driven surrogate, based on multivariate third-order polynomial regression, was trained using the validated simulation dataset. This surrogate enables closed-form prediction of key thermal responses – such as nip-point temperature, maximum temperature, and immediate cooling rate – from primary process parameters, offering a practical tool for process optimization and control in AFP in-situ consolidation.
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15:10
20 mins
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Experimental Assessment of Compaction Pressure Distribution in Automated Fiber Placement: Model Validation and Unforeseen Mechanisms
Benjamin Francis, Matthew Godbold, Ramy Harik
Abstract: The fabrication of large, low to medium contour composite shell structures is often achieved using Automated Fiber Placement (AFP). Among process parameters relevant to AFP, compaction pressure applied by the roller to the substrate is critical for reducing voids, ensuring interfacial bonding, and achieving target mechanical properties. To support process planning, a predictive compaction pressure model was previously developed, but experimental validation remained incomplete. This work presents an experimental campaign to validate the proposed model and pertinent phenomena identified in the resultant data. Trials were conducted using the Integrated Structural Assembly of Advanced Composites (ISAAC) AFP system at NASA Langley Research Center, and pressure fields were captured using a pressure mapping system. Low error (under 20%) was shown with predictive models, but large deviations (up to 330%) were observed on a complex tool surface. Beyond validation, new sources of variability were revealed by analysis. Vertical striping of elevated pressure was observed, corresponding to the perforation pattern on the roller, while lighter horizontal striping was observed and was attributed to small inter‑tow gaps. As highlighted by these findings, roller design and tow placement introduce pressure fluctuations not included in the current model. In this study the present model’s predictive accuracy is quantified, and previously unrecognized mechanisms with direct implications for AFP process parameter selection, roller design, and defect mitigation are identified.
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15:30
20 mins
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Effects of repassing on the geometric characteristics of CF/LM-PEAK tapes deposited via Humm3-assisted in-situ consolidated AFP
Gamar Ismayilova, Andre Florindo, Daniël Peeters
Abstract: Automated Fiber Placement (AFP) with in-situ consolidation provided by the Humm3 pulse lamp allows for the automated production of thermoplastic composites without the high variably coming from hot air and safety requirements from lasers. Yet, on the search for lower production times, the increasingly higher heating and subsequent cooling rates can adversely affect the tape’s surface topology. Such irregular surface together with features such as gaps and overlaps increase the likelihood of air pockets that not only reduce the interlaminar bonding quality, it also undermines follow-up joining methods such as welding.
As gaps and overlaps might be unavoidable, this research focuses on reducing the tape’s surface irregularities by introducing a combined heating and compacting step right after each tape’s placement. This step is typicality named either repassing or in-situ annealing and has rarely been reported in the literature, especially using the Humm3. This paper aims to investigate the effects of repassing on the tape’s surface topology and its implication while staking layers.
In this study, a KUKA KR 210 R2700 robot equipped with the pulse light Humm3 is used to manufacture thermoplastic specimens made of carbon fiber LM-PEAK. Each sample contains manufactured overlaps of different dimensions by varying compaction force while keeping the nip-point temperature constant. Surface topography is then measured with a laser line scanner mounted on the AFP head and later validated against an optical microscope.
The conclusions of this work aim to analyze the effects of the repassing step on the tape’s geometry, including its surface roughness, thickness and width. This work will therefore further expand the knowledge of the deconsolidation phenomenon that affects AFP with in-situ consolidation and evaluate an approach to mitigate its effects. These findings will ultimately contribute to improve the reliability of automated production of thermoplastic composites.
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