11:20
Session 9: Modelling and Characterisation of AFP
11:20
20 mins
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Generative Geometric Approach for Structured Meshing of AFP‑Fabricated Composite Parts: Geometry‑Driven Modeling and Validation
Willian dos Santos Pinto, Alain Rassineux, Cédric Huchette, Christian Fagiano, Juan Manuel Garcia
Abstract: Automated fiber placement (AFP) is a manufacturing process widely employed on aeronautical sector. This process involves a robotic arm that lays down pre-impregnated tows, thereby enhancing automation, accuracy and repeatability in manufacturing of composite parts. In addition, AFP allows a bigger possibility of design, including components with non-conventional placement path. Nevertheless, despite these advantages, two types of singularities are inherently generated during the AFP manufacturing process: gaps and overlaps. These singularities must be considered on the part design since they impact the mechanical performance of the final product. Consequently, modeling strategies to predict the behavior of structures with the presence of singularities is needed in order to optimize the AFP part design. This work aims to develop a strategy to mesh the AFP composite parts based on the placement path. The mesh method, called Generative Geometric Approach, uses the coordinates of robot trajectory to reconstruct the AFP structure mesh resulting in a structured and conformal mesh. Some geometric aspects intrinsically emerge from this method, such as ply waviness, void regions and local thickness variation. This method, which is purely based on the geometric path, leads to discrepancies between the mesh geometry and the final AFP part, as thermo-mechanical effects are not considered. Therefore, a geometric validation is carried out on the model by comparing it with imaging technique observations. This comparison reveals whether the model over- or underestimate ply waviness and/or local thickness variation, allowing the model to be adapted to best represent the AFP composite geometry. Conversely, finite‑element analysis highlights how the geometry influences the kinematic response induced by ply waviness and local thickness variations, emphasizing the need to use an accurate geometric model to obtain a representative mechanical behavior.
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11:40
20 mins
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Effects of Toolpath Direction on Temperature Gradients in Automated Fiber Placement
Rowen Burney, Ben Francis, Matthew Godbold, Ramy Harik
Abstract: Automated Fiber Placement (AFP) is an advanced composite manufacturing process that enables efficient fabrication of high-precision structures. Optimizing process parameters to enhance layup consistency and reduce defects remains challenging. Heating influences key material characteristics such as tack, void content, crystallinity, and mechanical performance. Although detailed AFP heating models exist, few address the combined effects of surface geometry and toolpath direction on heat application. This work examines how surface curvature and layup direction together shape temperature gradients during deposition. By quantifying surface curvature magnitude and direction relative to the layup path, representative temperature gradients are derived. These gradients inform the selection of optimal layup paths. The chosen paths are then integrated into an existing surface temperature prediction model. This integration achieves more uniform heating and minimizes thermal inconsistencies. The resulting method enhances part uniformity and reduces temperature-related defects such as bridging and wrinkling. By minimizing these defects, manual rework time is significantly lowered, reducing layup cycle time and improving process repeatability across components.
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12:00
20 mins
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Thermoplastic Gap Filling in AFP Layups for Mitigating Microcracking under Cryogenic Conditions
Jonas Appels, Daniel Stefaniak, Clemens Dransfeld
Abstract: Automated Fibre Placement (AFP) enables manufacturing of lightweight composite structures for cryogenic hydrogen storage. However, during placement on double-curved surfaces, unavoidable triangular gaps are formed between tows. These gaps fill with pure epoxy during autoclave curing, creating resin-rich regions that differ in thermal expansion from the surrounding laminate. Under cryogenic cycling, these regions act as hotspots for microcrack initiation, posing a major challenge for linerless Type V cryogenic hydrogen tanks.
This research investigates a microscale toughening concept to mitigate crack initiation by filling AFP gaps with thermoplastic materials of higher fracture toughness. The study focuses on the interphase formation between Polyetherimide (PEI) and the epoxy system Hexcel 8552, exploring how fibre presence and orientation (parallel vs. orthogonal to the gap) affect resin diffusion, interphase thickness, and local crack resistance.
Tensile specimens were manufactured from Hexcel 8552/AS4 slit-tape prepreg with intentional gaps, either left unfilled or filled with PEI film and different fibre orientations. Interphase characterisation is performed through optical microscopy and scanning electron microscopy (SEM), while tensile tests at room and cryogenic temperatures assess mechanical performance.
Initial results show that the PEI filler upon deliberate selection of cure parameters and fibre orientations forms a distinct interphase with the epoxy matrix with varying thicknesses. The interphase exhibits a characteristic droplet morphology due to reaction-induced phase separation (RIPS). This confirms diffusion-driven interaction under the applied cure cycle. Specimens with PEI-filled gaps demonstrate delayed crack initiation and altered fracture morphology compared to unfilled specimens.
These findings provide the first experimental insight into interphase-controlled gap-filling as a local toughening strategy for AFP laminates. The ongoing mesoscale investigations aim to link interphase morphology to microcrack initiation and permeability behaviour, supporting the development of leakage-resistant composite hydrogen tanks.
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12:20
20 mins
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Enhancing Pressure Uniformity and Dwell Time Control on Complex Moulds Using Adjustable-Stiffness Compaction Rollers
Amir Hafez Yas, Mehdi Hojjati
Abstract: Automated Fiber Placement (AFP) has advanced composite manufacturing to a higher level of automation by enabling the production of large and geometrically complex structures with high repeatability and reduced waste. However, the fabrication of thermoset composites using this method is highly dependent on process parameters such as compaction pressure, contact width, and temperature, which must be precisely controlled to ensure consistent laminate quality. Insufficient bonding between layers can result in the formation of defects such as tape folding, bridging, and wrinkles. When manufacturing on complex moulds with concave or convex geometries, process parameters can vary significantly due to changes in surface curvature and roller conformity. This study aims to minimize the alteration of process parameters during AFP layup over curved molds by varying the stiffness of the compaction roller along its length through modifications to its shaft. In the first stage, finite element (FEM) simulations were conducted to determine the optimal shaft dimensions and depth levels for concave and convex mould configurations, enabling the roller to maintain uniform pressure under various curvature conditions. Based on the numerical results, polyurethane rollers with corresponding shaft geometries were manufactured to experimentally validate the numerical predictions. Pressure-sensitive films were employed to capture the pressure distribution over flat, concave, and convex surfaces, and the results were compared against the FEM outcomes. The findings demonstrate that adjusting roller stiffness by the design of its shaft geometry, pressure uniformity, and formability of the roller can be enhanced. This study highlights the crucial role of compaction roller stiffness on its formability over complex moulds and how certain designs can provide better uniformity of pressure distribution and formability of the roller.
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