15:50
Session 4: Manufacturing Simulation
15:50
20 mins
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Is laser cutting a suitable alternative for cutting carbon fibre preforms?
Dominic Stratton
Abstract: Large aerospace composite structures rely on accurate, reliable and rate capable cutting processes to ensure the components are manufactured on time to the near net-edge design tolerances. Classically composite preforms are cut mechanically with various types of blades or knifes . These mechanical cutting systems start having issues when the preform thickness increases. This manifests as increased blade breakages, reduced cutting speed, and reduced cutting accuracy. The cutting process needs to develop to achieve the rate and quality requirements of the composites industry including a reduction in post-cure machining operations. This has motivated an exploration of alternative methods.
This study investigated laser cutting as a potential solution. Initial trials found two suitable laser cutting systems to focus our development efforts. Development trials then focused on understanding the how the lasers settings influenced cut quality. Data was gathered on focal position, cutting speed, laser power, multi-pass cutting strategy, multi-pass with changing focal positions, tooling, and cooling solutions. Using this data, three possible pathing strategies were designed and used to manufacture test coupons. When infusing the laser cut preforms it is evident that there is little difference to the infusion-rate and the preforms accepted resin during infusion when compared to virgin material. Mechanical tests of the infused preforms highlighted a trend that the higher the energy density of the laser cut, the worse the coupon would perform in mechanical testing via ASTM D3039.
This project has demonstrated laser cutting as a technology capable of achieving cutting rate requirements (100mm/s) at preform thicknesses of ≈5mm and have successfully cut a carbon fibre preform at 18mm thickness. Work is ongoing to understand the effect of laser cut edges and the heat affected zone. The estimated Technology Readiness Level (TRL) for this process is TRL III. To conclude this study has developed an increased understanding on the potential for laser cutting carbon fibre preforms at rate for large structure aerospace applications, and whilst the are results are promising, further study, particularly on the mechanisms of mechanical performance degradation is required.
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16:10
20 mins
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Composite Thermoforming Defect Identity Cards: Cause, Prevention, Detection, Significance, and Progression
Matthew Godbold, Ben Francis, Liam Burns, Ramy Harik
Abstract: Thermoforming of composite materials is a key process in automated manufacturing, valued for its ability to rapidly produce net-shape and contoured components. Despite these advantages, effective management of defects remains a critical challenge. Knowledge regarding these defects is often fragmented, existing in discipline-specific silos that hinder a holistic understanding across the design-to-inspection lifecycle. This research addresses this need by developing defect identity cards to consolidate multi-disciplinary knowledge into a unified and accessible format. To achieve this, a viewpoint modeling methodology was employed to systematically capture and structure information from the distinct perspectives of designers, manufacturing engineers, analysts, and inspection professionals. The knowledge base was synthesized from a comprehensive literature review, supplemented by practical laboratory experience and consultation with industry experts. The primary result is a foundational set of defect identity cards for common composite thermoforming defects. Each card serves as a single source of truth, detailing a defect's (1) fundamental causes, (2) strategies for its prevention, (3) key indicators for its detection, (4) engineering significance, and (5) potential for progression in-service. This research establishes a practical methodology for classifying and communicating critical defect information by creating the first comprehensive set of defect identity cards for composite thermoforming, providing the structured understanding necessary to bridge communication gaps, enhance training, and advance right first time manufacturing strategies.
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16:30
20 mins
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The effect of dry vs. wet winding on residual stresses in composite pressure vessels
Ivan Komala, Julien van Campen, Daniël Peeters, Morteza Abouhamzeh, Sebastian Heimbs
Abstract: Filament winding is a well-established manufacturing technology for producing thermoset composite pressure vessels (CPVs). Over the past decade, carbon fiber/epoxy towpreg has become the preferred material due to some advantages, including relatively constant fiber volume fraction and waste reduction. However, the transition from wet to dry winding process introduces, among other effects, winding friction variations which directly affects the slippage coefficient. This enables a larger range of possible winding angles and alters the distribution of winding angles throughout the dome section which affects the thickness at the dome. The thickness variation influences the temperature distribution during the curing process: thicker domes experience longer time to achieve the prescribed curing temperature and consequently non-uniform degree of cure over the time. In addition to residual stresses from cooling down and interlaminar stresses, this non-uniform curing was expected to increase the residual stress which accelerates the probability of crack initiation. Understanding this coupling between slippage coefficient, geometric consequences and residual stresses is essential for optimizing CPV performance.
In this study, curing-induced residual stresses in CPV were predicted through numerical analysis using a temperature-dependent constitutive model that accounts for stiffness evolution, chemical shrinkage and viscoelasticity. An axisymmetric CPV model was generated based on non-geodesic winding paths with different slippage coefficients. The external thermal loads were assumed uniform to justify the axisymmetric simplification. The variations in winding angles, which were induced by different slippage coefficients, influence the dome thickness. This thickness was calculated using the parabola method [1]. The other factors such as bandwidth and fiber tension along with temperature-independent material properties are assumed to be constant. The manufacturer-recommended curing cycle was applied as the loading condition, and the cooling down process was assumed to be unconstrained and free to deform.
The full paper will investigate the influence of slippage coefficient on the thickness variation, and the resulting residual stresses from curing process.
Reference:
[1] Lin J. et al., 2023. Prediction of composite pressure vessel dome contour and strength analysis based on a new fiber thickness calculation method
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