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ItemTesting of Two-Phase Cooling of Bipolar Plates for Fuel Cells( 2025)Hydrogen-powered fuel cells are the preferred energy source for electric aircraft. However, for aircraft applications, it is of upmost importance to reduce the mass of the fuel cell system. A considerable amount of the total system mass is due to the fuel cell cooling system. This paper discusses two-phase cooling of the bipolar plates in a fuel cell stack. A twostep approach was used. First, test were carried out with machined plates with a geometry similar to bipolar plates. In a second step, actual bipolar plates were tested, including the membranes, seals and gaskets that are present in a fuel cell. These bipolar plates are from a standard fuel cell stack and are intended for water/glycol cooling. The tests show that these standard bipolar plates can be used with two-phase cooling with methanol
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ItemAutomated aircraft defect risk analysis utilising maintenance and pilot reports(Informit, 2025)This paper demonstrates Natural Language Processing (NLP) on a dataset of tens-of-thousands of maintenance and pilot reports for a fleet of aircraft, which includes the defect description text and the scheduled departure delay in minutes or if the flight was cancelled. The NLP framework is developed by fine-tuning pretrained Large Language Models (LLMs) for predicting the risk level that a defect report poses to fleet availability. The model is trained on a portion of the reports, utilising the delay duration or cancellation status to determine a low or high impact based on time threshold values. This LLM approach goes beyond using hard coded rules based on individual words in reports and enables more nuanced contextual analysis of all report text that May not be apparent at an individual report level. Results for fine-tuned pretrained LLMs demonstrate an overall test accuracy of 72%, with a greater accuracy of 90% when filtering for higher confidence predictions of low or high impact reports. The impact and likelihood of reoccurrence based on dates determines the overall risk of aircraft parts, location and condition across the fleet. Subsequently, the fine-tuned model is applied to Federal Aviation Administration (FAA) Service Difficulty Reporting System (SDRS) data, presenting an alternative analytical view to conventional reliability reporting of the risks to fleet aircraft. Furthermore, it is demonstrated that fine-tuned LLMs can distinguish reports for part failures with greater accuracy than legacy NLP processes, which could save hours in reliability analysis. Overall, these NLP approaches could enable aircraft maintainers to make decisions on how to manage resources, vary maintenance schedules and optimise sustainment programs with a predictive risk model that can be applied to new incoming maintenance and pilot reports.
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ItemEnhancing the shear strength of hybrid titanium-composite joints by out-of-plane protrusions(SAMPE, 2025)With the increasing usage of composite parts in aerospace, automotive and other sectors, there is a growing need for hybrid joining technologies. Innovation is desired in terms of joining methods to join metal and composite constituents. Traditional mechanical fastening methods, e.g. bolting and riveting, involve point contacts resulting in stress concentration, and labour and weight penalties. In this study, 3D-printed titanium is joined to unidirectional carbon fibre-reinforced thermoplastic composite. This type of joint is particularly challenging due to chemical incompatibility and mismatches of thermo-mechanical properties. The hybrid joint is constructed by hot press forming, as the heat and pressure control enable improved mechanical properties. Laser powder bed fusion is used to realize bespoke protrusions in the out-of-plane direction of the titanium faying surface that mechanically interlock with the composite material. Fabricated joints, with and without protrusions, are tensile tested in a single lap shear configuration. Results show that mechanical interlocking gives a 17x improvement compared to protrusion-free joints. The measured ultimate joint shear strength was on average 11.6 MPa. Moreover, this shear strength can be correlated to the feature size of the additively fabricated protrusions. Altogether, this gives valuable engineering insight for the design parameter optimisation of hybrid titanium-composite joints.
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ItemEffect of Interlayer Temperature Control on Interlayer Strength for Large Format Additive Manufacturing of High Performance Thermoplastics(SAMPE, 2025)With the increase of printing dimensions inherent to Large Format Additive Manufacturing (LFAM), the main challenge of extrusion-based additive manufacturing processes is also magnified: achieving a high interlayer bond quality. Parts manufactured through this process typically exhibit 50–75% lower mechanical performance in the Z-direction (across layers) with respect to X- and Y-directions. The impact of interlayer temperature control on the interlayer strength of a semi-crystalline polymer printed using LFAM has been evaluated. By using assisted heating during printing, the substrate temperature can be raised to the optimal processing range, allowing for the creation of high-quality bonds between the consecutive layers. In this study, multiple sets of specimens are printed at different interlayer temperatures using neat and carbon fibre reinforced LMPAEK™ material. The interlayer bond strength is evaluated through mechanical testing and microscopy analysis, and compared with in-line measurements of the interlayer temperature. The results of this research demonstrate that active heating enables higher quality interlayer bond compared to unassisted printing, reducing the anisotropy of 3D printed parts.
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ItemInduction Welding Technology for Thick Composites(SAMPE, 2025)Induction welding offers significant benefits for joining thermoplastic composites. Although it is commonplace to weld thin composites, welding thick composites remains a challenge due to the low magnetic field strength at the weld interface and overheating of the substrate closer to the coil. This study aims to develop an induction welding methodology based on KVE INDUCT® for thick composite substrates up to 8 mm thickness each, and demonstrate it for the first time. Quasi-isotropic C/LM-PAEK laminates were manufactured at thicknesses of approximately 4 mm and 8 mm. 4 mm + 8 mm and 8 mm + 8 mm substrates were welded from the thicker side. Several approaches were employed to weld the substrates: using a susceptor, adjusting the process parameters (weld speed & current), using additional heat sinks/constraints, and utilizing a magnetic flux concentrator. Welding thick composites required significantly lower speeds and higher currents compared to thin laminates. However, an innovative coil design involving a magnetic flux concentrator facilitated increasing the weld speed and lowering the current to values compared to standard thickness substrates (2.2 mm). Constraints placed along the edges of the substrates helped to constrain the flow by setting a physical boundary and extracting excess heat. Robust and high quality welds were realized with the innovative coil and additional heat sinks combined, demonstrated by C-scan analysis, without using a susceptor.