Other publications

Permanent URI for this collection

https://reports.nlr.nl/handle/10921/1451
Other than NLR reports

Browse

Recent Submissions

Now showing 1 - 5 of 175
  • Item
    Microlattices with tailored properties as thermoplastic composite sandwich cores
    ( 2025) Vos, C.J. de ; Bal D.B.M. ; Pragt, I.J. ; Wits, W.W. ; Veul, R.P.G.
    Carbon microlattices demonstrate potential as substitutes for traditional honeycomb cores in aerospace applications due to their exceptional combination of ultra-low weight, high compression strength and stiffness. Integrating them into thermoplastic composite structures could be one of their first industrial applications. This study demonstrates that composites with carbon core materials can be realised and that carbon microlattices can be produced at a larger scale using commercially available stereolithography and sintering equipment.
  • Item
    Evaluation of Reduced Order Aerodynamic Models for Transonic Flow over a Multiple-Swept Wing Configuration
    (AIAA, 2025) Ghoreyshi, M. ; Aref, P. ; Stradtner, M. ; Panagiotopoulos, A. ; Rooij, M.P.C. van ; Blom, P.H.L. ; Hulshoff, S.J.
    This study is a collaborative effort within the NATO Science & Technology Organization, bringing together multiple institutions to advance reduced-order modeling. Aerodynamic reduced-order models were developed using two pseudorandom binary sequence (PRBS) training maneuvers, where the angle of attack and pitch rate varied in a periodic, deterministic manner with white-noise-like properties. The first maneuver maintained a constant Mach number of 0.85, while the second varied Mach from 0.1 to 0.9. The test case involved a generic triple-delta wing, simulated using the DoD HPCMP CREATE™-AV/Kestrel/Kestrel tools. Prescribed-body motion was used to vary input parameters under given freestream conditions. The resulting models predicted static and stability derivatives across different angles of attack and Mach numbers. They were also used to predict aerodynamic responses to arbitrary motions, including sinusoidal, chirp, Schroeder, and step inputs, showing good agreement with full-order data. Additionally, models predicting surface pressure accurately captured upper surface pressures across different spanwise and chordwise locations for both static and dynamic conditions.
  • Item
    Analytical LPBF Melt Pool Simulation and Experimentation for Metamaterial Lattices
    (Eccomas, 2025) Wits, W.W. ; Vos, C.J. ; Koenis, T.P.A. ; Smit, M.J. de
    Laser Powder Bed Fusion (LPBF) has emerged as a pivotal additive manufacturing technique, enabling the fabrication of complex geometries with high precision. Metamaterial lattices, characterized by architected periodic structures, have garnered significant interest due to their unique mechanical properties and potential applications across various engineering domains. Sizing of the lattice struts requires accurate prediction of the melt pool geometry. In particular, unsupported overhanging struts, exemplary for auxetic lattice structures, are challenging to fabricate with consistent quality. Traditional finite element analysis are computationally intensive and may not be practical for optimization. Analytical models offer a more efficient approach to predict melt pool characteristics, yet their application to the fabrication of complex metamaterial lattices remains underexplored. In this study, we present an analytical model tailored to predict melt pool dimensions specific to the fabrication of metamaterial lattices using LPBF. Our model integrates key process parameters, including laser power, scanning speed and material properties, to estimate melt pool width, depth and length. The model has been validated for stainless steel 316L based on thin-walled structures. To predict the processability of unsupported overhanging structures, the thermal behaviour of consolidating directly on powder has been considered. Results show that in particular the melt pool depth and most significantly the length are influenced. LPBF experiments have been conducted, in which horizontally overhanging struts are fabricated. The experimental results show agreement with the predictions of our analytical model with deviations within understandable margins. Subsequently, optimal LPBF process parameters were select to successfully fabricate a number of metamaterial lattice structures, including hard-to-print auxetic structures. Our findings provide valuable insights into the complex relationships between LPBF process parameters and resulting melt pool geometry. The models rapid predictive capabilities make it a valuable asset for selecting optimal parameters, reduce extensive empirical testing and enable the fabrication of high-quality metamaterial lattices.
  • Item
    Advanced RAIM and Local Effects Models for Rail, Maritime and UAVs Sectors
    (MDPI, 2025) De Toro De Murga, J. ; Fidalgo, J. ; Domínguez, E. ; Sanz, C. ; Moreno, G. ; Buendia, F. ; Labrador, E. ; Mistrapau, F. ; Clopot, R. ; Cezón, A. ; Snijders, M. ; Engwerda, H.J.A. ; Casals Sadlier, J. ; Damy, S. ; Sgammini, M.
    Advanced Receiver Autonomous Integrity Monitoring (ARAIM) represents an advancement over RAIM, designed to utilize dual-frequency and multi-constellation technologies. Originally developed for aviation, the European Commission (EC) is now exploring its broader application. This paper examines the adaptation of ARAIM for rail, maritime, and Unmanned Aerial Vehicles (UAVs) sectors. It briefly discusses aspects of the integrity concept, including architecture and user algorithms while the main focus is on characterizing local error models for local effects using real data campaigns. Keywords: ARAIM; integrity; local errors; rail; maritime; UAVs
  • Item
    Compression and fatigue performance of additively manufactured NiTi architected shape memory alloys
    (IOP Publishing Ltd, 2025) Zwerink, B.B. ; Biffi, C.A. ; Fiocchi, J. ; Mehrpouya, M.
    Additive manufacturing of architected materials—particularly lattice or porous structures—has gained significant attention in recent years due to their enhanced strength-to-weight ratios, load-bearing capabilities, and energy absorption properties. The integration of these structures with shape memory alloys offers multifunctional performance for advanced engineering applications. This study investigates the compressive fatigue behavior of NiTi lattice structures fabricated by Laser powder bed fusion. Initial quasi-static compression tests, carried out to full structural collapse, were used to define load levels for subsequent fatigue experiments. Fatigue testing was then conducted at 40 °C to induce pseudoelastic behavior, and an S–N curve was generated to characterize fatigue performance. Results showed that the NiTi lattice could sustain cyclic loading at 8 kN for an average of approximately 86 000 cycles, and around 18 000 cycles at 11 kN. Post-mortem microstructural analyses revealed martensite accumulation near fracture regions, attributed to stress-induced phase transformation.