Fibre-reinforced laminated composites are constructed layer-by-layer, enabling ease of directional stiffness tailoring. Their vast design space is typically explored using two-steps. First, the optimum stiffness for given loads is conceptualised using continuous optimisation of lamination parameters (LPs). Then, discrete optimisation determines a fibre stacking sequence (SS) that closely matches these LPs. While fibre angles are conventionally limited to 45°multiples, finer increments (e.g., ±15°) can enable lighter structures. However, existing SS design methods do not scale well with this increased problem dimensionality. To overcome this challenge, we propose LP2SS, a novel methodology utilising fast Fourier transforms (FFT) and a branch-and-bound optimiser. By treating LPs as a signal, FFTs identify the number of fibre layers oriented at different angles, akin to estimating the magnitude of different frequencies within a signal. This fibre angle distribution guides the branch-and-bound optimiser, enabling efficient SS design with accurate LP matching, while satisfying empirical design rules. The ingenious use of FFTs is key to LP2SS's performance, achieving solutions within tenths of a second, compared to minutes required by state-of-the-art methods. Validated on established benchmarks and a newly proposed comprehensive test set, LP2SS marks a significant advancement in the optimal design of large-scale laminated composite structures.

This study investigates a filament-wound tube model incorporating fiber undulation from the filament winding process. The model was analyzed using the finite element method in the linear regime, then compared with the shell model and radial crushing experiment. Results showed that the solid model predicts the radial compression stiffness with a higher level of accuracy than the shell model due to the inclusion of the fiber undulation feature. This model is a first step towards the development of a composite pressure vessel model where fiber undulation is more frequent, and also for predicting failure initiation and damage propagation.

This study aims to develop a model to predict the burst pressure of a dry filament wound cord-rubber composite pressure vessel under hydrostatic internal pressurization using a submodelling based global–local FEA model. The model links the global displacements of a rebar-based model to obtain the local deformation state in a single rhomboidal representative volume. Emphasis is placed on capturing the local stress concentrations in the fibers due to the unique filament winding mosaic pattern. Fiber damage is included in the local model using a maximum principle strain criteria. Verification of the created model is done experimentally on industrially manufactured burst-test specimens. Measurements for displacement during the experiments are taken photographically, while the burst pressure is captured using a pressure transducer. The final error between the burst pressure of the samples and the experimental demonstrators is approximately 6.5%, a marked improvement over conventional models with truss and rebar elements as fibers.

Hydrogen is being investigated as aviation fuel, with the objective to achieve an energy transition for the aviation sector. Effective storage solutions are crucial to mitigate the aerodynamic penalty caused by its low volumetric energy density. The focus of this study is the integration of a cryo-compressed vacuum-insulated storage vessel into the primary structure of aircraft, aiming to enhance structural efficiency. This is achieved by implementing analytical methods to analyse the thermo-mechanical loading of the inner and outer walls of the fuel tank. It is envisioned that the inner wall rather than the outer wall is more suitable to sustain additional loads. However, it is unclear how the cryogenic environment affects the stress state of the composite material.

In 2022 Airbus and Boeing combined delivered 1203 commercial aircraft. With an annual predicted growth of 4.3% for the coming 20 years there is an urgent need for end of life solutions that go beyond down-cycling of parts that cannot be reused. Especially carbon fibre reinforced composites are hard to recycle, and attempts to deliver recyclable short fibre reinforced thermoplastic materials see a reduction in specific properties. This is a problem because, the life cycle impact of an aircraft part is predominantly determined by its weight, which drives cumulative CO ₂-emissions over its lifetime. The transition to renewable energy sources by the aviation sector has the potential to change this relationship drastically. Therefore, it is necessary to begin developing methods to account for life cycle impact already at the start of the mechanical design of an aircraft part. This study proposes to apply variable stiffness laminate design to compensate for relatively lower mechanical performance of a recyclable short fibre reinforced composite laminate, with the objective of an overal better life cycle performance of the composite part. This approach is demonstrated using the example of a rectangular plate under uniaxial compression on board of an ATR72. The results show the impact of weight-optimisation on the cumulative CO ₂-emissions for the life span of the aircraft. Two different energy sources are considered: the aircraft powered by conventional jet fuel, and the aircraft powered by hydrogen which has been generated using non-fossil energy sources. The results furthermore clearly show that moving from conventional to renewable energy sources, reduces the impact of part-weight on the accumulated CO ₂-emissions very significantly, bringing recycling considerations more into focus, especially for parts which require regular replacement during the lifespan of the aircraft, for example hydrogen storage tanks.

This Editorial mentioned a paper by Nishimoto et al [1], which was not available to be cited at the time. The paper has now been included in this issue and the reference for it is below. [1] M. Nishimoto, M. T. Kezirian, Safety requirements for Hyperloop transportation systems: Applying NASA human spaceflight safety practices, J. Space Saf. Eng. 10 (4) (2023) 397 – 406, doi: 10.1016/j.jsse.2022.02.009

Type IV composite pressure vessels represent the current state-of-the-art for compressed gaseous hydrogen storage in fuel cell electric vehicles. A combination of highly demanding safety regulations and the need for cost competitive solutions make the topic of CPVs particularly challenging. Given the elevated material price of carbon fiber, structural optimality is essential to meet both requirements. Thorough understanding of design parameters and mechanical performance of composite pressure vessels is prerequisite to structural optimality. In this paper we investigate the relation of stacking sequence and circumferential ply drop locations on the mechanical performance of type IV composite pressure vessels subjected with internal pressure. This paper builds on previous studies by the authors, which are enhanced by new numerical and experimental results. An experimental set is used, where for a given layup composition the stacking sequence and the circumferential ply drop locations are varied. The experimental results are complemented by a computationally efficient numerical framework, which is composed by the output of a commercial filament winding software, a self-developed geometry correction algorithm and an automated FE model generation program. The numerical results are compared with outer surface strains obtained by means of three-dimensional digital image correlation, the final burst pressures and the vessel remainders. The achieved burst pressures vary between 152.6 and 188.6MPa, depending on design configuration. For the layup composition in this investigation, the placement of tangentially reinforcing layers (e.g. circumferential and high-angle helical layers) as innermost layers led to overall higher cylinder strengths compared to sequences, where these layers were located as outermost. The retraction of circumferential ply drop locations was found to impact the burst performance differently in dependence of the stacking sequence. For sequences, where circumferential layers were located as outermost, a retraction of ply drop locations by 12mm showed barely any differences in burst pressure (-1.9%). For sequences, where these layers were located as innermost, a severe decrease (-19.1%) was noticed once the ply drop locations were retracted by up to 9mm. The results not only underlined the criticality of both design parameters and their interaction with each other, but also showcased a computationally efficient numerical framework capable of capturing distinct mechanical responses for a variety of layups at least trend-wise.

The industrialization of fuel cell electric vehicles demands cost efficient storage solutions for hydrogen. While gaseous storage in type IV pressure vessels is currently the most mature technology, further structure optimization needs to be undertaken in order to meet cost requirements. This research investigates the effects of stacking sequence of composite pressure vessels regarding laminate quality, structural deformation and finally burst pressure. Therefore, a known laminate is studied on a subscale vessel geometry with changing stacking sequences. The specimens are pressurized in a specially designed chamber up to burst pressures of 166.11 MPa. Through a multisensor arrangement of stereometric systems, the deformation is tracked up to burst by using 3D digital image correlation. The experimental results show a difference of 67% in burst pressure between the investigated stacking sequences. Experimental cylinder strains and burst pressures are compared to results derived from 3D elasticity theory with implemented first ply failure criterion. Additionally, using X-ray computed tomography and acid digestion tests, insights about the distribution of fiber volume fraction and porosity are provided. For the investigated sequences in this research, the results show the considerable influence of stacking sequence on the laminate quality, the structural deformation and finally the burst pressure of composite pressure vessels. Moreover, it is shown that while the used 3D elasticity approach proved to be a useful tool for the prediction of strains and failure in the cylindrical section, discrepancies between prediction and experiment can arise based on preliminary failure occuring at the cylinder-dome transition. The results therefore emphasize the need for analytical and numerical analysis strategies to consider transition-related effects between cylinder and dome.

Mechanical properties of fiber-reinforced laminated composite materials are direction-ally dependent. Contemporary laminated composite design aims to make effective use of these directional properties by means of stacking sequence design, selecting the fiber orientation angle of each ply from a predefined set. Automated fiber-placement (AFP) technology can be used to improve the efficacy of composite materials by means of fiber steering. The variation of fiber orientation angles per ply of the laminate yields a variable stiffness (VS) laminate. For optimization purposes it is attractive to design such laminates in terms of lamination parameters (LP), as the number of design variables per point in the structure can be reduced to as little as four dimensionless variables considering balanced symmetric layups, and because many lay-up optimization problems can be made convex by describing them in terms of LPs. VS laminate design in terms of LP requires the obtained LP distribution to be converted into an actual fiber angle design. In a previous study the authors proposed a method to convert VS laminate designs using LPs into fiber angle designs. This method includes a constraint on in-plane curvature, a manufacturing constraint related to AFP. Thickness build-up will occur due to fiber steering. The amount of thickness build-up that results from the obtained fiber angle designs is discussed here as a function of the constraint on fiber curvature. The streamline analogy is used to obtain an estimate for thickness build-up and to determine fiber paths. A square plate loaded in biaxial compression is used to demonstrate the effect of the in-plane curvature constraint on thickness build-up, and several fiber angle designs, thickness distributions and fiber paths are given for this structure.