Elastic and acoustic metamaterials with locally resonant (LR) arrays can generate bandgaps that attenuate or block elastic waves. Although extensive research has explored thermally induced tuning or single-mode mechanical pre-deformation, systematic comparative analyses of different pre-deformation strategies remain insufficient. To address this research gap, this study incorporates shape memory alloys (SMAs) into metamaterial architectures to realize tunable bandgaps via pre-tension, pre-bending, pre-twisting, and composite pre-deformations strategies, while also exploring the feasibility of achieving lower-frequency bandgaps. Experiments demonstrate that distinct pre-deformation modes induce differentiated shifts in the bandgap, and systematic trends throughout heating are presented. As temperature increases, these shifting effects progressively diminish due to the shape memory effect of the SMA, thereby establishing a temperature-dependent tuning range. To further elucidate the underlying tuning mechanism, numerical simulations investigate symmetric pre-bending and pre-twisting at various angles, revealing the quantitative relationship between pre-deformation magnitude, temperature, and bandgap tunability. The contributions of bending and twisting in hybrid configurations are also examined, providing insights into the optimal structural design of such systems. Finally, the study extends to two-dimensional metamaterial plate structures incorporating SMA resonators. Simulation show broader and more flexible bandgap tunability under thermal actuation, underscoring their potential for adaptive low-frequency vibration isolation and control.

Full-span tests in transonic wind tunnels frequently experience unsteady flow, which induces vibrations in the model–balance–sting assembly. These vibrations compromise test accuracy, restrict the test envelope, and may lead to structure failure. This paper first measures and analyzes the vibration characteristics of typical transonic wind tunnel full-span tests with different methods. The correlation analysis indicates that the shift of the correlation between normal force and pitching moment is a precursor to the dangerous vibration. The vibration problem is then modeled as a double-section cantilever beam incorporating lumped mass and inertia. A finite element method utilizing a beam–brick mixed element is proposed. The method evaluates changes in the frequency and mode shape of the model–balance–sting assembly resulting from variations in the lumped mass and inertia of the scaled aircraft model. Experimental validation confirms the method's effectiveness and accuracy. The proposed approach enables rapid and precise assessment of the scaled aircraft model's impact on overall dynamic characteristics and provides practical guidance for optimal vibration sensor placement.

Unmanned aerial vehicle (UAV) technology has revolutionized numerous sectors, including precision agriculture, infrastructure inspection and defense. Consequently, there is a critical need to develop a unique composite structures that offer high durability, low density, and enhanced mechanical properties for UAV airframes. This study addresses this demand by investigating the enhancement of glass and carbon fiber reinforced polymer (GFRP/CFRP) composites through the integration of multi-walled carbon nanotubes (MWCNTs at 0.5 and 1 wt%). The mechanical properties including tensile, flexural, and interlaminar shear strength (ILSS) were experimentally characterized and microstructural analysis was performed using scanning electron microscopy (SEM). The results indicated that carbon fiber composites (CFRP) with 1.0 wt% MWCNTs achieved a strength of 289 MPa, representing a 9.5 % improvement in tensile strength over the 0.5 wt% CFRP. However, the CFRP with 0.5 wt% MWCNTs demonstrated better performance in both flexural and ILSS strength, exhibiting 8.8 % and 13.6 % higher than the 1.0 wt% CFRP sample, respectively the same pattern was observed for glass fiber composites (GFRP), where the 0.5 wt% MWCNTs showed higher flexural and ILSS characteristics compared to the 1.0 wt% GFRP sample. SEM analysis confirmed that the superior performance of the 0.5 wt% samples was due to better fiber-matrix adhesion and uniform dispersion. It was concluded that a 0.5 wt% MWCNTs is optimal for both CFRP and GFRP, providing the best balance of mechanical properties for weight sensitive UAV applications, while higher concentrations lead to property degradation due to agglomeration.

Weight reduction of low-pressure turbine blades remains a critical design challenge, as it must be achieved without compromising aerodynamic efficiency or aeroelastic stability. This study aims to investigate the impact of significant mass reduction through structural modification, specifically hollow and lattice-filled designs, on the aerodynamic damping of an LPT blade. Three designs of the T106 C profile blade were analyzed: a solid baseline, a hollowed blade, and a lattice-based blade. The lattice-based design achieved a ≈33% mass reduction. Their modal parameters, derived from experimental modal analysis, were used in the numerical simulation method to compute aerodynamic damping. Aerodynamic damping coefficient was predicted over a range of reduced frequencies at an inter-blade phase angle of 0° for the first flexural mode. The results demonstrate that the lattice-based blade not only achieves the target weight reduction but also exhibits higher aeroelastic stability, showing aerodynamic damping coefficient levels approximately 21.7% higher than the solid baseline at higher exit Mach numbers. By improving the natural frequency and thus the reduced frequency, not only is weight reduction achieved but also higher aeroelastic stability.

A morphing skin must withstand local aerodynamic loads while remaining flexible enough to accommodate the shape changes of the morphing aircraft. The conflicting requirements can be satisfied by tuning the mechanical properties of the variable stiffness composites. In the present study, the variable stiffness composite is investigated by varying the lamina angles through 3D printing of curvilinear continuous fibre. At first, the design requirements and application scenario are introduced. The fabrication method is introduced and tensile tests are also performed to obtain the mechanical properties of the printed composite lamina. Then, the numerical model is established to explore the mechanical properties of the variable stiffness composite. Optimisation is carried out to balance the different mechanical properties. Finally, a composite sample is manufactured, which is tested to validate the proposed concept. The results demonstrate that the variable stiffness composite exhibits significant improvements in mechanical properties compared with the straight fibre composite.

Abstract An overview is given of investigations on a 70° slender delta wing applying pressure-sensitive paint (PSP) and particle image velocimetry (PIV) in parallel. Experiments are conducted within the range of Reynolds number from 0.6 $$\times$$ × 106 to 1.2 $$\times$$ × 106 and angle of attack from 15° to 30°. The focus is on systematically studying the correlation between leading-edge vortex (LEV) and surface pressure distribution under different conditions. It is found that the suction peak does not exactly coincide with the vortex center. The shift of the suction peak is more pronounced at higher angles of attack or Reynolds numbers, reflecting the effect of the asymmetry of the corresponding velocity gradient distribution on the pressure distribution. Additionally, under certain conditions, the reduction of streamwise variation may weaken the three-dimensionality of the LEVs, which has a significant impact on their pressure distribution.

Active noise and vibration control (ANVC) in coupled vibro-acoustic systems often suffers from severe convergence imbalance and poor numerical conditioning caused by heterogeneous acoustic and structural channels. To address these challenges, this paper proposes an adaptive control framework based on a block-diagonal stochastic natural gradient descent (BDSNGD) algorithm. By introducing structured metric preconditioning within a Riemannian metric space, the proposed method effectively aligns the dominant spatial eigenvalues of heterogeneous actuation channels, thereby eliminating convergence disparity without requiring computationally expensive full-rank matrix inversion. Furthermore, to overcome the trade-off between transient convergence speed and steady-state excess mean square error (EMSE), a correlation-driven variable step size (CVSS) strategy is developed. Instead of relying on raw error energy, the step size is regulated using the normalized temporal correlation of residual errors, enabling fast adaptation to structured disturbances while suppressing unnecessary updates under uncorrelated noise and impulsive perturbations. Comprehensive theoretical analyses, numerical simulations, and real-time experimental validations on a multichannel vibro-acoustic platform demonstrate that the proposed CVSS-BDSNGD algorithm achieves rapid, synchronous, and well-balanced convergence across heterogeneous channels, superior steady-state noise reduction, and strong robustness against impulsive disturbances, while maintaining a low computational complexity comparable to the conventional FxLMS algorithm.

As researchers continue to develop morphing aerospace structures capable of changing shape in real time to adapt to varying operating conditions, minimising the actuation effort required for shape change remains a persistent challenge. Excessive actuation mass, structural complexity, and energy consumption may offset the aerodynamic performance benefits provided by morphing capability. One promising approach to tackle these problems is to use dynamic response to actuate the structures at resonance. For example, actuating bending dominated morphing structures with integrated piezoelectric materials near their resonance frequency can produce significant displacements with reduced energy requirements. However, in this case, the actuation frequency is limited to the resonance frequency, as determined by the mass, stiffness, and damping of the structure within its operating environment, which may constrain the application scenarios. If instead, a stiffness tuning mechanism is integrated into the system, then resonance across a broader range of actuation frequencies would be possible by actively tuning the system stiffness. In the current study, a mechanism for achieving tunable stiffness in the context of a bending dominated morphing structure is first proposed. The mechanism can increase or reduce the structure stiffness, which can eventually change the resonance frequency. A theoretical analysis and finite element simulation are then performed to investigate the structural properties of the mechanism. Based on the specific stiffness of a particular camber morphing concept, the stiffness tuning mechanism is then optimised to expand the range of obtainable stiffnesses. At last, an experimental demonstrator is built to validate the mechanism by measuring the trailing edge displacement when the resonance actuation is applied with varying actuation frequencies. The concept is validated on a morphing trailing edge mechanism, illustrating its practical potential in aerospace structures requiring frequency-adaptive actuation.

The aim of this study is to investigate the necessity of a swing-wing system to maximize the aerodynamic efficiency of an unconventional tailless VTOL platform. This is accomplished by comparing the aerodynamics of two different wing configurations mounted on an identical fuselage with a chine forebody, using both wind tunnel tests and numerical simulations. To assess and compare lift, drag, and the behavior of vortical flow structures in cruise mode, two subscale models were designed: one featuring a straight leading-edge wing representative of the cruise configuration in a variable-sweep design, and the other with a fixed 58-degree forward-swept wing representing a non-variable fixed-wing solution. Wind tunnel experiments included force measurements and particle image velocimetry at a Reynolds number of 1.706 x 105. The results reveal substantial differences not only in lift-to-drag characteristics but also in the behavior of vortical patterns on the aft-body, driven by interactions between the chine vortices and wing-generated turbulence. These interactions produce distinctly different flow structures, including oscillating vortex cores and varying breakdown patterns. Details regarding post-processing and data quantification are presented in this paper.

Ammonia is a carbon-free fuel but suffers from low reactivity and high nitrogen-based emissions. This study numerically investigates ammonia-ether dual-fuel operation in a heavy-duty compression ignition engine using five ether-based pilot fuels: dimethyl ether (DME), diethyl ether (DEE), and polyoxymethylene dimethyl ethers (PODE1-3). Simulations were conducted at a fixed ammonia energy share of 50 % under four injection strategies with different ammonia and pilot fuel timings. Under the specific engine configuration and operating conditions considered, strategies with ammonia injected before or simultaneously with the pilot fuel yield higher indicated thermal efficiency, with PODE1 achieving the highest. Injecting ammonia after the pilot fuel significantly reduces nitrogen-based emissions, with PODEs achieving approximately 34-48 % lower indicated specific NO than DME and DEE. While PODE1 produces higher CO due to delayed ignition, PODE2 and PODE3 show the lowest combined nitrogen-based and CO emissions. HCN emissions are negligible under the investigated conditions.

This paper explores the potential applications of 4D printing technology in the aerospace field, with a focus on the mechanical properties and reusability of honeycomb metamaterials with shape memory characteristics fabricated using shape memory polymers (SMPs). Currently, research on the reusability of SMP-based metamaterials is limited, particularly regarding the influence of cellular unit geometries on their recovery performance, which remains unclear. To address this gap, this study combines typical cellular units with positive, negative, and zero Poisson's ratio properties into various structures. Through quasi-static compression experiments, complemented by three-dimensional digital image correlation (DIC) technology and finite element analysis, the mechanical compression performance and deformation mechanisms of the three structures are compared in detail. The deformation patterns under compression are elucidated, and the influence of geometric shapes on deformation behavior and mechanical response is analyzed. Shape memory recovery experiments, including single-cycle and multi-cycle tests, are designed to evaluate the 4D smart recovery performance of the three structures in terms of key metrics such as recovery rate and restoring force. This study systematically characterizes the compressive mechanical properties and shape memory recovery characteristics of honeycomb structures with different Poisson's ratio combinations, providing significant guidance for the research and development of 4D-printed mechanical metamaterials. Highlights Metamaterial structures combining unit cells with different Poisson's ratios. DIC and FEM are used to assess the effects of unit cells on deformation and failure. ZAZ structure shows superior stiffness and energy absorption in compression. Evaluate the shape memory performance of SMP under loading conditions. ZAP structure exhibits more stable cyclic recovery behavior under loading.

PurposeThis study aims to assess the aero-elastic response (deformation and acceleration) of two structurally modified low-pressure turbine blade models compared to the traditional solid blade by using one-way fluid-structure interaction. The structurally modified designs include a weight-reduced blade and a lattice-based blade modeled by a novel location-based lattice integration technique.Design/methodology/approachNumerical modal analysis is conducted on the three blades to determine their natural frequencies, and two of them are additively manufactured for experimental modal analysis to validate the results and calculate damping ratios. Computational fluid dynamics is performed to analyze the acting forces (steady and unsteady) based on two- and three-dimensional models, including those with and without tip clearance, at an operating flow condition, to determine the aero-elastic response of all blade designs.FindingsThe lattice-based blade is similar to 33% lighter than the solid blade with enhanced natural frequencies for flex and torsional modes by 15.31% and 8.71%, respectively. Meanwhile, the weight-reduced turbine blade model is 35% lighter and has enhanced modes by 8.86% and 4.04%. The aero-elastic response presents the lowest deformation but the highest levels of acceleration (1.5 g's) for the solid blade. The lattice-based design deforms slightly higher than solid with the lowest acceleration levels (0.92 g's).Practical implicationsThe utilization of lattice-based blades can decrease the weight of the gas turbine engine, with lesser fuel consumption having the capability of higher RPM speeds.Originality/valueThe comparison between the structurally modified turbine blade models based on aero-elastic response to the traditional solid high-aspect ratio blade has not been investigated earlier.

Wearable electronics and microsystems using flexoelectric hydrogel-based triboelectric spherical cap microgenerators have a primary application in energy harvesting. Using mechanical energy derived from environmental vibrations or human motion, small devices, sensors, and medical implants are powered by electrical energy. An investigation of advanced energy harvesting and nonlinear forced vibration characteristics of sandwich spherical cap triboelectric microgenerators is presented as the main contribution of this work. The microgenerator structure is innovatively designed with a hydrogel core, sandwiched between polydimethylsiloxane (PDMS) layers and flexoelectric materials on the top and bottom surfaces. The strain gradient theory incorporates size effects, which are essential to accurate microscale modeling. A complex interaction between mechanical and electrical fields can be captured by using Hamilton’s principle and higher-order shear deformation theory (HSDT). A precise and efficient numerical analysis is achieved using the differential quadrature method (DQM) and Newmark approach to solve these coupled electromechanical equations of motion. Taking surface stresses into account, the maximum dynamic deflection, output voltage, and generated electrical power decreased by 23

In this study, a Body-Centered Cubic (BCC) lattice structure is integrated into a low-pressure turbine (LPT) high-lift profile (T106C) blade to evaluate the enhancement in the structural dynamics under both Unit and Aerodynamic loading conditions. This is demonstrated numerically and experimentally by cost-effective turbine blade prototyping, using Polylactic Acid (PLA). Five PLA blade models (Solid, Hollow, and three BCC location-based designs) are numerically analyzed for mass and natural frequencies, from which two blades (Hollow and BCC blade with the best location combination) are selected for experimental validation. Furthermore, vibrational response characteristics (displacement, acceleration, and stress) of these selected blades are evaluated at their resonating frequencies and compared. The BCC blade design showed that it is 33.2% lighter than the solid blade while enhancing the natural frequencies by 16.4% and 8.6%. Compared to the Hollow blade, the BCC reduced the acceleration by 9%, displacement by 24%, and overall equivalent (von Mises) stress by a factor of two.

This study presents a rapid water-triggered hardening strategy for ethanol-softened shape memory polyurethanes (SMPU), including thermoset foams and thermoplastic polyurethane (TPU) films/membranes. The SMPU foam, once softened by 70 % ethanol, becomes highly compressible for minimally invasive delivery. Subsequent immersion in water effectively removes ethanol and restores mechanical stiffness of the foam within minutes, with the Young's modulus increasing from 0.001 MPa (softened state) to over 0.8 MPa after 5 min-far surpassing air drying alone. This ethanol-water exchange mechanism enables shape fixation without the need for thermal activation or toxic solvents. The concept is further validated in TPU films and electrospun membranes, which exhibit localized and programmable shape recovery under similar treatment. In vascular phantom models, the SMPU foam demonstrates conformal filling of aneurysmal geometries with secure fixation post-hardening. These findings suggest a solvent-responsive, biocompatible platform suitable for embolization and other minimally invasive biomedical applications, offering a safer and faster alternative to traditional shape memory approaches.

This study examines the effects of hydrogen addition to propane in a lean premixed burner. Four hydrogen mole fractions (15 %, 25 %, 35 %, and 45 %) are analyzed to assess their impact on flashback, combustion performance, and instability. Large eddy simulation (LES) with flamelet-generated manifold (FGM) models are used to evaluate combustion regimes in a fully three-dimensional computational domain. Combustion regime maps are created for various operating conditions, based on equivalence ratio and air mass flow rate. Increasing hydrogen mole fractions leads to flashback at lower air mass flow rates and higher equivalence ratios. However, hydrogen also improves heat output by 9.6-17.7 % and reduces carbon monoxide emissions per unit heat output by 22.6-40.4 %, depending on the conditions. Flashback can be effectively prevented across a wide range of conditions by modifying the mixing tube to a conical shape. Combustion instability analysis shows that hydrogen addition does not cause instabilities, except in the conical mixing tube at higher equivalence ratios and lower air mass flow rates.

Since the introduction of 4D printing in 2012, shape memory hybrids (SMHs) have emerged as a versatile solution for tailoring thermomechanical properties. This study developed UV cross-linkable hybrid resins for additive manufacturing (AM) with high performance and body-temperature programmable shape memory effect (SME). These resins combine polycaprolactone (PCL) as the transition component with a commercial elastic UV cross-linkable resin. The thermomechanical properties and shape memory performance were evaluated using differential scanning calorimeter, Shore hardness, and tensile tests. The SMHs exhibited tuneable properties and excellent SMEs, with shape fixing and recovery ratios exceeding 97.5% for 40% PCL (PCL-40). Increased PCL content improved Shore hardness at room temperature while enabling softness near body temperature for easy programming. Feasibility for AM was demonstrated using extrusion-based and volumetric additive manufacturing techniques. Proof-of-concept experiments showed successful 2D-to-3D shape transitions programmed at body temperature with full recovery upon reheating. These findings highlight the potential of UV cross-linkable SMHs for applications in wearable devices, medical tools, and other technologies requiring body-temperature shape adaptation.

The large-scale deployment of aerospace composite structures has become a defining trend in modern aeronautics; however, hidden damage is difficult to detect over the full life cycle with conventional non-destructive inspection. This creates an urgent demand for on-line, high-fidelity structural health monitoring (SHM) technology. Optical-fiber sensors—featuring minimal mass, micron-scale diameter, immunity to electromagnetic interference and the ability to be co-cured into composite laminates for distributed measurement—are widely regarded as the key enabling technology. This paper presents a comprehensive review of recent advances and engineering applications of optical fiber sensing. Emphasis is placed on its engineering applications covering wing strain mapping, landing-gear load tracking, fuselage deformation localization, and cure-process monitoring and low-velocity impact damage identification of composite materials. Emerging intelligent assessment methodologies are examined. Finally, the development trends of optical fiber sensing technology are prospected, offering a reference framework for future theoretical innovation and engineering deployment of aerospace composite SHM technology.

This study presents a novel approach for predicting the location and fatigue life of degenerative intervertebral discs (IVDs) under cyclic loading conditions, aiming to improve the understanding of disc degeneration mechanisms. Based on mechanical theories linking IVD degeneration to stress imbalance and water loss, a finite element (FE) model of the L4–L5 lumbar spine was developed, combining probability-weighted anatomical structures, inverse dynamics, and cumulative fatigue mechanics. By quantifying stress variations and calculating cumulative damage across disc regions, stress-concentration areas prone to degeneration were identified, and validation via a case study of a retired weightlifter diagnosed with intervertebral disc disease (IVDD) demonstrated that the predicted degeneration location correlated well with affected areas observed in CT scan images. These findings suggest that prolonged, abnormal stress imbalances within the disc may contribute significantly to degeneration, offering potential clinical applications in preventive assessment and targeted treatment for spine health.

Multi-functionality and high mission adaptability are important trends in the development of future aircrafts. Trans-domain aircraft, with their unique take-off and landing capabilities and cross-medium capability, have significant potential in the field of emergency rescue, marine monitoring and tourism. Trans-domain aircraft will meet various flight conditions in different domains. Therefore, the design of wing structures must consider the mechanical effects of different media on the aircraft. In the current study, a fishbone variable camber wing is proposed based on the concept of a camber morphing wing. The relationship between the actuation force and the trailing edge deflection is analyzed using the fluid–structure interaction. The flight performance of the flight conditions including cruise or climb underneath and cruise above the water can also be evaluated in the design iteration since the load-carrying capability can be satisfied and the structural deformation of the fluid loads and the actuators is taken into account. Finite element analysis is also employed for the structural verification. Finally, a structural model is manufactured, which is tested above and under water by measuring the trailing edge deflection using the digital image correlation technology.