In aerospace, automotive, shipbuilding, and new energy applications, fiber-reinforced composite structures often incorporate functional holes that can lead to local stress concentrations and premature failure if local deformations are not properly controlled. To address warpage and deformation compatibility in perforated composite structures, this study proposes a variable stiffness design optimization method integrating structural hole design and manufacturability. Based on the Normal Distribution Fiber Optimization (NDFO) interpolation scheme and the Artificial Weak Element (AWE) method, a multi-point shape preserving variable stiffness optimization model is developed to minimize structural compliance while constraining local deformation energy. Explicit sensitivity formulations are derived explicitly for both the objective and constraints with respect to fiber angle design variables. Numerical examples on flat and curved composite structures demonstrate that the proposed approach effectively suppresses warpage in hole regions and improves structural integrity. A discrete-to-continuous fiber path filtering strategy is further employed to ensure high manufacturability with minimal stiffness loss. This work offers a theoretical-practical framework for the integrated design and manufacturing of perforated fiber-reinforced composites in lightweight structural applications.

High-aspect-ratio wings for solar-powered UAVs (Unmanned Aerial Vehicles) require ultra-lightweight structural designs capable of withstanding large deformations induced by aerodynamic loads. Traditional topology optimization methods often overlook the interplay between geometric nonlinearity and aero-structural coupling, limiting their effectiveness for flexible wing systems. This study proposes a multi-material topology optimization framework that integrates geometric nonlinearity with weak aero-structural coupling. The three-field approach, incorporating directional length scale control and deformation control, is employed for the geometrically nonlinear multi-material optimization. A nodal displacement-based inverse modeling method enables efficient data transfer between aerodynamic and structural meshes, while a deformation-driven load update strategy reduces computational costs. A straight wing with four case studies demonstrates that incorporating aero-structural coupling shifts high-stiffness material toward the wing root, optimizing load transfer and reducing deformation. The reconstructed truss-based design achieves an 11.29 % mass reduction via size optimization while maintaining bending and torsional constraints. This framework bridges structural optimization with aero-structural coupling, providing a systematic approach for designing lightweight, main spar-ribs based, and deformation-resistant wings.

Compared with rigid robotic arms, soft robotic arms have shown better continuous deformation capability, environmental adaptability, and flexible contact characteristics. Soft robotic arms can realize a variety of complex postures through active deformation, and can adaptively intervene in complex and narrow spaces for target tasks, increasingly demonstrating valuable potential in real-world applications. However, insufficient capability for multifunctional integration and a lack of complete motion perception and control methods severely hinder the practical applicability of existing soft robotic arms. Here, we report a multi-segmented soft robotic arm with integrated stiffness-tunable function, end-effector high-precision deformation function, internal tool-transfer function, multi-degree-of-freedom flexibility function, and deformation self-sensing function. Using the handle shank, we achieve deep intervention of continuously bending narrow pipes, extraction of waste liquid, and laser sintering and cutting inside the pipes. Afterward, we demonstrate the tool-transfer functions in the situations where the soft robotic arm with a smaller diameter cannot integrate all the required tools. Using flexible sensors, we realize the 3D visualization function of soft robotic arm. We use a long short-term memory network (LSTM) to implement the sensory perception of the end trajectories of the soft robotic arm. By combining the established inverse kinematics models with LSTM neural network and a feedback controller, we achieve the trajectory tracking verification for perception-trained soft robotic arms that shows good agreement between calculated and actual motion trajectories.

Dielectric elastomers (DEs) with high energy conversion density are highly desirable for flexible actuation and sensing applications. However, current DEs only perform well under electrical actuation, incapable of regulating interfacial interactions between materials and their environment, such as active control of electroadhesion and electrowetting-on-dielectric (EWOD). Herein, we report a method using polar small-molecule additives to enable electroactive interfacial regulation in DEs. For electroadhesion, the electroactive interface-enhanced dielectric elastomer (EIEDE) with a metal mesh electrode attains adhesion strength of 31.75 kilopascals at 14 megavolts per meter, which is 488 times greater than that before modification. For EWOD performance, the EIEDE induces droplet contact angle to decrease sharply from 83.15° to 9.92°, showing the best electric-field response among DEs and enabling functions like droplet transport and shape modulation. The EIEDE simultaneously integrates large-strain deformation with electroactive interfacial regulation, achieving breakthrough performance in superhigh electroadhesion and excellent EWOD performance.

Eigenvalue formulation methods for determining the frequencies of antiresonance and local extrema in the frequency response have been shown to be successful in the numerical simulation for undamped structures under force excitation. In aerospace engineering, however, base-excited vibrations during launch and flight pose critical threats to sensitive components, demanding accurate prediction of these frequencies to guide structural optimization and modification for targeted vibration suppression. To address this, we extend our previous eigenvalue formulation method to include harmonic base excitation in this paper, making it more versatile. As demonstrated in the orbital module case study, this extension enables accurate frequencies prediction for large-scale complex spacecraft under base excitation scenarios. Furthermore, a comprehensive theoretical explanation of why the structural natural frequencies appear in various eigenvalue formulation methods for determining antiresonant frequencies is provided, addressing a previously unexplained aspect of this methodology. To demonstrate the proposed method, besides the numerical application, vibration experiment for a cantilever beam with base excitation was also carried out. The test results confirm the theoretically predicted antiresonant and extremum response frequencies. The test results also support the validity of undamped assumption for structures with light damping.

During low cycle fatigue (LCF) at 400 degrees C, the coarsening behaviors of secondary/tertiary gamma ' phase in FGH99 superalloys are elucidated. As the total strain amplitude h epsilon t/2 increases, the secondary/tertiary gamma ' phases coarsen simultaneously. The coarsening behaviors of the secondary gamma ' phase rely on the formation of a dendritic structure via preferential growth within the primary gamma ' phase (h epsilon t/2 from 0.6% to 0.7%) and coalescence with adjacent secondary gamma ' phase (h epsilon t/2 = 0.8%). Additionally, the Hf-containing mu phase particle can inhibit the coarsening of the secondary gamma ' phase by restricting the formation of dendritic structures in the primary gamma ' phase. The coarsening behaviors of the tertiary gamma ' phase are related to the coalescence of cellular structures and the dissolution/ detachment of growing secondary gamma ' phase. The correlation models between the average equivalent radius and fatigue fractured time, h epsilon t/2 and fatigue life were established, respectively. The average equivalent radius exhibit a nonlinear relationship with the cyclic loading time. The prediction accuracy of LCF life is within a 1.3fold error band.

Alumina-based eutectic ceramics exhibited high high-temperature strength but their intrinsic brittleness constrained broad structural applications. Here, we broke this limitation by introducing high-entropy rare-earth aluminate (REAlO3, RE = Gd0.25Eu0.25Nd0.25Sm0.25) into the Al2O3 matrix via directional solidification. The resulting dual-phase eutectics exhibited a unique architecture where single-crystalline Al2O3 was interlocked with bicrystalline high-entropy REAlO3, forming nanoscale coherent grain boundaries (~57.5 nm) and semi-coherent phase boundaries (lattice misfit <5.1%). The tailored microstructure and orientation relationship enabled a synergistic enhancement of Vickers hardness (19.4 GPa) and fracture toughness (5.5 MPa·m1/2), outperforming all reported binary alumina-based counterparts. The property synergy originated from a cascaded strengthening mechanism that spanned atomic-scale lattice distortion to nanoscale coherent interfaces, coupled with multi-mode toughening via crack deflection, bifurcation, and bridging. Our work establishes a high-entropy eutectic design strategy for engineering ceramics with exceptional mechanical performance under extreme conditions.

The thin-walled structure with lattice and stiffeners is a typical hybrid structure and effectively combines the load-bearing merits of lightweight lattices and thin-walled stiffened configurations, while demonstrating significant multifunctional potential that provides novel technical solutions for aerospace structural lightweighting. The increasing maturity of metal additive manufacturing technologies has laid a reliable foundation for the practical application of lattice structures. To facilitate the implementation of lattice structures in aerospace engineering, this paper focuses on thin-walled structures with lattice and stiffeners, primarily from the perspective of load-bearing structural design and its practical applications. Building upon the joint team's recent exploratory applications, this paper systematically outlines four critical aspects: fundamental characteristics of lattice structures, macroscale mechanical analysis methodologies, design of the lattice Representative Volume Element (RVE), eptimization design methodologies for thin-walled load-bearing structures with lattice and stiffeners. These systematic analyses aim to establish comprehensive reference guidelines for engineering designers. Furthermore, based on challenges encountered in aerospace, aviation, and aero-engine applications, this paper identifies priority research domains requiring urgent attention and critical technologies demanding breakthroughs in the hybrid structure design, offering valuable insights for researchers in related fields.

The integration of topology optimization (TO) and additive manufacturing (AM) is transforming the design and production of advanced multifunctional structures, offering innovative solutions to complex engineering challenges. While these technologies are well-established in the aerospace industry, the present work highlights their synergistic potential within the nuclear sector by redesigning a representative multifunctional bottom nozzle used in nuclear assemblies. Focusing specifically on foreign debris filtration performance, this study introduces, for the first time, a foreign debris filtering constraint by tailoring the design space of the fluid channel according to the characteristic dimensions of foreign debris. Fluid topology optimization is then applied within this customized design space, resulting in a thin-walled filtering lattice that minimizes energy dissipation. Subsequently, continuum topology optimization is utilized to enhance the load-bearing capacity of the supporting structure, revealing a rib-like load transfer path that reinforces the bottom nozzle. Finally, an integrated lightweight design is achieved by tessellating the optimized filtering lattice into the reinforced load-bearing structure. Performance validation shows that the topology-optimized bottom nozzle significantly outperforms traditional design, improving foreign debris filtration by 6.66%, reducing pressure drop by 10.29%, and increasing structural stiffness by 21.95%, demonstrating the promising application potential of this methodology in the nuclear energy sector.

Twisted-and-coiled polymer actuators (TCPAs) based on spandex offer large stroke and low-cost fabrication; yet, their reproducible design and operational stability remain constrained by ad-hoc processing and incomplete electro-thermo-mechanical descriptions. This work develops an integrated fabrication-to-function framework that quantitatively connects process parameters, helical geometries, and actuation responses, validated using single-fibre tests, to an application-level demonstrator. Systematic experiments delineate how the pre-stretch ratio, twist density, and winding load shape the helix formation and free-stroke strain, leading to a reproducible fabrication criterion that eliminates empirical trial-and-error. A compact analytical model that couples anisotropic thermal expansion with helical kinematics is calibrated under free-stroke conditions, accurately predicting strain-time trajectories across power densities (Coefficient of determination = 0.953; root mean square error = 1.16%). Mapping the power-response landscape further identifies a stability window (stable at 23.4 mW.mm(-1); degraded beyond 25.2 mW.mm(-1)) and clarifies the mechanisms of failure, including modulus softening, helix-angle drift, and friction-induced losses. Scaling by parallel fibre bundles enhances the load capacity (similar to 3 N for a 16-fibre TCPA) without compromising the strain output. Finally, a differentially driven morphing wing demonstrates continuous and controllable bending between 0 degrees and 26.7 degrees (approximate to 15 degrees within 10 s at 23.4 mW.mm(-1)), confirming system-level practicality. By uniting a reproducible fabrication rule, calibrated geometry-anisotropy model, and mapped power-density regime, this study transforms TCPA development from intuition-based tuning to prediction-guided engineering, advancing their applications in adaptive structures and soft robotics.

Compared to the rigid wing, the flexible morphing wing is more intelligent and flexible, allowing the aircraft to more flexibly adapt to different flight mission requirements. Based on deformable pneumatic wing ribs and dielectric elastomer (DE) smart skins, here we report an intelligent flexible morphing wing to achieve the cooperative deformation of the overall wing structure. In addition, the posture-locking structure and lateral adsorption structure are designed to achieve the stiffness regulation and the control of adhesion and de-bonding between different wing units. Meanwhile, experiments are conducted to measure the bending angle and output force of the morphing wing under the combined effect of the pneumatic wing ribs and DE skin. Subsequently, the adhesion properties are experimentally measured by installing the posture-locking structure and lateral adsorption structure onto the morphing wing. Finally, by placing multiple units in parallel, the independent and integral deformation capabilities of a multi-unit assembled wing are demonstrated.

In recent years, superelastic shape memory alloys (SMA) have been incorporated into carbon fiber reinforced polymer (CFRP) composites to enhance their impact resistance. However, while SMA integration improves mechanical performance, it also introduces challenges such as increased curing stress and deformation. This study investigates the evolution of residual stress during curing and its impact on the mechanical response of SMA-CFRP composites through numerical modeling and experimental validation, including microscale mechanical property calculations, macroscopic tensile analysis, and mesoscale RVE-based simulations. The results reveal that the pronounced mismatch in thermal expansion coefficients between SMA wires and the CFRP matrix is the primary cause of significant residual stress concentration during curing. The peak compressive residual stress within SMA-CFRP reaches 174.5 MPa, considerably higher than that in pure CFRP. Furthermore, the RVE model captures stress gradients and directional anisotropy at the interface, arising from elastic modulus mismatches between adjacent phases. These residual stresses lead to reductions in both strength and stiffness, by approximately 4-5 % and 5-8 %, respectively. The findings demonstrate that SMA-reinforced composites require careful interfacial design and process optimization to fully realize their mechanical advantages.

This paper investigates the impact of mechanical pre-training on the structural fatigue of NiTi pseudoelastic shape memory alloy (SMA) wires. Pseudoelastic NiTi wires were subjected to various training processes, incorporating different stress amplitudes, frequencies, and numbers of cycles. Subsequently, stress-and strain-controlled fatigue tests were conducted. A theoretical model was then proposed to elucidate the mechanism of the training effect, based on the energy stored in transformation-induced plasticity (TRIP). The local plasticity density was evaluated using an electrical resistivity-based approach. The results reveal several key findings: (i) the stored energy of TRIP from over-stressed training improves fatigue resistance by mitigating concentrated local stress; (ii) macroscopic plastic strain exhibits independence from local plasticity, suggesting its limited relevance to the training effect; (iii) the local plasticity density, measured by electrical resistivity, serves as an indicator of low-cycle fatigue life in trained NiTi SMAs. Based on these insights, a fatigue prediction model for trained NiTi SMAs was established and experimentally validated. Through an appropriate training process, the structural fatigue lifetime of NiTi SMAs can be extended up to tenfold.

This study proposes a simple design method for metallic bistable shells, realized by combining two open cylindrical shell elements with mutually orthogonal initial curvatures. This structure creates a double-well potential, enabling shape morphing between two stable states, while the initial curvature provides the stiffness required for shape preservation. Two pairing modes with distinct mechanical properties are designed in this study: opposite-sense pairing and equal-sense pairing. In addition, two types of bistable shells with different driving modes are fabricated: force-driven bistable shells made of beryllium copper (BeCu) and thermally driven bistable shells fabricated by combining shape memory alloy (SMA) with BeCu. A quasi-static bending energy model is established to analyse the effects of geometric parameters, element matching relationships, and the elastic modulus ratio on the bistability of the structure. Corresponding experiments are conducted, including four-point bending tests for force-driven shells, in which force and curvature are measured, and temperature-controlled tests for thermally driven shells, in which temperature and curvature evolution are monitored. The experimental results agree well with the theoretical predictions, providing a theoretical basis for designing bistable shells with customizable mechanical and thermal responses. Moreover, the thermally driven shell design enables a non-contact and convenient regulation strategy by leveraging the temperature-dependent elastic modulus ratio. Finally, this study successfully extends the orthogonal-curvature method to the fabrication of chevron-shaped bistable shells, thereby expanding the range of potential application scenarios.

Strength design is a critical aspect of ensuring the safety and reliability of composite structures in service, as stress concentration will lead to fracture, damage, and fatigue. Multi-scale variable stiffness design optimization of fiber-reinforced composites, through concurrent optimization of structural topology and fiber orientation, enhances their potential for lightweight design and stress reduction. When stress-related constraints are introduced, multi-scale variable stiffness optimization of composite materials faces additional challenges. These arise from the complex failure modes of anisotropic materials, where a single stress measure cannot adequately represent failure mechanisms; the inherent coupling between macro-scale topology and micro-scale fiber orientation, which demands efficient characterization methods for coordinated optimization; and intrinsic difficulties of variable stiffness design. Therefore, Based on the first-order shear deformation theory, the normal distribution fiber optimization interpolation scheme is employed, this study develops a multi-scale variable stiffness optimization framework for composite structures under Tsai-Wu failure constraints. This study is based on the first-order shear deformation theory, thereby enabling a more general and consistent assessment of stress and failure in laminated composite structures. To address the large-scale constraint issue, the p-norm approach is adopted to aggregate the Tsai-Wu failure criterion into a reduced set of stress-related constraints, and a stress penalization method is applied to mitigate stress singularities. Using the adjoint vector method, explicit sensitivities of macro-scale topology and micro-scale fiber angle design variables are derived for both with respect to the compliance minimization and the Tsai-Wu failure constraints. Numerical studies on a single-layer L-shaped beam, a multi-layer L-shaped laminated plate, and a single-layer corbel-shaped beam for multi-scale optimization demonstrate the proposed framework. Comparisons between designs with and without stress-related constraints are performed in terms of stress distribution, Tsai-Wu failure factor, objective function value, macro-scale topology configuration, and micro-scale fiber orientation, to validate its effectiveness. The results provide a theoretical and methodological basis for the multi-scale strength optimization of composite structures.

The contact pressure of an asperity is the fundamental parameter for constructing a single asperity contact model and analyzing the contact load and contact stiffness of the mechanical joint surfaces. In response to the defects of existing models in contact pressure analysis that have non-monotonic changes or do not conform to physical laws, this paper proposes a novel nonlinear contact model that can achieve continuous monotonic changes in contact pressure in accordance with physical laws. This model considers the continuous deformation of the asperity after load application, and can describe three deformation states: elastic, elastic-plastic, and plastic during the loading process. For the elastic and plastic deformation stages, this paper characterizes them using the classic Hertz elastic contact theory and the complete plastic contact theory. For the elastic-plastic deformation stage, the contact pressure is characterized using an empirical pressure function, and expressions for other contact parameters are derived. Furthermore, based on the principle of probability and statistics, the solution expression for the contact parameters of the rough interface is obtained, and a novel rough interface contact model is established. By comparing with existing experimental and simulation results, it is found that: 1) The model in this paper achieves monotonic and continuous changes in contact pressure during the contact process of the asperity, while complying with physical laws; 2) The new model is in good agreement with experimental and simulation results, verifying the universal effectiveness and correctness of the proposed model in solving the contact parameters of the rough interface; 3) The new model has simplicity in expression and high computational efficiency.

Perforated fiber-reinforced composites are widely employed in aerospace and new energy power equipment. The functional holes play a crucial role in achieving an overall lightweight design, high stiffness, and effective deformation control, which are essential for maintaining geometric accuracy. This study addresses the local warping deformation control problem in the multi-scale lightweight design of fiber-reinforced composite structures with holes. Based on the Normal Distribution Fiber Optimization (NDFO) discrete material interpolation scheme, the paper proposes a multi-point shape preserving concurrent multi-scale variable stiffness design optimization method for fiber-reinforced composites. This approach achieves structural lightweight while suppressing warping deformation around holes. By introducing the Artificial Weak Elements (AWE) and multi-point shape preserving, quantitative measure and constraint local warping deformation near structural holes are achieved. Analytical sensitivity for both macro-scale topology and micro-scale fiber orientation variables relative to the objective function, and multi-point shape preserving constraints are derived. Furthermore, by employing the first-order shear deformation theory and a multi-scale continuous filtering strategy for discrete fiber angles, the effectiveness and engineering applicability of the proposed method are demonstrated through both numerical simulations and experimental validation, offering a novel approach for achieving lightweight design and deformation control in composite materials.

Heat exchangers, as critical thermal exchange equipment, are widely used in fields such as aerospace and energy chemical engineering. However, the design of traditional heat exchangers is often constrained by structural design and manufacturing processes. The triply periodic minimal surfaces (TPMS), an advanced porous structure derived from nature with mathematically definable properties, offers a novel solution to overcome these limitations when integrated with additive manufacturing (AM). This study employs a parametric design methodology based on TPMS structures to systematically construct a series of heat exchanger models. These models utilize Gyroid, Diamond, and Schwarz as unit cells with varying unit cell dimensions and wall thicknesses. Through thermal-fluid coupling simulations, the effect of key geometric parameters on the macroscopic performance of the heat exchangers is investigated. The results indicate that TPMS structures can effectively enhance heat transfer performance. Smaller unit cell dimensions contribute to intensified heat transfer, with the temperature difference between hot and cold fluids under optimal conditions reduced to 8.74% of the initial temperature difference. Variations in unit cell wall thickness have a minor impact on the performance of the heat exchangers studied here once steady state is achieved. Among the different TPMS configurations, the Diamond unit cell demonstrates superior heat transfer performance due to its multi-branch flow channel structure. This study provides a theoretical foundation and design reference for the development of high-performance heat exchangers based on TPMS structures and additive manufacturing.

Continuous fiber-reinforced polymer (CFRP) composites manufactured via additive manufacturing (AM) offer significant potential for the design of high-performance lattice structures. However, existed design methods have not yet fully tapped the potential of gradient infill lattice with varying fiber ratio. In this work, a novel concurrent multi-scale topology optimization framework is proposed for CFRP lattice structures with spatially tunable fiber morphology, leveraging an RVE-based homogenization approach. The effective mechanical properties are evaluated by incorporating micro-scale fiber characteristics (i.e., fiber volume ratio and orientation) together with meso-scale lattice unit cell geometry. The divergence constraint based on fiber decomposition is introduced to suppress abrupt curvature transitions and guide the formation of smooth fiber trajectories. The proposed optimization problem simultaneously considers macro-scale structural compliance as the objective and treats fiber parameters and unit cell dimensions as design variables across multiple scales. Furthermore, an enhanced wave projection method is developed to convert discrete design variable fields into printable fiber paths with multiple tows, enabling a continuous and realizable fiber layout. In general, the proposed concurrent multi-scale optimization scheme leverages spatially tunable fiber ratios to realize gradient infill within the lattice architecture, thereby offering superior load-bearing capacity and improved manufacturability over existing design methods. Overall, this framework provides a robust and manufacturable design strategy for CFRP lattice structures with customized topology and fiber morphology.

Thin-walled conformal cooling structures are essential for the thermal management of complex curved electronic and aerospace devices. The traditional topology optimization of conformal cooling structures requires cumbersome post-processing reconstruction and inevitably induces thermal performance deviations of the optimized results. To address this issue, this paper proposes a feature-driven topology-optimization method based on parametric mapping for the design of conformal cooling structures. The parametric mapping is introduced to map 3D complex curved design domains into 2D parametric domain where the B-Spline Offset Feature (BSOF) is defined to model the fluid channels. A generalized extrusion operator is adopted to achieve uniform pseudo-density distribution and consistent physical properties throughout the structural thickness direction. Numerical examples including cylindrical and spherical thin-walled conformal cooling structures are studied to demonstrate the effectiveness of the proposed method.