Magnetic soft materials derive their programmable shape morphing from spatially encoded magnetic anisotropy, which typically requires the controlled reorientation of magnetic particles during fabrication. Magnetic fluids or suspensions, in which magnetic particles possess high rotational freedom, offer a promising platform for constructing and programming such materials. However, the intrinsic fluidity of magnetic suspensions also leads to severe magnetofluidic instabilities, preventing precise magnetic programming. Here, we introduce capillary locking as a general physical strategy to stabilize magnetic fluids in open systems. By infiltrating a magnetic polymer solution containing hard-magnetic microparticles into an interconnected porous scaffold, capillary forces at solid-liquid-air interfaces immobilize the fluid while preserving the rotational freedom of the magnetic particles. This interfacial confinement suppresses magnetically induced flow and surface instabilities without encapsulation, enabling stable magnetic domain programming under weak magnetic fields. The capillary locked magnetic phase can be reversibly liquefied and resolidified through solvent exchange, allowing repeated reprogramming and fabrication of flexible magnetic composites with programmable magneto-mechanical responses. Owing to the open porous architecture, the system further supports solvent-assisted processing, modular assembly, and material recycling. These results establish capillary locking as a universal route for constructing reprogrammable magnetic soft materials from inherently unstable magnetic fluids.

To mitigate the high susceptibility to shrinkage porosity in Mg-10Gd-2Y alloys induced by their wide solidification temperature range, a pulsed magnetic field (PMF) is employed during solidification. By combining multiscale experiments and multiphysics simulations, this study systematically investigates the evolution of electromagnetic and flow fields and quantitatively characterizes the reconstruction of feeding channels within the alpha-Mg solid skeleton. The results reveal that the synergistic interaction of electromagnetic force, forced convection, and Joule heating not only refines the grains but, more importantly, reconstructs the feeding channels. Quantitative analysis of the three-dimensional network demonstrates that this reconstruction yields a significantly higher channel density, lower tortuosity, and enhanced branching connectivity. Permeability calculations confirm that these structural optimizations enhance liquid-feeding capability, with the improvement scaling positively with the PMF voltage. Consequently, under 150 V, the shrinkage porosity volume fraction decreases by 83.3%, while yield strength, ultimate tensile strength, and elongation increase by 20%, 25%, and 118%, respectively. Furthermore, a quantitative empirical correlation framework is constructed to bridge processing parameters (voltage), 3D defect topologies, and mechanical properties. This model decouples the contributions of shrinkage porosity features, identifying that the reduction of shrinkage porosity size and the optimization of its morphology are the dominant factors driving performance enhancement. Overall, this study creates a closed-loop framework that links external field parameters, microstructural quantization, and performance evaluation, providing both theoretical insight and an analytical framework for manufacturing highperformance magnesium alloy castings.

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.

While carbon fiber-reinforced polymer (CFRP) composites are widely utilized in aerospace applications due to their exceptional specific strength and stiffness, they are inevitably subjected to impact loads during service, which can easily induce internal damage such as delamination. To mitigate these issues, this study investigates the low-velocity impact behavior of an SMA-reinforced CFRP U-shaped structure, emphasizing the critical role of curing-induced residual stresses. A numerical model incorporating the thermal-mechanical manufacturing history was developed and validated against experimental data. Results indicate that while embedded superelastic SMA wires effectively suppress crack propagation and enhance energy absorption, neglecting residual stresses leads to a significant overestimation of structural rigidity and peak loads. Due to the coefficient of thermal expansion mismatch between the SMA wires and the resin matrix, the SMA-CFRP system exhibits higher sensitivity to initial internal stresses than pure CFRP. By accounting for the residual stress field, the relative error in predicted peak force and absorbed energy for the SMA-CFRP model was reduced from 9.3% to 3.5% and 18.9% to 7.8%, respectively. These findings demonstrate that residual stress lowers the failure threshold and is essential for capturing the synergistic effects of SMA phase transformation and matrix damage, providing a more accurate reconstruction of the structural energy balance.

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.

Origami structures achieve high directional stiffness while preserving foldability, offering significant potential for smart morphing structures. This study proposes an active morphing Kresling core, which consists of a Kresling tube integrated with a two-way shape memory alloy (SMA) spring. The structure deforms upon heating and recovers upon cooling. A parametric modeling framework is established to define the geometric characteristics of the Kresling tube, and the material properties of both the tube and SMA are characterized. Based on an analytical model, parameter sensitivity is evaluated, and the optimal configuration is identified using a multi-island genetic algorithm. The generated dataset is used to construct a radial basis function neural network model. Experiments and simulations consistently demonstrate the deformation behavior of the assembled active morphing Kresling core. Furthermore, a honeycomb-inspired array concept is discussed to illustrate a possible extension of the proposed core toward multimodal morphing structures. The results show that the active Kresling core can achieve reversible shape change and programmable curvature, indicating its potential as a reconfigurable cellular element for active morphing structures.

Thermal buckling presents a significant challenge to the stability of thin-walled structures exposed to elevated temperatures. The thermally induced phase transformation deformation of NiTi shape memory alloys can counteract thermal expansion, thereby exhibiting the so-called anti-thermal buckling behavior. This study experimentally investigates the out-of-plane thermal buckling deformation, as well as the stress and strain responses, of NiTi alloy thin plates under increasing temperature. The anti-thermal buckling mechanism is systematically elucidated. Through the introduction of appropriate pre-strain, thermally induced phase transformation deformation can eliminate out-of-plane deformation caused by thermal buckling and also reduce thermal stress. A theoretical model was developed based on elastic buckling theory and quadruple strain decomposition to explain the deformation mechanism and to predict the effects of pre-strain on the stress and strain responses of NiTi alloy thin plates. The comparison between experimental results and theoretical predictions confirms the accuracy and effectiveness of the proposed model. This study offers both theoretical and experimental foundations for the design of thermally stable structures reinforced with SMA thin plates.

The high-fidelity prediction of high-temperature flow stress is a prerequisite for the accurate simulation of manufacturing processes and microstructural control in titanium alloys. Although the strain-compensated Arrhenius model is widely employed, its traditional identification through sequential linearized regression often suffers from truncation error accumulation and ignores the intrinsic coupling between deformation parameters. In this study, a robust Global Parameter Identification Strategy (GPIS) is proposed for an Optimized Arrhenius Model (OAM) to describe the flow behavior of a low-cost Ti-4.5Al-1V-3Fe alloy. By reformulating the hyperbolic sine relation into an explicit stress predictor with a reduced parameter set, the identification problem is transformed into a one-step global optimization, thereby eliminating the systematic errors inherent in stepwise methods. A generalized function library is introduced to autonomously capture the bivariate evolution surfaces of constitutive parameters with respect to strain and temperature. The results demonstrate that the GPIS-OAM framework achieves superior predictive accuracy (R²=0.9964, AARE = 6.84%) compared to traditional Arrhenius, Johnson-Cook, and modified Zerilli-Armstrong models. The proposed method provides a physics-based analytical form with accuracy competitive with advanced machine learning regressors (ANN, SVR, k-NN), offering a reliable tool for high-precision metallurgical calculations and finite element simulations of titanium alloy processing.

This paper presents a comprehensive numerical investigation into the transverse compressive properties and progressive damage mechanisms of three-dimensional (3D) braided composites, which are increasingly valued for their structural efficiency in engineering applications. A mesoscale finite element model was developed to explicitly capture the intricate braided architecture of the composites, encompassing yarn configurations and matrix distribution. The mesoscale finite element model simulations demonstrate good agreement with experimental results from macroscopic compressive tests, thereby validating the modeling approach. Using this validated framework, the mechanical response under transverse compressive loading was analyzed in detail, covering stress distribution patterns, load-displacement characteristics, and critical transition points in the deformation process. To accurately distinguish failure modes across different material phases, Hashin's criterion was applied to fiber-dominated failures, while the Hou criterion targeted matrix-dominated damage. It has been shown that the transverse compressive strength is lower than the longitudinal compressive strength, with a more pronounced disparity observed in their compressive moduli for 3D four-directional braided composites. Under compressive loading, fiber fracture initiates at the surface regions where the matrix interfaces with individual fiber bundles, and as the compressive displacement increases, such fracture propagates rapidly along the edges. These insights provide valuable guidance for optimizing the structural design of such materials.

This paper presents a method for significantly enhancing the bending actuation capacity of tape actuators through a shape memory effect (SME)-activated cross-sectional curvature transition from a flat configuration to an arc-shaped one. NiTi shape memory alloy (SMA) sheets, with a thickness of 0.3 mm and a width of 24 mm, were trained to acquire SME along the transverse direction by annealing at 550 degrees C for 30 min while constrained within stainless steel molds. These SMA variable curvature strips (SMA-VCS) were subsequently subjected to folding and unfolding tests, monitored by a high-speed camera and an infrared camera. The folding process exhibited behavior similar to that of a traditional tape spring, while the unfolding process under applied loads proved significantly more complex. Upon heating, the SMA-VCS initially demonstrated stable bending recovery with its cross-section remaining flat. Once a critical angle was reached, a snap-through transition occurs, causing the SMA-VCS to "jump" back to its nearly original unbent position as the cross-section abruptly shifted from flat to arc-shaped. A significant improvement in bending actuation capacity was observed: under a constant load of 200 g applied to the ends of a 0.3 mm thick beam, traditional SMA actuators with a flat cross-section achieved a recovery angle of only 56.77 degrees upon efficient heating, whereas the SMA-VCS returned to its nearly original unbent position (90 degrees), representing an improvement of 32.32 degrees. Finally, an SMA transformation-point bending actuation model is proposed to describe the critical points governing the bending performance. The predicted actuation angles and corresponding temperatures align closely with experimental results.

Carbon fiber reinforced polymer (CFRP) composites are highly valued for their excellent specific strength and stiffness. However, CFRP is vulnerable to impact damage, which is often unavoidable in practical applications. This study investigates the enhancement of impact resistance in CFRP composites through the incorporation of superelastic shape memory alloy (SMA) wires into the CFRP matrix. Unidirectional and bidirectional SMA-reinforced CFRP laminates were fabricated and subjected to low-velocity impact testing. The surface and internal interlaminar damage patterns of the laminates were observed through a combination of visual inspection and ultrasonic C-scan imaging. The impact response of the laminates was analyzed by examining the time-varying curves of impact force and impact point displacement. The results indicate that SMA-reinforced CFRP (SMA-CFRP) demonstrates shallower delamination cracks and reduced interlaminar damage after impact. The maximum impact force of the unidirectional and bidirectional SMA-reinforced CFRP increased by 26.1 % and 29.5 %, respectively, indicating a significant enhancement in the matrix stiffness after the incorporation of SMA. The mechanical mechanisms behind the improved impact resistance were further investigated through simulation analysis, the importance of SMA phase transformation in the energy absorption process during impact was highlighted. The results of the parametric analysis indicate that reducing the spacing or introducing pre-stress of SMA wires contributes to a slight improvement in impact resistance. This study offers new insights for the design and optimization of impact-resistant composites.

Inspired by counterintuitive water “swelling” ability of the hydrophobic moss of the genus Sphagnum (Peat moss), we prepared a hydrophobic pseudo-hydrogel (HPH), composed of a pure hydrophobic silicone elastomer with a tailored porous structure. In contrast to conventional hydrogels, HPH achieves absorption-induced volume expansion through surface tension induced elastocapillarity, presenting an unexpected absorption-induced volume expansion capability in hydrophobic matrices. We adopt a theoretical framework elucidating the interplay of surface tension induced elastocapillarity, providing insights into the absorption-induced volume expansion behavior. By systematically programming the pore structure, we demonstrate tunable, anisotropic, and programmable absorption-induced expansion. This leads to dedicated self-shaping transformations. Incorporating magnetic particles, we engineer HPH-based soft robots capable of swimming, rolling, and walking. This study demonstrates a unusual approach to achieve water-responsive behavior in hydrophobic materials, expanding the possibilities for programmable shape-morphing in soft materials and soft robotic applications. Shape-changing materials have potential in a range of applications, but these transformations can be challenging to control. Here, the authors report the hydrophobic pseudo-hydrogel, which utilizes absorption-induced expansion via elastocapillarity to enable versatile soft robotic applications.

This paper introduces an innovative approach to the deployment of folding wings on cruise missiles, aiming to overcome the issues associated with explosive devices. The proposed solution involves employing NiTi shape memory wires for a nonexplosive self-deploying wing mechanism. The fundamental concept of the design revolves around the utilization of NiTi wires, which contract upon electric heating. This contraction action severs the shear pin, consequently releasing the folded wings. The operational performance of the NiTi wire is thoroughly examined through a series of electro-thermo-mechanical tests, offering valuable insights for selecting the appropriate wire material. Moreover, the mechanical dynamics involved in the self-deploying process are elucidated through finite element simulations. The simulations highlight that the thermally-induced phase transformation within the NiTi wires generates substantial actuation forces, exceeding 700 N, and strokes of over 6 mm. These forces are deemed sufficient for breaking the aluminum shear pin and effecting wing deployment. The proposed mechanism’s practical viability is substantiated through prototype tests, which conclusively establish the superiority of the nonexplosive self-deploying wing mechanism when compared to conventional methods. The experimental outcomes underscore the mechanism's capability to markedly reduce overload stress while remaining compliant with the designated requirements and constraints.

This study investigates the influence of braiding angles on the mechanical behavior and damage mechanisms of three-dimensional (3D) braided composites under uniaxial compressive and tensile loading. By integrating uniaxial compression and tension tests with finite element (FE) analysis, the relationships between mesoscale damage initiation, propagation, and the macroscopic mechanical properties were revealed. Results demonstrate that the 3D4d-20° model exhibits higher stiffness and compressive strength but lower compressive failure strain compared to the 3D4d-40° model, attributed to differences in fiber spatial arrangement and matrix cracking propagation. Conversely, the 3D4d-40° model shows enhanced tensile performance but greater matrix-dominated damage under tension. Moreover, as the braiding angle increases, the ratio of tensile strength to compressive strength in 3D braided composites decreases accordingly. Comparative analysis of damage evolution pathways reveals that smaller braiding angles (20°) initiate damage earlier under compression, while larger angles (40°) promote transverse fiber bundle failure and matrix degradation. This research not only elucidates the underlying microscale damage mechanisms of 3D braided composites under compression loading but also highlights the differences in damage patterns between compressive and tensile loading, providing theoretical foundations for structural design and performance optimization of such composite materials. Future work will focus on incorporating interfacial effects and manufacturing-induced defects to refine the model further.

In this work, the high-velocity impact behavior of Z-pinned composite laminates is investigated by experiment and numerical modeling. High-velocity impact tests for Z-pinned composite laminates with different Z-pin spacing are carried out. The damage states in Z-pinned composite laminates are experimentally characterized to investigate the mechanisms underlying high-velocity impact damage. Delamination results are obtained using ultrasonic C-scan and scanning electron microscope techniques. It is found that the fiber breakage area decreased with the presence of the Z-pins, whereas matrix cracking increased. An appropriate numerical model incorporating a zero-thickness cohesive zone formulation is developed to predict the impact response of Z-pinned composite laminates. In this model, the specific cohesive elements are inserted in each layer, which reflects reinforcement effect of Z-pin. This approach can effectively capture both the spontaneous initiation and subsequent growth of delamination cracks. Consequently, the numerical model is validated through comparison of simulated and experimental high-velocity impact responses of Z-pinned laminates, demonstrating both accuracy and effectiveness. The characteristic values of impact mechanical responses and damages are investigated by the numerical model. In addition, the approach can be adapted to systemically study Z-pinned composites with different designed parameters under high-velocity impact.

On account of the dissipative martensite phase transformation, NiTi shape memory alloy can exhibit large pseudoelastic deformation and high damping capacity, making it a promising candidate in engineering vibration control. The main objectives of this paper are twofold: to investigate the free vibration behavior of the NiTi wires and to design a NiTi wire-based vibration isolator to verify its effectiveness in vibration control. The free vibration system consists of a mass and two antagonistic NiTi wires; finite element simulation on this system is carried out. The material model used in the simulation is created by implementing a generalized SMA model into commercial software by means of a user-defined material subroutine. Uniaxial tensile tests on the pseudoelastic NiTi wires and cables were conducted to determine the model parameters. Parametric analysis of the vibration system shows that the mass affects the frequency, the initial deflection affects the dissipation of the vibration energy in the first few cycles, and the pre-strain decreases the stabilized amplitude. Finally, a NiTi-based vibration isolator is designed, which can dissipate 95% of the vibration energy in 0.3 second, showing good ability to recenter the device in a short time.

This work evaluates the viability of a cutting-edge flexible wing prototype actuated by Shape Memory Alloy (SMA) wire actuators. Such flexible wings have garnered significant interest for their potential to enhance aerodynamic efficiency by mitigating noise and delaying flow separation. SMA actuators are particularly advantageous due to their superior power-to-weight ratio and adaptive response, making them increasingly favored in morphing aircraft applications. Our methodology begins with a detailed delineation of the fishbone camber morphing wing rib structure, followed by the construction of a multi-mode morphing wing segment through 3D-printed rib assembly. Comprehensive testing of the SMA wire actuators’ actuation capacity and efficiency was conducted to establish their operational parameters. Subsequent experimental analyses focused on the bi-directional and reciprocating morphing performance of the fishbone wing rib, which incorporates SMA wires on the upper and lower sides. These experiments confirmed the segment’s multi-mode morphing abilities. Aerodynamic assessments have demonstrated that our design substantially improves the Lift-to-Drag ratio (L/D) when compared to conventional rigid wings. Finally, two phases of flight tests demonstrated the feasibility of SMA as an aircraft actuator and the validity of flexible wing structures to adjust the aircraft attitude, respectively.

This study introduces an active shape-morphing lattice structure along with a method for controlling its deformation. A shape memory alloys (SMA) based smart lattice unit cell is proposed, this smart lattice unit cell is capable of accomplishing three distinct types of basic deformations by activating various SMA actuators through heating. By assembling these smart lattice unit cells, an entire structure can be constructed, which can undergo various modes of deformation through the activation of different actuators. To assess the deformation effects, a 3D printed active shape morphing lattice structure model is employed. Furthermore, a deformation control method for active shape morphing lattice structure using topology optimization approach is established. The optimization model takes into account both energy consumption and structural deformation errors. To illustrate the application of this approach, a numerical example involving an airfoil structure with bending deformation is presented. The desired deformation is attained with minimal energy consumption and only a 1% margin of error in deformation.

The foldable tail wing system of UAVs offers advantages such as reducing the envelope size and improving storage space utilization. However, due to the compact tail wing space, achieving multi-modal locking and unlocking functionality presents significant challenges. This paper designs a new smart SMA actuator for the use of UAV foldable tail wings. The prototype testing demonstrated the advantages and engineering practicality of the actuator. The core content includes three main parts: thermomechanical testing of the SMA actuation performance, structural design of the actuator, and the fabrication and actuation testing of the prototype. The key parameters related to actuation performance, such as phase transformation temperature and actuation force, were determined through DSC and tensile testing. The geometric parameters of the tail wing were determined through kinetics and kinematic analyses. Through the linkage design of two kinematic pairs, the SMA actuator enables both the deployment and locking of the tail wing. The prototype testing results of the folding tail wing show that, after vibration and temperature variation tests, the SMA actuator is still able to output an actuation stroke of 2.15 mm within 20 ms. The SMA actuator integrates locking for both modes of the tail wing and unlocking during mode transitions, offering advantages such as fast response and minimal space requirements. It provides an effective solution tailored to the needs of the foldable tail wing system.