Search Results (167)

Metamaterials with tailored structural architectures enable negative thermal expansion through geometric mechanisms that counteract constituent-level positive expansion. This study evaluates the thermomechanical performance and structural limits of polymer and hybrid NTE lattices. We systematically classify the dominant kinematic mechanisms, including bimetallic bending, rotational squares, and re-entrant honeycombs, and quantify the inherent trade-offs between effective thermal contraction, structural stiffness, and mass efficiency. The analysis demonstrates that reliance on idealized linear–elastic and rigid-lever models leads to significant predictive discrepancies when evaluating the physical response of polymeric and hybrid prototypes. We establish that these deviations are fundamentally governed by localized stress singularities at multi-material interfaces and the profound thermoviscoelastic softening of polymers as they approach the glass transition temperature ($T_g$). We conclude that accurate prediction of the cyclic lifespan and dimensional stability of these systems requires a transition to coupled multiphysics frameworks. Specifically, integrating temperature-dependent cohesive zone modeling and time–temperature superposition principles is essential for capturing interfacial delamination and thermal ratcheting in high-performance polymeric NTE metamaterials. Full article

Negative Poisson’s ratio materials show great potential in aerospace, automotive engineering, and military protection owing to their unique deformation behavior and superior mechanical properties. Nevertheless, current negative Poisson’s ratio honeycomb structures suffer from an inherent conflict between stiffness and energy absorption, along with poorly understood mechanical regulation mechanisms in complex three-dimensional nested configurations. To address these issues, this paper proposes a novel Cross Re-entrant Hexagon Nested Star-shaped Cell (CRNSC). Through theoretical derivation, finite element simulation, and quasi-static compression experiments, the mechanical properties and energy absorption characteristics of the structure are systematically investigated. A geometric characterization system based on length, angle, and thickness parameters is established. The results show that the cell wall thickness significantly increases the relative density, while the angle θ between the inner inclined strut and the horizontal line induces polarity reversal of the Poisson’s ratio. The outer inclined strut angle α and the inner angle θ exhibit monotonic or nonlinear regulatory effects on the equivalent Poisson’s ratio and the effective Young’s modulus, respectively. The optimal load-bearing configuration (α = 65°, θ = 35°) achieves a peak stress of 1.01 MPa, and the optimal deformation configuration (α = 55°, θ = 25°) reaches an ultimate strain of 4%. Theoretical, simulated, and experimental results are in good agreement with errors below 7%, validating the model’s effectiveness. Full article

Steel–UHPC composite beams are widely used in bridge engineering due to their high strength, durability, and suitability for prefabricated construction. However, the mechanical performance of shear connectors in UHPC differs significantly, and the uniform use of a single connector type along the beam span may result in a mismatch between connector mechanical characteristics and regional force demands, leading to suboptimal force transfer and inefficient utilization of connector capacity along the beam span. While previous studies have mainly focused on the local behavior of individual connectors, a system-level design strategy considering regional force demands is still limited. This study proposes a system-level design method for combined shear connectors in steel–UHPC composite beams, in which headed stud connectors and trapezoidal composite dowel connectors are arranged according to bending moment distribution and interface shear demand, thereby integrating connector mechanical characteristics with the spatial variation in internal forces along the beam span. The design procedure includes shear span division, longitudinal interface shear calculation, and resistance verification of different connector types. The method is applied to a practical steel–UHPC composite beam in a long-span approach bridge. Results show that headed studs provide reliable uplift resistance and ductile behavior in negative bending regions, whereas composite dowel connectors are shown to be more suitable for shear-dominated positive bending regions due to their higher shear capacity and stiffness. The combined system ensures effective composite action under different stress states and reduces total connector steel consumption compared with a stud-only layout. The proposed approach advances connector design toward performance-oriented and system-level structural optimization, providing a practical framework for connector arrangement in steel–UHPC composite beams. Full article

Calcium–silicate–hydrate (C-S-H), the primary binding phase governing cement paste cohesion, undergoes progressive physicochemical transformation upon carbonation—a process that critically dictates concrete durability in atmospheric environments. When CO₂ penetrates the porous cement matrix, it triggers a cascade of degradation mechanisms: calcium leaching decalcifies the C-S-H structure, inducing polymerization of silicate chains from dimeric to longer-chain configurations, while concurrent precipitation of calcium carbonate and amorphous silica gel fundamentally reconstitutes the nanoscale architecture. These nanoscale alterations propagate to macroscopic property evolution, manifesting as initial strength and stiffness gains due to pore-filling carbonation products followed by eventual deterioration as the cohesive binding network deteriorates. This review synthesizes current understanding of carbonation-induced structural evolution, examining the coupled influences of environmental parameters—CO₂ concentration, relative humidity, and temperature—alongside C-S-H intrinsic chemistry (Ca/Si ratio, aluminum substitution, and alkali content) on reaction kinetics and material performance. However, significant knowledge gaps persist: predictive models for in-service carbonation rates remain elusive due to the disconnect between idealized laboratory conditions and the heterogeneous, cracked reality of field concrete; the causal linkage between nanoscale C-S-H alteration and macroscale cracking patterns along with physical performance is poorly resolved, and most mechanistic studies rely on synthetic C-S-H, neglecting the compositional complexity of real Portland cement systems. We further propose emerging protection strategies, including surface barrier coatings and low-carbon alternative binders (geopolymers, calcium sulfoaluminate cements, carbon-negative materials such as recycled cement), which demonstrate enhanced carbonation resistance. Future research priorities include developing effective coating barriers for carbonation protection, developing operando characterization techniques for real-time reaction monitoring, deploying machine learning algorithms to bridge atomistic simulations with structural-scale predictions, and establishing long-term field performance databases to validate laboratory-derived degradation models. Full article

Traditional ready-to-wear garments can mostly not conform to different body shapes because of the adoption of the generic sizing system, which leads to the local strain of concentration and morphological misfit. Auxetic structures, which have a negative Poisson’s ratio, permit enhanced redistribution of stress and geometry and allow deformation. Two auxetic knitted structures were developed by using 100% polyester and 100% nylon yarns with a fabric density of 41 Wales and 40 courses per inch. Characterization of the initial fabrics involved checking the behavior of negative Poisson’s ratio (NPR) where the polyester line (P1) structure shows the highest auxeticity, with a NPR of approximately −0.4 and peak strain reductions of 80–90%, as well as air permeability, moisture management, bend test, compression, roughness, friction properties and stiffness tests to check the mechanical and comfort-related performances. The standardized tunic garment was modeled in CLO 3D on three female body shapes—hourglass, pear and rectangle—with a constant size of 34. The fit map showed a strain of 91.49% in auxetic and 509.75% in single-jersey fabric at the hip area of the pear body shape when measuring fabric and body interaction. The findings indicate lower peak strain levels, which ascertain that increased adaptability is possible and support its use in the development of adaptive ready-to-wear garments. Full article

To address the detuning sensitivity of conventional linear vibration absorbers under wide-frequency harmonic excitation and the limited effectiveness of nonlinear energy sinks (NESs) in low-energy regimes, this study investigates a bistable nonlinear energy sink (BNES) based on a negative-stiffness support. A coupled model of the primary system and the BNES is established, and the analytical steady-state amplitude–frequency relationship of the system is derived using the harmonic balance method. The accuracy of the analytical solutions is verified through numerical integration. Based on the first Lyapunov method, the instability regions of the system are identified, and the effects of system parameters on the amplitude–frequency response of the primary structure are analyzed. On this basis, a comprehensive performance index that accounts for both peak suppression and average vibration reduction over the frequency band is constructed, and an improved particle swarm optimization algorithm is employed for parameter optimization. The results demonstrate that the optimized BNES can effectively suppress isolated high-amplitude response branches and significantly reduce the response of the primary system within the resonance frequency band, exhibiting superior broadband vibration mitigation performance and enhanced stability. Full article

To evaluate the seismic performance of single-degree-of-freedom (SDOF) systems under mainshock–aftershock (MS–AS) seismic excitation, nonlinear time-history analyses were conducted on SDOF systems with various parameter combinations, using 50 sets of real MS–AS sequences and 150 sets of artificial sequences generated by repetition, random, and attenuation methods. The results indicate that the ground motion characteristics of MS–AS sequences generated by the repetition, random, and attenuation methods differ from those of real MS–AS sequences, with the repetition and random methods tending to overestimate the peak ground motion parameters and acceleration response spectra of MS–AS sequences, and the attenuation method potentially underestimating them, while all three methods for generating MS–AS sequences are prone to overestimating the ground motion duration of MS–AS sequences. Residual deformation is influenced by relative yield strength coefficient (η), aftershock relative intensity (χ), post-yield stiffness ratio (r), natural vibration period (T) and the hysteresis model under MS–AS seismic excitation, and residual deformation exhibits a positive dependence on aftershock intensity (χ) and a negative dependence on post-yield stiffness ratio (r), while the relationship between residual deformation and relative yield strength coefficient (η) is influenced by the natural vibration period (T), showing a positive correlation in the short-period range and a negative correlation in the mid-to-long period range. A log-normal distribution can be adopted to describe the probability distribution of the ratio of residual deformation to peak elastic-plastic deformation subjected to MS–AS seismic excitation with different parameters. Finally, a probabilistic prediction model for residual deformation under MS–AS seismic excitation was proposed which can effectively predict residual deformation under MS–AS seismic excitation. Full article

With inherent negative stiffness and nonlinearity, reluctance magnetic levitation systems struggle to sustain satisfactory control performance across a long stroke. To address this issue, theoretical analysis, control strategy design, and experiments are performed. First, the magnetic and dynamic behavior are analyzed, and the corresponding mathematical model is derived. Then, the control system analysis is conducted, and the feedback properties are described from a physically intuitive perspective. Moreover, with a standard PD/PID compensator, a clear trade-off emerges between robustness at small air gaps and tracking performance at large air gaps. Subsequently, a control strategy combining feedforward compensation with gain scheduling PD is designed. It is directly mapped from the reluctance actuator parameters without relying on engineering experience and can be flexibly configured to meet performance requirements. Finally, time-domain and frequency-domain experiments are conducted. The positioning control results show that the proposed strategy effectively shortens the settling time of long-stroke step responses and improves the uniformity of the dynamic performance. The frequency response evidence shows a more uniform response over the full stroke and simultaneous improvements in robustness and tracking, effectively resolving the long-stroke conflict. Full article

Traveling wave ultrasonic motors (TWUMs) are critical components in precision systems, yet their performance is susceptible to degradation under dynamic disturbances in harsh operating environments. This paper presents a monolithic U-shaped rotor designed to intrinsically achieve quasi-zero stiffness (QZS). Unlike conventional QZS systems that rely on assembling discrete positive and negative stiffness elements, the proposed design generates the target mechanical characteristic through the tailored nonlinear response of a unified U-shaped structure, thereby improving preload stability. Through exploring the critical parameters of the rotor cross-section, the finite element method (FEM) is employed to optimize the geometry configuration and characterize the mechanical performances. The simulation results show the QZS behavior demonstrating a stable force plateau of 320 ± 10 N across a 0.7 mm displacement range. A maximum von Mises stress of 788 MPa is obtained, well within the material’s safety margin, thereby ensuring the structural integrity. Experimental tests validate the effectiveness of the proposed design. This compact, monolithic U-shaped rotor provides a robust and reliable QZS solution, demonstrating significant potential for enhancing the stability of TWUMs in applications prone to harsh environments such as wide-range temperature fluctuations, thermal cycling conditions, and shock environments. Full article

This study provides computational insights into the flexural strengthening of reinforced concrete (RC) T-beams in the negative moment region using steel-reinforced polymer cement mortar (PCM) overlays. A validated three-dimensional nonlinear finite element (FE) model was developed using the Advanced Tool for Engineering Nonlinear Analysis (ATENA) software (version 2023.0.0.22492) to simulate the behavior of beams retrofitted with 40 mm thick PCM layers embedded with 13 mm and 16 mm deformed bars. Model validation was performed against previously published experimental results reported by the authors, demonstrating excellent agreement, with normalized mean square error (NMSE) values expressed as fractions between 0.0001 and 0.0022, and experimental-to-numerical ultimate load ratios ranging from 0.99 to 1.01. Parametric analyses were then conducted to investigate the influence of key variables, concrete compressive strength, PCM overlay thickness, and longitudinal reinforcement ratio on the global flexural performance. The results revealed that increasing the overlay thickness raised the ultimate load capacity by up to 15.4% and improved energy absorption by 43%. Enhancing concrete strength led to gains of up to 12.5% in load capacity and 15.8% in stiffness. Variations in reinforcement ratio had the most significant impact, increasing peak load by up to a factor of 2.02 and improving energy absorption by up to a factor of 1.49. Despite these improvements, reductions in ductility were observed across all strengthening configurations, underscoring a strength–deformability trade-off critical for seismic applications. These findings affirm the efficacy of steel-reinforced PCM overlays and provide design-oriented insights for optimizing negative moment retrofitting strategies in RC bridge girders and continuous beam systems. Full article

The power package of high-speed internal combustion units generates complex excitation forces during operation. These forces cause excessive vibration in the driver’s cab, negatively affecting the driver’s working conditions. Therefore, optimizing the isolation system design is essential. This study established a rigid body dynamic model of a single-layer isolation system to determine initial stiffness parameters. A refined finite element (FE) model of the diesel locomotive body was also developed to analyze vibration characteristics. Using the global response surface method, multi-objective optimization was performed. The three-dimensional stiffness of the isolator served as the design variable, while the maximum force transmissibility at the vehicle reference point was the optimization objective. The optimization accuracy was verified through FE modeling, experiments, and simulations considering coupled wheel–rail excitations. Results showed that the force transmissibility at the cab’s center floor decreased from 44.05% to 32.65%. Furthermore, the comfort index met the requirements under all working conditions. These findings indicate that the proposed design method effectively improves the efficiency of the power pack isolation system and provides a valuable reference for future designs. Full article

The vehicle suspensions have the primary task of attenuating the forces coming from the road surface. The performance is directly linked to the stiffness of the suspension system. Traditional suspensions, composed of linear elements, effectively damp high frequencies but perform poorly at low frequencies. In this regard, non-linear suspensions, characterized by a non-linear force–displacement relationship, have been introduced. These types of suspensions achieve this characteristic by combining elements with positive stiffness with elements with negative stiffness, resulting in an equivalent system with quasi-zero stiffness (QZS) around the equilibrium. The performance of the QZS suspension system is analyzed here using the Multibody Dynamics software MSC Adams^® (2022.2). Static characteristics, transmissibility, and isolation performance are investigated through dynamic tests based on road profiles according to ISO 8608 regulations generated using MATLAB^® (R2022b). The proposed quasi-zero stiffness suspension demonstrates an improvement of approximately 19% in vibration attenuation compared to a conventional suspension system under realistic road excitations. Full article

Background/Objectives: Lupus Nephritis (LN) is a major complication of Systemic Lupus Erythematosus (SLE) leading to significant morbidity. While biopsy is the gold standard, non-invasive tools are needed for longitudinal monitoring. This study aims to evaluate the diagnostic utility of Shear Wave Elastography (SWE) in detecting subclinical renal damage (fibrosis) in SLE patients with a history of LN who are currently in clinical remission (inactive disease), and to compare its efficacy with Doppler ultrasonography (DUS). Methods: This cross-sectional study included 80 SLE patients and 41 age- and sex-matched healthy controls. Crucially, all SLE patients were in the clinically inactive disease (SLEDAI-2K < 6) at the time of evaluation. Patients were stratified into two groups: those with a history of LN (LN Group, n = 37) and those without (Non-LN SLE Group, n = 43). Strict exclusion criteria were applied to eliminate non-SLE renal comorbidities. Renal parenchymal stiffness (kPa) was measured using SWE, and the renal resistive index (RI) was assessed using DUS. SWE findings were correlated with renal function tests and disease activity scores. Results: Despite being in clinical remission, the LN group exhibited significantly higher renal stiffness values (Median: 1.60 kPa) compared to the non-LN SLE group (1.40 kPa, p < 0.001) and healthy controls (1.32 kPa, p < 0.001). No significant difference was observed between the non-LN SLE group and controls. Unlike SWE, renal RI values showed no statistically significant difference among the groups (p > 0.05). Correlation analysis revealed that renal stiffness was positively associated with prior serum creatinine and disease activity (SLEDAI-2K), and negatively associated with eGFR. Conclusions: SWE is superior to DUS (RI) in detecting renal parenchymal changes in LN patients. The persistence of elevated stiffness during the inactive disease suggests that SWE captures cumulative chronic damage (remodeling and fibrosis) rather than just acute inflammation. Consequently, SWE holds promise as a non-invasive surrogate for monitoring disease chronicity in SLE patients. Full article

High-sensitivity, high-resolution electric field sensors (EFS) find extensive applications across multiple domains, including atmospheric monitoring, aerospace, power grid management, and industrial automation. While conventional electric field measurement techniques suffer from integration challenges and high-power consumption, micro-electromechanical systems (MEMS)-based EFS offer distinct advantages through miniaturization, integration capability, and functional intelligence. This research incorporates frequency modulation technology into MEMS EFS, leveraging its inherent noise immunity, long-range transmission capacity, and compatibility with digital systems to enhance measurement precision. The sensor’s lateral and axial symmetry configurations are systematically investigated to reveal how asymmetric stiffness perturbations (negatives vs. positives) optimize performance, aligning with symmetry principles in MEMS design. Experimental results demonstrate that the lateral configuration achieves optimal performance with a sensitivity of 0.091√Hz/(kV/m) and a resolution of 1.01 kV/m, whereas the axial configuration yields an average sensitivity of 0.038 √Hz/(kV/m) with a corresponding resolution of 2.37 kV/m. The measurement range of the sensor is from −193.4 kV/m to 193.4 kV/m. Full article

Background: Familial Mediterranean fever (FMF) is a chronic autoinflammatory disorder characterized by sustained systemic inflammation that may affect cardiac structure and function. Colchicine is the cornerstone of FMF therapy and has cardiovascular benefits in inflammatory settings. Methods: This cross-sectional study enrolled 106 participants: 53 patients with FMF receiving long-term colchicine therapy and 53 age- and sex-matched controls. Participants underwent transthoracic echocardiography with speckle-tracking imaging. Conventional parameters and strain-derived indices of the left ventricular (LV) and left atrial (LA) function were assessed. Correlation analyses and multivariable linear regression models were used to evaluate the association between FMF presence and cardiac strain parameters. Results: The LV ejection fractions were comparable between the groups. The FMF group showed thinner ventricular walls and larger chamber dimensions than the control group. Patients with FMF exhibited higher LA reservoir strain, while conduit and contractile atrial contributions were reduced, as shown by lower passive and active emptying fractions and reduced LA ejection fraction. LA volumes and stiffness indices were lower in the FMF group, indicating smaller and more compliant atrial structures. Left ventricular global longitudinal strain (LVGLS) was more negative in patients with FMF, indicating preserved LV longitudinal systolic function. FMF was independently associated with LVGLS and LA strain parameters after adjusting for cardiovascular risk factors. Conclusions: In patients with FMF receiving long-term colchicine therapy, cardiac strain imaging showed preserved LV longitudinal function and distinct LA mechanics with preserved reservoir strain but reduced conduit and contractile function. Strain echocardiography may provide insights into cardiac involvement in well-controlled FMF, although prospective studies are needed to clarify the clinical significance of these findings. Full article