Search Results (672)

A novel self-centering variable friction damper (SC-VFD) was designed, which has the characteristics of high bearing capacity and good durability. This damper has a dual self-centering mechanism, which can provide restoring force via a coil spring under small earthquakes, as well as restoring force via a coil spring and a disc spring under medium or large earthquakes. In addition, this damper has variable friction capacity under different earthquakes. The configuration and the working mechanism of the SC-VFD was studied, and the mechanical model was established; then, finite element analysis of the SC-VFD was carried out. The results show that the SC-VFD has good self-centering performance and energy dissipation capacity; the residual displacement could be controlled by adjusting the preload and the stiffness of the disc spring; the hysteresis curves obtained through theoretical calculation and numerical simulation are in good agreement, verifying the correctness of the theoretical model and the finite element model. Finally, a four-story steel frame structure was designed for seismic performance analysis in order to verify the effect of the SC-VFD on the energy dissipation and vibration reduction of the frame structure. The results show that the vibration reduction rates of the SC-VFD can reach 33% under frequent earthquakes and 51% under rare earthquakes. Therefore, the SC-VFD has good seismic effects and can be applied to increase the resilience of building structures. Full article

Pneumatic artificial muscles exhibit pronounced hysteresis in the force-contraction domain, which complicates accurate force modeling under pressure-dependent operation. This work presents a discrete-time quasi-static hysteresis model for a compact pneumatic artificial muscle using a memristive system-based branch-memory formulation. The model combines separate loading and unloading force surfaces through a bounded internal state and is evaluated on experimental data acquired at a force-change rate of $4\mathrm{N}/\mathrm{s}$. Measurements were performed at 13 pressure levels from 0 to 0.6 MPa in 0.05 MPa increments, with 32 unloading points and 32 loading points per pressure level and five repetitions for each operating condition. Representative branch curves were obtained by median reduction in the repeated measurements, and the loading and unloading surfaces were identified with the five-parameter Sárosi–Fabulya exponential-bilinear function. The state update parameter was evaluated over a fixed grid, and the best loop reconstruction on the present dataset was obtained for the hard-switching case $\alpha =1$. Benchmark comparisons with Prandtl–Ishlinskii, discrete Preisach, Maxwell-slip, and sampled Bouc–Wen-type models show that Preisach and Bouc–Wen provide higher loop-reconstruction accuracy. The proposed memristive formulation should not be interpreted as a best-fit benchmark model, but as a low-order global branch-memory representation that preserves pressure dependence and branch asymmetry within a single analytical framework over the investigated quasi-static operating range. Full article

This study combines theoretical analysis with experimental investigation to examine the hysteretic behavior and seismic mechanisms of self-centering timber frames incorporating reinforced concrete slabs through tests on two full-scale comparative specimens. One specimen was constructed with a floor slab, while the other was designed without a slab, and both were subjected to low-cycle reversed loading under identical test conditions. The seismic performance of the two specimens was comparatively evaluated in terms of hysteresis curves, load-carrying capacity, stiffness degradation, and energy dissipation capacity. The experimental results indicate that, under the adopted test configuration, the presence of the slab increases the initial stiffness of the frame by 81.25% and enhances its load-carrying capacity. In addition, prior to concrete cracking, the slab improves the energy dissipation efficiency through composite action. The slab also reduces the rate of post-tensioning loss by approximately 12.5%, indicating its beneficial role in mitigating such loss. Overall, this study provides both theoretical and experimental support for the quantitative evaluation of slab effects in self-centering timber frames. Full article

Surface Acoustic Wave (SAW) magnetic sensors are traditionally fabricated on rigid substrates, which severely limits their application on curved or irregular surfaces. To address this critical limitation, this paper presents a novel flexible SAW magnetic sensor based on a grating-arrayed Terfenol-D thin film deposited on a 50 µm thick flexible lithium niobate (LiNbO₃) substrate. Unlike conventional designs using a continuous magnetostrictive layer, the proposed grating-arrayed structure is designed to aid in hysteresis compensation and minimize measurement errors associated with residual magnetization. As demonstrated experimentally, the sensors achieve a high sensitivity of 85.8 kHz/mT for devices with λ-wide gratings and a maximum frequency shift of 377 kHz at 5 mT. A systematic investigation reveals that sensitivity is critically dependent on the grating width and film thickness, with 500 nm thick gratings yielding optimal performance. Crucially, the sensor’s functionality under mechanical deformation is validated, and a differential measurement method is introduced to effectively compensate for stress-induced frequency shifts, ensuring reliable operation in practical, non-ideal conditions. The results confirm the sensor’s robust performance under the tested stress conditions, positioning this flexible SAW magnetic sensor as a promising solution for advanced, conformable sensing applications. Full article

Magnetic hysteresis strongly influences energy dissipation and efficiency in power magnetic components under time-varying excitation. This work proposes a compact dynamic hysteresis model using a Hammerstein structure, consisting of a closed-form arctangent static operator followed by a first-order relaxation dynamic stage. The formulation enables direct datasheet-based parameterization and avoids iterative differential solvers or distributed hysteron representations, resulting in low calibration effort and computational cost. The static hysteresis behavior is characterized using four static parameters directly identified from manufacturer B-H datasheets, while dynamic effects are captured using two global calibration parameters derived from datasheet loss curves. This formulation enables accurate reconstruction of major and minor hysteresis loops, while introducing frequency-dependent phase lag and dynamic loop opening. Model performance is evaluated under diverse excitations, including sinusoidal, amplitude-modulated, FORC and chirp signals, showing waveform deviations below 7.2% peak-to-peak NRMSE relative to classical hysteresis models. Energy-loss predictions are validated against manufacturer datasheet curves for ferrite material 3C90 across multiple frequencies, yielding a root-mean-square relative error of 8.3% with 89% of operating points within ±20% deviation. The proposed model provides a datasheet-driven framework for hysteresis and energy-loss prediction in power magnetic components. Full article

Stabilization/solidification (S/S) is a crucial technology for the engineering reuse of oil-contaminated soil. A key challenge, however, is preventing the migration of residual oil under varying hydraulic conditions. This study investigates the efficacy of a lime and fly ash binder in treating oil-contaminated soil. We systematically compared the performance of untreated (UOCS) and treated (TOCS) soils under different aqueous environments (humidity injection, water injection, and permeation). We evaluated oil migration, water-holding capacity, and permeability characteristics. The results demonstrate that the lime–fly ash treatment effectively adsorbed and immobilized oil contaminants, restricting their mobility to a remarkably low range of 0.54% to 4.90%. Furthermore, the S/S treatment significantly improved the soil’s hydraulic properties: it enhanced the water-holding capacity, reduced the soil-water characteristic curve hysteresis, and counteracted the oil-induced hydrophobicity. Consequently, the effective permeation channels were restored, leading to a higher permeability coefficient in TOCS compared to UOCS. Crucially, the hydro-mechanical performance of the treated soil met the criteria of the Solidification/Stabilization Resource Guide, confirming its suitability for engineering applications. Full article

Fatigue failure in scaffolding components poses significant risks to worker safety, particularly in high-altitude construction environments. This study investigates the fatigue behavior of scaffolding stirrups, a critical structural element prone to premature failure. The objective is to analyze the fatigue damage mechanisms in stirrups through a combined experimental and numerical approach. Mechanical characterization and micro-hardness testing were conducted to assess the material properties of the stirrup, while finite element modeling (FEM) was employed to simulate its performance under cyclic loading. The Johnson–Cook material model was utilized to compare experimental hysteresis curves with FEM results, validating the numerical approach. Additionally, the Extended Finite Element Method (XFEM) was applied to model crack initiation and propagation. Results reveal that material hardening and fatigue crack growth are the primary causes of stirrup failure, with distinct fatigue zones and crack paths identified. The study quantifies the relationship between crack growth stages and stirrup bending, providing insights into the failure process. These findings contribute to improving the safety and lifespan of scaffolding systems by identifying key factors influencing stirrup durability. Full article

In earthquake engineering and hydraulic engineering, the dynamic mechanical behavior of cohesive soils is crucial to ensure structural stability. However, most existing dynamic constitutive models fail to adequately account for the influence of strain history, which is essential for accurately predicting soil behavior under seismic loading. This study conducted a series of cyclic single-shear tests on both in situ and disturbed Changsha cohesive soils. Hysteresis curves were obtained under varying shear strain amplitudes to investigate the degradation patterns of the dynamic shear modulus and the evolution of the damping ratio. Furthermore, multi-cycle loading tests under constant strain amplitude were carried out to clarify the correlation between damping ratio, dynamic shear modulus, and the number of loading cycles. A simplified practical dynamic model, applicable to general cohesive soils, is proposed. This model incorporates the effect of strain history and provides a valuable reference for analyzing the dynamic response of soils subjected to earthquake actions. Full article

Wire rope isolators (WRIs) exhibit typical nonlinear and asymmetric hysteretic behavior, with their mechanical performance being significantly influenced by the coupled effects of multiple parameters. This study investigates the dynamic response of large-sized spiral WRIs under axial loading. Within the framework of an asymmetric hysteresis model, a novel algebraic closed-form formulation is adopted for parameter identification and numerical simulation. Furthermore, a characteristic parameter, A, is introduced to quantify the unique mechanical behavior induced by the structural configuration of WRIs. Five types of large-sized spiral WRIs are selected as test specimens. For each WRI, tests are conducted under 30 distinct working conditions, yielding a total of 150 cyclic loading tests across all scenarios. By systematically varying the displacement amplitude, loading frequency, and preloading pressure, the influences of these key parameters on the dynamic characteristics of WRIs are comprehensively analyzed. These characteristics encompass the axial hysteresis loop shape, energy dissipation capacity, equivalent viscous damping, and average secant stiffness. The results indicate that these three loading parameters exert substantial effects on the mechanical properties of large-sized WRIs. Additionally, the simulated hysteresis curves derived from the identified parameters exhibit excellent agreement with the experimental observations. Compared with conventional mechanical models, the proposed algebraic closed-form model demonstrates slightly higher fitting accuracy, thereby validating its effectiveness and applicability in characterizing the mechanical behavior of large-sized WRIs. This research provides a crucial reference for the engineering application of large-sized spiral WRIs and facilitates the broader adoption of the proposed modeling approach. Full article

The development of eco-efficient construction materials requires optimisation strategies that reduce cement consumption, valorise industrial by-products, and enhance performance without increasing material demand. Clay–cement sealing suspensions used in geotechnical engineering offer significant sustainability potential due to their high mineral content and compatibility with supplementary cementitious materials such as siliceous fly ash. The early-age rheological properties are essential for the design of geotechnical sealing barriers, yet the influence of chemical additive sequencing on flow behaviour remains poorly understood. This study examines how the priority of sodium silicate addition—introduced either before cement and siliceous fly ash (the “Prior” series) or after them (the “After” series)—affects the flow curves, yield stress, thixotropy, and equilibrium shear stress of clay–cement–fly ash sealing suspensions. Ascending flow curves were fitted to the Casson, Herschel–Bulkley, and Ostwald–de Waele models, and a shear-rate-resolved thixotropic power density analysis was applied to decompose the hysteresis behaviour. The results demonstrate that the Prior series produces deflocculated colloidal clay networks with localised cementitious agglomerates, exhibiting lower shear stresses at low shear rates but markedly higher yield stress amplitudes and larger hysteresis loop areas. The After series yields more uniformly distributed nucleation–coagulation networks with smaller hysteresis loops and pronounced structural rebuilding at low shear rates during the ramp-down phase. These findings provide a physicochemical framework for tailoring the early-age rheology of clay–cement suspensions through controlled additive sequencing, with direct implications for pumpability, injectability, and post-placement structural recovery in geotechnical applications. Full article

Accurate prediction of surface rupture induced by seismogenic fault displacement is essential for the seismic safety assessment of major engineering projects. Most existing numerical simulations adopt quasi-static approaches, in which the effect of fault displacement is simplified as static loading. As a result, these methods cannot represent the dynamic characteristics of the fault rupture process, such as stress-wave propagation, soil inertial effects, and the influence of dynamic loading paths on rupture extension in soil layers. To address this issue, a full-process simulation method is established for simulating rupture of overlying soil subjected to dynamic fault displacement: Firstly, a non-uniform dynamic fault displacement loading is formulated for the two sides of the fault based on viscoelastic artificial boundaries, allowing the differential motion of the bedrock on both sides of the fault to be represented. Secondly, an improved dynamic skeleton curve constitutive model of soil is developed by introducing a minimum modulus constraint, providing an improved description of soil nonlinear dynamic behavior from small-strain hysteresis to large-strain shear failure. The reliability of the proposed method is verified through element-level tests and horizontal-site response simulation. As a benchmark, its ability to reproduce key rupture characteristics under quasi-static conditions is also assessed by comparison with classical quasi-static rupture studies. The method is then applied to simulate rupture extension and deformation response of overlying soil under strike-slip fault displacement. The results show that, compared to quasi-static analysis, dynamic fault displacement produces similar cumulative slip for surface rupture initiation and full connection, but induces transient amplification of peak surface displacement and a wider deformation zone with gentler displacement gradients. These findings demonstrate the necessity of considering dynamic fault dislocation of bedrock–overlying soil interaction in seismic assessments of engineering projects crossing active faults. Full article

Although the cyclic bending behavior of circular and elliptical steel tubes has been widely studied, the combined effects of major-to-minor axis length ratio and curvature ratio on the deformation characteristics and buckling life of galvanized steel elliptical tubes remain insufficiently understood. This study experimentally investigates the cyclic bending response and failure behavior of galvanized steel elliptical tubes with major-to-minor axis length ratios of 1.5, 2.0, 2.5, and 3.0 under curvature ratios of −1, −0.5, and 0. The curvature ratio is defined as the minimum controlled curvature divided by the maximum controlled curvature. Buckling is defined as the cycle at which a pronounced 20% drop in peak bending moment is observed. The response is characterized by moment (N⋅m)–curvature (m⁻¹) hysteresis and minor-axis variation with curvature, while failure is evaluated using the relationship between curvature range and number of cycles to buckling. The results show that stable elastoplastic hysteresis loops develop for all curvature ratios, with slight cyclic relaxation observed at curvature ratios of −0.5 and 0. Increasing the axis length ratio slightly reduces the peak moment under a fixed curvature ratio. Minor-axis variation increases progressively with cycle number, exhibiting serrated curves at an axis ratio of 1.5 and butterfly-shaped curves at higher axis ratios. Symmetric behavior is observed at a curvature ratio of −1, whereas asymmetric responses occur at −0.5 and 0. The failure results indicate that larger curvature ranges and higher axis length ratios reduce the number of cycles to buckling, while curvature ratios closer to −1 enhance buckling life. On a log–log scale, the relationship between curvature range (m⁻¹) and number of cycles to buckling becomes linear. A theoretical model is proposed and shows good agreement with the experimental results. Full article

An innovative preparation route for iron-based soft magnetic materials is presented, focusing on the influence of the mechanical surface treatment of powder particles on their structural and magnetic properties. High-purity Fe (99.98% purity) and FeNiMo (supermalloy) powders were mechanically milled (ball-to-powder ratio of 6:1; 120 min), surface-treated by controlled milling, coated with an inorganic SiO₂ insulating layer, and subsequently compacted into ring-shaped specimens. Structural characterization was carried out using optical microscopy and scanning electron microscopy. Magnetic properties were evaluated by hysteresis loop measurements, initial magnetization curves, and coercivity analysis at 200 K. The results demonstrate that mechanical surface treatment improves the homogeneity and continuity of the SiO₂ insulating layer. This improvement leads to reduced coercivity from 2100 to 1980 A·m⁻¹ for Fe powders, while FeNiMo powders showed a decrease from 1990 to 1910 A·m⁻¹, along with lower energy losses. The proposed method provides a laboratory-scale approach for studying the influence of powder surface treatment on the magnetic behavior of Fe-based soft magnetic composites. Full article

First, the properties of the linear magnetizing curve and low static permeability are summarized. Second, a design for technical implementation of mechanical stress-induced anisotropy in metal-amorphous nanocomposites (MANCs) is presented. Stress annealing, which creates the conditions for a linear magnetizing curve, is an order of magnitude more effective with Co-based MANCs than with Fe-based ones. Permeabilities between 3000 and 100 and between 100 and 10 can be obtained in Fe- and Co-based nanocomposites, respectively, at similar applied tensile stresses. A measure of linearity is introduced based on the parameters of the hysteresis loop, which is proven to be equal to the fraction of the crystalline phase responsible for the induced anisotropy. Lastly, experimental results concerning linearity and related properties are discussed. Full article

Bentonite serves as a critical engineered barrier in deep geological repositories, necessitating a reliable description of its temperature-dependent water retention behavior. This study determined soil water retention curves (SWRCs) for four bentonites (Sab65, GMZ, B75 powder, B75 pellet) along drying/wetting paths at 20–80 °C using vapor equilibrium technique, spanning a suction range of 5–300 MPa. All exhibit S-shaped SWRCs. Higher temperature systematically reduces water content at given suction, shifting SWRCs downward; this effect weakens at high suction where adsorption dominates. Material responses differ: Sab65 shows highest water content at low suction but strongest decrease at high suction and elevated temperature. Drying-wetting hysteresis is material-dependent. The van Genuchten (VG) model reproduced the drying-path SWRCs with high accuracy. The fitted parameter α increased with temperature (particularly for Sab65 and B75), whereas n showed only minor changes, indicating that heating primarily shifts the SWRC along the suction axis while the overall curve shape remains broadly similar. These findings elucidate the synergistic effects of temperature, mineralogy, and form on bentonite retention, thereby providing essential insights for the long-term performance assessment of engineered barriers under thermal conditions. Full article