Friction Force Research Articles

Assessment of the microstructure, adhesion and elevated temperature erosion resistance of plasma-sprayed NiCrAlY/cr3C2/h-bn composite coating

This study uses an air jet erosion tester to investigate the erosion behavior of NiCrAlY/Cr3C2/h-BN composite coatings that are plasma-sprayed at three different temperatures and 40 m/s on T22 boiler steel alloy. 30 and 90° are the impingement angles. To identify the erosion mechanism, SEM and X-ray diffraction techniques are used to analyze the surface morphology and phase generated on the eroded surface. Findings of erosion test indicate that the erosion resistance was notably enhanced by addition of Cr3C2 and h-BN because of its lubricating characteristics and capacity to reduce frictional forces during erosion. The combined influence of Cr3C2 and h-BN enhanced the coating hardness and erosion wear resistance, thereby improving its overall resistance to erosion. The weight loss method was employed to calculate the erosion rate, and the NiCrAlY/Cr3C2/h-BN coating showed up to 30.55% and 34.48% lower erosion rate as compared to uncoated T22 substrate at 600 °C for 30° and 90° impact angles, respectively. This characteristic is affected by the hard reinforcement Cr3C2's high-temperature stability, the h-BN's self-lubricating ability, the formation of a protective oxide layer that forms at 600 °C, and the eroded coating's ductile behavior of material removal. The study also reveals that the NiCrAlY/Cr3C2/h-BN coating system on T22 boiler steel alloy has excellent erosion resistance, making it suitable for use in high-temperature and erosive environments in boiler systems and similar industries.

Force Element Analysis in Vortex-Induced Vibrations of Side-by-Side Dual Cylinders: A Numerical Study

A numerical investigation was conducted in this study utilizing Force Element Analysis to explore the vortex-induced vibration (VIV) mechanism of side-by-side dual cylinders under the conditions of Reynolds number Re = 100, mass ratio m* = 10, and spacing ratios L/D ranging from 3 to 6. The hydrodynamic forces by force element formulas were incorporated into the vibration response calculations of elastically supported rigid cylinders using a User-Defined Function (UDF) and the fourth-order Runge–Kutta method. A comprehensive analysis was performed to elucidate the combined effects of the spacing ratio L/D and reduced velocity Ur on the vibration responses, quantifying the hydrodynamic forces involved in the mutual interaction during VIV for side-by-side dual cylinders. The influence mechanisms of inter-cylinder interaction and their effects on the resultant hydrodynamic phenomena were discussed. It was revealed that for side-by-side arranged dual cylinders outside the “lock-in region”, the lift and drag forces are predominantly supplied by the volume vorticity forces in conjunction with surface vortices (including frictional) forces. However, within the “lock-in region”, the surface acceleration lift forces provide greater force contributions, and the volume vorticity lift force contributes significantly to negative values. Notably, alterations to the spacing ratio do not change the proportion of force element components. The amplitudes of the cylinders’ mutual interaction forces are identical in magnitude but opposite in phase. Additionally, the “slapping” phenomenon near the “lock-in region” leads to “bounded” trajectories of cylinders.

Research on a Novel Citrus Reticulata ‘Chachi’ Orientation Adjustment Mechanism (COAM) and Machine Vision Guidance Control

The initial processing of Citrus Reticulata ‘Chachi’ involves peeling as a crucial step. Currently, there is some semi-automatic peeling equipment available. However, due to the requirement of adjusting the orientation of Citrus Reticulata ‘Chachi’ to ensure the stem (or navel) is facing upwards before peeling and because the peeling process must retain the stem as a marker for fresh fruit picking, the loading of Citrus Reticulata ‘Chachi’ for peeling still solely relies on manual operation, resulting in low efficiency and poor standardization. With the rapid growth of the pericarp of the Citrus Reticulata ‘Chachi’ industry, semi-automatic processing equipment is no longer able to meet production demands. The loading issue before peeling Citrus Reticulata ‘Chachi’ is a complex hand–eye coordination problem. In response to this issue, this paper proposes a novel Citrus Reticulata ‘Chachi’ orientation adjustment mechanism (COAM). This mechanism utilizes frictional force to adjust the orientation of Citrus Reticulata ‘Chachi’. First, the conceptual design and kinematic modelling analysis of the mechanism were conducted. Next, the omnidirectional friction-driven wheels were optimized in design. Subsequently, a prototype was manufactured and assembled to conduct validation tests on its open-loop motion performance. Finally, a visual feedback-guided algorithm was introduced to complement the kinematic model, enabling the automatic and rapid adjustment of Citrus Reticulata ‘Chachi’ orientation. The experimental results indicate that the COAM designed in this study can effectively and rapidly adjust the orientation of Citrus Reticulata ‘Chachi’ fruits of different sizes and shapes. It demonstrates strong adaptability, and under visual feedback guidance, the orientation adjustment error is less than 10% of the fruit’s diameter. This meets the requirements for automated production in the initial processing of Citrus Reticulata ‘Chachi’. The research presented in this paper also provides new insights for the orientation adjustment and loading of similar spherical fruits.

THREADED LUBRICANTS FOR DRILL PIPES BASED ON OIL PRODUCTION WASTE

The oil and gas industry occupies a leading position in the development of the country's fuel and energy complex, and the effectiveness of its activities largely depends on the technical and economic indicators of drilling. When performing well work and operating oil and gas wells, many material costs are associated with the operation of oil pipes, namely the reliability of threaded connections operating at high pressures and temperatures in aggressive environments. The need to develop deeper and deeper horizons, the use of forced drilling modes, the transition to later stages of operation of most oil and gas fields, the aging of existing funds and the increase in the volume of overhauls leads to an increase in tripping operations, and therefore the requirements for the reliability of the connection of oil-grade pipes are moving to a new level. Studies have shown that up to 87 % of all drill string accidents are related to poor thread condition. This unsatisfactory condition of the locking threaded joints forces us to look for ways to improve durability. Many foreign and domestic scientists have been studying and improving threaded joints in drill pipes. According to the authors, one of the most promising ways to increase the TEI of drilling is to develop and use more and more effective lubricants for locking joints of drilling tools. Studies have shown that conventional lubricants are not effective enough in modern realities, and sometimes lubricants are completely washed out of threaded joints. In addition, as the drilling depth increases, the friction force increases and the hydrodynamic load increases, and the increase in pressure in the threaded connection complicates the conditions due to the effect on the lubricant of chemically active and abrasive drilling muds and many other factors. The article discusses the obtained results of studies of lubricant bases for threaded connections of drill pipes used for the oil industry, the distinctive features of which are physical and chemical composition, including low molecular weight polyethylene, synthetic rubber, rubber softeners, powdered graphite, vegetable oils.The authors of the article selected the basis of lubricant from industrial rubber production waste, and also presented the advantages of the developed lubricants and materials. The practical significance of the obtained research results lies in the possibility of increasing the wear and sealing properties of threaded pipe joints used in drilling oil and gas wells.

Identification of the coefficient of sliding friction from an apparent non-Coulomb behavior between wood and steel

This study investigates the sliding friction fluctuations through hysteresis cycles, observed between a steel sphere and wood specimens of beech and spruce, by using a tribometer and a profilometer. At first, the tracked wear profiles revealed a correlation between the normal force variation and the surface waviness. However, the normal force variation alone was not able to explain the observed friction force fluctuation. Hence, to explain most of the observed non-Coulomb friction hysteresis behavior, the wear-scar interaction is taken into account through an optimization framework used for data post-processing and leading to an optimal friction coefficient. A comparative study showed similar values between the identified optimal friction coefficient, the mean and energy-based friction coefficients.

Comparative study on rolling resistance force in tire-ice interaction with a variation of tread rubber compound

Abstract The complex phenomenon involved in the tire-ice interaction can be better understood by studying the tire and ice properties. A significant force at the contact patch is the rolling resistance force. To study the effect of tire characteristics on rolling resistance forces, data collected from a free-rolling tire can be used as there is no tractive or braking torque applied to the wheel and thus the data representing the longitudinal forces is only related to resistive forces viz. friction and rolling resistance force. Although a lot of research and literature has been developed for tire-ice interaction over the years, there is a significant lack of work in the subsection of free-rolling tires specifically to study the effect of ice parameters on rolling resistance forces. To fulfill the aim of this study, several sets of experiments for 16 winter tires of 8 different rubber compounds in free-rolling conditions were conducted. The experimental data was compared with predictions of 4 well-known formulations from the literature. Based on the findings and the relative error between the predicted and measured values, it was proposed that the high error percentage could be due to the variation in the viscoelastic properties of the tread rubber. The longitudinal force generated during those tests would thus be a combination of frictional forces due to adhesion between the tread rubber and its viscoelastic nature in addition to the contribution from the remaining sections of the tire. The data collected from the experiments and results from implementing the existing models to obtain frictional force will further help in analyzing the relation between the rolling resistance force with variation in normal load, inflation pressure, and change in camber angle once a generic formulation considering the rubber compound effects is incorporated. Another significant finding of this work is that formulations in literature used for finding the rolling resistance coefficient of radial passenger car tires were found to highly underestimate the coefficient when compared to the equivalent coefficient of friction found from experimental results. The future scope may include the development of a model which will incorporate the viscoelastic properties, especially the loss moduli and loss tangent to evaluate the coefficient of friction and rolling resistance force in the free-rolling condition of a winter tire on ice as the rolling resistance losses are found to be highly correlated to these two properties.

Lubrication Characteristics of Dry-Gas Seals with Spiral Grooves

To obtain an optimal range of structural parameters for dry-gas seals with good performance, this study employed advanced sensing technology to monitor and analyze the internal flow characteristics of dry-gas seals in real time. Additionally, the validity of the calculation program was verified through experimentation. Using steady-state performance parameters as evaluation indices, a calculation model with lubrication characteristics was developed. The results indicate that when there are 12 grooves, the gas film pressure distribution is uniform and has a high value. At pressures greater than 2 MPa, the opening force, leakage, and gas film stiffness change significantly due to enhanced dynamic pressure effects with high-pressure differences, which reduces the local contact forces and frictional forces. At a constant speed, decreasing the gas film thickness increases the pressure difference while increasing both the opening force and film stiffness; however, at higher rotational speeds where the gas flow becomes non-uniform, the stability of the gas film is affected, leading to increased frictional forces. When there are between 10 and 16 grooves with depths ranging from 5.0 to 6.0 μm, dynamic pressure effects caused by pressure gradients become apparent, resulting in good dry-gas sealing performance being achieved. This research provides a theoretical reference for optimizing the design of dry-gas seals, as well as their steady-state seal performance.

Study on the improvement of grouting stone properties in coal mine goafs using combined denitrifying bacteria.

Grouting can effectively reduce residual deformation of coal mine goafs, but fly ash grouting materials suffer from poor flowability and slow early strength development. Microbially -induced calcite precipitation (MICP), with its high environmental compatibility and minimal disturbance to geotechnical bodies, effectively improves the injectability of grouting slurry in goafs. This study combined Castellaniella denitrificans and Sporosarcina pasteurii to induce calcite precipitation, preparing cement-fly ash slurry with varying water-solid ratios, solid ratios and denitrifying bacteria concentrations. The physical properties of the slurry and the mechanical properties of the grouted stone bodies under sealed curing conditions were measured. Results show that the dual-bacteria MICP improves stone body performance by enhancing cohesive, frictional and interlocking forces, so that the strength of the stone bodies cured by MICP increased rapidly within 7 days, and the strength reached the standard 2.03 MPa at 28 days under conditions of low solid ratio and high water-solid ratio, with the best compressive strength at a denitrifying bacteria concentration with an optical density of 0.8 at 600 nm wavelength. At a water-solid ratio of 1 : 1.2 and a solid ratio of 15%, initial and final setting times were 67.2 and 96 h, respectively, which prolonged the initial setting time and final setting time by nearly 70% and 110% compared with that of the slurry without MICP treatment, indicating that MICP enhances slurry fluidity, providing more time for grouting construction in goafs.

Macroscopic modeling of gas permeability in hierarchical micro/nanoporous media: A unified characterization of rarefaction using Klinkenberg theory and equivalent diameter

Estimating gas transport through a hierarchical micro/nanoporous system is challenging due to non-equilibrium gas dynamics. The primary difficulty lies in determining the rarefaction level, because identifying a representative flow dimension in a complex porous system with multiple pore scales is not straightforward. Our study performed a pore-level analysis for gas permeability in dual-scale porous media with varying porosity, throat size, and secondary pore size under different rarefaction conditions. We found that secondary porosity negatively affects permeability due to increased friction forces, with this influence growing as the secondary pore size and porosity increase until the secondary pore becomes comparable to the throat. However, rarefaction reduces the effects of secondary pores due to boundary slip. Traditional Knudsen number (Kn) calculations based on Darcy-defined height failed to accurately describe the rarefaction effects on gas permeability. Instead, we introduced an equivalent diameter to calculate the Kn, which provided an accurate normalization of apparent gas permeability independent of pore geometry. The extended Kozeny–Carman–Klinkenberg model developed in our previous study successfully yielded a macroscopic model for apparent gas permeability in hierarchical micro/nanoporous systems as a function of the traditional Darcy height and porosity.

Sedimentation and photophoretic levitation of aerosol clusters in the free molecular regime

Sedimentation of fractal aerosol clusters in rarefied gas medium in the dark and under external illumination similar to sunlight is studied in a numerical experiment taking into account orientation effects, depending on fractal dimension varying within a broad range. The calculation of forces and their moments, including friction forces and photophoretic forces, was carried out on the basis of approximation of free molecular gas kinetic regime and previously developed Monte-Carlo algorithms. Calculation involved 10000 clusters, each of them containing 160 primary spherical particles and efficiently absorbing sunlight and IR radiation, similarly to the particles of soot aggregates.The velocity of multi-particle cluster settling in the absence of illumination, when particle temperatures are equal to the temperature of the gaseous environment, is a distinct function of fractal dimension and is rather close to the velocity of settling of single spherical particles. The settling velocity approximation depending on fractal dimension has been obtained.Illumination brings dramatic changes into sedimentation pattern. The range of cluster sedimentation rate variations broadens substantially, which is a manifestation of gravito-photophoretic effect, so that some clusters even start to levitate. The proportion of levitating clusters is essentially dependent on fractal dimension. For soot-like clusters under irradiation similar to sunlight and pressure equal to atmospheric at the altitude of 30 km, the proportion of levitating aggregates is approximately 7%, which is in good agreement with the experimental data. In the dark and under irradiation, the aggregates rotate, and their trajectories are shaped as spirals.In the context of photophoretic phenomena, a result of principle has been obtained: under irradiation with sunlight, gravito-photophoretic levitation of aerosol soot-like aggregates composed of identical primary particles is possible at a pressure corresponding to the stratospheric altitudes. This result points to the possibility of substantial influence of gravito-photophoretic effect on transport and localization of soot aerosol in the Earth’s stratosphere and mesosphere.

A novel cohesive interlayer model considering friction

To understand the influence of friction on the shear-slip behavior of heterogeneous brittle composites, a novel cohesive interlayer model that can effectively capture the friction effect was proposed based on the classical Park-Paulino-Roesler model. Meanwhile, the unified potential energy function governing the interface tangential and normal behaviors was introduced to realize the mechanical interaction between Mode I fracture and Mode II fracture, and a smooth friction growth function was added in the elastic deformation stage for calculating the accurate contact pressure and friction force. Furthermore, the capability of the proposed model in addressing unloading and reloading was improved, and the fracture energy can vary accordingly during cyclic loading. To verify the effectiveness of the proposed model, it was examined by modelling the shear behavior of a masonry wallette. The results show that the relative error of the proposed model is 14.92% which is much lower than those of the other three pre-existing models when calculating the displacement corresponding to peak shear stress. Meanwhile, in terms of peak shear stress and initial displacement at residual stage, the relative errors of the proposed model are only 1.82% and 5.04%, respectively, indicating the high accuracy. Besides, the tangent stiffness determined by the second-order integration of the potential energy function is also continuous and smooth, which ensures the effective convergence of the proposed cohesive model.

Модель расчёта момента силы трения при вращательном движении тела

The article discusses one of the types of mechanical movement – rotational movement. To automate the calculation of the frictional moment, an algorithm was proposed and a program was written in Python. The algorithm consists of a block for inputting initial data, blocks for calculating intermediate values and the desired value, and outputting the calculation results. Keywords: FRICTION FORCE, MECHANICAL MOTION, BODY, PYTHON LANGUAGE, ROTATION AXIS, ALGORITHM, LOAD

Low friction characteristics and tribochemistry analysis of novel AlTiN/a-C based nanocomposite coatings

Friction reduction of AlTiN-based hard coatings is gaining much attention among researchers worldwide to broaden their tribological applications. Metal/non-metal inclusions, as well as the design of a novel coating architecture, are primarily focused on reducing friction while retaining wear resistance. This study investigates the tribological characteristics of magnetron sputtered AlTiN coatings by incorporating amorphous carbon (a–C) at different concentrations (5–25 at.%), as well as the compositionally graded AlTiN/a-C coatings (CGC). The XPS and Raman spectroscopy results confirm the presence of a-C features, while XRD reveals the formation of ceramic carbide phases in AlTiN coatings with higher carbon content and CGC coatings. The CGC AlTiN/a-C have shown a maximum hardness of 34.3 GPa and an elastic modulus of 321 GPa due to their refined grain structure. The CGC had the lowest friction (0.18 at 300 K and 0.37 at 673 K), as well as improved wear resistance (2.74 × 10−7 mm3/Nm (300 K) and 4.93 × 10−7 mm3/Nm (673 K)). The tribolayers are found to be mainly composed of sp2/sp3 bonded a-C features (including C=C/C─C, C─N, and C─O), which reduces the friction force significantly. The CGC AlTiN/a-C coating has exhibited improved wear resistance behavior due to their finely grained structure and improved mechanical properties.

УТОЧНЕНА МОДЕЛЬ ДВОКАНАЛЬНОГО ЕЛЕКТРОПРИВОДА ПОДАЧІ З ПІДСУМОВУВАННЯМ РУХІВ НА ХОДОВІЙ ГАЙЦІ ДЛЯ ВИСОКОТОЧНИХ МЕТАЛОРІЗАЛЬНИХ ВЕРСТАТІВ

The iterative two-channel feed electric drive (ED) with the summation of movements on the rotating sliding nut (RSN) is designed to increase the speed and accuracy of traditional single-channel ED feed mechanisms (FM) of metal-cutting machines with an inertial working tool (WT). A refined generalized mathematical model of movement of the two-channel ED with RSN was obtained, which was built for WT FM of the high-precision coordinate metal-cutting ma-chine of the 24К60АФ4 model. The model takes into account the main static moments of resistance during metalwork-ing, as well as the nonlinear nature of the sliding friction forces in the machine WT FM. Convenient recurrence rela-tions are obtained for the calculation and modeling of sections of the linearized friction characteristic. The structural-algorithmic diagram of the compensated iterative two-channel feed ED with subordinate configuration of control chan-nels is proposed, which makes it possible to compensate in steady-state conditions the negative impact on the accuracy of WT feed of the main static moments of resistance and nonlinearities of sliding friction forces in the drive load. Ref. 9, fig. 3, table.

Onset, rate, and depth of wetting front progression in membrane distillation

In this study, electrochemical impedance spectroscopy (EIS) is used to characterize the onset, rate, and depth of wetting front progression in real time through commercial polytetrafluoroethylene (PTFE) membrane distillation (MD) membranes. Results showed that higher salinities, elevated transmembrane hydraulic pressures, and larger membrane pore sizes are associated with earlier onset, higher rates, and/or greater depths of wetting front progression – but, notably, in the absence of pore breakthrough. It was also shown that wetting is not an on/off switch; instead, membrane wetting resistance acts as a frictional force that can slow down or stop wetting front progression at different depths in the membrane. PTFE MD membranes were observed to often operate in a deeply wetted, but stable, transition state with normalized impedance values of ∼0.6 to ∼0.1, indicating mid-depth wetting, where the wetting front progresses into the bulk of the membrane and holds its position, or deep wetting, where the wetting front holds its position near the distillate-side surface of the membrane without pore breakthrough. Normalized impedance values as low as 0.04 held constant throughout a 14-day experiment in which pore breakthrough did not occur. These new impedance results strongly support the hypothesis that during MD, for saline feed solutions and under elevated transmembrane pressures – and especially for larger membrane pore sizes – the distillate-side surface can act as a final barrier to pore breakthrough.

Study on the Effect of Starved Lubrication on the Dynamic Characteristics of Locally Failed Roller Bearings

When the lubricant is not enough to maintain the ideal lubrication state of the bearing, the deep groove ball bearing will enter the starved lubrication state, which leads to the change of the vibration response of the deep groove ball bearing with localized defects. Previous bearing dynamics models mainly consider the lubrication state as an ideal lubrication condition, which may not reveal the effect of starved lubrication on the vibration characteristics of defective bearings. In this paper, the internal interaction of the system under starved condition is taken into account, and a dynamic model of defective deep groove ball bearings with insufficient lubricant is established to investigate the effects of different starved lubrication degrees on the contact force, friction force, cage speed, and system vibration characteristics. The results show that the lubricant insufficiency significantly changes the contact force inside the bearing, and the increase in friction caused by the increase in the degree of starved lubrication leads to the suppression of the degree of bearing slipping. The root mean square (RMS) value of the time-domain signal and the outer ring fault frequency both increase with the increase of the starved degree. The results of the study are helpful for fault diagnosis and condition monitoring of related equipment.

Heterogeneous solvent dissipation coupled with particle rearrangement in shear-thinning non-Brownian suspensions.

Dense non-Brownian suspensions exhibit significant shear thinning, although a comprehensive understanding of the full scope of this phenomenon remains elusive. This study numerically reveals intimate heterogenous coupled dynamics between many-body particle motions and solvent hydrodynamics in shear-thinning non-Brownian suspensions. In our simulation systems, we do not account for frictional contact forces, reflecting experimental conditions under low shear rates where shear thinning occurs, while hydrodynamic interactions are directly incorporated using the Smoothed Profile Method. We demonstrate the spatially correlated viscous dissipation and particle motions; they share the same characteristic length, which decreases with increasing shear rate. We further show that, at lower shear rates, significant particle density changes are induced against the incompressibility of the solvent, suggesting the cooperative creation and annihilation of gaps and flow channels. We discuss that hydrodynamic interactions may substantially restrict particle rearrangements even in highly dense suspensions, influencing the quantitative aspects of macroscopic rheology.

Construction of a Science Teacher's Topic-Specific Pedagogical Content Knowledge in the Gifted Class

This study examines a science teacher's pedagogical content knowledge during instruction on the topics work and energy, simple machines, and friction force in a gifted class. The research adopts a single case study approach, employing qualitative methods. The participant is a middle school science teacher, and data collection tools include interviews, observations, card-sorting activities, and lesson plans. The main findings of the study are: (1) gifted students required additional science practice beyond the scope of the traditional curriculum, (2) the participating teacher encountered challenges when designing and implementing enrichment activities, (3) the characteristics of gifted students positively influenced the development of the teacher's pedagogical content knowledge, and (4) the presence of gifted students prompted a shift in the teacher's science teaching orientation from traditional methods to reform-based practices. Teachers need to have additional knowledge bases or Pedagogical Content Knowledge components. Notably, the research underscores the relevance of the knowledge of enrichment curriculum and knowledge of characteristics of gifted students in the training of science teachers, along with the crucial role of STO in the education of gifted students, especially in the context of teaching physics. These findings offer significant implications for the curriculum designed for gifted students, particularly concerning the teaching and learning of physics topics.

Large Scale Simulation of 3D Fault Rupture Subjected to Far‐Field Loading With PDS‐FEM: Application to the 2018 Palu Earthquake

AbstractSimulating dynamic rupture of fault systems can be computationally demanding, as it requires reproducing complex fault geometry and accurately capturing waves propagating away from the rupture front. It is in particular challenging to predict an initial stress state consistent with fault geometries, heterogeneous distribution of surrounding materials, and far‐field tectonic loading. While standard techniques such as contact analysis and Lagrangian multipliers can be used to model the fault, it can lead to significant computational overhead in FEM. We extended Particle Discretization Scheme‐FEM, which provides numerically efficient crack treatment, without requiring contact analysis, to simulate dynamic fault rupture as a frictional crack propagating along a pre‐existing shear crack surface. Initial stress, which is consistent with initial frictional forces, material distribution and fault geometry, is derived using Coulomb friction and far‐field boundary conditions. The study first demonstrates the ability of the numerical method to reproduce a 2D ideal supershear scenario, and the underlying Burridge‐Andrew rupture mechanism. The methodology is then applied to the large scale simulation of the 2018 Palu earthquake on the Palu‐Koro fault. The simulation successfully reproduces the early and sustained supershear rupture which was observed for the Palu earthquake. Also, it indicates that the presence of an off‐fault damage zone can contribute to the low rupture velocity measured during the earthquake. Unlike sub‐Rayleigh earthquakes, the shockwave propagation was observed to lead to significant amplitudes of the ground motion even far from the fault.

Tunable High-Static-Low-Dynamic Stiffness Isolator under Harmonic and Seismic Loads

High-Static-Low-Dynamic Stiffness (HSLDS) mechanisms exploit nonlinear kinematics to improve the effectiveness of isolators, preserving controlled static deflections while maintaining low natural frequencies. Although extensively studied under harmonic base excitation, there are still few applications considering real seismic signals and little experimental evidence of real-world performance. This study experimentally demonstrates the beneficial effects of HSLDS isolators over linear ones in reducing the vibrations transmitted to the suspended mass under near-fault earthquakes. A tripod mechanism isolator is presented, and a lumped parameter model is formulated considering a piecewise nonlinear–linear stiffness, with dissipation taken into account through viscous and dry friction forces. Experimental shake table tests are conducted considering harmonic base motion to evaluate the isolator transmissibility in the vertical direction. Excellent agreement is observed when comparing the model to the experimental measurements. Finally, the behavior of the isolator is investigated under earthquake inputs, and results are presented using vertical acceleration time histories and spectra, demonstrating the vibration reduction provided by the nonlinear isolator.